segmentation of the himalayan megathrust around the gorkha earthquake 25 april 2015 in nepal abstract we put the 25 april 2015 earthquake of nepal mw 7 9 into its structural geological context in order to specify the role of the segmentation of the himalayan megathrust the rupture is mainly located nw of kathmandu at a depth of 13 15 km on a flat portion of the main himalayan thrust mht that dips towards the n ne by 7 10 the northern bound of the main rupture corresponds to the transition towards a steeper crustal ramp this ramp which is partly coupled during the interseismic period is only locally affected by the earthquake the southern bound of the rupture was near the leading edge of the lesser himalaya antiformal duplex and near the frontal footwall ramp of the upper nawakot duplex the rupture has been affected by transversal structures on the western side the judi lineament separates the main rupture zone from the nucleation area on the eastern side the gaurishankar lineament separates the 25 april 2015 rupture from the 12 may 2015 mw 7 2 rupture the origin of these lineaments is very complex they are probably linked to pre himalayan faults that extend into the indian shield beneath the mht these inherited faults induce transverse warping of the upper lithosphere beneath the mht control the location of lateral ramps of the thrust system and concentrate the hanging wall deformation at the lateral edge of the ruptures the mht is therefore segmented by stable barriers that define at least five patches in central nepal these barriers influence the extent of the earthquake ruptures for the last two centuries the 1833 mw 7 6 earthquake was rather similar in extent to the 2015 event but its rupture propagated south westwards from an epicentre located ne of kathmandu the patch south of kathmandu was probably affected by at least three earthquakes of mw 7 that followed the 1833 event a few days later or 33 years 1866 event mw 7 2 later the 1934 earthquake mw 8 4 had an epicentre 170 km east of kathmandu may have propagated as far as kathmandu and jumped the gaurishankar lineament this combined structural approach and earthquake study allows us to propose that the mht in the central eastern himalaya is segmented by stable barriers that define barrier type earthquake families however for each individual earthquake within a family the rupture histories could be different furthermore the greatest earthquakes could have broken the barriers and affected the patches of several families the concept of a regular recurrence of characteristic earthquakes is therefore misleading to describe the succession of himalayan earthquakes

transversal and oblique structures at the serres de llevant thrust belt mallorca island the serres de llevant thrust and fold segment outcrops along the se coast of mallorca balearic isles spain and represents the eastern continuation of the external zones of the alpine betic range the structure of the serres de llevant consists mainly of northwest directed thrusts which involve a sedimentary series ranging in age from upper triassic to middle miocene the thrusts form a thrust system developed both by piggy back and out of sequence thrusting thrust sheets are imbricated to the se and to the sw and in the northern part also to the ne giving rise to a complex 3 d pattern the thrusts and related folds developed during the oligocene and the lower and middle miocene the thrust transport direction has been inferred from the stratigraphic facing directions of all mapped ramps and has been determined with the aid of other transversal structures the resulting transport direction is from se to nw n310e one of the most significant structural features of the serres de llevant thrust segment is the existence of several lateral and oblique structures these structures are ramps which display stratigraphic facing directions both to the ne and sw other lateral structures represented in the northern part of the thrust segment are tear and drop faults in the southern part kilometric scale oblique folds are exposed

balanced section in thrust belts part 1 construction balanced geological cross sections are an important aid to understanding thrust belt structures and to estimating their hydrocarbon bearing potential two approaches to section balancing have been taken in the past construction of retrodeformable sections from raw data and modification of previous interpretations after an evaluation procedure these approaches may be unified by use of a langrangian grid projection of datum locations dips and stratigraphic thicknesses onto the section plane is performed directly by calculation or graphically using plunge lines spline interpolation and parallel fold modeling are the simplest ways of filling gaps in the sectional data but isogon interpolation yields rheologically more realistic results faults are interpolated using cutoff geometries as constraints fault tips are located from distance displacement plots whereas the depth to detachment is obtained by a modified chamberlin construction interpolations made on the section are directed back to the geologic map via plunge lines although these techniques of section construction do not guarantee a balance especially when complexities such as growth structures diapirs or strike slip faults are present they eliminate many potential errors

growth of a thrust fault array in space and time an example from the deep water niger delta abstract the temporal and spatial evolution of thrust fault arrays is currently poorly understood and marine fold and thrust belts at the toe of passive margin gravitational systems imaged by commercial 3d seismic reflection datasets afford a unique opportunity to investigate this problem in three dimensions using an extensive 3d seismic data set and age data the total cumulative strain shortening and interval strain rates have been calculated for 11 thrust related folds mapped in the toe thrust region of the southern lobe of the niger delta for the first time the sequence of thrust nucleation propagation and linkage through time at a scale of 10 s km both along and across strike is documented short thrust segments had nucleated throughout the entire study area by 15 ma they then grew largely by lateral growth and linkage increasing the fault trace length and generating asymmetric strain distance plots for the first 50 of their history thereafter growth continued by shortening with minimal along strike increase in fault length changes in shortening distance data between adjacent structures across strike suggest that the change in growth mode occurred once the thrusts had linked in 3d through the common underlying detachment over the entire thrust array the strain rate varies through time starting slowly

possible dust devils vortices on mars this paper presents the results of a study of local vortices and dust devils on mars as observed by viking landers 1 and 2 it is found that these vortices are most common during martian spring and summer as occurs on earth seven of the vortices involve wind speeds that may raise dust from the martian surface there is no indication that these possible dust devils contribute to the planet wide spread of major dust storms however it appears that they may help in maintaining the atmospheric dust content the data indicate that there is no preference in rotation direction at least to core diameters of 300 m corresponding to a region of influence of about 3 km diameter

dust devil speeds directions of motion and general characteristics observed by the mars express high resolution stereo camera abstract a total of 205 dust devils were detected in 23 high resolution stereo camera hrsc images taken between january 2004 and july 2006 with the esa mars express orbiter in which average dust devil heights were 660 m and average diameters were 230 m for the first time dust devil velocities were directly measured from orbit and range from 1 to 59 m s the observed dust devil directions of motion are consistent with data derived from a general circulation model gcm in some respects hrsc dust devil properties agree favorably with data from the nasa mars exploration rover spirit dust devil analyses the spatial distribution of the active dust devils detected by hrsc supports the conjecture that the ascending branch of the hadley circulation is responsible for the increase in dust devil activity especially observed during southern summer between 50 and 60 s latitude combining the dust lifting rate of 19 kg km2 sol derived from the spirit observations with the fewer in number but larger in size dust devils from various other locations observed by hrsc we suggest that dust devils make a significant contribution to the dust entrainment into the atmosphere and to the martian dust cycle

