increased late pleistocene erosion rates during fluvial aggradation in the garhwal himalaya northern india the response of surface processes to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution in the himalaya most large rivers feature prominent fill terraces that record an imbalance between sediment supply and transport capacity presumably due to past fluctuations in monsoon precipitation and or effects of glaciation at high elevation here we present volume estimates chronological constraints and 10 be derived paleo erosion rates from a prominent valley fill in the yamuna catchment garhwal himalaya to elucidate the coupled response of rivers and hillslopes to pleistocene climate change although precise age control is complicated due to methodological problems the new data support formation of the valley fill during the late pleistocene and its incision during the holocene we interpret this timing to indicate that changes in discharge and river transport capacity were major controls compared to the present day late pleistocene hillslope erosion rates were higher by a factor of 2 4 but appear to have decreased during valley aggradation the higher late pleistocene erosion rates are largely unrelated to glacial erosion and could be explained by enhanced sediment production on steep hillslopes due to increased periglacial activity that declined as temperatures increased alternatively erosion rates that decrease during valley aggradation are also consistent with reduced landsliding from threshold hillslopes as a result of rising base levels in that case the similarity of paleo erosion rates near the end of the aggradation period with modern erosion rates might imply that channels and hillslopes are not yet fully coupled everywhere and that present day hillslope erosion rates may underrepresent long term incision rates

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

new insights into lightning processes gained from triggered lightning experiments in florida and alabama analyses of electric and magnetic fields measured at distances from tens to hundreds of meters from the ground strike point of triggered lightning at camp blanding florida and at 10 and 20 m at fort mcclellan alabama in conjunction with currents measured at the lightning channel base and with optical observations allow us to make new inferences on several aspects of the lightning discharge and additionally to verify the recently published two wave mechanism of the lightning m component at very close ranges a few tens of meters or less the time rate of change of the final portion of the dart leader electric field can be comparable to that of the return stroke the variation of the close dart leader electric field change with distance is somewhat slower than the inverse proportionality predicted by the uniformly charged leader model perhaps because of a decrease of leader charge density with decreasing height associated with an incomplete development of the corona sheath at the bottom of the channel there is a positive linear correlation between the leader electric field change at close range and the succeeding return stroke current peak at the channel base the formation of each step of a dart stepped leader is associated with a charge of a few millicoulombs and a current of a few kiloamperes in an altitude triggered lightning the downward negative leader of the bidirectional leader system and the resulting return stroke serve to provide a relatively low impedance connection between the upward moving positive leader tip and the ground the processes that follow likely being similar to those in classical triggered lightning lightning appears to be able to reduce via breakdown processes in the soil and on the ground surface the grounding impedance which it initially encounters at the strike point so at the time of channel base current peak the reduced grounding impedance is always much lower than the equivalent impedance of the channel at close ranges the measured m component magnetic fields have waveshapes that are similar to those of the channel base currents whereas the measured m component electric fields have waveforms that appear to be the time derivatives of the channel base current waveforms in further confirmation of the two wave m component mechanism

measurements of atmospheric layers from the nasa dc 8 and p 3b aircraft during pem tropics a tropospheric vertical structure was analyzed using in situ measurements of o3 co ch4 and h2o taken on board the nasa dc 8 aircraft during three pacific exploratory missions pems pem west a september october 1991 in the western pacific pem west b february march 1994 in the western pacific and pem tropics a september october 1996 in the central and eastern pacific pem tropics a added measurements from the nasa p3 b aircraft we used a new mode based method to define a background against which to find layers using only o3 and h2o we found 472 layers in pem tropics a 0 72 layers per vertical kilometer profiled 237 layers in pem west a 0 54 layers km and 158 layers in pem west b 0 41 layers km using all constituents we found 187 layers in pem tropics a 0 43 layers km 128 layers in pem west a 0 29 layers km and 80 layers in pem west b 0 21 layers km stratospheric air sometimes mixed with trapped pollution was the dominant layer source in all three missions the larger number of layers per kilometer in pem tropics a was probably due to repeated profiling of several superlayers visible in many of the mission lidar and potential voracity profiles the thickness of the superlayers was of order 1 km and the horizontal extent was of order 1000 km we found that layers have an important effect on the thermal structure an example based on ozonesonde data from tahiti is shown where a dry subsiding layer was stabilized by much greater radiative cooling at the base than at the top the stabilized layer can trap pollution and force vertical plumes to spread into horizontal layers

an anomalous triggered lightning flash in florida 1 an anomalous rocket and wire triggered lightning flash a flash whose leaders do not follow the triggering wire remnants to ground is characterized via high speed video images at 10 and 300 kilo frames per second still camera images 66 72 mhz source locations from a lightning mapping array channel base current and electric field and electric field derivative de dt measurements this is the first anomalous flash of about 410 classically triggered flashes in north central florida the flash began with an upward positively charged leader upl initiating from the tip of the upward moving triggering wire about 280 m above ground level all but the bottom 17 m of wire exploded became luminous 37 6 ms after upl initiation a stepped leader initiated likely from the top of the wire remnants 282 m above ground level about 1 3 ms after the wire explosion and propagated downward for 2 1 ms attaching to the top of a grounded utility pole 117 m southwest of the launching facility the line charge density on the stepped leader is estimated to be of the order of 10 3 c m 1 contrary to previously reported anomalous flashes in france and new mexico roughly 16 and 31 respectively of their triggered flashes in our event there was not a tens of milliseconds current zero period preceding the stepped leader there was no observed downward dart leader in the upl channel prior to the stepped leader to ground and there was a failed attempt to reestablish current in the exploded wire channel between the upl and ground

effects of charge and electrostatic potential on lightning propagation 1 three dimensional lightning mapping observations are compared to cloud charge structures and electric potential profiles inferred from balloon soundings of electric field in new mexico mountain thunderstorms for six individual intracloud and cloud to ground flashes and for a sequence of 36 flashes in one storm the comparisons consistently show good agreement between the altitudes of horizontal lightning channels and the altitudes of electric potential extrema or wells lightning flashes appear to deposit charge of opposite polarity in relatively localized volumes within the preexisting lower positive midlevel negative and upper positive charge regions associated with the potential wells the net effect of recurring lightning charge deposition at the approximate levels of potential extrema is to increase the complexity in the observed storm charge structure the midlevel breakdown of both normal intracloud flashes and negative cloud to ground flashes is observed to be segregated by flash type into the upper and lower parts of the deep potential well associated with the midlevel negative charge the segregation is consistent with perturbations observed in the bottom of the negative potential well due to embedded positive charge that was probably deposited by earlier flashes it is also consistent with an expected tendency for vertical breakdown to begin branching horizontally before reaching the local potential minimum the joint observations reconcile the apparent dichotomy between the complex charge structures often inferred from balloon soundings through storms and the simpler structures often inferred from lightning measurements

satellite detection long range transport and air quality impacts of volcanic sulfur dioxide from the 2014 2015 flood lava eruption at barðarbunga iceland the 2014 2015 bar arbunga vei ivotn fissure eruption at holuhraun produced about 1 5 km3 of lava making it the largest eruption in iceland in more than 200 years over the course of the eruption daily volcanic sulfur dioxide so2 emissions exceeded daily so2 emissions from all anthropogenic sources in europe in 2010 by at least a factor of 3 we present surface air quality observations from across northern europe together with satellite remote sensing data and model simulations of volcanic so2 for september 2014 we show that volcanic so2 was transported in the lowermost troposphere over long distances and detected by air quality monitoring stations up to 2750 km away from the source using retrievals from the ozone monitoring instrument omi and the infrared atmospheric sounding interferometer iasi we calculate an average daily so2 mass burden of 99 49 kilotons kt of so2 from omi and 61 18 kt of so2 from iasi for september 2014 this volcanic burden is at least a factor of 2 greater than the average so2 mass burden between 2007 and 2009 due to anthropogenic emissions from the whole of europe combining the observational data with model simulations using the united kingdom met office s numerical atmospheric dispersion modelling environment model we are able to constrain so2 emission rates to up to 120 kilotons per day kt d during early september 2014 followed by a decrease to 20 60 kt d between 6 and 22 september 2014 followed by a renewed increase to 60 120 kt d until the end of september 2014 based on these fluxes we estimate that the eruption emitted a total of 2 0 0 6 tg of so2 during september 2014 in good agreement with ground based remote sensing and petrological estimates although satellite derived and model simulated vertical column densities of so2 agree well the model simulations are biased low by up to a factor of 8 when compared to surface observations of volcanic so2 on 6 7 september 2014 in ireland these biases are mainly due to relatively small horizontal and vertical positional errors in the simulations of the volcanic plume occurring over transport distances of thousands of kilometers although the volcanic air pollution episodes were transient and lava dominated volcanic eruptions are sporadic events the observations suggest that i during an eruption volcanic so2 measurements should be assimilated for near real time air quality forecasting and ii existing air quality monitoring networks should be retained or extended to monitor so2 and other volcanic pollutants

characteristics of lightning vhf radiation near the time of return strokes by using a crossed base line interferometer lightning vhf source positions correlated in time with electric field change measurements have been obtained we present data in this paper showing azimuth and elevation pictures with high time resolution of the vhf 34 3 mhz radiation for events near the time of return strokes from their common characteristics we infer spatial and temporal features of these processes no radiation was seen that could be attributed to the return stroke wave front itself radiation from stepped leaders continued up to and in some cases after initiation of the first return stroke a strong burst of radiation often followed the first return stroke strong radiation began before subsequent return strokes coinciding with the electric field change usually associated with the dart leader the end of the radiation was independent of the return stroke the source of this radiation was a well defined region within the cloud a second burst often followed the return stroke located in the same region as that prior to the stroke sources from stroke to stroke showed horizontal displacement with little apparent change in elevation

regions where lightning flashes began regions where 773 flashes began during 13 thunderstorms were located by calculating centroids of the sources of the first six or 10 vhf pulses that were emitted by each flash sources were located by measuring differences in the times at which their pulses arrived at five widely spaced receivers stationed on the ground we found that the distribution of origin heights was bimodal with peaks at 5 3 and 9 2 km above mean sea level amsl standard errors in the coordinates of flash origins were estimated to be 20 80 m in x and y and 160 240 m in the height coordinate z there were 431 flashes in the lower group and 342 in the higher flashes in the lower group were more numerous in 10 storms in three storms high flashes were in the majority there was evidence to suggest that this condition depended partly on the phase of the host thunderstorm recorded e field changes produced by 165 flashes whose paths we had mapped convinced us that the vast majority of the 773 flashes including the 342 high flashes had also been negative flash origins tended to cluster in regions that were a few kilometers or less in horizontal diameter densities of flash origins in these regions ranged from 1 25 to 25 km 3 the origins of 658 flashes were mapped onto radar precipitation patterns of their host storms we found that 66 of the flashes began within one picture element approximately 270 m of the contours for 20 dbz 27 began inside these contours and most of these began at edges of high reflectivity cores the remaining 7 began outside the 20 dbz contours similar results 73 19 8 were obtained for 276 high flashes that began at heights above 7 4 km amsl but 195 ground flashes scored 54 36 9 and showed a greater tendency to begin inside the 20 dbz contours the distribution of distances between origins and their nearest 20 dbz contours showed a marked peak near zero we concluded that charge density in thunderclouds was affected by the presence of heavy precipitation and that 20 dbz surfaces enclosed regions that carried excess negative charge

