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

global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

the coastal ridge sequence at rio grande do sul a new geoarchive for past climate events of the atlantic coast of southern brazil since the mid holocene abstract we present here the first geochronometric analysis of a large succession of coastal ridges that developed south of rio grande do sul inlet aided by osl dating of samples taken in this succession that amounts c 306 coastal ridges this succession allows defining epochs of enhanced coastal drift or fluvial transport to the river mouth additionally changes in the preservation of ridges also suggest the additional effect of transverse winds that create blow outs while changes in the ridge packages planview onlap suggest possible changes in the dominant longshore drift four osl samples located strategically allow defining the age of five main stages of this succession the first stage comprises 2 substages the first substage shows ridges 1 to 36 onlapping the boundary coastal scarp northwardly while the second ridges 37 to 84 shows an inversion of ridge shape wedging out southwards until coast returns to be quasi parallel to the initial coastal scarp estimated to be c 6 ka we estimate this first stage to comprise enhanced coastal drift due to higher and sandier ridges ending at c 4 1 ka the second stage ridges 85 to 124 ridges is marked by a slight unconformity and indicates a period of enhanced fluvial progradation and less coastal drift suggesting milder winds up to 3 6 ka the third stage ridges 125 to 204 initiates with erosion of ridges near the delta front being higher and sandier ridges suggesting enhanced coastal drift due to windier conditions being the windiest time bracketed between 3 3 and 2 35 ka the fourth stage ridges 205 to c 270 shows again as second stage a tendency of wedging out southwards suggesting enhanced fluvial progradation estimated between 2 34 and 1 7 ka the fifth stage is defined by a complete change of coastal plain progradation due to the rapid recycling of beach ridges into a complex of blow outs and arcuate sand dunes ridges are sparsely recognized in cases they developed during short lived events of enhanced longshore drift with an outstanding group ridges 288 to 290 that we correlate to a 1 1 0 9 ka cooling event future studies improving the chronostratigraphy of the beach ridges succession at rio grande and comparing it with the parana river delta ridges will help understanding the complex environmental history of south america that include a reversal of the longshore drift given the fact they are among the most complete upper holocene geoarchives available

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

charge rearrangement by sprites over a north texas mesoscale convective system 1 charge rearrangement by sprites is analyzed for a mesoscale convective system mcs situated in north texas and east new mexico on 15 july 2010 during the thunderstorm electric field data were recorded by the langmuir electric field array lefa while magnetic field data were recorded by the charge moment network near duke university a high speed 12500 fps video system operated at langmuir laboratory recorded telescopic images of the sprites data from the national lightning detection network nldn show that each sprite was preceded by a series of cloud discharges and cloud to ground discharges the triggering event preceding the sprite was typically a positive cloud to ground cg stroke for one out of the 10 sprites that were recorded there was a positive hump in the electric field a few milliseconds after the cg return stroke the size and shape of the hump roughly matched the light intensity emitted from the sprite the electric field hump is fit by a sprite current that originates in the ionosphere and propagates downward producing the same effect as a downward moving positive current the integral under the current hump was 23 9 c when the velocity of the current pulse was between 0 25 c and 0 55 c the large sprite current was followed by impulsive electromagnetic radiation which has not been previously reported and could be a recoil effect similar to what is called a k change when it is observed in a lightning flash

dancing sprites detailed analysis of two case studies on 29 30 october 2013 a low light video camera installed at pic du midi 2877 m recorded transient luminous events above a very active storm over the mediterranean sea the minimum cloud top temperature reached 73 c while its cloud to ground cg flash rate exceeded 30 fl min 1 some sprite events have long duration and resemble to dancing sprites we analyze in detail the temporal evolution and estimated location of two series of sprite sequences as well as the cloud structure the lightning activity the electric field radiated in a broad range of low frequencies and the current moment waveform of the lightning strokes i in each series successive sprite sequences reflect time and location of corresponding positive lightning strokes across the stratiform region ii the longer time delayed 20 ms sprite elements correspond to the lower impulsive charge moment changes icmc of the parent strokes 200 c km and they are shifted few tens of kilometers from their sp cg stroke however both short and long time delayed sprite elements also occur after strokes that produce a large icmc and that are followed by a continuing current iii the long time delayed sprite elements during the continuing current correspond to surges in the current moment waveform they occur sometimes at an altitude apparently lower than the previous short time delayed sprite elements possibly because of changes in the local conductivity iv the largest and brightest sprite elements produce significant current signatures visible when their delay is not too short 3 5 ms

interannual and decadal cycles in river flows of southeastern south america abstract the time series of annual streamflow of four rivers in southeastern and south central south america the negro paraguay parana and uruguay rivers for the period 1911 93 are analyzed application of the multitaper method shows that the following features are significant at the 95 level 1 a nonlinear trend 2 a near decadal component and 3 interannual peaks with enso timescales the trend and near decadal components are most marked in the two more central rivers the paraguay and parana with enso timescale variability most pronounced in the negro and uruguay rivers in the southeast composites of sst are made for each of the statistically significant oscillatory components of river flow by reconstructing each component using singular spectrum analysis these composites confirm the influence of enso on the streamflow variability of the negro and uruguay rivers with el nino associated with enhanced streamflow on the decadal timescale high river runoff is associated with anomalously coo

sea level pressure variability around antarctica since a d 1750 inferred from subantarctic tree ring records a tree ring chronology network recently developed from the subantarctic forests provides an opportunity to study long term climatic variability at higher latitudes in the southern hemisphere fifty long 1911 1985 homogeneous records of monthly mean sea level pressure mslp from the southern latitudes 15 65 s were intercorrelated on a seasonal basis to establish the most consistent long term trans polar teleconnections during this century variations in summer mslp between the south america antarctic peninsula and the new zealand sectors of the southern ocean are significantly correlated in a negative sense r 0 53 p 0 001 climatically sensitive chronologies from tierra del fuego 54 55 and new zealand 39 47 were used to develop verifiable reconstructions of summer november to february mslp for both sectors of the southern ocean these reconstructions which explain between 37 and 43 of the instrumentally recorded pressure variance indicate that inverse trends in mslp from diametrically opposite sides of antarctica have prevailed during the past two centuries however the strength of this relationship varies over time differences in normalized mslp between the new zealand and the south america antarctic peninsula sectors were used to develop a summer trans polar index stpi which represents an index of sea level pressure wavenumber one in the southern hemisphere higher latitudes tree ring based reconstructions of stpi show significant differences in large scale atmospheric circulation between the nineteenth and the twentieth centuries predominantly negative stpi values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the new zealand sector during the 1800s in contrast cyclonic activity appears to have been stronger in the mid twentieth than previously for the south american sector of the southern ocean recent variations in mslp in both regions are seen as part of the long term dynamics of the atmosphere connecting opposite sides of antarctica a detailed analysis of the mslp and stpi reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3 3 3 6 y cross spectral analysis between the stpi reconstruction and the southern oscillation index suggests that teleconnections between the tropical ocean and extra tropical mslp variations may be influencing climate fluctuations at southern latitudes