erosion rates on mars and implications for climate change constraints from the pathfinder landing site the observation that the mars pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1 8 3 5 ga allows quantitative constraints to be placed on the rate of change of the site since that time the abundance of erosional features such as an exhumed former soil horizon sculpted wind tails ripplelike and other tag deposits and ventifacts fluted and grooved rocks all suggest the site has undergone net deflation or loss of 3 7 cm of material the presence of barchan dunes and ventifacts argues for erosion by saltating crystalline sand size particles entrained in the wind most ventifacts probably formed soon after the catastrophic flood which likely introduced a large fresh supply of sand size particles distributed across the rocky plain the strongest winds blew toward the northwest during this time resulting in the sculpting of ventifacts deflation of the surface collections of dunes within big crater and other lows and possibly preferentially eroding small crater rims the predominant wind direction changed to blow toward the southwest similar to today these winds further deflated the surface completed the deposition of sand size material in dunes and ultimately trapped these dunes in lows the erosional features observed by pathfinder indicate extremely low long term deflation rates of 0 01 0 04 nm yr since the end of the hesperian 1 8 3 5 ga similar to less precise rates of 1 nm yr based on the preservation of craters at the viking 1 and pathfinder landing sites short term redistribution rates deposition and removal of atmospheric dust at the pathfinder landing site and preexisting dust and sand at other locations on mars are up to 10 5 nm yr estimates of erosion rates on mars show a rapid decrease by 3 6 orders of magnitude from 10 2 10 4 nm yr in noachian terrains characterized by rimless flat floored craters and valley networks to the exceedingly slow rates 10 2 10 nm yr operating during the hesperian and amazonian noachian erosion rates comparable to low continental denudation rates on earth are consistent with erosion by running water and perhaps a more clement climate the rapid decrease in erosion rates is consistent with a major climatic change during the noachian at the tail end of heavy bombardment and a cold dry desiccating climate similar to today s since that time

balanced cross sections and their implications for the deep structure of the northwest alps reply abstract the structure of the northwest external french alps around the internal belledonne and mont blanc massifs in the beaufortain area can be explained by foreland wnw propagating thrust tectonics the internal belledonne massif is interpreted as having developed by imbrication of an originally thin skin of basement with a mesozoic cover above this massif all thrusts tend to climb lateral sections to the south to converge with the frontal pennine thrust the southern termination of the mont blanc massif is merely a spectacular example of such a lateral ramp

numerical modeling of propagation and overlap of thrust faults with application to the thrust fold belt of central alberta abstract we use two computer programs to analyze the propagation of multiple thrust faults and their influence on the geometry of a thrust belt they use algorithms based on current equations of fault propagation to generate graphical simulations the simulations are used to demonstrate a model of thrust propagation and thrust belt development that fits current knowledge of fault propagation an alternative to the thrust transfer zone model is proposed called thrust overlap zones the computer simulations provide useful information about the generation and behavior of multiple faults the number of faults the positions of their nucleation points and hence their density the rock properties and rate of fault propagation govern the uniformity of the shortening along the thrust belt thus shortening of a thrust belt can be distributed more evenly by means of propagation of a large number of small faults than by a few large faults the final geometry of a large thrust fault on a geological map provides few clues about its origin i e whether it was produced by the coalescence of a series of en echelon thrust faults or from only a single fault a simple kinematic model based on map length and position of known thrust faults imitates the curved fault map patterns of a segment of the thrust fold belt of central alberta

the effects of pre existing normal faults on thrust ramp development an example from the northern apennines italy the umbria marche foreland fold and thrust belt in the northern apennines of italy provides excellent evidence to test the hypothesis of synsedimentary structural control on thrust ramp development this orogenic belt consists of platform and pelagic carbonates late triassic to miocene in age whose deposition was controlled by significant synsedimentary extension normal faulting mainly active from jurassic through late cretaceous paleogene time resulted in significant lateral thickness variability within the related stratigraphic sequences by late miocene time the sedimentary cover was detached from the underlying basement and was deformed by east verging folds and west dipping thrusts two restored balanced cross sections through the southernmost part of the belt show a coincidence between the early synsedimentary normal faults and the late thrust fault ramps these evidences suggest that synsedimentary tectonic structures such as faults and the related lithological lateral changes can be regarded as mechanically important controlling factors in the process of thrust ramp development during positive tectonic inversion processes

convective vortices on mars a reanalysis of viking lander 2 meteorological data sols 1 60 dust devil data from mars is limited by a lack of data relating to diurnal dust devil behaviour previous work looking at the viking lander meteorological data highlighted seasonal changes in temporal occurrence of dust devils and gave an indication of typical dust devil diameter size and internal dynamics the meteorological data from viking lander 2 for sols 1 to 60 have been revisited to provide detailed diurnal dust devil statistics results of our analysis show that the viking lander 2 experienced a possible 38 convective vortices in the first 60 sols of its mission with a higher occurrence in the morning compared to earth possibly as a result of turbulence generated by the lander body dust devil events have been categorised by statistical confidence and intensity some initial analysis and discussion of the results is also presented assuming a similar dust loading to the vortices seen by mars pathfinder it is estimated that the amount of dust lofted in the locality of the lander is approximately 800 10 kgsol 1km 2

measurements of martian dust devil winds with hirise 1 we report wind measurements within martian dust devils observed in plan view from the high resolution imaging science experiment hirise orbiting mars the central color swath of the hirise instrument has three separate charge coupled devices ccds and color filters that observe the surface in rapid cadence active features such as dust devils appear in motion when observed by this region of the instrument our image animations reveal clear circulatory motion within dust devils that is separate from their translational motion across the martian surface both manual and automated tracking of dust devil clouds reveal tangential winds that approach 20 30 m s 1 in some cases these winds are sufficient to induce a 1 decrease in atmospheric pressure within the dust devil core relative to ambient facilitating dust lifting by reducing the threshold wind speed for particle elevation finally radial velocity profiles constructed from our automated measurements test the rankine vortex model for dust devil structure our profiles successfully reveal the solid body rotation component in the interior but fail to conclusively illuminate the profile in the outer regions of the vortex one profile provides evidence for a velocity decrease as a function of r 1 2 instead of r 1 suggestive of surface friction effects however other profiles do not support this observation or do not contain enough measurements to produce meaningful insights

energy balance and deformation mechanisms of duplexes abstract a duplex consists of a series of imbricate faults that are asymptotic to a roof thrust and a floor thrust depending on the final orientations of the imbricate faults and the final position of the branch lines a duplex may be hinterland dipping foreland dipping or an antiformal stack the exact geometry depends on various factors such as the initial dimensions of the individual slices horses their lithology the amount of displacement normalized to size of horse on each fault and the mechanics of movement along each fault the energy required in duplex formation can be determined by calculating the total work involved in emplacing each horse this is given by where w t w p w b w g w i wp is the work involved in initiating and propagating a fracture wb is the work involved in basal sliding which may be frictional or some form of ductile flow wg is the work done against gravity during the emplacement of the horse and wi is the work involved in the internal deformation of the horse by calculating and comparing these work terms it is possible to predict the conditions under which the different types of duplexes will form normally the development of a hinterland dipping duplex is most likely however if deformation conditions are favorable displacements on individual imbricate faults may be very large compared to the size of the horses leading to the formation of either antiformal stacks or foreland dipping duplexes