lightning leader characteristics in the thunderstorm research international program trip we have used high speed streaking photographic techniques to time resolve the luminous compnents of cloud to ground lightning flashes all recordings were made during our participation in the thunderstorm research international program trip conducted at the kennedy space center florida during the summers of 1977 and 1978 and at the langmuir laboratory near socorro new mexico during the summer of 1979 twenty one dart leaders four dart stepped leaders and three stepped leaders were recorded the majority under daylight conditions the mean two dimensional propagation speed of the dart leaders evaluated over channel lengths less than or equal to 0 8 km above ground is 11 106 m s with a range of 2 9 to 23 106 m s several of the dart leaders reveal a decrease in propagation speed as ground is approached however four of the dart leaders in two separate flashes show an increase in speed near the ground an observation not previously reported in the literature in two multistroke flashes we examine the variation of dart leader propagation speed along the channel and find very similar behavior for different strokes in the same flash the speed variations that we observe may be predominantly caused by geometrical variations of the channel the dart leader propagation speeds reported in this study are compared with the earlier works of schonland mceachron and kitagawa and brook agreement among the studies is good with a common range of observed dart leader propagation speed of 2 to 23 106 m s the major discrepancy among these studies is the observation by schonland of a distribution of dart leader propagation speeds positively skewed toward the lower limit of reported values eleven of the dart leaders are analyzed at upper and lower levels along the visible channel to give 22 dart lengths they range from 7 to 75 m with a mean of 34 m for these 22 determinations we calculate a correlation coefficient of 0 85 between the dart length and the dart leader propagation speed the correlation of greater dart length with higher propagation speed is consistent with the slower decay of channel luminosity due to the greater initial input of energy to the channel by the faster and presumably more energetic dart leader four dart stepped leaders are examined in detail with regard to variation of propagation speed step length stepping interval and luminous intensity during propagation between the cloud base and ground significant differences in the tendencies of these parameters are found within these four leaders for example one dart stepped leader recording shows a decreasing propagation speed and an increasing step interval near ground whereas another shows the opposite behavior in the best event recorded several of the individual steps reveal a photographic film density structure with the lower portion of the step exhibiting a distinct bright tip that fans out into a symmetrically diffuse image in the upper portion of the step our analysis indicates that this spread in the upper portion of the step image is not the result of streaking photography distortion but rather represents the luminous structure of the step we estimate that the step image is recorded in less than 1 s consequently with a measured step length of 20 m the luminous pulse must propagate along the step at a speed of at least 2 107 m s the mean propagation speed for three stepped leaders is found to be 1 1 106 m s all three stepped leaders are very faint and were recorded only in the last 100 200 m above ground two stepped leaders and one dart stepped leader do not propagate completely to ground before initiation of the return stroke apparently these leaders are met by an upward propagating discharge at heights above ground of 20 30 and 20 m respectively other stepped and dart stepped leader cases are indeterminate because an obstacle or the horizon prevent the recording of the leaders near the ground connecting discharges are not observed for any of the dart leader events with a resolution of 10 m at 5 km implying that upward discharges initiated by the approach of dart leader do not occur or are substantially less than a few tens of meters in length dart leaders apparently propagate completely to ground

three dimensional imaging of upward positive leaders in triggered lightning using vhf broadband digital interferometers 1 upward positive leaders upls in two artificially initiated lightning flashes were imaged in three dimensions using vhf broadband digital interferometers and a high speed video camera with time synchronized channel base current measurements locatable vhf sources of the two upls began at 1 1 km and 1 5 km a few milliseconds after the upl inception and ascended to 2 4 km and 3 7 km respectively with average 3 d speeds on the order of 106 ms 1 the initial stage currents for both flashes were unusually large and had peak values of 6 ka and 18 ka vhf sources associated with positive leader propagation were located when the average current was higher than 3 ka and had significant pulse activity the source altitudes and channel base currents suggest that there might have been a region of significant negative charge at altitudes from 2 to 4 km which is below the freezing level of typical thunderstorms in florida

correlated high speed video and radio interferometric observations of a cloud to ground lightning flash a six stroke cloud to ground lightning flash has been studied using observations from a high speed video camera 1000 frames s 1 and a vhf radio interferometer 1 s time resolution as well as additional electric magnetic and optical measurements the flash produced strokes along two channels to ground and a long 550 ms continuing current the video observations provided time resolved pictures of stepped and dart leaders short and long continuing currents and m components during the continuing currents and complemented and confirmed the interferometer observations of flash structure and development the m components were initiated by fast negative streamers inside the cloud which propagated into the conducting channel of the continuing current and subsequently brightened the channel to ground we call this sequence an m event dart leaders and the fast streamers of m and k events were found to be significantly brighter than stepped leaders and continuing currents to ground a number of streamers did not initiate m events that were identical to in cloud k streamers analysis of the m and k event occurrences indicated that the conducting channels of the continuing current both expanded and contracted with time an m type event was also observed during a dart leader it is proposed that the channel multiplicity within the flash resulted from cutoff of the channel to ground while charge continued to flow down the channel from the stroke source region stranding negative charge along the channel dart stepped leaders such as occurred during the third stroke are similarly explained because the stranded charge is observed to be greatest for initial strokes new channels to ground of stepped and dart stepped leaders are expected to follow initial strokes as is usually observed the video and electric field observations indicate that all return strokes have at least a short continuing current of the order of one or a few milliseconds the results also reinforce the well known observation that long continuing currents tend to follow relatively weak return strokes

layered lightning activity the horizontal extent of lightning channels reconstructed acoustically from several storms is significantly larger than the vertical extent furthermore an examination of all the reconstructed lightning structure in each of three storms one in arizona one in colorado and one in florida shows that the lightning activity tends to occur in layers 2 3 km thick in the arizona and florida storms there were two layers of activity temperatures at the lower boundary of the layers were near 4 c and 18 c in the arizona storm and 11 c and 39 c in the florida storm in the colorado storm there was a single layer having a lower boundary near the 0 c isotherm our interpretation is that each of the two layers in the arizona and florida storms is associated with a corresponding charged region in the dipole of the thundercloud charge distribution we suggest that the single layer in the colorado storm was a result of the dipolar regions being closer together in altitude

two simultaneous charge structures in thunderstorm convection 1 a pair of simultaneous horizontally displaced thunderstorm electric field soundings are used to investigate an existing conceptual model of thunderstorm charge structure the soundings show that two different vertical charge structures one in the updraft and one outside the updraft can exist at the same time inside a storm as depicted in the existing model the data suggest that the two charge structures can be relatively close together since the soundings are separated by only 3 to 8 km horizontally in the convective region of the storm horizontal extent of the charge structures is estimated to be at least 4 km 4 km the differences in the two charge structures are coincident with substantial differences over this same 3 to 8 km horizontal distance in the reflectivity structure updraft speed and lightning activity of the convection the nonupdraft sounding was made through the intense reflectivity core found at middle levels in the convection additional electric field complexity and additional charge regions were found in the nonupdraft sounding and the lightning related electric field changes tended to be larger in magnitude and more numerous in that sounding than in the updraft sounding

esr in the 21st century from buried valleys and deserts to the deep ocean and tectonic uplift abstract electron spin resonance esr dating can date many materials including hydroxyapatite in enamel and some fish scales aragonite and calcite in corals molluscs some travertine and calcrete and quartz from ash fluvial deposits and some flint dating studies using these materials have numerous potential applications in many varied quaternary settings esr dating uses signals resulting from trapped charges created by radiation in crystalline solids ages are calculated by comparing the accumulated radiation dose in the dating sample with the internal and external radiation dose rates produced by natural radiation in and around the sample and produced by cosmic radiation when compared to other dating techniques age agreement has been excellent for teeth corals molluscs and quartz recent improvements have included using a more complex modelling technique to calculate the cosmic dose rates and more detailed modelling techniques for dealing with variable external dose rates methods in development include using quartz from buried fluvial valleys to date geomorphic surfaces and using the signals in barnacles and benthic foraminifera for dating fossils or their associated sediment new chronometer applications recently developed include using coral and mollusc dates to build sealevel curves and to monitor volcanic activity and tectonic uplift using tooth and mollusc dates to assess water availability in deserts and using isochron data to assess u uptake processes into teeth when coupled with other geochemical and geomorphological techniques esr can provide the chronometric control to build paleoclimatic and other paleoenvironmental records many other applications are possible from heating studies for artefacts to dating sulphates and other minerals on distant planets

controls on the patterns of topography and erosion rate in a critical orogen 1 we solve for the steady state patterns of erosion rate and topography in a critical wedge to understand the mutual adjustment of tectonics erosion and topography in the absence and presence of spatial variations in precipitation rate we consider steady state systems in which tectonics favors a critical topographic form assumed to be the mean elevation across the range and in which surface erosion by rivers and hillslopes operates on a two dimensional landscape we find that 1 a nonuniform critical topographic form implies a nonuniform pattern of ridge valley relief and hence a nonuniform pattern of erosion rate and 2 when the system is forced by local variations in precipitation rate maintenance of the critical topographic form requires a local response of rock uplift that greatly dampens changes in topography we apply these concepts to the western side of the olympic mountains of washington state where mean elevation ridge valley relief and precipitation rates increase from the coast to the topographic crest of the range we find that the main control on the erosion rate pattern is the pattern in mean elevation and the amount of precipitation in contrast the pattern of precipitation is only a minor control as a whole our work demonstrates an approach for developing the theoretical context that is necessary for interpreting spatial associations between patterns in topography precipitation and erosion in natural orogens

using data insertion with the name model to simulate the 8 may 2010 eyjafjallajokull volcanic ash cloud a data insertion method where a dispersion model is initialized from ash properties derived from a series of satellite observations is used to model the 8 may 2010 eyjafjallajokull volcanic ash cloud which extended from iceland to northern spain we also briefly discuss the application of this method to the april 2010 phase of the eyjafjallajokull eruption and the may 2011 grimsvotn eruption an advantage of this method is that very little knowledge about the eruption itself is required because some of the usual eruption source parameters are not used the method may therefore be useful for remote volcanoes where good satellite observations of the erupted material are available but little is known about the properties of the actual eruption it does however have a number of limitations related to the quality and availability of the observations we demonstrate that using certain configurations the data insertion method is able to capture the structure of a thin filament of ash extending over northern spain that is not fully captured by other modeling methods it also verifies well against the satellite observations according to the quantitative object based quality metric sal structure amplitude location and the spatial coverage metric figure of merit in space

horizontal lightning propagation preliminary breakdown and electric potential in new mexico thunderstorms 1 characteristics of lightning flashes in three storms are compared to simultaneous electric field e measurements at various altitudes to examine three hypotheses the first is the idea that horizontal lightning branches propagate at altitudes near potential extrema or wells the analyses show that horizontal lightning activity and potential extrema are coincident in time and altitude and so are consistent with the idea that lightning moves charges into potential wells as a means of using a storm s electrostatic energy to drive a lightning flash s dielectric breakdown processes second these data are used to verify the usual interpretation of breakdown polarity of lightning radiation sources detected by the lightning mapping array the third hypothesis investigated is that normal cloud to ground flashes have a period of preliminary breakdown if and only if a potential well for negative charge exists between the altitudes of flash initiation and ground the analyses show that in 14 flashes when a low level well was indicated the period of preliminary breakdown before the first return stroke lasted an average of 117 ms considerably longer than the average lifetime of a stepped leader in 15 flashes in which no low level well was indicated the time between initiation and first return stroke averaged 15 ms