mid holocene climatic variability reconstruction from pollen records 32 52 s argentina abstract this study reviews 42 published pollen records to gain a better understanding of holocene climate variability especially of the past displacement and location of the arid semiarid region asr between 32 and 52 s in argentina at present the asr is delimited approximately between the 500 mm isohyet in the pampa region and the 300 mm isohyet in the andean sector south of 37 s represented by arid and semiarid climate types where precipitation can be as low as 200 mm mid holocene climatic variability affected the regional vegetation patterns and the borders of the asr paleoenvironmental reconstruction is based on comparison of fossil pollen records from different depositional environments maps of distribution patterns of plant formations are reconstructed at 2000 500 year intervals from 8000 to 4000 14 c years bp vegetation changes are mainly explained by changes in the position and the seasonal amplitude of latitudinal shifts of the pacific and atlantic anticyclones and of the westerlies from 8000 to 4000 bp the eastern limit of the asr was displaced eastward the western limit reached the maximum eastward displacement in the southern extreme of patagonia at 6000 years bp at this time at the center of asr shrub steppes and the monte developed suggesting maximum dry conditions and the establishment of the arid diagonal north of 42 s while the present day espinal dry pampa ecotone became established at 4000 years bp paleodata suggest a transitional stage towards the present situation of the asr

the manso glacier drainage system in the northern patagonian andes an overview of its main hydrological characteristics the manso glacier 41 s 72 w in the northern patagonian andes of argentina is a regenerated glacier that like many other glaciers in the region and elsewhere has been showing a significant retreat glacial melt water feeds the manso superior river which before crossing the andes to reach a pacific outfall flows through the mascardi a deep oligotrophic and monomictic lake and significantly smaller hess and steffen lakes harmonic analysis of mascardi s lake level series suggests that the el nino southern oscillation signal has been strong during the 1985 1995 decade but has grown weaker during the initial decade of the 21st century hydrological trend analyses applied in data recorded in the uppermost reaches show a monthly and annual decreasing trend in the manso superior river discharge series and mascardi s lake level which are connected with both decreasing melt water discharge and austral wintertime atmospheric precipitation downstream the decreasing signal initially looses statistical significance and then when flowing through steffen lake reverses the lake level trend that becomes significantly positive this suggests that on its way to the pacific ocean the manso river receives abundant andean snow melt water and atmospheric precipitation which are sufficient to obliterate the negative trend recorded in the uppermost reaches the reason for this local phenomenon is that the manso is an antecedent river aka superposed stream and hence the valley crossing the andes allows the incursion of pacific humidity that modifies the hydrological regime several hundred kilometres inland copyright 2012 john wiley sons ltd

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

coordinated observations of sprites and in cloud lightning flash structure 1 the temporal and spatial development of sprite producing lightning flashes is examined with coordinated observations over an asymmetric mesoscale convective system mcs on 29 june 2011 near the oklahoma lightning mapping array lma sprites produced by a total of 26 lightning flashes were observed simultaneously on video from bennett colorado and hawley texas enabling a triangulation of sprites in comparison with temporal development of parent lightning in particular negatively charged stepped leaders in three dimensional space in general prompt sprites produced within 20 ms after the causative stroke are less horizontally displaced typically 30 km however both prompt and delayed sprites are usually centered within 30 km of the geometric center of relevant lma sources with affinity to negative stepped leaders during the prior 100 ms interval multiple sprites appearing as dancing jumping events associated with a single lightning flash could be produced either by distinct strokes of the flash by a single stroke through a series of current surges superposed on an intense continuing current or by both our observations imply that sprites elongated in one direction are sometimes linked to in cloud leader structure with the same elongation and sprites that were more symmetric were produced above the progression of multiple negative leaders this suggests that the large scale structure of sprites could be affected by the in cloud geometry of positive charge removal based on an expanded dataset of 39 sprite parent flashes by including more sprites recorded by one single camera over the same mcs the altitude above mean sea level msl of positively charged cloud region tapped by sprite producing strokes declined gradually from 10 km msl 35 c to around 6 km msl 10 c as the mcs evolved through the mature stage on average the positive charge removal by causative strokes of sprites observed on 29 june is centered at 3 6 km above the freezing level or at 7 9 km above ground level

vegetational changes during the holocene in extra andean patagonia santa cruz province argentina abstract modern pollen vegetation relationship was used in the interpretation of stratigraphical sequences from two archeological sites la martita cave 48 24 s 69 15 w and alero cardenas 47 18 s 70 26 w located in extra andean patagonia in the santa cruz province the modern pollen assemblages are related to vegetation units that extend from the andes toward the atlantic coast reflecting the increase of aridity from west to east the more humid areas in the west are represented by grass steppe with festuca pallescens in those areas of intermediate humidity shrub steppe can be found with a conspicuous stratum of stipa s speciosa s humilis and s chrysophylla and shrubs nardophyllum obtusifolium berberis heterophylla senecio filaginoides mulinum spinosum and in the most arid areas scrub steppe expands with nassauvia glomerulosa and cushion plants such as azorella caespitosa accantholippia seriphiodes chuquiraga aurea brachyclados caespitosus a vegetational and paleoclimatic history is presented based on comparison with modern analogs and with other palynological records from southern patagonia prior to 8000 yr b p a grass steppe extended indicating relatively high precipitation under cold conditions between 8000 and 6000 yr b p an increase of shrub steppe taxa dominated by asteraceae tubuliflorae would relate to an increase in temperature while precipitation remained in the previous range of about 200 mm the mid holocene 5000 yr b p is reflected in the la martita sequence by a short term return of steppe taxa primarily grasses this steppe could indicate cold conditions similar to those of the early holocene or an increase in precipitation after 4500 yr b p the vegetation is represented by grass shrub steppe after 3500 yr b p the alero cardenas record shows a shrub steppe dominated by asteraceae tubuliflorae in records near the steppe forest ecotone at 47 and 50 s the more extensive late holocene forest suggests greater effective moisture probably related to cooler temperatures in alero cardenas grasses increase and shrubs are irregularly present in altiplanicie central steppe vegetation is analogous to the present vegetation in the present century taxa indicative of disturbance are present rumex acetosella and brassicaceae

the geochemical signature of suspended sediments in the parana river basin implications for provenance weathering and sedimentary recycling abstract the parana river basin is one of the largest hydrological systems in south america the present study focuses on the mineralogical and chemical composition of the suspended sediments exported by the parana river to the atlantic ocean with the aim of analyzing their provenance the chemical weathering signature and the likelihood of sedimentary recycling the particulate matter of the middle parana river and its main tributaries i e the paraguay and the upper parana rivers is mostly composed of quartz plagioclase k feldspar and clays such as illite and kaolinite different geochemical approaches indicate that the suspended sediments transported by the parana river preserve the chemical signature of its sources and its composition is not significantly modified during transport these sediments are mainly supplied by acidic arc sources located in the andean headwaters of the bermejo and pilcomayo rivers and transported by the paraguay river and by tholeiitic basalts outcropping in the headwaters of the upper parana river the incomplete mixing of both main tributaries produces a transverse geochemical asymmetry in the particulate material of the middle parana river which was detected 32 km downflow the confluence the suspended load transported by the paraguay river which includes the contributions from the bermejo and pilcomayo rivers indicates incipiently to moderately weathering whereas the particulate matter exported by the upper parana river reveals a higher degree of chemical alteration this is the result of the different lithology and climatic regimes that prevail in the headwaters of both tributaries the weathering signature of the middle parana river s suspended load resembles that of the paraguay river which in turns supplies most of the particulate matter through the bermejo river this work also shows that the suspended load exported by the parana river basin has a mixed origin where the chemical signatures from young materials derived from undifferentiated volcanic rocks and from recycled materials affected by intracrustal differentiation can be distinguished