structural style of the okcheon fold thrust belt in the taebaeksan zone korea abstract structural interpretation of the distinct map pattern defined by highly connected thrust traces in the map view of the taebaeksan zone provides insight into the structural style of the northeastern okcheon belt the map pattern can generally be explained by either a folded imbricate fan or a hinterland dipping duplex the same geometry could also be formed by a complex combination of major imbricate thrusts and their connecting splays having the structural architecture of a typical fold thrust belt however a folded imbricate fan model is not adequate to explain the absence of late paleozoic to early mesozoic strata i e the pyeongan supergroup between two major thrusts viz the pyeongchang and machari thrusts in this area this result further suggests that the yeongwol area the western part of the taebaeksan zone is a duplex that corresponds to a more internal and deeper hinterland part of the fold thrust belt while the imbricate thrusts with low connectivity in the taebaek area the eastern part of the taebaeksan zone indicate a more external and shallower foreland portion of the belt in addition cross cutting relations and newly obtained sensitive high resolution ion microprobe shrimp u pb zircon ages from a cross cutting dike and syntectonic sedimentary rocks suggest limited thrust reactivation after the early jurassic and early tertiary respectively in spite of this the original geometry of the fold thrust wedge in the taebaeksan zone remained well preserved

characteristics of summer stationary waves in the northern hemisphere abstract summer stationary waves in the northern hemisphere are separated by a midlatitude transition zone into the subtropical monsoon regime with a vertical phase reversal and the subarctic regime with a vertically uniform structure the dynamics and maintenance mechanism of the subtropical stationary waves have been investigated in the context of monsoon circulation depicted in terms of streamfunction with 40 yr ecmwf re analysis era 40 the dynamic characteristics of stationary waves in the transition zone and the subarctic region are thus the focus of this study the dynamics and maintenance mechanism of these waves were explored with the streamfunction budget and the velocity potential maintenance equations stationary waves across the transition region consist of anticyclonic shear zones over the north pacific and north atlantic and a cyclonic shear zone in east eurasia these transition elements are linked to subtropical oceanic anticyclones and continental thermal lows at high latitudes a th

kinematic model for out of sequence thrusting motion of two ramp flat faults and the production of upper plate duplex systems abstract kinematic models developed here suggest a bewildering array of structural styles can be generated during out of sequence thrusting many of these structures would be difficult to distinguish from a normally stacked thrust sequence and the process can produce younger on older faults that could easily be misinterpreted as normal faults this paper considers a small subset of this problem within a large model space by considering structures that develop along a pair of ramp flat faults that are moving simultaneously or sequentially motion on the lower ramp warps the structurally higher fault due to fault bend folding and when the fault ruptures through the warp it transfers a horse to the upper hanging wall continuity of the process generates what is referred to here as an upper plate duplex to distinguish the structure from a conventional duplex kinematic parameters are developed for two models within this general problem 1 a system with a fixed ramp in the lower thrust overridden by an upper thrust and 2 a double duplex system where a conventional duplex develops along the lower fault at the same time as an upper plate duplex is formed along the upper fault the theory is tested with forward models using 2d move software and these tests indicate different families of structural styles form in association with relative scaling of ramp systems slip ratio between faults and aspect ratios of horse blocks formed in the upper plate duplex a first order result of the analysis is that an upper plate duplex can be virtually indistinguishable from a conventional duplex unless the trailing branch lines of the horses are exposed or imaged a condition seldom met in natural exposures restoration of an upper plate duplex produces counterintuitive fault geometry in the restored state and thus restorations of upper plate duplexes that erroneously assume a conventional duplex model would produce restored states that are seriously in error in addition in most of the models some fault segments place younger rocks on older rocks which could be easily misinterpreted as normal fault systems in some models younger on older juxtapositions are significant and if scaled to crustal scale would produce core complex style structures that would be difficult to recognize as contractional features collectively these observations imply that many areas where simultaneous contraction and extension are inferred may be entirely contractional with younger on older relationships generated by out of sequence thrust systems examples where this process may have occurred are in southwestern north america and the moine thrust system and future studies should evaluate these systems in light of these models distinguishing upper plate duplex from conventional duplex is potentially important in economic evaluations of thrust systems because fluid migration paths would be very different in the two alternatives the process may also be important in seismogenic mechanisms particularly in subduction megathrusts because faults warping faults could produce fault irregularities that would form transient asperities along the fault

ancient synsedimentary structural control on thrust ramp development an example from the northern apennines italy the umbria marche sabina foreland fold and thrust belt northern apennines italy provides excellent test cases for the hypothesis of ancient syndepositional structural features controlling thrust ramp development the sedimentary cover late triassic to miocene in age is made of platform and pelagic carbonates whose deposition was controlled by significant synsedimentary extension normal faulting mainly during the jurassic and the late cretaceous palaeogene determined sensible lateral thickness variations within the relative sequences by late miocene the sedimentary cover was detached from its basement along a mainly evaporitic horizon and was deformed by means of eastward verging folds and thrusts in order to locate the points where thrust ramps branch off the basal detachment both line length and equal area techniques were used in the construction of a balanced cross section through three major fault related folds in southeastern umbria the nucleation of thrust ramps was controlled by the occurrence of jurassic and cretaceous palaeogene synsedimentary normal faults these interrupted the lateral continuity of the evaporitic unit the late triassic anidriti di burano fm at the base of the sedimentary cover and acted as obstacles to the eastward propagation of the thrust system giving rise to major folds which originated from tip line folding processes therefore the inferred relationships between ancient normal faults and late thrusts indicate that synsedimentary tectonic structures and the related lateral stratigraphic variations can be envisaged as mechanically important perturbations which effectively control the nucleation and development of thrust ramps