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

catastrophic landslides and their effects on the upper indus streams karakoram himalaya northern pakistan abstract the paper examines the nature and geomorphic influences of deposits from rock avalanches that obstruct rivers most of the 115 rockslide rock avalanche events identified in the karakoram himalaya straddled one or more stream valleys at least 73 of these landslides formerly dammed the indus or its tributaries upstream of the barriers remnants exist of once very extensive lacustrine deposits the stability and long term survival of dams from large rock avalanches is addressed and the reasons for the gradual or phased rather than catastrophic and sudden breaching case histories emphasise the erosional and depositional forms associated with the barriers they are reconstructed in terms of the emplacement and properties of the deposits from rock avalanches and the response of the river to interruption by them these barriers have exerted a substantial control over stream response and development for most of the holocene at least today they are associated with distinctive features of channel form and thalweg river terrace systems intermontane sediment sinks and sources and local erosional forms in bedrock more broadly the landslide barriers have created a naturally fragmented river system deposition and erosion in the lower few tens or hundreds of meters of the upper indus stream valleys have been dominated by epicycles of aggradation trenching and downcutting that mainly reflect the scale timing and history of each barrier the landforms involved are only indirectly related to the late glacial and paraglacial conditions that have hitherto been regarded as the main explanation

horizontal electric fields from lightning return strokes measurements are presented of simultaneous horizontal and vertical electric fields from 42 lightning return strokes in 27 flashes at distances from 7 to 43 km the data were obtained at the nasa kennedy space center florida using an elevated spherical antenna having a system bandwidth of 3 hz to 4 mhz the strokes studied occurred in a 6 min interval from 1850 to 1856 ut on august 11 1984 the 42 measured horizontal fields exhibited initial peaks having a mean half width of 0 52 s the ratio of the amplitude of the peak horizontal field to the associated vertical field peak had a mean value of 0 030 with a standard deviation of 0 007 the measured horizontal field wave shapes are compared with those obtained from calculations using the measured vertical fields and theory the wavetilt formula that models the fields as plane wave radiation over a homogeneous ground of uniform conductivity and permittivity the local ground conductivity measured as a function of depth using the wenner four probe method was found to increase with depth within the region relevant to this study from the surface to a depth of a few meters the conductivity was 8 2 10 3 mho m between the surface and a depth of 2 2 m and 3 1 10 2 mho m below this layer to a depth of 11 m if a ground conductivity equal to that of the top layer is used in the wavetilt formula the calculated horizontal field peaks are found to be on average about 33 wider and larger than the measured field peaks errors and compensation procedures for tilt of the spherical antenna for electronic system distortion and for electric field distortion at the antenna due to proximity of the ground and of the antenna support structure are described

episodic fluvial incision of rivers and rock uplift in the himalaya and transhimalaya abstract seventeen strath terraces in northern india were dated using 10 be surface exposure methods ages range from c 7 to c 735 ka and provide fluvial incision rates of 0 02 0 003 to 2 6 1 9 mm a 1 on the northern side of the ladakh range incision rates are c 1 mm a 1 in the northern zanskar range they are 0 06 0 005 mm a 1 new and published incision rates in southernmost lahul range from 0 1 0 02 to 13 2 6 2 mm a 1 rates for ages 35 ka are 0 4 0 2 mm a 1 across the himalaya and transhimalaya holocene fluvial incision rates range from c 0 02 to c 26 0 mm a 1 whereas pleistocene incision rates are 5 mm a 1 many of the holocene incision rates exceed exhumation rates whereas pleistocene incision rates are comparable with exhumation rates this suggests that long term fluvial incision is in dynamic steady state with exhumation the temporal pattern for rates of fluvial incision is probably controlled by episodic incision linked to significant precipitation changes throughout the quaternary suggesting that strath terraces with ages 35 ka can be used for assessing long term rates of rock uplift in contrast rates of fluvial incision based on late glacial and holocene strath terraces reflect changes in monsoon intensity and deglaciation events by determining ages for multiple samples on flights of strath terraces it is possible to document changes in incision rate assess whether post abandonment transient shielding has occurred and help elucidate tectonic v climatic controls on their formation supplementary material tables ds1 4 for previously published data and recalculated ages for strath terraces and figures ds1 and ds2 showing plots of incision rates against time for the himalaya and transhimalaya are available at http www geolsoc org uk sup18454

the siwaliks of western nepal ii mechanics of the thrust wedge abstract comparison between numerical models and structural data is used for a better understanding of the evolution of the siwalik thrust belt of western nepal the numerical model involves discontinuities within a critical wedge model a kinematic forward model of serial cross sections and a linear diffusion algorithm to simulate erosion and sedimentation in western nepal large piggy back basins duns are located above thick thrust sheets that involve more than 5500 m of the neogene siwalik group whereas piggy back basin sedimentation is less developed above thinner thrust sheets 4300 m thick numerical model results suggest that thrust sheet thickness and extension of wedge top basins are both related to an increase of the basal decollement dip beneath the duns the west dang transfer zone wdtz is a n ne trending tectonic lineament that limits the westward extent of the large piggy back basins of mid western nepal and is linked to a thickening of the himalayan wedge eastward the wdtz also affects the seismotectonics pattern the geometry of the thrust front the lateral extent of lesser himalayan thrust sheets and the subsidence of the foreland basin during middle siwalik sedimentation numerical models suggest that the individualisation of the piggy back basins at the transition between the middle siwalik and upper siwaliks followed the deposition of the middle siwaliks that induced a geometry of the foreland basin close to the critical taper as wdtz induces an e w thickning of the himalayan wedge it could also induce a northward shift of the leading edge of the ductile deformation above the basal detachment in greater himalayas of far western nepal field data locally suggest episodic out off sequence thrusting in the frontal thrust belt of western nepal whereas numerical results suggests that episodic out off sequence reactivation could be a general characteristic of the himalayan wedge evolution often hidden by erosion

charge transfer and in cloud structure of large charge moment positive lightning strokes in a mesoscale convective system 1 lightning observations in the very high frequency band and measurements of ultra low frequency magnetic fields are analyzed to investigate the charge transfer and in cloud structure of eight positive cloud to ground cg strokes in a mesoscale convective system although no high altitude images were recorded these strokes contained large charge moment changes 1500 3200 c km capable of producing nighttime sprites even though the convective region of the storm was where the flashes originated and where the cg strokes could occur the charge transferred to ground was mainly from the stratiform region the post stroke long continuing currents were connected to highly branched negative leader extension into the stratiform region while the storm dissipated the altitude of negative leader propagation in the stratiform area dropped gradually from 8 to 5 km indicating that in some and perhaps all of these strokes it was the upper positive charge in the stratiform region that was transferred

accuracy of the lightning mapping array 1 the location accuracy of the new mexico tech lightning mapping array lma has been investigated experimentally using sounding balloon measurements airplane tracks and observations of distant storms we have also developed simple geometric models for estimating the location uncertainty of sources both over and outside the network the model results are found to be a good estimator of the observed errors and also agree with covariance estimates of the location uncertainties obtained from the least squares solution technique sources over the network are located with an uncertainty of 6 12 m rms in the horizontal and 20 30 m rms in the vertical this corresponds well with the uncertainties of the arrival time measurements determined from the distribution of chi square values to be 40 50 ns rms outside the network the location uncertainties increase with distance the geometric model shows that the range and altitude errors increase as the range squared r2 while the azimuthal error increases linearly with r for the 13 station 70 km diameter network deployed during steps the range and height errors of distant sources were comparable to each other while the azimuthal errors were much smaller the difference in the range and azimuth errors causes distant storms to be elongated radially in plan views of the observations the overall results are shown to agree well with hyperbolic formulations of time of arrival measurements e g proctor 1971 two appendices describe 1 the basic operation of the lma and the detailed manner in which its measurements are processed and 2 the effect of systematic errors on lightning observations the latter provides an alternative explanation for the systematic height errors found by boccippio et al 2001 in distant storm data from the lightning detection and ranging system at kennedy space center

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

very low frequency sferic bursts sprites and their association with lightning activity 1 recent observations have revealed the occurrence of burst like vlf activity lasting from tens of milliseconds up to a few seconds associated with the onset of many sprites these sferic bursts are thought to be due to the horizontal in cloud component of lightning activity since they have been observed to propagate only short distances a few hundred kilometers in the earth ionosphere waveguide and are generally not reported by lightning detection networks the possible involvement of in cloud lightning in sprite production has been previously suggested on the basis of the observed long delays and spatial displacement between causative cloud to ground cg discharges and sprite events in this work we investigate the association between sprites and sferic bursts using vlf data and a large set of sprite observations between 1995 and 2000 we compare the occurrence of sferic bursts in association with sprites for thousands of observations through many different dates and thunderstorms results indicate that sprite causative cgs are more commonly found in association with bursts of sferic activity than those cg discharges without sprites and that furthermore the distribution of sferic burst vlf energy is significantly higher for sprite associated events we further investigate the source of these bursts by comparing vlf data to lightning mapping array lma data of vhf pulses due to lightning such comparisons show that most sferic burst events can be explained as radiation from the horizonal in cloud components of cg lightning as detected by the lma