sprite initiation altitude measured by triangulation 1 high time resolution 10 000 frames per second images of sprites combined with multistation concurrent video recordings have provided data for triangulation of the altitude of the initial sprite onset the high speed images were obtained from the langmuir laboratory new mexico during summer campaigns in 2007 and 2008 with video observations from sites at portales new mexico and las vegas new mexico sprites start with one or more downward propagating streamer heads the triangulated onset altitudes of this initial downward streamer vary between 66 and 89 km in some sprites the downward streamers are followed a little later by upward propagating streamers the upward streamers start from a lower altitude and existing luminous sprite structures and their triangulated altitudes vary from 64 to 78 km the downward streamers create c sprite characteristics while the upward streamers form the broad diffuse tops of carrot sprites in the sprites analyzed the higher onset altitudes for the downward propagating initial streamers were associated with c sprites and the lower with carrot sprites but our larger data set indicates that this is not generally the case it appears that the dominant sprite types vary from year to year indicating that some longer lasting environmental parameter such as mesospheric conductivity and composition or thunderstorm cloud dynamics may play an important role in determining the types of sprites observed

on the series of cg lightning strokes in dancing sprite events in dancing sprite events sprite entities and groups appear in rapid succession together with a corresponding series of parent lightning strokes dancing sprite events including a case with possible sprite rebrightening were recorded on video simultaneously from two observation sites above a mesoscale convective system in central europe on the night of 6 august 2013 joint analysis of triangulated locations of sprite elements position type and peak current of lightning strokes from the linet lightning detection network database and current moment waveforms deduced at the hylaty station poland showed that subsequent sprite parent lightning strokes occurred no further than 21 km from the closest preceding sprite entity in the cases analyzed in this study additionally it was found that longer sprite delay times tend to correspond to larger sprite location offsets from the parent cg stroke these observations the occurrence of cg lightning stroke and sprite sequences as well as sprite sprite delay times and displacements can be explained if cg strokes are part of one extended lightning flash a corresponding production mechanism based on previous findings on the formation of sprite producing and general cg lightning discharges is suggested plain language summary in dancing sprite events sprites appear in rapid succession together with a corresponding series of parent lightning strokes dancing sprite events were recorded on video simultaneously from two observation sites above an extended thunderstorm system in central europe on the night of 6 august 2013 comparison of triangulated sprite locations and the locations of corresponding lightning activity revealed that subsequent sprite parent lightning strokes occurred below or relatively near the location of the closest preceding sprite entity in the examined cases in this paper a mechanism is suggested for the development of lightning flashes that produce dancing sprites the proposed mechanism accounts for prompt and delayed sprites relative to their parent lightning stroke highlights the role of the variation of lightning current in sprite production and can explain the observed closeness of the next cg lightning stroke to the area of previous sprites

three years of lightning impulse charge moment change measurements in the united states 1 we report and analyze 3 years of lightning impulse charge moment change icmc measurements obtained from an automated real time lightning charge moment change network cmcn the cmcn combines u s national lightning detection network nldn lightning event geolocations with extremely low frequency 1 khz data from two stations to provide icmc measurements across the entire united states almost 14 million lightning events were measured in the 3 year period we present the statistical distributions of icmc versus polarity and nldn measured peak current including corrections for the detection efficiency of the cmcn versus peak current we find a broad distribution of icmc for a given peak current implying that these parameters are at best only weakly correlated curiously the mean icmc does not monotonically increase with peak current and in fact drops for positive cg strokes above 150 ka for all positive strokes there is a boundary near 20 c km that separates seemingly distinct populations of high and low icmc strokes we also explore the geographic distribution of high icmc lightning strokes high icmc positive strokes occur predominantly in the northern midwest portion of the u s with a secondary peak over the gulf stream region just off the u s east coast high icmc negative strokes are also clustered in the midwest although somewhat south of most of the high icmc positive strokes this is a region far from the locations of maximum occurrence of high peak current negative strokes based on assumed icmc thresholds for sprite production we estimate that approximately 35 000 positive polarity and 350 negative polarity sprites occur per year over the u s land and near coastal areas among other applications this network is useful for the nowcasting of sprite producing storms and storm regions

blocking in the southern hemisphere abstract the focus of this paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the southern hemisphere the analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more composite flow and anomaly fields for several cases are presented and examined in detail the geographical distribution of the frequency of lame amplitude 150 gpm anomalies at 500 mb that persist for only 1 3 days is very similar to that of the high frequency band 2 8 day period variances that identity the storm tracks in the southern hemisphere the primary location for blocking in the southern hemisphere is in the new zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli

freshwater discharge into the caribbean sea from the rivers of northwestern south america colombia magnitude variability and recent changes the monthly averaged freshwater discharge data from ten rivers in northern colombia caribbean alluvial plain draining into the caribbean sea were analysed to quantify the magnitudes to estimate long term trends and to evaluate the variability of discharge patterns these rivers deliver similar to 340 9 km 3 yr 1 of freshwater to the caribbean sea the largest freshwater supply is provided by the magdalena river with a mean discharge of 205 1 km 3 yr 1 at calamar which is 26 of the total fluvial discharge into this basin from 2000 to 2010 the annual streamflow of these rivers increased as high as 65 and upward trends in statistical significance were found for the mulatos canal del dique magdalena and fundacion rivers the concurrence of major oscillation processes and the maximum power of the 3 7 year band fluctuation defined a period of intense hydrological activity from approximately 1998 2002 the wavelet spectrum highlighted a change in the variability patterns of fluvial systems between 2000 and 2010 characterised by a shift towards a quasi decadal process 8 12 years domain the intertropical convergence zone itcz el nino southern oscillation enso events and quasi decadal climate processes are the main factors controlling the fluvial discharge variability of these fluvial systems c 2013 elsevier b v all rights reserved

television image of a large upward electrical discharge above a thunderstorm system an image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low light level television camera the discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher the image which had a duration of less than 30 milliseconds resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops large upward discharges may create a hazard for aircraft and rocket launches and by penetrating into the ionosphere may initiate whistler waves and other effects on a magnetospheric scale such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud to earth lightning strokes an unusually high rate of such photometric events was recorded during the night of 22 to 23 september 1989 during a storm associated with hurricane hugo