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

thrusting magmatic intraplating and metamorphic core complex development in the archaean belleterre angliers greenstone belt superior province quebec canada abstract the belleterre angliers greenstone belt in the pontiac subprovince is the youngest and southernmost of the greenstone belts in the archaean superior province of the canadian shield the greenstone belt has been disrupted into three fragments from north to south the baby belleterre and lac des bois groups respectively the belleterre angliers greenstone belt has sheared contacts with younger pontiac metasediments and older tonalites the pontiac metasediments dip beneath the baby group and are tectonically interlayered with the tonalites thus the belleterre angliers belt is interpreted to be a thrust sheet 6 km thick in the north thinner in the south above a mid crustal duplex consisting of metasedimentary and tonalite imbricates the thrust sheet was transported from the north but age and geochemical constraints rule out derivation from the abitibi subprovince it probably roots in a band of ultramafic rocks that mark a major south vergent thrust in the northern pontiac subprovince after emplacement the belleterre angliers sheet and the adjacent pontiac metasediments were deformed by a system of linked extensional shears and transfer faults that border dome or antiformal areas in a style similar to phanerozoic metamorphic core complexes the orientation of shear zones and foliations indicates that the regional far field stresses were compressional both before and after extensional shearing since the system of extensional shears is intruded by a suite of monzodiorite granodiorite syenodiorite and syenite plutons with high mg number it is concluded that crustal inflation caused by the injection intraplating of large volumes of magma perturbed the regional compressive stress field and facilitated extensional faulting

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

using laterally compatible cross sections to infer fault growth and linkage models in foreland thrust belts abstract we investigate changes in shortening displacement and fold geometry to understand the detailed along strike structural variation within fold thrust belts and infer thrust growth and linkage mechanisms field observations from the vercors in se france are used to characterise deformation style in the region parallel cross sections are constructed analysed and used to create shortening and thrust displacement profiles from the northern to southern vercors sections show changes in structural style and shortening accommodation from thrust dominated in the north to fold dominated in the south the total shortening distance in the vercors does not change significantly along strike 3400 4650 m however displacements along individual thrust zones do vary significantly and displacement profiles show a range in displacement gradients 16 107 m km despite relatively simple shortening patterns in the vercors sections show a more complex 3d internal structure of the fold thrust belt thrust displacements and geometries suggest both large scale thrust zones and small scale thrusts are soft linked transferring displacement along strike through transfer zones short soft linked thrust segments indicate an intermediate stage of thrust growth and linkage well documented for normal fault systems which form prior to the formation of thrust branches and hard linked displacement transfer

convective vortices and dust devils at the msl landing site annual variability two hundred fifty two transient drops in atmospheric pressure likely caused by passing convective vortices were detected by the rover environmental monitoring station instrument during the first martian year of the mars science laboratory msl landed mission these events resembled the vortex signatures detected by the previous mars landers pathfinder and phoenix however the msl observations contained fewer pressure drops greater than 1 5 pa and none greater than 3 0 pa apparently these vortices were generally not lifting dust as only one probable dust devil has been observed visually by msl the obvious explanation for this is the smaller number of strong vortices with large central pressure drops since according to arvidson et al 2014 ample dust seems to be present on the surface the annual variation in the number of detected convective vortices followed approximately the variation in dust devil activity dda predicted by the marswrf numerical climate model this result does not prove however that the amount of dust lifted by dust devils would depend linearly on dda as is assumed in several numerical models of the martian atmosphere since dust devils are only the most intense fraction of all convective vortices on mars and the amount of dust that can be lifted by a dust devil depends on its central pressure drop sol to sol variations in the number of vortices were usually small however on 1 martian solar day a sudden increase in vortex activity related to a dust storm front was detected

an investigation of boundary forcing sensitivities in a regional climate model the sensitivity of a regional climate model to lateral upper and lower dynamical forcing is evaluated for a pan arctic domain the experiments focus on a month long case study of may 1990 but the results are shown to be extendable to january and july 1990 although the control simulation is found to adequately represent major tropospheric circulation features a large negative geopotential height bias of up to 700m is found at the upper levels of the model experiments find these biases are remedied through the replacement of a reflective rigid lid upper boundary condition with a local wave absorbing layer geopotential height biases are reduced to a maximum underestimation of only 50m at the upper boundary substantial improvement is also found in the simulated temperature and zonal wind profiles transient heat and momentum fluxes and stationary eddies as seen through the eliassen palm flux divergence with this wave absorbing upper boundary condition in place additional improvement is found using a gravity wave drag parameterization appropriate for this domain s 100km horizontal resolution additional sensitivity to lateral forcing is examined and the relative role of the upper boundary condition to skillful simulations within the arctic basin domain is discussed

a new kinematic evolutionary model for the growth of a duplex an example from the rangit duplex sikkim himalaya india abstract the lesser himalayan duplex lhd is a prominent structure through much of the lesser himalayan fold thrust belt in the darjeeling sikkim himalaya a component of the lhd is exposed in the rangit window as the rangit duplex rd the rd consists of ten horses of the upper lesser himalayan sequence gondwana buxa upper daling the duplex varies from hinterland dipping in the north through an antiformal stack in the middle to foreland dipping in the south the ramgarh thrust rt is the roof thrust and based on a balanced cross section the main himalayan sole thrust is the floor thrust at a depth of 10 km and with a dip of 3 5 n retrodeformation suggests that the rd initiated as a foreland dipping duplex with the early ramgarh thrust as the roof thrust and the rt as the floor thrust the rt became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent rt reactivation this kinematic history best explains the large translation of the overlying mct sheets the restoration suggests that rd shortening is 125 km and the original gondwana basin extended 142 km northward of its present northernmost exposures within the window

upwelling on the continental slope of the alaskan beaufort sea storms ice and oceanographic response 1 the characteristics of pacific born storms that cause upwelling along the beaufort sea continental slope the oceanographic response and the modulation of the response due to sea ice are investigated in fall 2002 a mooring array located near 152w measured 11 significant upwelling events that brought warm and salty atlantic water to shallow depths when comparing the storms that caused these events to other aleutian lows that did not induce upwelling interesting trends emerged upwelling occurred most frequently when storms were located in a region near the eastern end of the aleutian island arc and alaskan peninsula not only were these storms deep but they generally had northward tending trajectories while the steering flow aloft aided this northward progression the occurrence of lee cyclogenesis due to the orography of alaska seems to play a role as well in expanding the meridional influence of the storms in late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site it is argued that the reduction in amplitude was due to the onset of heavy pack ice while the decreased frequency was due to two different upper level atmospheric blocking patterns inhibiting the far field influence of the storms

numerical simulation of dust lifting within dust devils simulation of an intense vortex abstract based on an advanced dust devil scale large eddy simulation les model the atmosphere flow of a modeled dust devil in a quasi steady state was first simulated to illustrate the characteristics of the gas phase field in the mature stage including the prediction of the lower pressure and higher temperature in the vortex core the dust lifting physics is examined in two aspects through the experimental data analysis it is verified again that the horizontal swirling wind can only make solid particles saltate along the ground surface based on a lagrangian reference frame the tracks of dust grains with different density material and diameter are calculated to show the effect of dust particles entrained by the vertical swirling wind field the movement of solid particles depends on the interactions between the aloft dust particles and the airflow field of dust devils in which the drag and the centrifugal force component on the horizontal plane are the key force components there is the trend o

convective vortices and dust devils at the phoenix mars mission landing site 1 the phoenix mars lander detected a larger number of short 20 s pressure drops that probably indicate the passage of convective vortices or dust devils near continuous pressure measurements have allowed for monitoring the frequency of these events and data from other instruments and orbiting spacecraft give information on how these pressure events relate to the seasons and weather phenomena at the phoenix landing site here 502 vortices were identified with a pressure drop larger than 0 3 pa occurring in the 151 sol mission ls 76 to 148 the diurnal distributions show a peak in convective vortices around noon agreeing with current theory and previous observations the few events detected at night might have been mechanically forced by turbulent eddies caused by the nearby heimdal crater a general increase with major peaks in the convective vortex activity occurs during the mission around ls 111 this correlates with changes in midsol surface heat flux increasing wind speeds at the landing site and increases in vortex density comparisons with orbiter imaging show that in contrast to the lower latitudes on mars the dust devil activity at the phoenix landing site is influenced more by active weather events passing by the area than by local forcing