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

using lightning observations as a volcanic eruption monitoring tool lightning commonly occurs in the eruption columns produced by explosive volcanic eruptions there are several different kinds of lightning detection instruments that could be employed to help monitor volcanoes each with their own advantages and disadvantages very low frequency vlf instruments have the ability to detect lightning at long ranges but tend to have low sensitivity due to network geometry and typically can provide only the time and 2 d location of a cloud to ground return stroke or similar high amplitude pulse produced by an intracloud discharge low frequency lf and medium frequency mf instruments typically have more sensitivity than a vlf network but can only be used for detection on a regional scale very high frequency vhf lightning mapping instruments also provide only regional coverage but detect all lightning within their range during the 2009 eruption of redoubt volcano alaska usa each of these types of instruments detected lightning from redoubt s ash plume the vhf system consistently detected lightning before the other two during each distinct explosive event and also detected more lightning than the others by one or two orders of magnitude lightning observations could be used to confirm and in some cases detect explosive volcanic activity the rapid response provided by lightning monitoring is a valuable tool for fast identification of potentially hazardous ash clouds

the incision variations of poiqu documented by the zhangmu landslide in the upper himalaya of tibet abstract aiming at the rate and causes of the incision variations in the upper himalaya orogenic belt of tibet a new method of incision rate estimation based on the analysis of the evolution of zhangmu landslide and its spatial and temporal relationship with the surrounding gullies is applied the research results are 1 the zhangmu landslide was an ancient huge landslide occurred at 24 2 2 4 ka bp consisting of an ancient bedrock landslide and subsequent deposit landslides with an area of 1 23 km2 and remaining volume of 23 4 106 m3 2 the fluvial incision rate shows variations in poiqu and its branch which may be controlled by the discharge and decreases from the poiqu 11 5 1 2 mm a to the tributaries from 4 8 0 5 mm a in the bangcundong gully to 2 4 0 2 mm a in zhangmu gully 3 the fluvial incision rate also shows temporal variations in the poiqu there are two periods of low rate and high rate incision processes in the poiqu while the section shape transforms from a gentle slope to a cliff in the low rate period from 24 2 ka bp to 10 0 ka bp in the poiqu valley the incision rate was 10 4 1 0 mm a while the high fluvial incision rate since 10 0 ka bp was 13 0 1 3 mm a 4 the fluvial incision promotes the landscape evolution and triggers the potential landslide in thousands of years

determining the contribution of volcanic ash and boundary layer aerosol in backscatter lidar returns a three component atmosphere approach 1 a solution of the lidar equation is discussed that permits combining backscatter and depolarization measurements to quantitatively distinguish two different aerosol types with different depolarization properties the method has been successfully applied to simultaneous observations of volcanic ash and boundary layer aerosol obtained in exeter united kingdom on 16 and 18 april 2010 permitting the contribution of the two aerosols to be quantified separately first a subset of the atmospheric profiles is used where the two aerosol types belong to clearly distinguished layers for the purpose of characterizing the ash in terms of lidar ratio and depolarization these quantities are then used in a three component atmosphere solution scheme of the lidar equation applied to the full data set in order to compute the optical properties of both aerosol types separately on 16 april a thin ash layer 100 400 m deep is observed average and maximum estimated ash optical depth 0 11 and 0 2 it descends from 2800 to 1400 m altitude over a 6 hour period on 18 april a double ash layer 400 m deep is observed just above the morning boundary layer average and maximum estimated ash optical depth 0 19 and 0 27 in the afternoon the ash is entrained into the boundary layer and the latter reaches a depth of 1800 m average and maximum estimated ash optical depth 0 1 and 0 15 an additional ash layer with a very small optical depth was observed on 18 april at an altitude of 3500 4000 m by converting the lidar optical measurements using estimates of volcanic ash specific extinction derived from other works the observations seem to suggest approximate peak ash concentrations of 1500 and 1000 g m3 respectively on the two observations dates

erosion and exhumation in the himalaya from cosmogenic isotope inventories of river sediments the outward erosional flux is a key factor in the tectonic evolution of mountain belts and there is much debate about the feedbacks between tectonics erosion and climate here we use cosmogenic nuclides 10be and 26al analysed in quartz from river sediments from the upper ganges catchment to make the first direct measurements of large scale erosion rates in a rapidly uplifting mountain belt the erosion rates are highest in the high himalaya at 2 7 0 3 mm yr 1 errors fall to 1 2 0 1 mm yr on the southern edge of the tibetan plateau and are 0 8 0 3 to 0 6 mm yr in the foothills to the south of the high mountains these relative estimates are corroborated by the nd isotopic mass balance of the river sediment analysis of sediment from an abandoned terrace suggests that similar erosion rates have been maintained for at least the last few thousand years the data presented here along with data recently published for european river catchments demonstrate that a log linear relationship between relief and erosion rate holds over three orders of magnitude variation in erosion rate and between very different climatic and tectonic regimes the erosion rate estimates from cosmogenic nuclides correlate well with exhumation rates calculated from previously published apatite fission track ages in the indian himalaya this confirms that much of the exhumation in the himalayan mountain chain is now balanced by erosion however exhumation rates calculated from high blocking temperature systems such as 40ar 39ar in muscovite imply lower exhumation rates rocks presently at the surface must have undergone a three to six fold increase in exhumation rate within the last few million years we show how this could be explained either by climatic forcing of erosion rate changes or by tectonics published evidence for equally rapid changes of exhumation rate in the past and the probable diachroneity in the time at which the present exhumation rates accelerated imply that tectonics has moderated at least some of the change in exhumation rates

modern erosion rates in the high himalayas of nepal abstract current theories regarding the connections and feedbacks between surface and tectonic processes are predicated on the assumption that higher rainfall causes more rapid erosion to test this assumption in a tectonically active landscape a network of 10 river monitoring stations was established in the high himalayas of central nepal across a steep rainfall gradient suspended sediment flux was calculated from sampled suspended sediment concentrations and discharge rating curves accounting for solute and bedload contributions the suspended sediment fluxes were used to calculate watershed scale erosion rates that were then compared to monsoon precipitation and specific discharge we find that in individual watersheds annual erosion rates increase with runoff in addition our data suggest average erosion rate increases with discharge and precipitation across the entire field site such that the wetter southern watersheds are eroding faster than the drier northern watersheds the spatially non uniform contemporary erosion rates documented here are at odds with other studies that have found spatially uniform long term rates 10 5 10 6 yr across the pronounced rainfall gradient observed in the region the discrepancy between the modern rates measured here and the long term rates may be reconciled by considering the high erosional efficiency of glaciers the northern catchments were much more extensively glacierized during the pleistocene and therefore they likely experienced erosion rates that were significantly higher than the modern rates we propose that in the northern watersheds the high rates of erosion during periods of glaciation compensate for the low rates during interglacials to produce a time averaged rate comparable to the landslide dominated southern catchments

late quaternary landscape evolution and genesis of the 2009 catastrophic landslide in the hsiao lin area southwestern taiwan abstract with cumulative rainfall of 1700 mm typhoon morakot triggered a catastrophic landslide at hsiao lin 9 august 2009 which dammed the river buried the village and killed 400 people we conducted a geomorphic study to understand the origin of this landslide in the context of the long term evolution of the hillslope the landslide originated from a broad poorly drained slope 21 23 and ran down along two first order channels the erosion up to 80 m thick has created a concave shape slope and exposed mostly loose debris which implies that the landslide was mainly the reworking of ancient colluviums the genesis of the concave shape slope where the source sediments of the landslide resided reflects the weakness of the mudstone shale bedrock underlying this slope in contrast to the sandstone based transport area the two channels in the transport area also follow old faults or joints given that the source area has been subject to erosion during large landslides the subsequent deposition here was likely achieved by minor colluvial processes this deposition continued until the catastrophic failure in 2009 which could be controlled by 1 the amount of sediments deposited which determined the slope angle and 2 the headward expansion of the channels from the transport area which enhanced groundwater convergence and later provided routes for the landslide materials to run downslope extensive mass wasting motions had occurred in the area as shown by the prevalence of 20 m thick landslide debris flow sequences on the lower part of the hillslope which are dated 21 14 9 13 7 and 12 0 ka by the radiocarbon method these mass wasting events had hindered the long term incision of the trunk river in response to the rapid tectonic uplift at least the 12 0 ka event which caused extensive mud flow deposition had dammed the river overall this study shows how bedrock lithology and structures controlled the shape of a hillslope and caused extremely unsteady mass wasting transport in the active mountains of taiwan

statistical analysis of storm electrical discharges reconstituted from a lightning mapping system a lightning location system and an acoustic array in the framework of the european hydrological cycle in the mediterranean experiment project a field campaign devoted to the study of electrical activity during storms took place in the south of france in 2012 an acoustic station composed of four microphones and four microbarometers was deployed within the coverage of a lightning mapping array network on the 26 october 2012 a thunderstorm passed just over the acoustic station fifty six natural thunder events due to cloud to ground and intracloud flashes were recorded this paper studies the acoustic reconstruction in the low frequency range from 1 to 40 hz of the recorded flashes and their comparison with detections from electromagnetic networks concurrent detections from the european cooperation for lightning detection lightning location system were also used some case studies show clearly that acoustic signal from thunder comes from the return stroke but also from the horizontal discharges which occur inside the clouds the huge amount of observation data leads to a statistical analysis of lightning discharges acoustically recorded especially the distributions of altitudes of reconstructed acoustic detections are explored in detail the impact of the distance to the source on these distributions is established the capacity of the acoustic method to describe precisely the lower part of nearby cloud to ground discharges where the lightning mapping array network is not effective is also highlighted

lightning subsequent stroke electric field peak greater than the first stroke peak and multiple ground terminations for 46 multiple stroke flashes in which each stroke ground termination was located using a tv camera network and thunder ranging 15 flashes 33 had one or more subsequent return strokes whose initial electric field peak normalized to 100 km was greater than the first stroke field peak of the flash in 9 of these 15 flashes the subsequent strokes with field peaks greater than the first stroke followed the same channel as the first stroke in five flashes the subsequent strokes with the greater peaks followed a different channel to ground and in one flash the subsequent strokes with the greater peaks occurred both in the first stroke channel and in a different channel the interstroke intervals immediately preceding the 13 larger subsequent strokes that followed the first stroke channel had a geometric mean gm duration of 98 ms 1 7 times greater than the gm of 57 ms for all 199 interstroke intervals 46 flashes without any selection eight of the 13 larger subsequent strokes for which leader durations were measurable had a gm leader duration of 0 55 ms 3 3 times smaller than the gm of 1 8 ms for 117 subsequent leaders with measurable duration in a previously formed channel of the 46 multiple stroke flashes for the six larger subsequent strokes that created a new channel to ground the preceding interstroke interval had a gm of 130 ms and the leader duration had a gm of 15 ms no subsequent stroke with peak field exceeding the first in any category had a preceding interstroke interval less than 35 ms analysis of direct current measurements from switzerland shows that subsequent stroke currents exhibit many features similar to those of florida subsequent stroke electric fields in 22 florida single stroke and multiple stroke ground flashes the distances between multiple channel terminations in a given flash 33 measurements ranged from 0 3 km to 7 3 km with a gm of 1 7 km