interannual and interdecadal variability of the south atlantic convergence zone interannual variations of the summertime january march atmospheric circulation over subtropical south america are examined during the period 1958 97 using the national centers for environmental prediction national center for atmospheric research reanalysis data it is found from an empirical orthogonal function analysis that an anomalous upper tropospheric large scale stationary eddy in the lee of the andes tends to accompany a dipole in anomalous vertical motion an anomalous cyclonic anticyclonic eddy accompanies an intensified diffuse south atlantic convergence zone sacz with anomalous descent ascent to the southwest the cold core equivalent barotropic vertical structure of the anomalous cyclonic eddy and the 200 hpa vorticity balance are both characteristic of a stationary rossby wave the tendency for the eddy to be advected downstream by the mean westerlies is compensated by meridional advection of planetary vorticity and stretching associated with vertical motion the anomalous cyclonic flow at low levels reinforces the thermally direct circulation associated with the sacz a weak funneling of submonthly rossby wave activity into this descent region is also identified the interannual time series of the eddy is significantly correlated with north south dipolar sea surface temperature sst anomalies over the southwest atlantic one standard deviation 200 hpa wind speed anomalies of up to 5 m s21 are accompanied by sst anomalies of up to 0 38c a near cyclic 15 yr component is identified which the authors corroborate from independent analyses of southwest atlantic ssts and river flows both are

influence of cross andes flow on the south american low level jet abstract by analyzing the 15 yr 1979 93 reanalysis data of the european centre for medium range weather forecasts ecmwf it has been found that the seasonal and synoptic time scale variations of the south american low level jets lljs are largely controlled by an upper level trough and associated low level zonal flow rather than by horizontal temperature gradients along the slope of the andes the northerly lljs are maintained by strong zonal pressure gradients caused by the upstream trough and westerly flow crossing the andes through lee cyclogenesis the process involves both baroclinic development of the upper level trough and mechanical deflection of the westerly flow by the andes when an anticyclonic circulation replaces the trough and westerly flow over the eastern south pacific the northerly lljs tend to diminish or reverse into southerly lljs the dependence of the lljs upon the upstream wind pattern helps to explain how the seasonal variation of the south american lljs is related to the s

modeling the daily suspended sediment concentration in a hyperconcentrated river on the loess plateau china using the wavelet ann approach abstract the complexity of the relationship between suspended sediment concentration ssc and river discharge q remains a challenge for ssc prediction in hyperconcentrated rivers in this study the wavelet artificial neural network model wann was built to predict ssc in the kuye river a representative hyperconcentrated river in the middle yellow river catchments of china in the wann model the observed daily time series for q and ssc of 2193 days from 1967 to 1972 were decomposed into subseries at different scales using discrete wavelet analysis then the effective subseries were selected to construct q ssc inputs to the feed forward back propagation artificial neural network bp ann to predict ssc 1 day in advance the time resolution of the observed data the coefficient of determination r2 and root mean square error rmse were adopted to evaluate the model s performance the wann model showed higher prediction accuracy r2 0 846 and rmse 29 82 than the sediment rating curve src model r2 0 537 and rmse 55 40 or the ann model r2 0 664 and rmse 43 13 the wann model exhibited more robust performance than the src and ann models indicated by the appropriate values of error autocorrelation and input error correlation negative values of predicted ssc occurred in ann and in wann models by adjusting the negative values to zero the wann r2 was improved by 4 3 from 0 846 to 0 882 in general the results illustrate that the wann model better predicts ssc in a hyperconcentrated river setting with highly nonlinear and nonstationary time series

paleoenvironmental insights into the quaternary evolution of the southern brazilian coast based on fossil and modern diatom assemblages abstract diatom assemblages provide a strong basis for detailed interpretations of paleoceanography and diatom paleoecology of the southern brazilian coast nine cores obtained in the coastal plain shelf and continental slope and thirteen surface sediment samples of the patos lagoon provide an excellent opportunity to use a paleoecological approach to study detailed quaternary environmental changes in the southern coasts in the interval studied the basin sedimentation occurred in a marine dominated environment related to humid periods prior to 43 500 year bp abundant diatom taxa are highlighted as excellent indicators of environmental changes including salinity sediment composition and transport by incised valleys providing additional insights into coastal evolution paralia sulcata is dominant in all analyzed cores occurring continuously from late pleistocene to holocene but is rare in the modern sediments non marine diatom assemblages occurred continuously but in very low densities in periods before and after the last glacial maximum abrupt changes in sedimentation have been recorded related to shifts from marine dominated to shallow estuarine deposition during the holocene sea level rose rapidly which is responsible for the progressive coastal flooding prior to 8420 7930 year bp the holocene barrier system became more continuous and patos lagoon developed consequently the secondary former inlets from the jacui and camaqua rivers are closed and only one single inlet rio grande channel remains active the spatial distribution of modern assemblages is controlled by salinity gradient wind action and climate forcing the bottom sediments of patos lagoon are dominated by freshwater diatom aulacoseira veraluciae aulacoseira sp 2 and marine estuarine species of cyclotella litoralis

the time space structure of the asian pacific summer monsoon a fast annual cycle view abstract despite the seemingly intricate and multifold time space structure of the mean asian pacific summer monsoon apsm its complexity can be greatly reduced once the significance of fast annual cycles has been recognized and put into perspective the apsm climatology is characterized by a slowly evolving seasonal transition slow annual cycle superposed by pronounced singularities in the intraseasonal timescale termed the fast annual cycle in this study the fast annual cycles show nonrepetitive features from one episode to another which are often divided by abrupt change events the apsm fast annual cycles are composed mainly of two monsoon outbreaks each marking a distinctive dry wet cycle the first cycle spans from the middle of may to early july and the second cycle from late july to early september when the first cycle reaches its peak in mid june a slingshot like convection zone described as the grand onset pattern rules an area from the arabian sea to the indochina peninsula then b

southern patagonia s perito moreno glacier lake argentino and santa cruz river hydrological system an overview summary an overview of the hydrological data from patagonia s perito moreno glacier lake argentino and santa cruz river system reinforces our previous assertion that the el nino southern oscillation enso and the antarctic oscillation aao are teleconnected with the rupture sequence when the glacier s snout harmonically dams during certain interannual periods the rico branch of lake argentino it is clear however that the incidence of interannual climatic anomalies is not uniform in time and appears embedded in decadal or quasi bidecadal periods of relative damming inactivity the use of nonparametric tests shows that there are no significant positive trends in the river s annual discharge with the only exception of the yearly snowmelt ice melt periods september october when riverine flow appears to increase with statistical significance the question of the glacier s stability looks like a complex multivariate process although we do not rule out the occasional role of enso aao a longer hydrological data series i e 100 years would prove useful in casting some light on this intriguing process surely accounting for the glacier s response time

regime shift in indian summer monsoon climatological intraseasonal oscillations 1 using a high resolution daily rainfall data over indian continent between 1951 and 2004 summer monsoon climatological intraseasonal oscillations ciso and its regime shift around mid seventies is investigated explaining 20 40 of intraseasonal oscillation iso amplitude the summer monsoon ciso represents a significant predictable component of the monsoon isos indian monsoon ciso is characterized by a dominant northward propagating episode in both pre seventies 1951 75 pre75 and in the post seventies 1979 04 post79 the dominant episode starts in the beginning of july during pre75 in contrast to beginning of june during post79 period we find that the iav of the initial phase of both the first and the second iso episodes worked in tandem with the changes in the northward propagation speed in producing the phase locking for the second episode during pre75 while for the first episode during post79 change in northward propagation speed is shown to be consistent with changes in easterly vertical shear and meridional gradient of low level humidity during the two climate regimes