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

an observational study of the northern hemisphere extratropical summertime general circulation abstract the three dimensional structure of the extratropical northern hemisphere summertime general circulation is documented by making use of twice daily operational analyses at nine pressure levels 1000 100 mb for 12 summers 1966 77 two distinct regimes of standing waves quite unlike the wintertime standing waves appear a subtropical regime which is clearly a monsoonal response to thermal forcing and a higher latitude regime in which the standing waves are of smaller scale and much weaker than in winter and tend to be equivalent barotropic in structure with almost no vertical tilt in the mid and upper troposphere while the transient eddies shift poleward from their wintertime location and are weaker in summer their properties and relation to the mean flow are much the same as blackmon et al 1977 lau 1978 1979a b and lau and wallace 1979 found for the winter in both seasons the regions of strongest transient activity generally coincide with the regions where the height scale of the m

multitemporal observations of identical active dust devils on mars with the high resolution stereo camera hrsc and mars orbiter camera moc abstract active dust devils were observed in syria planum in mars observer camera wide angle moc wa and high resolution stereo camera hrsc imagery acquired on the same day with a time delay of 26 min the unique operating technique of the hrsc allowed the measurement of the traverse velocities and directions of motion large dust devils observed in the hrsc image could be retraced to their counterparts in the earlier acquired moc wa image minimum lifetimes of three large avg 700 m in diameter dust devils are 26 min as inferred from retracing for one of these large dust devil 820 m in diameter it was possible to calculate a minimum lifetime of 74 min based on the measured horizontal speed and the length of its associated dust devil track the comparison of our minimum lifetimes with previous published results of minimum and average lifetimes of small 19 m in diameter avg min lifetime of 2 83 min and medium 185 m in diameter avg min lifetime of 13 min dust devils imply that larger dust devils on mars are active for much longer periods of time than smaller ones as it is the case for terrestrial dust devils knowledge of martian dust devil lifetimes is an important parameter for the calculation of dust lifting rates estimates of the contribution of large dust devils 300 1000 m in diameter indicate that they may contribute at least regionally to 50 of dust entrainment by dust devils into the atmosphere compared to the dust devils

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

a year of convective vortex activity at gale crater abstract atmospheric convective vortices which become dust devils when they entrain dust from the surface are prominent features within mars atmosphere which are thought to be a primary contributor to the planet s background dust opacity buoyantly produced in convectively unstable layers at a planet s surface these vertically aligned vortices possess rapidly rotating and ascending near surface warm air and are readily identified by temporal signatures of reduced atmospheric surface pressure measured within the vortex as it passes by we investigate such signatures in surface pressure measurements acquired by the rover environmental monitoring station aboard the mars science laboratory rover located within gale crater during the first 707 sols of the mission 245 convective vortices are identified with pressure drops in the range of 0 30 2 86 pa with a median value of 0 67 pa the cumulative distribution of their pressure drops follows a power law of slope 2 77 and we observe seasonal and diurnal trends in their activity the vast majority of these pressure signatures lack corresponding reductions in rems measured uv flux suggesting that these vortices rarely cast shadows upon the rover and therefore are most often dust free the relatively weak magnitude dustless vortices at gale crater are consistent with predictions from mesoscale modeling indicating that the planetary boundary layer is suppressed within the crater and are also consistent with the almost complete absence of both dust devils within mars science laboratory camera images and gale crater surface dust devil streaks within orbiter images

physical analog modeling of pull apart basin evolution abstract pull apart basins are structural depressions formed by localized extension along strike slip fault systems typically at releasing bends or steps in the fundamental strike slip system analog modeling is used to evaluate the sequence of structural evolution of pull apart basins and factors that control their degree of structural asymmetry and geometry basin evolution internal structure and overall symmetry are investigated for oblique releasing step angles and with varying rates of displacement between brittle and ductile crust on opposing sides of the strike slip system while maintaining relative rates between brittle crust on opposing sides of the basin pull apart basin evolution is separated into three stages incipient early and mature incipient pull apart basins are characterized by formation of a normal fault bounded graben or half graben parallel to the oblique step between main strike slip zones in the early stage of formation additional normal faults form toward the basin interior from the original bounding faults and cross basin strike slip faults cut diagonally across the basin interior basin bounding normal fault systems are characterized by lateral variations of fault throw and localized relay ramps in the mature stage of evolution strike slip and normal faults join to completely bound the pull apart basin analog model results indicate that displacement associated with cross basin faults causes development of a through going strike slip fault that links the two main strike slip displacement zones ultimately resulting in a decline in normal fault activity asymmetric symmetric and hybrid pull apart basins all follow the same overall deformation sequence just described the asymmetry of a pull apart basin is controlled by the degree of decoupling between brittle and ductile crust beneath the two crustal blocks in relative motion this is modeled by maintaining a constant relative rate of motion between opposing fault blocks in all models but varying the rate between the blocks and the fixed model basement absolute rate models in which one side of the detachment is fixed with respect to the basement form asymmetric pull apart basins defined by a half graben with the master fault on the mobile side in models where opposing sides of the fault system are equally decoupled from the basement symmetrical pull apart basins form defined by horst and graben structures and master fault dominance switching sides along the length of the basin fault segmentation associated with relatively immature pull apart basins may be capable of arresting earthquake rupture late linkage of main strike slip zones by a cross basin fault could extend potential rupture area dramatically increasing the possibility for large magnitude earthquakes

maintenance of the boreal forest rainbelts during northern summer abstract it is not unreasonable to expect that boreal forests that exist along 60 n in the eurasian and north american continents were created and are maintained by warm seasonal rainfall as revealed from satellite observations and various precipitation sources zonally elongated rainbelts appear along these forests previous studies show that a relationship may exist between the frontal zone along the arctic seaboard and regional patterns of high latitude precipitation it was observed by this study that baroclinic zones associated with strong arctic westerlies coincide with minor storm tracks and boreal forest rainbelts only in eastern canada in contrast this coincidence does not occur in northern europe eastern siberia and the alaska pacific coast because boreal forest rainbelts in these regions are located farther south of strong arctic westerlies and ahead of high latitude troughs over central eurasia the bering sea the labrador sea and the norwegian sea therefore instead of baroclinicity