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

three dimensional fractal modeling of intracloud lightning discharge in a new mexico thunderstorm and comparison with lightning mapping observations 1 the direct comparison of lightning mapping observations by the new mexico tech lightning mapping array lma with realistic models of thundercloud electrical structures and lightning discharges represents a useful tool for studies of electrification mechanisms in thunderstorms initiation and propagation mechanisms of different types of lightning discharges as well as for understanding of electrical and energetic effects of tropospheric thunderstorms on the upper regions of the earth s atmosphere this paper presents the formulation of a new three dimensional probabilistic model for investigating the structure and development of bidirectional positive and negative lightning leaders the results closely resemble structures observed by the lma during intracloud discharges the model represents a synthesis of the original dielectric breakdown model based on fractal approach proposed by niemeyer et al 1984 and the equipotential lightning channel hypothesis advanced by kasemir 1960 and places special emphasis on obtaining self consistent solutions preserving complete charge neutrality of the discharge trees at any stage of the simulation a representative simulation run is compared to a typical intracloud discharge measured by lma in a new mexico thunderstorm on 31 july 1999 following the conclusions from coleman et al 2003 the comparison of the model and observed discharges reveals that an adequate choice of the electrical structure of the model thundercloud permits the development of a model intracloud discharge reproducing principal features of the observed event including the initial vertical extension of the discharge between the main negative and upper positive charge regions of the thundercloud and the subsequent horizontal propagations in these regions also consistent with observations e g coleman et al 2003 negative and positive leaders mainly develop in the upper positive and main negative charge regions respectively for the particular model case presented in this paper the total charge transfer the vertical dipole moment and the average linear charge density associated with the development of bidirectional structure of leader channels are estimated to be 37 5 c 122 c km and 0 5 mc m respectively in good agreement with related data reported in the refereed literature the model results also demonstrate that the bulk charge carried by the integral action of positive and negative leaders leads to a significant up to 80 reduction of the electric field values inside the thundercloud significantly below the lightning initiation threshold

giant landslides topography and erosion abstract distributions of slope angles in tectonically active mountain belts point to the development of threshold conditions where hillslopes attain a critical inclination or height at which they fail readily because of limitations in material strength it has been proposed that hillslopes adjust to rapid uplift and bedrock incision through an increase in the rate of relief limiting landsliding rather than gradual slope steepening here we test this concept by investigating the relationship between mean local relief h which we take to be a proxy of long term erosion rates e and the occurrence of over 300 of the largest v 10 8 m 3 terrestrial landslides on earth we find that nearly two thirds of these giant landslides have occurred in the steepest 5 of the earth s land surface where relief is close to its proposed upper strength limit they are primarily located in deeply incised valleys along fault bounded fringes of active mountain belts and in volcanic arcs this distribution coincides with areas of high long term erosion rates 4 mm yr 1 confirming that giant landslides contribute to rapid denudation of mountains most of the eroded volume is concentrated in the smallest but steepest parts of mountain belts and volcanic arcs first order estimates of minimum erosion rates accomplished by the largest landslides are 0 01 mm yr 1 these rates are between 1 and 10 of the late pleistocene to holocene mean erosion rates in a given area importantly the landslide erosion rates show a nonlinear increase with mean local relief suggesting that the contribution of giant landslides in total and per event increases significantly with increasing overall erosion rates however giant landslides also occur in areas of lower than average relief h 300 700 m irrespective of whether threshold hillslopes have developed or not factors contributing to these failures include soft rocks extensive low angle discontinuities high rates of fluvial bedrock incision and tectonically driven deformation and slope loading

lightning location relative to storm structure in a supercell storm and a multicell storm relationships between lightning location and storm structure are examined for one radar volume scan in each of two mature severe storms one of these storms had characteristics of a supercell storm and the other was a multicell storm data were analyzed from dual doppler radar and dual vhf lightning mapping systems the distributions of vhf impulse sources were compared with radar reflectivity vertical air velocity and their respective gradients in the supercell storm lightning tended to occur along streamlines above and downshear of the updraft and reflectivity cores vhf impulse sources were most concentrated in reflectivities between 30 and 40 dbz and were distributed uniformly with respect to updraft speed in the multicell storm on the other hand lightning tended to coincide with the vertical reflectivity and updraft core and with the diverging streamlines near the top of the storm the results suggest to us that the location of lightning in these severe storms was most directly associated with the wind field structure relative to updraft and reflectivity cores since the magnitude and vertical shear of the environmental wind are fundamental in determining the reflectivity and wind field structure of a storm we suggest that these environmental parameters are also fundamental in determining lightning location

storm structure during aircraft lightning strike events a small set of in situ aircraft and ground based radar data acquired during the 1981 and 1982 joint agency turbulence experiment is used to study the relationship of aircraft lightning strikes to storm precipitation turbulence severity and wind shear the strikes were found to be strongly correlated with vertical drafts predominantly downdrafts strikes were also well correlated with regions of strong turbulence however since most strong turbulence episodes encountered by the aircraft were not associated with lightning use of lightning location methods to map hazardous turbulence within storms is considered unreliable the strikes occurred in storm regions having a radar reflectivity factor between 25 and 35 dbz dbz represents 10 log z where z is the reflectivity factor these regions were generally on the boundaries of the dominant storm precipitation cores storm wind shear was frequently high in regions near aircraft strikes

exhumation and incision history of the lahul himalaya northern india based on u th he thermochronometry and terrestrial cosmogenic nuclide methods abstract low temperature apatite u th he ahe thermochronology on vertical transects of leucogranite stocks and 10 be terrestrial cosmogenic nuclide tcn surface exposure dating on strath terraces in the lahul himalaya provide a first approximation of long term 10 4 10 6 years exhumation rates for the high himalayan crystalline series hhcs for northern india the ahe ages show that exhumation of the hhcs in lahul from shallow crustal levels to the surface was 1 2 mm a and occurred during the past 2 5 ma bedrock exhumation in lahul fits into a regional pattern in the hhcs of low temperature thermochronometers yielding plio pleistocene ages surface exposure ages of strath terraces along the chandra river range from 3 5 to 0 2 ka two sites along the chandra river show a correlation between tcn age and height above the river level yielding maximum incision rates of 12 and 5 5 mm a comparison of our ahe and surface exposure ages from lahul with thermochronometry data from the fastest uplifting region at the western end of the himalaya the nanga parbat syntaxis illustrates that there are contrasting regions in the high himalaya where longer term 10 5 10 7 years erosion and exhumation of bedrock substantially differ even though holocene rates of fluvial incision are comparable these data imply that the orogen s indenting corners are regions where focused denudation has been stable since the mid pliocene however away from these localized areas where there is a potent coupling of tectonic and surface processes that produce rapid uplift and denudation plio pleistocene erosion and exhumation can be characterized by disequilibrium where longer term rates are relatively slower and shorter term fluvial erosion is highly variable over time and distance the surface exposure age data reflect differential incision along the length of the chandra river over millennial time frames illustrate the variances that are possible in himalayan river incision and highlight the complexity of himalayan environments

lightning and precipitation in a small multicellular thunderstorm radio images of 26 consecutive lightning flashes are described in relation to radar pictures of the storm these flashes all started in two vertical turrets where reflectivity factors exceeded 25 dbz five large cloud flashes pervaded an almost horizontal plume or low level anvil and ground flashes occurred on the opposite side in the propagating flank of this storm observers on the ground reported a light hailfall and copious rain most of the lightning occurred in a region that was 3 5 km above ground agl flashes originated at heights that ranged from 3 1 km where the environmental air temperature was 5 c to 5 1 km agl 16 c and they began at a mean height of 3 94 km agl 10 c the standard deviation of 26 heights at which flashes began was 440 m recorded electric field changes showed that the channels were charged negatively and we inferred that negative charge had accumulated at these heights in the vertical turrets and that the paths followed by cloud flashes were influenced by positive charge which had accumulated in a plume that was nearly horizontal and which had formed on the flank opposite to the propagating flank of the storm the estimated total length of 18 consecutive lightning flashes that had occurred during a 3 min interval was 486 km measurements of electric field change magnitudes were used to estimate totals of 440 c and 106 c that had been discharged in 180 s from two cells whose volumes enclosed by 30 dbz surfaces were 260 and 80 km3 respectively this paper also describes the geometries of stepped leaders that cause electric field changes of the bil form it discusses a continuing current which was carried by a cloud flash

dating the onset of lower tagus river terrace formation using electron spin resonance in the western iberian peninsula staircases of fluvial terraces have been the subject of several recent studies in particular many recent publications have focused on the quaternary fluvial chronostratigraphy of the lower tagus basin however there are still doubts with respect to the timing of the first incision into the late tertiary basin fill deposits their upper part already recording a fluvial environment basin inversion which was the start of terrace formation this is because most dating methods are ineffective for this type of deposit generally without organic and or volcanic materials in the last 10 years new dating methods such as electron spin resonance esr applied to sedimentary quartz now facilitate more accurate chronologies this paper presents the results of the esr dating of the older terraces of the lower tagus basin portugal with extrapolation on the age of early drainage network evolution according the results the oldest fluvial terrace was formed around 900 ka so the origination of the portuguese tagus river terrace system can be attributed to the final part of the early pleistocene

serial profiles of electrostatic potential in five new mexico thunderstorms 1 profiles of electric potential v integrated from balloon borne electric field e measurements are used to investigate the electrical evolution of thunderstorms over the mountains in central new mexico with sequential soundings through multiple storms the time skew associated with obtaining v from a noninstantaneous sounding is also studied the data show that a basic v profile with a maximum above a minimum forms in the early stage of the storm and is maintained throughout its mature stage series of soundings from individual storms show only a gradual evolution in the v profile from the early through the mature stage as the extrema descend in altitude and become shallower and vertically closer together more evolution occurs in the late stage when the shape of the v profile reverses to have a minimum above a maximum the 17 v z profiles from the mature stage of five different storms are also very similar in overall shape suggesting that the basic shape is not significantly affected by differences in lightning flash rate among these storms the findings indicate that the potential profile during a typical sounding in the mature stage is relatively stable and the overall shape of the mature stage v profile does not change markedly on the time scale of a particular balloon sounding 10 30 min through new mexico mountain storms thus time skew problems in the v profiles are minor during a storm s mature stage

post earthquake landsliding and long term impacts in the wenchuan earthquake area china abstract the ms 8 0 wenchuan earthquake on may 12 2008 triggered tens of thousands of landslides and produced large amounts of loose material the loose material accumulated in gullies or on slopes provides abundant sources for the consequent debris flows which will endanger resettled residents and destroy urban reconstruction during the 5 years following the wenchuan earthquake event heavy rainfalls have already induced a great number of debris flows in the earthquake damaged area resulting in serious casualties and property losses the co seismic landslides and the debris flows induced by rainfalls in the mianyuan river basin are analyzed using multi temporal remote sensing images more than 2000 landslides were triggered and about 4 0 108 m3 of loose material was generated in the mianyuan river basin and the volume of erodible material is 6 0 107 1 6 108 m3 there were 1 27 107 m3 of bed load sediments and 6 3 105 m3 suspended load sediments transported into the river system in the past 5 years the active mass movements will last for a long period in the mianyuan river basin