the dissolved chemical and isotopic signature downflow the confluence of two large rivers the case of the parana and paraguay rivers summary the parana river basin is one of the largest hydrological systems in south america 2 6 10 6 km 2 downflow the confluence of tributaries most large rivers exhibit transverse and longitudinal inhomogeneities that can be detected for tens or even hundreds of kilometers concordantly a noticeable cross sectional chemical asymmetry in the dissolved load was distinguished in the middle parana river after the confluence of its main tributaries i e the paraguay and upper parana rivers water chemistry and isotopic signature in three cross sections along the middle parana river as well as from main and minor tributaries and some deep 105 m bs and shallow boreholes 15 m bs located near both river banks were analyzed in order to define the extent of mixing and identify possible contributions from groundwater discharges downflow the confluence of the upper parana and paraguay rivers a chemical and isotopic asymmetry was observed mainly through the values of ec major ions ca 2 na mg 2 cl and so 4 2 some trace elements fe u th ba sr as and ree and stable isotopes 18 o and 2 h toward its western margin higher elemental concentrations which resembled that of the paraguay river were measured whereas at the eastern border waters were more diluted and preserved the chemical signature of the upper parana river this variability remained detectable at least until 225 km downflow the confluence where differences between western and eastern margins were less evident at 580 km downflow the confluence a slight inversion in the transverse chemical asymmetry was observed this trend switch can be the result of the input of solutes from minor tributaries that reach the main channel from the east and or may be due to higher groundwater discharges from the east bank a mass balance model was applied as a first approach to estimate the groundwater inflow using the geochemical tracer 222 rn the results indicate that groundwater contributions represent between 0 5 and 6 of the total water inputs to the middle parana river under baseflow conditions this implies that the chemical asymmetry in the middle parana river is mostly due to the incomplete mixing of the main tributaries though the influence of groundwater is not a determining factor in the chemical variability of the river it may partially explain the higher concentrations of some trace elements found in the eastern margin 580 km downflow the confluence

sprite observations in the northern territory of australia sprites a form of brief luminous discharge in the upper atmosphere above a thunderstorm were observed and imaged on two video cameras in australia s northern territory these were the first such ground based observations made outside the united states sprite discharges typically took place between the altitudes of 50 km and 80 km and spanned an average width of 44 km many of the sprite events were of long duration with an average of 145 ms these spatial and temporal features were similar to those observed from the ground and the air in the united states during the longer events some luminous discharge elements were observed to decay as other new elements formed as the new elements were often laterally displaced from the old the sprites sometimes appeared to dance across the sky this phenomenon has been observed in colorado and named dancing sprites the lateral progression of sprite elements observed in the northern territory was overwhelmingly in one direction and covered distances of up to 90 km

recent advances in wavelet analyses part 2 amazon parana orinoco and congo discharges time scale variability this paper is devoted to illustrating new wavelet analysis methods in the field of hydrology new wavelet indicators are applied to long term hydrological and climatologic proxies they are first applied to four atlantic large river monthly discharges amazon parana orinoco and congo and then applied to two well known long term climatologic indexes the southern oscillation and the north atlantic oscillation this approach makes it possible to suggest physical explanations for time scale dependant relationships six month variability is present in all the rivers except in the parana in the congo river this signal is near stationary with strong entropy the strength of this scale coincides with higher discharge variability before 1920 and over the orinoco basin with higher discharge values between 1940 and 1955 an annual cycle is present in all the rivers but is much stronger along with the entropy in the rivers with a large tropical basin as in the amazon and the orinoco this annual signal is not permanent in the congo and much more intermittent in the parana where the annual recharge appears as very irregular a quasi biennial variability is apparent in all the equator ward rivers and a nearly permanent 2 year coherence is found between soi and the amazon discharge a 3 6 year oscillation typical of enso variability is observed in all the rivers it is intermittent observed before 1930 in all the rivers and after 1980 mostly in the amazon river these peaks of activity correspond to periods of major soi variability an 8 year variability is particularly strong in the parana river before 1940 and around 1970 and to a lesser extent in the orinoco river during the low nao index period between 1940 and 1970 the congo river exhibits that time scale around 1970 a 13 year variability common to soi nao and the south atlantic ocean circulation is observed in the parana and congo discharges in all the rivers the greatest entropy is observed at bi and multi decadal time scales with the greatest coherence with both nao and soi a near 20 year time scale is observed in most of the series around 1970 although it is strongest in amazon and parana discharges finally a 30 year time scale is observed between 1940 and 1970 it is to be noted that most of the time scale dominant activities in all the rivers may have been influenced by the interdecadal shifts that took place around 1940 and 1970 in the pacific and in the atlantic therefore in this contribution the application of new wavelet indicators combined continuous and multi resolution analysis wavelet entropy wavelet coherence wavelet cross correlation leads to several improvements in the analysis of these global hydrological signal fluctuations and of their mutual time varying relationships it is demonstrated that wavelets should be used more systematically in preference to the classical fourier analysis notably in hydrology

eastward propagating mjo during boreal summer and indian monsoon droughts improved understanding of underlying mechanism responsible for indian summer monsoon ism droughts is important due to their profound socio economic impact over the region while some droughts are associated with external forcing such as the el nino and southern oscillation enso many ism droughts are not related to any known external forcing here we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics we show that most ism droughts are associated with at least one very long break vlb breaks with duration of more than 10 days and that the processes responsible for vlbs may also be the mechanism responsible for ism droughts our analysis also reveals that all extended monsoon breaks whether co occurred with el nino or not are associated with an eastward propagating madden julian oscillation mjo in the equatorial indian ocean and western pacific extending to the dateline and westward propagating rossby waves between 10 and 25 n the divergent rossby wave associated with the dry phase of equatorial convection propagates westward towards indian land couple with the northward propagating dry phase and leads to the sustenance of breaks thus the propensity of eastward propagating mjo during boreal summer is largely the cause of monsoon droughts while short breaks are not accompanied by westerly wind events wwe over equatorial western pacific favorable for initiating air sea interaction all vlbs are accompanied by sustained wwe the wwes associated with all vlb during 1975 2005 initiate air sea interaction on intraseasonal time scale extend the warm pool eastward allowing the convectively coupled mjo to propagate further eastward and thereby sustaining the divergent circulation over india and the monsoon break the ocean atmosphere coupling on interannual time scale such as el nino can also produce vlb but not necessary

polarity and energetics of inner core lightning in three intense north atlantic hurricanes 1 we use the world wide lightning location network wwlln low frequency magnetic fields measured at duke university and storm intensity data winds and central pressure to examine the polarity and energetics of lightning within 100 km of the centers inner core regions of north atlantic hurricanes emily katrina and rita 2005 wwlln provides the lightning locations polarities peak currents and vertical impulse charge moment changes are derived from the duke magnetic field measurements in agreement with past studies we find episodic inner core lightning outbreaks prior to and during most changes in storm intensity a new result of our analysis indicates an increase in the relative number of positive cloud to ground lightning in the inner core prior to and during periods of storm weakening which is potentially important for hurricane intensity change forecasting additionally we find that the majority of inner core lightning located by wwlln had peak currents that surpassed the threshold needed to produce optical emissions elves and drive electron density perturbations in the lower ionosphere 80 105 km since these high peak current lightning occurred in short duration outbreaks they had an accumulated effect on the ionospheric electron density as shown by recent modeling studies our results suggest that the inner core lightning in intense hurricanes might be significant drivers of perturbations in the lower ionosphere during these inner core lightning outbreaks