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

topological constraints on imbricate thrust networks examples from the mountain city window tennessee u s a abstract the geometry of thrust belts is best described in three dimensions as a network of linear geometric elements trailing branch lines where two thrusts diverge leading branch lines where two thrusts converge tip lines where thrust displacement vanishes and cutoff lines where a stratigraphic horizon intersects a thrust plane there are a number of topological constraints in three dimensions on the interrelationship of these linear elements these constraints provide a method of deciphering the three dimensional structure of an area from the geologic map pattern alone if topography or structural culminations and depressions create significant structural relief the mountain city window tennessee is an example of an imbricate thrust network which reveals its topology on the map pattern because of the presence of culminations the analysis of linear elements in this area allows the regional structural geometry to be described and also two kinematically distinct types of imbricate thrust systems to be characterized namely hinterland and foreland dipping duplexes the doe ridges culmination is a hinterland dipping duplex characterized by leading branch lines in a common roof thrust with the branch lines arranged in the same order hinterland to foreland as in the undeformed state the limestone cove culmination is a foreland dipping duplex characterized by trailing branch lines in a common roof thrust with the branch lines reversed in order hinterland dipping duplexes are the common and well known type foreland dipping duplexes are formed by successive trailing branch lines moving up off the lower flat horizon onto the ramp at which the imbricate slices are formed

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

a complex thrust sequence in western himalaya the active medlicott wadia thrust the recent activity of the medlicott wadia thrust mwt is investigated by geomorphic and tectonic studies in the riasi zone south of the pir panjal range india jammu kasmir state of western himalaya in the riasi area the mwt forms a splay of five faults that dip northward the recent activity of the splay is quantified using a set of deformed quaternary alluvial units the central branch of the thrust splay moved precambrian limestones above quaternary sediments and is sealed by 36 3 ka youngest osl age deposits the other branches offset the top of a 15 1 ka youngest osl age alluvial fan by 180 to 120 m the two southernmost branches form 17 34 m high non cylindrical scarps and the two northernmost branches also offset the fan by 8 m and 54 m respectively a balanced cross section parallel to the n210 e thrust motion suggests that the sequence of activity is complex an in sequence propagation is found for the three southern tea scorpion and rain faults and an out of sequence reactivation for the northern pillar fault furthermore several thrusts simultaneously activated for intervals of a few thousand years whereas others are episodically inactive nearly 10 mm yr of india eurasia convergence is regularly absorbed by the mwt a value greater than the one estimated for the western segment of the mwt affected by the 2005 kashmir earthquake where the thrust tectonics interacts with the complex kinematics of the syntax this work indicates that the mwt is very active and might be related to thick skinned tectonics in the western himalaya

mars pathfinder convective vortices frequency of occurrence 1 the frequency of occurrence of small scale convective vortices at the mars pathfinder lander location exhibits a diurnal variation similar to terrestrial dust devil observations the 79 vortices detected via their pressure signatures during the 83 sol mission when combined with an assessment of the incompleteness of data temporal coverage implies that at least two vortices passed by the lander site each sol if the vortices are dust laden as inferred from lander imaging then the observed vortex frequency is capable of maintaining the observed atmospheric dust load against sedimentation loss the time of sol variation in vortex occurrence provided by pathfinder when combined with orbiter imaging of dust devils at a very limited time of sol offers a potential means of quantifying the effect of these small scale vortices upon the atmospheric dust cycle

martian and terrestrial dust devils test of a scaling theory using pathfinder data the mars pathfinder meteorological station recorded wind pressure and temperature fluctuations that have been interpreted as dust devils warm core vortices that form at the bottom of connective plumes we apply a scaling theory renno et al 1998 developed to explain terrestrial dust devil observations to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of martian dust devils the theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the connective vortices our findings are as follows for the best documented candidate event sol 25 observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil a number of other candidates less well documented however also are consistent with passage of a dust devil over or near the lander temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package the strongest dust devils predicted by our theory have a central pressure deficit of about 50 pa and wind speed of about 60 m s 1 the strongest dust devils are capable of lofting dust and hence support the interpretation of selected pathfinder images as showing the passage of dust devils within sight of the lander

maintenance of summer monsoon circulations a planetary scale perspective abstract the monsoon circulation which is generally considered to be driven by the landmass ocean thermal contrast like a gigantic land sea breeze circulation exhibits a phase reversal in its vertical structure a monsoon high aloft over a continental thermal low is juxtaposed with a midoceanic trough underlaid by an oceanic anticyclone this classic monsoon circulation model is well matched by the monsoon circulation depicted with the observational data prior to the first global atmospheric research program garp global experiment fgge however synthesizing findings of the global circulation portrayed with the post fgge data it was found that some basic features of major monsoon circulations in asia north america south america and australia differ from those of the classic monsoon circulation model therefore a revision of the classic monsoon theory is suggested with four different wave regimes selected to fit the horizontal dimensions of these monsoon circulations basic features common to

the alaskan arctic frontal zone forcing by orography coastal contrast and the boreal forest abstract experiments have been conducted with a regional climate model to indicate the conditions required to generate preferred regions of frontal activity in the alaskan region several objective methods of frontal identification were first investigated it was found that the vertical component of relative vorticity a thermal front parameter t850 n where t850 is the 850 hpa temperature and n is a unit vector in the direction of the 850 hpa temperature gradient and a parameter derived from the q vector as a measure of vertical motionwere useful in combination to determine the occurrence of fronts the preferred locations for frontal activity were located to the southern side of the eastern brooks range and over the alaska range these diagnostics were then used to characterize frontal frequency in a series of experiments removing topographic and vegetation contrasts it was found that the removal of the treeline contrast and its associated heating gradient had a small effect on frontal frequ

topographically generated gravity waves in the brooks range alaska amplified wind events are identified over the brooks range in alaska with observed wind speed increasing from calm to 5 ms 1 over 24 to 36 hours in simulations using an limited area climate system model the wind events are captured consistently although generally display greater strength than observed cooling associated with the wind events lead to an identification of the ne region of the north slope of alaska below the inversion as the source region for the air flow analysis of the wind event of 7th january 1992 supports the nonlinear hydraulic model of gravity waves