catastrophic rock slope failures and late quaternary developments in the nanga parbat haramosh massif upper indus basin northern pakistan abstract the nanga parbat haramosh massif has some of the greatest relief on earth and highest measured rates of uplift denudation and river incision in bedrock many studies have sought to understand how its morphology relates to geotectonic evolution and glaciations however few catastrophic rock slope failures had been recognised and many of their impacts had been attributed to other processes recently more than 150 of these landslides have been found within a 100 km radius of nanga parbat 8125 m new discoveries are reported east north and west of nanga parbat along the indus streams most generated long run out rock avalanches that dammed the indus or its tributaries some impounding large lakes they initiated episodes of intermontane sedimentation followed by trenching and removal of sediment valley floor features record a complex interplay of impoundment and sedimentation episodes superimposition of streams in pre landslide valley floors and exhumation of buried features these findings depart from existing reconstructions of quaternary events a number of the rock avalanche deposits were previously misinterpreted as tills or moraine and their associated lacustrine deposits attributed to glacial lakes features up to 1000 m above the indus formerly seen as tectonically raised terraces are depositional features emplaced by landslides or erosion terraces recording the trenching of valley fill in landslide interrupted river reaches unquestionably tectonics and glaciation have been important but decisive and misread formative events of the holocene involve a post glacial landslide fragmented fluvial system the latter has kept valley developments in a chronic state of disequilibrium with respect to climatic and geotectonic controls accepted glacial chronologies are put in doubt particularly the extent and timing of the last major glaciation the pace and role processes in the holocene have been seriously underestimated

lf vlf and vhf lightning fast stepped leader observations 1 this paper reports multiplatform observations of leader radiation preceding initial cloud to ground lightning return strokes by 6 ms specifically we present multistation ground based lf vlf recordings of events with large amplitude leader activity comparable in amplitude to the return stroke amplitude the events were selected for their coincidence with vhf observations by the forte satellite some forte vhf leader step observations have obvious direct and ground reflection components for these steps which temporally correspond to specific features in the ground lf vlf field change records we calculate a source height based on event satellite geometry we determine source heights between 4 0 and 5 5 km for forte records with multiple reflected events we calculate vertical leader propagation velocities on the order of 106 m s the determined vertical leader propagation speeds are an order of magnitude greater than those reported as typical values for stepped leader velocities associated with initial return strokes

time and space correlation between sprites and their parent lightning flashes for a thunderstorm observed during the hymex campaign during the night of 22 23 october 2012 together with the hydrology cycle in the mediterranean experiment hymex special observation period 1 campaign optical observations of sprite events were performed above a leading stratiform mesoscale convective system in southeastern france the total lightning activity of the storm was monitored in three dimensions with the hymex lightning mapping array broadband extremely low frequency very low frequency records and radar observations allowed characterizing the flashes and the regions of the cloud where they propagated twelve sprite events occurred over the stratiform region during the last third of the lightning activity period and well after the coldest satellite based cloud top temperature 62 c and the maximum total lightning flash rate 11 min 1 the sprite producing positive cloud to ground sp cg strokes exhibit peak current from 14 to 247 ka charge moment changes cmc from 625 to 3086 c km and impulsive cmc icmc between 242 and 1525 c km the cg flashes that do not trigger sprites are initiated outside the main convective core have much lower cmc values and in average shorter durations lower peak currents and shorter distances of propagation the cmc appears to be the best sprite predictor the delay between the parent stroke and the sprite allows classifying the events as short delayed 20 ms all long delayed sprites i e most of the time carrot sprites are produced by sp cg strokes with low icmc values all sp cg flashes initiate close to the convective core and generate leaders in opposite directions negative leaders finally propagate toward lower altitudes within the stratiform region that coincides with the projected location of the sprite elements

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

vhf radio pictures of lightning flashes to ground we present information obtained from vhf radio pictures of 47 lightning flashes that struck ground 1430 m above mean sea level msl to the north of johannesburg over a period of 16 years radio pictures were obtained using a hyperbolic method i e by taking differences between times at which radio noise from lightning arrived at five widely spaced stations these data were supplemented by recordings of electric field change we found that stepped leaders and intracloud streamers emitted pulses and progressed at speeds that averaged 1 6 105 ms 1 stepped leaders ranged in length from 3 to 13 km bil breakdown intermediate leader waveforms of electric field change were caused by stepped leaders whose branched channels followed complicated paths the electric field changes they recorded in an effective bandwidth of 3 5 khz could be reproduced faithfully by calculations based on an assumption that the radio sources became charged at the expense of a region near the origin of each leader some return strokes radiated trains of noise called q noise whose sources extended at speeds near 108 ms 1 sources of this q noise retraced leader channels before extending them at these high speeds interstroke processes radiated q noise whose sources extended at speeds that averaged 8 7 107 ms 1 most q sources 98 were directed vertically but they pervaded regions that retrogressed at speeds that averaged 2 2 104 ms 1 in directions away from the starting points of the flashes this retrogression was directed horizontally but the vertical q streamers caused j changes to have positive or negative slopes according to the relative positions of q sources and the reversal cone sixty percent of our sample of ground flashes were endowed with portions that were cloud flashes or were themselves minor components of cloud flashes a more detailed summary appears at the end of the paper

catastrophic landslide induced by typhoon morakot shiaolin taiwan abstract typhoon morakot induced the catastrophic and deadly shiaolin landslide in southern taiwan on 9 august 2009 resulting in more than 400 casualties we undertook a geological and geomorphological investigation with the aim of reconstructing the events leading up to this landslide and to clarify factors that contributed to its development cumulative rainfall reached up to 1676 5 mm in about three days under the influence of the typhoon and the shiaolin landslide with a volume of 25 106 m3 occurred one day after the peak in rainfall intensity the landslide occurred on a dip slope overlying late miocene to early pliocene sedimentary rocks consisting of silty shale massive mudstone and sandstone it started as a rockslide in the upper third of the landslide area and transformed into a rock avalanche that crossed a series of terraces and displaced or buried the village below it buried the riverbed of the chishan river and ran up the opposite slope creating a landslide dam 60 m high which was breached about 1 h and 24 min later flooding the village the velocity of the landslide is estimated to have been 20 4 to 33 7 m s 1 and its apparent friction angle was 14 which indicates its high mobility the detachments in the source area consist of combinations of bedding planes and joints or faults the landslide was preceded by gravitational deformation which appeared as hummocky landforms before the landslide and as buckle folds exposed after the event the landslide deposits consist of fragments of mudstone shale and sandstone as well as clayey material at its base this clayey material consisting of illite chlorite quartz feldspar and calcite is assumed to have strongly influenced the long rapid runout

ratio of leader to return stroke electric field change for first and subsequent lightning strokes the ratio of leader to return stroke electric field change versus distance is presented as a function of stroke order for 218 first and subsequent strokes in 70 cloud to ground flashes which occurred near tampa florida in 1979 the measured leader to return stroke field ratio tended to be more negative as the stroke order increased implying that the charge sources for successive strokes were on average progressively farther from both the observer and the ground strike point sixteen percent of all flashes analyzed contained at least one leader return stroke sequence with a negative net electric field change that is a ratio that is less than 1 these strokes were observed at distances from 2 5 to 11 6 km with 56 farther than 8 km they exhibited a strong tendency to occur late in a flash with 89 occurring after the fourth stroke the geometic mean initial electric field peak normalized to 100 km for strokes with a ratio less than 1 was found to be 1 1 v m 2 6 times lower than for all subsequent strokes in our data base

lightning location relative to storm structure in a leading line trailing stratiform mesoscale convective system 1 horizontal and line normal vertical cross sections and composite images of dallas fort worth lightning detection and ranging ldar ii vhf radiation sources and radar reflectivity over a 30 min period provide a unique perspective on lightning pathways within a leading line trailing stratiform llts mesoscale convective system mcs on 16 june 2002 the overwhelming majority of vhf lightning sources occurred within the leading convective line in a bimodal pattern in the vertical assuming that vhf source density maxima were most likely associated with positive charge then the ldar ii observations suggest that the gross charge structure of the convective region of the mcs was characterized by a tripole with net positive charge centered at 4 5 km agl 3 c and 9 5 km agl 35 c and net negative charge centered roughly in the relative minimum of the vhf source density maximum at 7 km agl 17 c a persistent lightning pathway and inferred positive charge zone sloped rearward by 40 50 km and downward by 4 5 km from the upper vhf source maximum in the convective line through the transition zone and into the radar bright band of the stratiform region in the stratiform region vhf lightning sources and inferred positive charge were concentrated in three layers centered at 4 5 6 and 9 km agl 2 c 11 c and 31 c respectively consistent with past electric field studies of symmetric llts mcss positive cloud to ground lightning flashes in the stratiform region were initiated in the convective line and followed the slanting pathway from the top of convective cores to the stratiform precipitation where they were horizontally extensive layered and highly branched the sloping lightning pathway was identical to hypothetical trajectories taken by snow particles these observations provide further support for the advection of charge on snow along the sloping pathway and the in situ generation of charge in the horizontal lightning layers as primary contributors to electrification and positive lightning production rearward of the convective line

grain size dependent concentration of cosmogenic 10be and erosion dynamics in a landslide dominated himalayan watershed for documenting recent or late quaternary erosion rates at the scale of a small watershed or even an entire mountain range the use of in situ terrestrial cosmogenic nuclides tcn such as 10be in river sediments has become widespread over the last decade in mountainous settings however landslides may induce a two fold complication in the cosmogenic nuclide budget first they may episodically deliver large amounts of sediment with low tcn concentrations to the river channel second they may generate a grain size concentration dependence in these sediments however studies that have explored grain size dependence in landslide dominated areas have reached differing conclusions and the underlying mechanisms remain poorly understood the present study focuses on the khudi khola river basin a small drainage basin in the central himalayas the area is characterized by steep slopes heavy rainfall and high sediment production rates importantly the watershed contains a large area of active landsliding in situ 10be was analyzed in sediments of grain sizes ranging from 75 m to 4 cm collected from five locations upstream downstream and in the small tributaries which drain the landslides in all sampling locations including those situated upstream of the landslides the finest grains 75 250 m are two to four times more concentrated in 10be than the largest clasts 4 7 mm we developed a numerical slope model which includes a low level of background soil erosion and episodic denudation from large mass wasting events we then introduced a coarsening of average grain size with soil depth to the model our simulation shows that the data available for this valley are compatible with a scenario in which landslides deliver coarse grains to the channel that are less concentrated in tcn and have deeper provenance best fit estimates of the model parameters suggest recurrence times of 3000 to 9000 years for a major landslide on the same slope and mean long term landslide denudation rates of 1 7 to 4 7 mm yr 1 a negative correlation between tcn concentration and grain size is also observed directly upstream and 5 km downstream of the landsliding area suggesting that nearly all of the sediment carried by the river is derived from ancient landslides while almost no sediment is supplied by erosion of soil mantled slopes despite these complications apparent denudation rates directly derived from the tcn concentrations and from previously published data in the region are all on the same order of magnitude around 2 mm yr 1 however a factor of three variability remains between the different studies depending on the location the year of sampling and the analyzed grain size fraction thus although tcn derived average denudation rates provide a useful first order estimate even in fast eroding terrains dominated by landslides caution should be applied when using quantitative results in such settings