climatic fluctuations in northern patagonia during the last 1000 years as inferred from tree ring records abstract millennium old alerce trees fitzroya cupressoides mol johnst have been used to develop a 1120 year reconstruction of the summer temperature departures for the andes of northern patagonia in argentina four main climatic episodes can be distinguished in this proxy paleoclimatic record the first a cold and moist interval from a d 900 to 1070 was followed by a warm dry period from a d 1080 to 1250 correlative with the medieval warm epoch of europe afterward a long cold moist period followed from a d 1270 to 1670 peaking around a d 1340 and 1650 these cold maxima are contemporaneous with two principal little ice age events registered in the northern hemisphere warmer conditions then resumed between a d 1720 and 1790 these episodes are supported by glaciological and palynological data in patagonia following a cold period in the early 1800s tree ring indices have oscillated around the long term mean except for a warmer period from a d 1850 to 1890 correlations between the rio alerce reconstruction and the regional weather stations indicate that the tree ring variations are correlated with a homogeneous summer weather pattern covering patagonia east of the andes from 38 to 50 s

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

an unusual sequence of sprites followed by a secondary tle an analysis of elf radio measurements and optical observations we present an extraordinary case of sprites in rapid succession four sprite clusters in only 400 ms followed by a secondary jet simultaneous elf and optical observations as well as lightning data enabled us to thoroughly document this unique event locations of the transient luminous events tles were triangulated using video recordings from nydek czech republic and sopron hungary we found that sprites were displaced up to 70 km from their parent lightning the current moment waveform and charge moment changes associated with the event were reconstructed from the elf electromagnetic signature recorded at the hylaty station poland by a new method the results suggest that both a short delayed and a long delayed sprite were generated by a single positive cloud to ground discharge that had an intense continuing current it had an unusual progression and lasted 200 ms a large increase in the current moment during the development of a massive carrot sprite provides evidence in favor of sprite current our results also support the formation of an electric environment hypothesized to be necessary for the generation of the secondary tles

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

further evidence of changes in the hydrological regime of the river paraguay part of a wider phenomenon of climate change abstract analysis of flow measured at 20 sites rainfall measured at 36 sites and a 95 year record of water level at one site in the basin of the river paraguay area 1095 10 3 km 2 showed that the flow regime during the approximate period 1960 1970 differed substantially from the flow regime both before and after the long record of ladario water levels suggested that the changes between one period and the next were considerably abrupt and that the periods differed not only in terms of mean water levels but also in terms of the year to year correlational structure within the record despite the fragmentary nature of rainfall records from 36 sites an explanation for the increased flows since 1970 was found in the increases of rainfall as assessed in terms of the frequency of annual rainfalls more than the long term mean rainfall there was some degree of consistency in the change of rainfall pattern across the paraguay basin as a whole a detailed examination of daily rainfall characteristics at two gauges where records were fairly complete showed that during the 1960 1970 period when river flows were low dry spells were more persistent and on days when rain did fall the amounts of rain were generally smaller the results obtained were compared with results obtained by other researchers using flow records from the rivers paraguay parana negro and uruguay in the la plata basin and rainfall records from other parts of south america there is now strong evidence of changes in the runoff regime of the la plata basin during the last 40 years not all of which can be attributed to land use change as there is complementary evidence of change in rainfall regime the results were also compared with findings from the congo basin which appears to exhibit changes in flow regime that are a mirror image of those found for the paraguay at ladario

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

impacts of enso on multi scale variations in sediment discharge from the pearl river to the south china sea abstract sediment load delivered by rivers is an important terrestrial factor in the evolution and productivity of coastal ecosystems and coastal morphology as the strongest interannual climate signal the el nino southern oscillation enso is closely related to variations in the hydrological cycle at global and regional scales however the influence of enso on temporal variations in sediment discharge is poorly understood in this paper we examine periodic variations in sediment discharge to the south china sea from the pearl river since the 1950s using wavelet transform analysis wt furthermore we apply cross wavelet spectrum xwt and wavelet coherence wtc to investigate the linkages between enso and sediment variability the wt results revealed that periodic oscillations in sediment discharge in the pearl river occurred annually 1 yr before the 2000s interannually 2 8 yr from 1960 2002 and decadally 10 16 yr from 1975 1995 these periodic variations in the sediment load series had common spectrum power with the water discharge and precipitation series indicating an important climatic control the xwt and wtc results revealed significant impacts of enso on precipitation water discharge and sediment load at interannual time scales of 2 4 6 yr from 1960 2002 with a shift of patterns of enso on sediment variability after the 1970s in addition an in phase relation between sediment discharge and enso at time scales of 10 16 yr from 1975 1995 was detected indicating that variations at decadal scales could be related to other climatic teleconnections such as the pacific decadal oscillation compared with the spectrum structures of periodic variations in precipitation and water discharge and their relationship with enso there was a loss of energy in the sediment load at annual time scales after 2002 that can be attributed to dam construction in the river basin our study provides perspectives on the connections between enso and sediment variability at different time scales which is of practical and scientific importance for forecasting global hydrological processes and for river management

decadal variation of the annual cycle in the australian dataset abstract during the 1970s and 1980s elements of the atmospheric circulation over the southern hemisphere changed markedly from their state in the two previous decades the change was evident in the zonal asymmetry especially in the zonal harmonic wave 3 at higher latitudes and in the semiannual wave in pressure and wind the semiannual wave changed in the same sense in all three southern oceans but by the largest amount in the south pacific ocean the second harmonic in a 12 month series by which we describe the semiannual wave dominates the shape of the long term mean annual curve of sea level pressure in mid and high latitudes this harmonic weakened during the period and its midlatitude peak disappeared in the south pacific ocean as part of the low frequency changes during the 18 years from 1972 to 1988 the central pressure in the subantarctic trough fell the trough moved northward and the subtropical ridge moved south the meridional movement of the trough and the ridge and the concurrent

discharge trends and flow dynamics of south american rivers draining the southern atlantic seaboard an overview summary river discharge time series in southern south america between 15 and 50 s show dissimilar historical trends in the rio de la plata drainage basin rpdb the record shows a runoff trend change from decreasing to increasing around the mid 20th century independently of the seasonal variation currently observed discharge change in the region is mainly accounted for by increased discharge during low flow periods in contrast most patagonian rivers show a negative discharge trend which mainly occurs in some austral summer months and is particularly significant in the negro river when considering the historical discharge variability in the southern part of south america the spectral analysis produced evidence of interannual quasi decadal and quasi bidecadal periodicities most rivers in the region show el nino like interannual periodicities with the exceptions of the bermejo and pilcomayo rivers in the rpdb during the 20th century interannual periodicity changed from the 2 to 5 year band to the 5 to 7 year band between 1935 and 1970 in patagonia the interannual oscillation showed maximum power 1930 and 1980 in the colorado whereas further south negro and chubut rivers maximum power appears 1950 the quasi decadal signal is strong in the rpdb in general and particularly in patagonia s colorado which runs close to the so called arid diagonal and bears this signal presumably due to the influence of the low level jets lljs this periodicity is conspicuously absent in other patagonian rivers finally a quasi bidecadal signature appears to be restricted to the bermejo and iguacu rivers in the rpdb and in patagonia s colorado and santa cruz rivers