coherence between the great salt lake level and the pacific quasi decadal oscillation the lake level elevation of the great salt lake gsl a large closed basin lake in the arid western united states is characterized by a pronounced quasi decadal oscillation qdo the variation of the gsl elevation is very coherent with the qdo of sea surface temperature anomalies in the tropical central pacific also known as the pacific qdo however such coherence denies any direct association between the precipitation in the gsl watershed and the pacific qdo because in a given frequency the precipitation variation always leads the gsl elevation variation therefore the precipitation variation is phase shifted from the pacific qdo this study investigates the physical mechanism forming the coherence between the gsl elevation and the pacific qdo pronounced and coherent quasi decadal signals in precipitation streamflow water vapor flux and drought conditions are found throughout the great basin recurrent atmospheric circulation patterns develop over the gulf of alaska during the warm to cool and cool to warm transition phases of the pacific qdo these circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western united states and in turn lead to the qdo in the hydrological cycle of the great basin as the gsl integrates the hydrological responses in the great basin the hydrological qdo is then transferred to the gsl elevation because the gsl elevation consistently lags the precipitation by a quarter phase about 3 yr in the quasidecadal time scale these processes take an average of 6 yr for the gsl elevation to eventually respond to the pacific qdo this creates a half phase delay of the gsl elevation from the pacific qdo thereby forming the inverse yet coherent relationship between them tree ring reconstructed precipitation records confirm that the quasi decadal signal in precipitation is a prominent feature in this region

modeling the thermodynamics of a sea ice thickness distribution 1 sensitivity to ice thickness resolution a one dimensional ice thickness distribution model is presented to determine the minimum number of ice thicknesses necessary to resolve the area averaged annual cycles of ice thickness and turbulent fluxes the baseline case includes 40 ice thickness categories ice thickness and area meltwater ponds ice salinity and age snow cover and surface albedo evolve independently for each ice category a ridging and ice export parameterization and a coupled one dimensional ocean mixed layer model are also included sensitivity studies indicate that 16 ice thickness categories can accurately resolve the baseline annual cycles of area averaged ice thickness and the summertime turbulent fluxes in this model provided that one third of the thickness categories represent ice thinner than 0 8 m resolving the distribution of ice in this thickness range is important in simulating the area averaged ice characteristics wintertime values of the turbulent fluxes differ from the baseline by up to 1 w m 2 for fewer than 40 ice thickness categories the large difference in turbulent fluxes between open water and ice thicker than 1 6 m makes the area averaged value sensitive to the number of ice thickness categories since this number can affect the categories that are merged the categories that melt completely ice that is ridged and the resolution of the ice thickness distribution this makes an accurate simulation of the baseline wintertime turbulent fluxes difficult model simulations with fewer than 40 categories provide a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 w m 2 the annually area averaged ice thickness is within 10 cm the model response to a heat flux perturbation of less than 5 w m 2 is similar for a wide range of ice thickness categories since the thickness distribution of ice thinner than 1 m is not affected

the boreal forest and the polar front the analysis presented in this paper suggests that the larger heating over the boreal forest in the spring and summer as contrasted with weaker heating over the adjacent tundra results in a preferred position of the polar front along the northern edge of the boreal forest this positioning is well documented in the literature see for example bryson 1966 barry and hare 1974 kreps and barry 1970 this heating results from the lower albedo of the boreal forest which is not compensated by an increase in transpiration even with the larger leaf area index of the forest the warmer temperatures are mixed upward by the deep boundary layer over the forest and mesoscale circulations which result from the patchiness of heating associated with the heterogeneous landscapes of the forest thus in contrast to previous assumptions in which the arctic front position in the summer determines the northern limit of the boreal tree line our study suggests the boreal forest itself significantly influences the preferred position of the front this conclusion reinforces the findings of bonan et al 1992 and foley et al 1994 on the important role of boreal forest tundra interactions with climate

the zagros hinterland fold and thrust belt in sequence thrusting iran abstract the collision of the iranian microcontinent with the afro arabian continent resulted in the deformation of the zagros orogenic belt the foreland of this belt in the persian gulf and arabian platform has been investigated for its petroleum and gas resource potentials but the zagros hinterland is poorly investigated and our knowledge about its deformation is much less than other parts of this orogen therefore this work presents a new geological map stratigraphic column and two detailed geological cross sections this study indicates the presence of a hinterland fold and thrust belt on northeastern side of the zagros orogenic core that consists of in sequence thrusting and basement involvement in this important part of the zagros hinterland the in sequence thrusting resulted in first and second order duplex systems mode i fault bend folding fault propagation folding and asymmetric detachment folding which indicate close relationships between folding and thrusting study of fault bend folds shows that layer parallel simple shear has the same role in the southeastern and northwestern parts of the study area e 23 4 9 1 a major lateral ramp in the basement beneath the talaee plain with about one kilometer of vertical offset formed parallel to the sw movement direction and perpendicular to the major folding and thrusting

interactive property of large thrust sheets with footwall rocks the sub thrust interactive duplex hypothesis a mechanism of dome formation in thrust sheets abstract recently acquired appalachian ultradeep core hole adcoh project site investigation seismic reflection data and geologic data from the appalachians and several other orogenic belts suggest an important mutually interdependent relationship exists between emplacement of large crystalline thrust sheets and the deforming foreland rocks beneath this relationship suggests isolated domes beneath crystalline thrust sheets may be produced by passive folding of the sheet as a result of formation of an antiformal stack duplex in the platform sedimentary sequence beneath suggestions that domes in crystalline thrust sheets formed by interference of late open folds is doubtlessly still valid in places but the platform duplex mechanism is probably also valid to explain the late doming of many crystalline and other large thrust sheets the dome beneath the shooting creek and brasstown bald windows in the adcoh site region is imaged as an antiformal stack duplex at depth the tallulah falls dome grandfather mountain and mountain city windows and smokies foothills duplex in the site region and elsewhere in the southern blue ridge are all late isolated domes and all are probably or demonstrably underlain by antiformal stack duplexes beneath the blue ridge piedmont composite crystalline thrust sheet the assynt window and footwall duplex benath the arnabol and moine thrusts in scotland and the engadine window in the alps may be similar structures

dust devils on earth and mars 1 dust devils particle loaded vertical convective vortices found on both earth and mars are characterized by high rotating wind speeds significant electrostatic fields and reduced pressure and enhanced temperature at their centers on earth they are subordinate to boundary layer winds in the dust cycle and except possibly in arid regions are only nuisance level phenomena on mars though they seem to support the persistent background atmospheric haze to influence the surface albedo through the formation of tracks on the surface and to possibly endanger future exploration because of their high dust load and large potential gradients high resolution numerical simulations and thermophysical scaling models successfully describe dust devil like vortices on mars but fitting dust devil action into the martian global dust cycle is still problematic reliable parameterizations of their erosional abilities and solid temporal and spatial distribution data are still required to build and test a complete model of dust devil action