regional crustal thickness and precipitation in young mountain chains crustal thickness is related to climate through precipitation induced erosion along the andes the highest mountains and thickest crust 70 km occur at 25 south a region of low precipitation westerly winds warm passing over the atacama desert precipitation is modest in the high andes and eastward over the altiplano severe aridity hence low erosion rates helps to account for the elevated volcanogenic contractional arc and high internally draining plateau in its rain shadow weak erosion along the north central arc provides scant amounts of sediment to the chile peru trench starving the subduction channel subcrustal removal might be expected to reduce the crustal thickness but is not a factor at 25 south the thickness of the gravitationally compensated continental crust cannot reflect underplating and or partial fusion of sediments but must be caused chiefly by volcanism plutonism and contraction contrasting climate typifies the terrane at 45 south where moisture laden westerly winds encounter a cool margin bringing abundant precipitation the alpine landscape is of lower average elevation compared with the north central andes and is supported by thinner continental crust 35 km intense erosion supplies voluminous clastic debris to the offshore trench and vast quantities are subducted however the southern andean crust is only about half as thick as that at 25 south suggesting that erosion not subcrustal sediment accretion or anatexis is partly responsible for the thickness of the mountain belt the himalayas plus tibetan plateau the sierra nevada plus colorado plateau and the japanese islands exhibit analogous relationships between crustal thickness and climate

evolution of the total lightning structure in a leading line trailing stratiform mesoscale convective system over houston texas 1 line normal vertical cross sections of houston lightning detection and ranging ldar vhf radiation sources and radar reflectivity provide new insights into the three dimensional total lightning structure and evolution of a leading line trailing stratiform llts mesoscale convective system mcs over houston texas on 31 october 2005 previous research examining only the mature stage of an mcs showed that the overwhelming majority of vhf lightning sources occurred in the convective region with a lightning pathway extending rearward and descending in altitude into the stratiform region this descending pathway was most likely associated with small charged ice particles advected from the convective line unlike previous research the lightning pathway observed during the evolution of the mcs on 31 october 2005 initially extended rearward 40 km at a nearly constant height of 9 10 km in less than an hour the lightning pathway evolved into a sloped pathway similar to that found by previous research with a horizontal extent between 50 to 60 km and downward descent of 4 to 5 km during the lightning pathway evolution radar analysis showed an increase of reflectivity in the midlevels of the stratiform region consistent with increased depositional and aggregational growth above the melting layer broadening increased range of values of radar reflectivity above the melting layer was most likely an indication of a strengthening mesoscale updraft in the stratiform region this strengthening updraft may have contributed to an increase in the growth of the small charge carrying ice crystals giving them a greater fall speed in addition the mesoscale updraft may have promoted an environment conducive to local stratiform region charge generation in the mixed phase region just above the melting layer

speed and current for lightning stepped leaders near ground as determined from electric field records the speed and current during the final stages of the lightning stepped leader were determined from features of the electric field waveform the average speed of the leader tip was found below the height where de dt was zero for close lightning this height was in the range 0 6 2 0 km for flashes at the distances considered here 3 6 5 7 km for 10 stepped leaders observed near tampa florida the mean final one dimensional speed was 4 4 105 m s the standard deviation was 3 8 105 m s and the range was 1 0 14 105 m s these speeds are consistent with other stepped leader speeds reported in the literature that were found using optical techniques the current was estimated when the leader was near ground from de dt during the last hundred microseconds before the return stroke for 62 stepped leaders observed at distances of 3 6 14 km the mean final leader current was 1 3 ka the standard deviation was 1 0 ka the geometric mean was 1 0 ka and the range was 110 a to 5 0 ka errors resulting from uncertainties in distance charge center height calibration ground channel inclination and channel branching were found to be about 40 50 rms for both speed and current

electric fields preceding cloud to ground lightning flashes we analyzed in detail the electric field variations preceding the first return strokes of 80 cloud to ground lightning flashes in nine different storms observed at the nasa kennedy space center during the summers of 1976 and 1977 the electric field variations are best characterized as having two sections preliminary variations and stepped leader the stepped leader electric field change begins during a transition period of a few milliseconds duration marked by characteristic bipolar pulses the durations of stepped leaders lie most frequently in the range 6 20 milliseconds we infer from our measurements and critical review of the previous literature that there is only one type of stepped leader not the two types and often referred to in the literature

radio interferometric observations of cloud to ground lightning phenomena in florida radio frequency observations of cloud to ground lightning in florida have been analyzed to document a number of features of the lightning the observations have been made using an interferometer system which determined the direction to the lightning radiation as a function of time during close lightning discharges observations are presented for about 50 radiating events during five multiple stroke normal polarity flashes to ground the results confirm and extend results of a similar study of new mexico lightning by rhodes et al 1994 dart leaders in cloud k events and attempted leaders are found to be the same phenomena namely a negative polarity streamer that propagates horizontally and or vertically to ground at estimated speeds of about 10 7 ms 1 down to 10 6 ms 1 the step or impulsive fast electric field change produced by some k events is found to be caused by positive breakdown back at the starting point of the negative streamer after the streamer has progressed over some or all of its distance this breakdown appears to initiate a forward stroke along the streamer channel which can renew the breakdown at the front end of the channel k breakdown which happens to occur during a continuing current discharge to ground produces an m event channel brightening when it connects with the conducting channel to ground the step fast field change of the m events is found to be produced at the time of connection inside the cloud no fast field change is detected when this breakdown reaches ground that would be associated with a return stroke m events can also be initiated by fast 10 7 ms 1 positive streamers which often propagate away from the leader source region within a few milliseconds of the arrival of a return stroke back in the source region these streamers often generate an even faster negative recoil event back along their extent which propagates down the channel to ground as the m event in all cases the current increase or channel brightening produced by k and m events is predicted to occur in a forward direction that is toward or down the channel to ground in the same direction as the initiating negative streamer positive breakdown is detected only immediately following return strokes or during some k streamers in both cases the electric stresses are expected to be very large suggesting that positive breakdown which produces a conducting channel is difficult to initiate results for one flash suggest that negative charge was left at low altitude by the initial stroke to ground this forced the subsequent leaders to develop a new path to ground first as series of attempted leaders and then as a dart stepped leader

climatic and topographic controls on the style and timing of late quaternary glaciation throughout tibet and the himalaya defined by 10be cosmogenic radionuclide surface exposure dating abstract temporal and spatial changes in glacier cover throughout the late quaternary in tibet and the bordering mountains are poorly defined because of the inaccessibility and vastness of the region and the lack of numerical dating to help reconstruct the timing and extent of glaciation throughout tibet and the bordering mountains we use geomorphic mapping and 10 be cosmogenic radionuclide crn surface dating in study areas in southeastern gonga shan southern karola pass and central western nyainqentanggulha shan and tanggula shan tibet and we compare these with recently determined numerical chronologies in other parts of the plateau and its borderlands each of the study regions receives its precipitation mainly during the south asian summer monsoon when it falls as snow at high altitudes gonga shan receives the most precipitation 2000 mm a 1 while near the margins of monsoon influence the karola pass receives moderate amounts of precipitation 500 600 mm a 1 and in the interior of the plateau little precipitation falls on the western nyainqentanggulha shan 300 mm a 1 and the tanggula shan 400 700 mm a 1 the higher precipitation values for the tanggula shan are due to strong orographic effects in each region at least three sets of moraines and associated landforms are preserved providing evidence for multiple glaciations the 10 be crn surface exposure dating shows that the formation of moraines in gonga shan occurred during the early mid holocene neoglacial and little ice age on the karola pass during the lateglacial early holocene and neoglacial in the nyainqentanggulha shan date during the early part of the last glacial cycle global last glacial maximum and lateglacial and on the tanggula shan during the penultimate glacial cycle and the early part of the last glacial cycle the oldest moraine succession in each of these regions varies from the early holocene gonga shan lateglacial karola pass early last glacial western nyainqentanggulha shan and penultimate glacial cycle tanggula shan we believe that the regional patterns and timing of glaciation reflect temporal and spatial variability in the south asian monsoon and in particular in regional precipitation gradients in zones of greater aridity the extent of glaciation has become increasingly restricted throughout the late quaternary leading to the preservation of old 100 ka glacial landforms in contrast in regions that are very strongly influenced by the monsoon 1600 mm a 1 the preservation potential of pre lateglacial moraine successions is generally extremely poor this is possibly because lateglacial and holocene glacial advances may have been more extensive than early glaciations and hence may have destroyed any landform or sedimentary evidence of earlier glaciations furthermore the intense denudation mainly by fluvial and mass movement processes which characterize these wetter environments results in rapid erosion and re sedimentation of glacial and associated landforms which also contributes to their poor preservation potential

forte radio frequency observations of lightning strokes detected by the national lightning detection network this work compares simultaneous observations of lightning from two complementary systems forte is a low earth orbit satellite carrying radiowave and optical instruments for the study of lightning the radio receivers aboard forte observe very high frequency vhf emissions from the air breakdown process preceding and sometimes accompanying a lightning current the national lightning detection network nldn is a ground based array of sensors in the contiguous united states observing the low frequency lf and very low frequency vlf radiation from vertical currents prior to the launch of forte in 1997 essentially no work had been done on the statistical correlations between 1 ground based lf vlf and 2 spaced based vhf remote sensing of lightning during a 6 month campaign in april september 1998 forte took most of its triggered vhf data over and near the contiguous united states and nldn data were specially postprocessed in a loosened criterion mode providing enhanced detection range beyond the coastline and borders of the array itself the time history of reported events from the two systems was compared and event pairs each pair containing one event from forte the other from nldn which were candidate correlations closer than 200 ms from each other were scrutinized to determine whether the members of a pair actually came from the same discharge process we have found that there is a statistically significant correlation for a subset of forte events this correlation is most likely to occur for intracloud and less likely to occur for cloud to ground discharges the correlated vhf and nldn events tend to occur within 30 s of each other after correction for the propagation of the vhf signal to forte from the nldn geolocated stroke location most correlations outside of 30 s turn out to be merely a statistical accident the nldn furnished geolocation allows the correlated forte detected vhf pulses to be better interpreted in particular we can deduce from the lag of the vhf ground reflection echo the height of the vhf emission region in the storm

coordinated lightning balloon borne electric field and radar observations of triggered lightning flashes in north florida this study examines coordinated storm and triggered lightning observations made in july august 2013 at the international center for lightning research and testing to determine why triggered flashes in florida typically transition from an upward vertical channel entering the cloud to horizontal structure near the storm s melting level data from a balloon borne electric field meter a mobile 5 cm wavelength radar and a small baseline vhf lightning mapping array acquired during a period in which three flashes were triggered on 1 august confirmed the hypothesis that the transition to horizontal lightning structure just above the melting level occurred in a layer of negative charge this experiment was the first to provide vertical profiles of the electric field in florida storms from which their vertical charge distribution could be inferred three dissipating storms observed on different days all had negative charge near the melting level but a growing mature storm had positive charge there

formation of charge structures in a supercell abstract lightning mapping electric field and radar data from the 26 may 2004 supercell in central oklahoma are used to examine the storm s charge structure an initial arc shaped maximum in lightning activity on the right flank of the storm s bounded weak echo region was composed of an elevated normal polarity tripole in the region of precipitation lofted above the storm s weak echo region later in the storm two charge structures were associated with precipitation that reached the ground to the left of the weak echo region six charge regions were inferred with positive charge carried on hail at the bottom of the stack farther forward in the storm s precipitation region four charge regions were inferred with negative charge at the bottom of the stack there were different charge structures in adjacent regions of the storm at the same time and regions of opposite polarity charge were horizontally adjacent at the same altitude flashes occasionally lowered positive charge to ground from the forwa