positive charge in the stratiform cloud of a mesoscale convective system a balloon sounding of electric field in the trailing stratiform cloud of a bow echo mesoscale convective system reveals only two substantial in cloud positive charge regions these charge regions are located at altitudes of 5 1 5 6 km and 6 4 6 8 km above the level of 0 c at 4 2 km the two positive charge regions are the likely sources of six positive cloud to ground flashes with large peak currents 32 ka that occurred within 60 km of the balloon during its flight the amount of charge transferred by three of these positive flashes that made q bursts is calculated in the range of 97 196 c flashes of this sort are known to produce sprites and elves in the mesosphere the positive charge regions in this stratiform cloud are substantially lower than the 10 km altitude commonly assumed for the positive charge in many sprite modeling studies

multi instrumental observations of a positive gigantic jet produced by a winter thunderstorm in europe 1 at 2336 56 utc on 12 december 2009 a bright gigantic jet gj was recorded by an observer in italy forty nine additional sprites elves halos and two cases of upward lightning were observed that night the location of the gj corresponded to a distinct cloud top 34 c west of ajaccio corsica the gj reached approximately 91 km altitude with a trailing jet reaching 49 59 km matching with earlier reported gjs the duration was short at 120 160 ms this is the first documented gj which emerged from a maritime winter thunderstorm only 6 5 km tall showing high cloud tops are not required for initiation of gjs in the presence of strong vertical wind shear the meteorological situation was different from typical outbreaks of fall and winter thunderstorms in the mediterranean during the trailing jet phase of the gj a sprite with halo triggered by a nearby cloud to ground lightning flash occurred at a relatively low altitude 72 km at the same time the trailing jet and beads were reilluminated electromagnetic waveforms from hungary poland and the usa revealed this gj is the first reported to transfer negative charge approximately 136 c from the ionosphere to the positively charged origins in the cloud i e a positive cloud to ionosphere discharge ci with a large total charge moment change of 11600 c km and a maximum current of 3 3 ka early vlf transmitter amplitude perturbations detected concurrently with the gj confirm the production of large conductivity changes due to electron density enhancements in the d region of the ionosphere

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

coordinated analysis of delayed sprites with high speed images and remote electromagnetic fields 1 simultaneous measurements of high altitude optical emissions and magnetic fields produced by sprite associated lightning discharges enable a close examination of the link between low altitude lightning processes and high altitude sprite processes we report results of the coordinated analysis of high speed sprite video and wideband magnetic field measurements recorded simultaneously at yucca ridge field station and duke university from june to august 2005 sprites were detected following 67 lightning strokes all of which had positive polarity our data showed that 46 of the 83 discrete sprite events in these sequences initiated more than 10 ms after the lightning return stroke and we focus on these delayed sprites in this work all delayed sprites were preceded by continuing current moments that averaged at least 11 ka km between the return stroke and sprites the total lightning charge moment change at sprite initiation varied from 600 to 18 600 c km and the minimum value to initiate long delayed sprites ranged from 600 for 15 ms delay to 2000 c km for more than 120 ms delay we numerically simulated electric fields at altitudes above these lightning discharges and found that the maximum normalized electric fields are essentially the same as fields that produce short delayed sprites both estimated and simulation predicted sprite initiation altitudes indicate that long delayed sprites generally initiate around 5 km lower than short delayed sprites the simulation results also reveal that slow 5 20 ms intensifications in continuing current can play a major role in initiating delayed sprites

northern hemisphere summer monsoon singularities and climatological intraseasonal oscillation abstract using climatological pentad mean outgoing longwave radiation olr and european centre for medium range weather forecasts analysis winds the authors show that the northern hemisphere summer monsoon displays statistically significant climatological intraseasonal oscillations cisos the extreme phases of ciso characterize monsoon singularities monsoon events that occur on a fixed pentad with usual regularity whereas the transitional phases of ciso represent the largest year to year monsoon variations the ciso results from a phase locking of transient intraseasonal oscillation to annual cycle it exhibits a dynamically coherent structure between enhanced convection and low level convergent upper level divergent cyclonic anticyclonic circulation its phase propagates primarily northward from the equator to the northern philippines during early summer may july and westward along 15 n from 170 e to the bay of bengal during august and september the propagation of ciso links monsoon singular

recent advances in theory of transient luminous events 1 this paper presents an overview of the recent modeling efforts directed to the interpretation of observed features of transient luminous events termed sprites blue jets and gigantic jets the primary emphasis is placed on interpretation of various emissions documented to date from sprites and comparison of exiting models with recent high speed video and satellite based observations of sprites we also discuss the recently advanced theories of blue jet and gigantic jet discharges describing electrodynamic conditions which facilitate escape of conventional lightning leaders from thundercloud tops and their upward propagation toward the ionosphere the paper concludes with a brief survey of the recent literature on chemical and global electric circuit effects of sprite and jet discharges

sediment load trends in the magdalena river basin 1980 2010 anthropogenic and climate induced causes abstract the colombian andes and its main river basin the magdalena have witnessed dramatic changes in land cover and further forest loss during the last three decades for the magdalena river human activities appear to have played a more prominent role compared to rainfall climate change to mobilize sediment however environmental authorities in colombia argue that climate change is the main trigger of erosion and floods experienced during the last decade here we present the first regional exercise addressing the following 1 what are the observed trends of sediment load in the northern andes during the last three decades and 2 are sediment load trends in agreement with tendencies in land use change and climate e g precipitation we perform mann kendall tests on sediment load series for 21 main tributary systems during the 1980 2010 period these gauging stations represent 77 of the whole magdalena basin area the last decade has been a period of increased pulses in sediment transport as seen by the statistical significant trends in load overall six subcatchments representing 55 of the analyzed magdalena basin area have witnessed increasing trends in sediment load also some major tributaries have experienced changes in their interannual mean sediment flux during the mid 1990s and 2005 further analysis of land cover change e g deforestation indicates that the basin has undergone considerable change forest cover decreased by 40 over the period of study while the area under agriculture and pasture cover agricultural lands 1 and 2 increased by 65 the highest peak of forest loss on record in the magdalena basin 5106 km2 or 24 of the combined deforestation in colombia occurred during the 2005 2010 period in contrast mann kendall tests on rainfall series for 61 stations reveal that precipitation shows no regional signs of increasing trends also increasing trends in sediment load match quite well with the marked increase in forest clearance during the 1990 2000 and 2005 2010 periods such signs of increasing sediment fluxes should not be attributed to climate change and rainfall variability alone as a whole the magdalena one of the top 10 rivers in terms of sediment delivery to the ocean 184 mt y 1 and its tributaries have experienced increasing trends in sediment load during the 1980 2010 period increases in close agreement with trends in land use change and deforestation during the last decade the magdalena river drainage basin has witnessed an increase in erosion rates of 34 from 550 t km 2 y 1 before 2000 to 710 t km 2 y 1 for the 2000 2010 period and the average sediment load for the whole basin increased to 44 mt y 1 for the same period similar to the global picture of human contribution to sediment generation the rate of anthropogenic soil erosion in the magdalena basin probably exceeds the rate of climate driven erosion by several orders of magnitude

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

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

leading role of internal dynamics in the 2009 indian summer monsoon drought 1 understanding the underlying dynamics of the indian summer monsoon ism extremes such as severe droughts is key to improving seasonal prediction of the ism rainfall a large number of ism droughts over the past century occurred unrelated to external forcing like the el nino southern oscillation enso in this study we challenge the perception that the 2009 ism drought was driven by enso and show that it was caused by internally driven processes the 2009 drought of ism was the result of two very long breaks one in the month of june and the other in july august ja while some studies provide strong evidence that the june break was caused by dry air intrusion associated with extratropical waves a mechanism for the equally important ja break has not been elucidated so far in this study we unravel a new process in which westward propagating convectively coupled planetary scale equatorial rossby pser waves emanating from the eastern pacific as a remnant of madden julian oscillation mjo interact with the monsoon intraseasonal oscillation miso modulate the active break spells and thereby influence the seasonal mean it was found that during ja 2009 the arrival of the divergent phase of this pser mode over the ism domain reinforced and extended the break condition initiated by the northward propagating miso thereby creating a long break nonlinear kinetic energy exchanges between the pser mode and the northward propagating miso were found to be at the heart of such interactions evidence of such interactions can be seen during different active break events in other monsoon seasons as well as both long breaks were primarily driven by internal dynamical processes of the atmosphere the study underscores the major role played by internal dynamics in causing the 2009 ism drought our discovery that interactions between pser waves and miso can lead to significant modulations of the active break spells opens up a new unexplored mechanism for understanding monsoon variability

tree ring based reconstructions of northern patagonia precipitation since ad 1600 long term reconstructions 400 years of seasonal and annual precipitation variations were developed for northern patagonia east of the andes using a new set of 16 tree ring width chronologies from austrocedrus chilensis d don endl reconstructions which capture between 41 and 50 of the precipitation variance show that the twentieth century contains the most extreme long periods of wetness and dryness in the past 400 years since about ad 1910 the reconstructions are also characterized by an increase in interannual variability and one of the highest rates of extreme events within the last 400 years a prominent oscillation on the order of 2 2 1 years in length has been identified in the reconstructions using spectral analysis quasi biennial oscillations have been shown to be very marked in some circulation indices of the southern hemisphere although significant oscillations within the preferred frequency domain of el nino southern oscillation enso are present in the reconstructions no clear trod consistent responses to enso have been observed correlations of reconstructions with mean sea level pressure around south america for the interval ad 1912 1984 reveal the influence of subtropical and high latitude features of the atmospheric circulation on precipitation variations in northern patagonia droughts result from an intensification of the subtropical pacific anticyclone off the chilean coast and the deepness of the circum antarctic trough over the south orkney antarctic peninsula sector mean sea level pressure reconstructions for the south atlantic sector of the southern oceans were used to evaluate the temporal stability of the relationships between northern patagonia precipitation and high latitude climatic variations since ad 1750 the influence of high latitude circulation on precipitation appears to be more significant during the twentieth century which in turn may respond to an intensification of wavenumbers 3 on the mean planetary wave structure over the southern hemisphere recent increase of precipitation variability in northern patagonia may reflect stronger interactions between middle and high latitude atmospheric circulation in the southern hemisphere during the twentieth century

high speed intensified video recordings of sprites and elves over the western mediterranean sea during winter thunderstorms we report the first intensified high speed video images of elves sprites and halos observed in europe all the events corresponded to winter season thunderstorms over the mediterranean sea the observations comprise many elves generated by both cloud to ground lightning current polarities in 8 of the 14 sprite observations we observed an elve previous to the sprite in three cases we observed also an elve quickly followed by a halo and a sprite in several observations we observed lightning light before the mesospheric transient luminous event we present a case where the lightning from cloud tops was visible during the entire event thanks to the high speed videos and their resolution and low intensifier phosphor persistence we analyzed the timing distribution of the development phase of sprite elements the persisting luminosity phase and the total duration finally we summarize one particular observation where a streamer collides and bounces with a previous formed column it may be a new phenomenon of collision between an existing column body that interacts with a later streamer point like tip which is not merged and attached

a numerical study of the magellan plume 1 in this modeling study we investigate the dynamical mechanisms controlling the spreading of the magellan plume which is a low salinity tongue that extends along the patagonian shelf our results indicate that the overall characteristics of the plume width depth spreading rate etc are primarily influenced by tidal forcing which manifests through tidal mixing and tidal residual currents tidal forcing produces a homogenization of the plume s waters and an offshore displacement of its salinity front the interaction between tidal and wind forcing reinforces the downstream and upstream buoyancy transports of the plume the influence of the malvinas current on the magellan plume is more dominant north of 50 s where it increases the along shelf velocities and generates intrusions of saltier waters from the outer shelf thus causing a reduction of the downstream buoyancy transport our experiments also indicate that the northern limit of the magellan plume is set by a high salinity discharge from the san matias gulf sensitivity experiments show that increments of the wind stress cause a decrease of the downstream buoyancy transport and an increase of the upstream buoyancy transport variations of the magnitude of the discharge produce substantial modifications in the downstream penetration of the plume and buoyancy transport the magellan discharge generates a northeastward current in the middle shelf a recirculation gyre south of the inlet and a region of weak currents father north

wavelet analysis of the interannual variability in southern quebec streamflow the objectives of this study are to describe the local interannual variability in southern quebec canada streamflow based on wavelet analysis and to identify plausible climatic teleconnections that could explain these local variations scale averaged wavelet power spectra are used to simultaneously assess the interannual and spatial variability in 18 contiguous annual streamflow time series the span of available observations 1938 2000 allows depicting the variance for periods up to about 12 yr the most striking feature in the 2 3 yr band and in the 3 6 yr band the 6 12 yr band is dominated by white noise and is not considered further is a net distinction between the timing of the interannual variability in local western and eastern streamflows which may be linked to the local climatology this opens up the opportunity to construct two regional time series using principal component pc analysis then for each band linear relationships are sought between the regional streamflow and five selected climatic indices the pacific north america pna the north atlantic oscillation nao the northern hemisphere annular mode nam the baffin island west atlantic bwa and the sea surface temperature anomalies over the nino 3 region enso3 the correlation analysis revealed the presence of a change point in the streamflow time series as reported by others occurring around 1970 for example the west and east 2 3 yr bands are positively correlated to pna since 1970 which was not the case prior to that change point the proposed regional east west divide is particularly evident prior to 1970 with a negative nam correlation for the west and a positive nam and negative enso3 for the east the picture for the less energetic 3 6 yr band is mixed with alternating dominance of teleconnection patterns but the 1970 change point holds