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 eyjafjallajokull eruption using lidar observations and name simulations 1 the eyjafjallajokull volcano in iceland erupted explosively on 14 april 2010 emitting a plume of ash into the atmosphere the ash was transported from iceland toward europe where mostly cloud free skies allowed ground based lidars at chilbolton in england and leipzig in germany to estimate the mass concentration in the ash cloud as it passed overhead the uk met office s numerical atmospheric dispersion modeling environment name has been used to simulate the evolution of the ash cloud from the eyjafjallajokull volcano during the initial phase of the ash emissions 14 16 april 2010 name captures the timing and sloped structure of the ash layer observed over leipzig close to the central axis of the ash cloud relatively small errors in the ash cloud position probably caused by the cumulative effect of errors in the driving meteorology en route result in a timing error at distances far from the central axis of the ash cloud taking the timing error into account name is able to capture the sloped ash layer over the uk comparison of the lidar observations and name simulations has allowed an estimation of the plume height time series to be made it is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range quantitative comparison with the mass concentrations at leipzig and chilbolton suggest that around 3 of the total emitted mass is transported as far as these sites by small 100 m diameter ash particles

the initial streamer of intracloud lightning flashes the initial development of four vertical intracloud lightning flashes has been studied using time resolved measurements of the electric field change from 7 8 ground locations at kennedy space center florida the initial field changes of the flashes were analyzed with a unidirectional piecewise linear streamer model in an attempt to determine the direction and sign of the initial charge transfer the results indicate that the discharges were initiated by an upward propagating negative streamer rather than by a downward propagating positive streamer the initial streamer appeared to progress upward at speeds between 1 and 3 105 m s for durations of 10 30 ms and deposited 1 to 4 coulombs per kilometer of extent these results disagree with those of earlier studies which used the shape of the overall electric field change to infer the sense of the streamer and which gave relatively low values for progression speeds 104 m s the results agree with observations of vhf radiation source locations by proctor in south africa

characteristics of infrasound from lightning and sprites near thunderstorm areas 1 research about thunder was mainly performed 20 30 years ago but has been renewed in recent years due to new interest about infrasound in the framework of the verification of the compliance of the comprehensive nuclear test ban treaty during the eurosprite 2005 campaign an infrasound miniarray has been set up in france to measure the characteristics of infrasound from lightning and sprites when these kinds of sources were close to the sensors that is for lightning distances lower than 100 km and sprite distances lower than 300 km for two large thunderstorms which passed over the station detection conditions of infrasound from lightning are detailed and some characteristics are thoroughly described e g amplitude variation with distance and spectrum of an individual event in the frequency range from 0 01 to 10 hz the locations of infrasound sources are determined using a 3 d inversion infrasound signals from sprites have also been detected and the 3 d inversion method used for lightning infrasound has been adapted to locate the sources of infrasound from sprites four different sprite infrasound events are analyzed in this way the infrasound source corresponds well to the sprite spatial characteristics deduced from camera observations questions about generation mechanisms of infrasound from lightning and sprites still remain these new results should help us to understand the sound generation processes

characterization and applications of vlf lf source locations from lightning using the huntsville alabama marx meter array 1 arrays that detect and locate the four dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency vhf regime with 15 km baselines or very low frequency low frequency vlf lf regime with 100 km baselines this paper details initial results from the newly developed huntsville alabama marx meter array hamma consisting of marx meters electric field change meters sensitive to a frequency band 1 hz to 400 khz the arrival time of hamma waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources the locations are compared with two well documented and operational arrays the national lightning detection network nldn and the north alabama lightning mapping array nalma the standard deviation of the difference between hamma and nldn locations of return strokes is 305 and 266 m in x and y respectively while the standard deviation of the difference between hamma and nalma sources is 237 226 and 688 m in x y and z respectively we further show that nldn intracloud locations differ in horizontal distance from the corresponding hamma locations by a median value of 479 m in addition we use hamma source locations to map several lightning flashes in the vlf lf and show hamma sources largely map out the same electrical extent as vhf sources and provide unique insights to the properties of the discharges occurring finally we show that vlf lf sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground copyright 2013 american geophysical union all rights reserved

a low frequency near field interferometric toa 3 d lightning mapping array we report on the development of an easily deployable lf near field interferometric time of arrival toa 3 d lightning mapping array applied to imaging of entire lightning flashes an interferometric cross correlation technique is applied in our system to compute windowed two sensor time differences with submicrosecond time resolution before toa is used for source location compared to previously reported lf lightning location systems our system captures many more lf sources this is due mainly to the improved mapping of continuous lightning processes by using this type of hybrid interferometry toa processing method we show with five station measurements that the array detects and maps different lightning processes such as stepped and dart leaders during both in cloud and cloud to ground flashes lightning images mapped by our lf system are remarkably similar to those created by vhf mapping systems which may suggest some special links between lf and vhf emission during lightning processes

quaternary glacial history of the central karakoram abstract the quaternary glacial history of the world s highest mountains the central karakoram is examined for the first time using geomorphic mapping of landforms and sediments and 10 be terrestrial cosmogenic nuclide surface exposure dating of boulders on the moraines and glacially eroded surfaces four glacial stages are defined the bunthang glacial stage 0 7 ma the skardu glacial stage marine oxygen isotope stage mis 6 or older the mungo glacial stage mis 2 and the askole glacial stage holocene glaciers advanced several times during each glacial stage these advances are not well defined for the oldest glacial stages but during the mungo and askole glacial stages glacial advances likely occurred at 16 11 13 5 and 0 8 ka the extent of glaciation in this region became increasingly more restricted over time in the braldu and shigar valleys glaciers advanced 150 km during the bunthang and skardu glacial stages while glaciers advanced 80 km beyond their present positions during the mungo glacial stage in contrast glaciers advanced a few kilometers from present ice margins during the askole glacial stage glacier in this region likely respond in a complex fashion to the same forcing that causes changes in northern hemisphere oceans and ice sheets teleconnected via the mid latitude westerlies and also to changes in monsoonal intensity

on β2 stepped leaders in negative cloud to ground lightning in their seminal lightning studies using streak cameras schonland et al 1938 identified four negative stepped leader events that they term 2 a rather rare variant of the type leader and in it the second and slower stage of the leader is associated with the appearance of one or more fast dart streamers which travel rapidly down from the cloud along the previously formed track and cease when they have caught up with the slower leader tip seven negative downward leaders that agreed with the description given by schonland et al for type 2 were recorded in tucson arizona usa and in sao jose dos campos sao paulo brazil all cases were recorded by a high speed camera operating at 4000 frames per second and electric field changes were measured for three of them their dart streamers had speeds between 106 and 107 m s 1 compatible with previous observations of recoil leaders rls also during the development of the three cases with correlated electric field changes it was possible to identify sequences of microsecond scale pulses preceding the propagation of a dart streamer in the channel it is proposed that the luminous process that occurs during the development of a type 2 stepped leader is the visible manifestation of one or more rls that begin inside the cloud and connect to the in cloud positive portion of the bipolar bidirectional leader and then travel downward to the lower end of the negative stepped leader path

volcanic ash layer depth processes and mechanisms the long duration of the 2010 eyjafjallajokull eruption provided a unique opportunity to measure a widely dispersed volcanic ash cloud layers of volcanic ash were observed by the european aerosol research lidar network with a mean depth of 1 2 km and standard deviation of 0 9 km in this paper we evaluate the ability of the met office s numerical atmospheric dispersion modelling environment name to simulate the observed ash layers and examine the processes controlling their depth name simulates distal ash layer depths exceptionally well with a mean depth of 1 2 km and standard deviation of 0 7 km the dominant process determining the depth of ash layers over europe is the balance between the vertical wind shear which acts to reduce the depth of the ash layers and vertical turbulent mixing which acts to deepen the layers interestingly differential sedimentation of ash particles and the volcano vertical emission profile play relatively minor roles

spatial and temporal evolution of horizontally extensive lightning discharges associated with sprite producing positive cloud to ground flashes in northeastern spain 1 during the evening of 6 august 2008 a small mesoscale convective system mcs entered the area of radar and 2 d interferometric lightning detection system coverage in northeastern spain and produced 17 sprites recorded by a camera at only 95 180 km distance this study presents an analysis of the in cloud component of the sprite associated lightning flashes and those of other flashes the analysis focuses on the horizontal development of sprite producing lightning by discussing three examples divided into the periods before the positive cloud to ground flash cg between cg and the end of the sprite and the period after the sprite location and horizontal size of sprites appear to be well explained by the temporal and spatial development of the lightning path the majority of sprite producing discharges started directly at the rear side of developing and mature convective cores within the decaying mcs either with the cg or with preceding negative leaders the cg started a burst of vhf sources during which the sprite developed delayed carrot sprites developed after a secondary smaller burst and were well collocated with the burst toward the rear of the mcs the order of development of elements in a grouped sprite followed the direction of lightning propagation during the burst stage the second part of the analysis concentrates on the metrics of sequences of vhf sources and shows that sprites are indeed produced by the largest longest lasting discharges with particularly large line perpendicular dimensions 37 km median compared with 11 km for cg 25 ka

constraints on the early uplift history of the tibetan plateau the surface uplift history of the tibetan plateau and himalaya is among the most interesting topics in geosciences because of its effect on regional and global climate during cenozoic time its influence on monsoon intensity and its reflection of the dynamics of continental plateaus models of plateau growth vary in time from pre india asia collision e g 100 ma ago to gradual uplift after the india asia collision e g 55 ma ago and to more recent abrupt uplift 7 ma ago and vary in space from northward stepwise growth of topography to simultaneous surface uplift across the plateau here we improve that understanding by presenting geologic and geophysical data from north central tibet including magnetostratigraphy sedimentology paleocurrent measurements and 40ar 39ar and fission track studies to show that the central plateau was elevated by 40 ma ago regions south and north of the central plateau gained elevation significantly later during eocene time the northern boundary of the protoplateau was in the region of the tanggula shan elevation gain started in pre eocene time in the lhasa and qiangtang terranes and expanded throughout the neogene toward its present southern and northern margins in the himalaya and qilian shan

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

interferometric observations of a single stroke cloud to ground flash vhf radiation source location measurements using an interferometric technique are presented for a single stroke cloud to ground lightning discharge the discharge began with 100 ms of preliminary activity during which several horizontal streamers developed inside the cloud one of which culminated in the development of a negative leader to ground and a return stroke the return stroke was followed by a 10 ms quiet period in the radiation and by a single fast k type event which appeared to transport negative charge horizontally into the region of initial breakdown completing the flash