observational evidence of a suppressed planetary boundary layer in northern gale crater mars as seen by the navcam instrument onboard the mars science laboratory rover abstract the navigation cameras navcam of the mars science laboratory rover curiosity have been used to examine two aspects of the planetary boundary layer vertical dust distribution and dust devil frequency the vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line of sight optical depth within gale crater and comparing this optical depth to column optical depths obtained using mastcam observations of the solar disc the line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere this suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of gale crater and the higher elevation meridiani planum in the case of dust devils despite an extensive campaign only one optically thick vortex 1 5 0 5 10 3 was observed compared to 149 pressure events 0 5 pa observed in rems pressure data correcting for temporal coverage by rems and geographic coverage by navcam still suggests 104 vortices should have been viewable suggesting that most vortices are dustless additionally the most intense pressure excursions observed on other landing sites pressure drop 2 5 pa are lacking from the observations by the rems instrument taken together these observations are consistent with pre landing circulation modeling of the crater showing a suppressed shallow boundary layer they are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

determination of the wind induced detachment threshold for granular material on mars using wind tunnel simulations experimental results are presented of wind induced grain detachment under mars simulation conditions a simple force balance equation is applied to quantify the wind shear stress required for removal of glass spheres from a sand bed the transport of fine grained martian dust is simulated by the detachment of hollow glass spheres which resemble low mass density dust aggregates observed to form during simulations when using mars analogue material the results agree well with observations of dust removal and wind speed measurements made by the nasa viking landers at the martian surface this work supports the suggestion that dust aggregate fragmentation allows wind induced dust entrainment at substantially lower wind shear than that of solid sand grains and has direct application to the study of global dust transport and martian climatology

geometric kinematic and erosional history of the central andean plateau bolivia 15 17 s 1 latitudinal changes in topography climate and thrust belt geometry in the central andes have led to conflicting hypotheses that climate or tectonics exert a first order control on orogen evolution the relative roles of climate and tectonics in the evolution of the andean orogen are difficult to quantify because of a lack of detailed observations for both the long term deformation and erosion history of the andean fold thrust belt we contribute to the resolution of this problem by presenting a sequentially restored balanced cross section based on new mapping across the northern bolivia portion of the thrust belt 15 17 s the timing and magnitude of exhumation across the cross section are determined by synthesizing 10 new and 70 previously published mineral cooling ages once balanced and restored the section was sequentially forward modeled using stratigraphic and cooling age constraints results indicate the eastern cordillera ec records the highest magnitudes of shortening 123 km or 55 the interandean zone ia has shortened 48 km or 30 in both the ec and ia individual thrust sheets are tightly folded and have minor offsets of 1 5 km the subandes sa has multiple levels of detachments allowing for thrust sheets with relatively large offsets 6 17 km total shortening in the sa is 66 km or 40 total magnitude of shortening for the entire fold thrust belt in this region is 276 km 40 new apatite and zircon fission track cooling ages in conjunction with published ages indicate two phases of rapid exhumation an earlier phase from 40 to 25 ma in the ec and one prior to 25 ma in the ia followed by distributed exhumation of the entire fold thrust belt from 15 0 ma combined exhumation estimates from the balanced cross section and thermochronology suggest 9 11 km of exhumation in the ec 5 9 km in the ia and 3 4 km in the sa long term shortening rates are 7 mm a for the ec and ia and 4 8 mm a for the sa the sa shortening rates are based on a 15 0 ma or 8 0 ma deformation window by linking cooling ages to location and magnitude of shortening we suggest an 10 17 ma pause or a dramatic deceleration in the rate of deformation and propagation of the fold thrust belt between 25 and 15 or 8 ma

aspects of the hydrological cycle of the ocean atmosphere system abstract the balance equations for atmospheric water vapor and freshwater in the oceans are used to illustrate that evaporation and precipitation represent the major linkage between the atmospheric and oceanic branches of the global hydrological cycle attempts are also made to establish the hydrological cycle of the coupled ocean atmosphere system using water vapor flux divergence precipitation and interoceanic freshwater transport estimates from previous studies as well as computational results with more recent data this hydrological cycle works as follows the atmospheric water vapor converged to the pacific results in an excess of precipitation and a freshwater transport across the bering strait and the arctic sea to the atlantic the atmospheric water vapor is then diverged out of the latter ocean due to an excess of evaporation there

clastic deposition provenance and sequence of andean thrusting in the frontal eastern cordillera and llanos foreland basin of colombia sedimentological provenance and detrital thermochronological results for basin fill at the modern deformation front of the northern andes 6 n latitude provide a long term eocene to pliocene record of foreland basin sedimentation along the eastern cordillera llanos basin boundary in colombia lithofacies assemblages and paleocurrent orientations in the upward coarsening 5 km thick succession of the nunchia syncline reveal a systematic shift from craton derived shallow marine distal foreland back bulge accumulation in the mirador formation to orogen sourced deltaic and coastal influenced sedimentation of the distal to medial foreland foredeep in the carbonera and leon formations to anastomosing fluvial and distributive braided fluvial megafan systems of the proximal foreland foredeep to wedge top basin in the lower and upper guayabo formation these changes in depositional processes and sediment dispersal are supported by up section variations in detrital zircon u pb and u th he ages that record exhumation of evolving compartmentalized sediment source areas in the eastern cordillera the data are interpreted in terms of a progressive eastward advance in fold and thrust deformation with late eocene oligocene deformation in the axial zone of the eastern cordillera along the western edge of floresta basin soapaga thrust early miocene reactivation inversion of the eastern margin of the mesozoic rift system pajarito and guaicaramo thrusts and middle late miocene propagation of a footwall shortcut fault yopal thrust that created the nunchia syncline in a wedge top piggyback setting of the eastern foothills along the transition from the eastern cordillera to llanos foreland basin collectively the data presented here for the frontal eastern cordillera define a general in sequence pattern of eastward advancing fold and thrust deformation during cenozoic east west shortening in the colombian andes

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

the arctic frontal zone as seen in the ncep ncar reanalysis abstract calculations of a thermal front parameter using ncep ncar reanalysis data over the period 1979 98 reveal a relative maximum in frontal frequencies during summer along northern eurasia from about 60 to 70 n best expressed over the eastern half of the continent a similar relative maximum is found over alaska which is present year round although best expressed in summer these high latitude features can be clearly distinguished from the polar frontal zone in the midlatitudes of the pacific basin and collectively resemble the summertime arctic frontal zone discussed in several early studies while some separation between high and midlatitude frontal activity is observed in all seasons the summer season is distinguished by the development of an attendant mean baroclinic zone aligned roughly along the arctic ocean coastline and associated wind maxima in the upper troposphere the regions of maximum summer frontal frequency correspond to preferred areas of cyclogenesis and to where the summertime

the corrugation and bifurcation of fault surfaces by cross slip abstract the formation of corrugated and stepped fault surfaces by conservative shear is discussed it is suggested that fault boundaries which lie parallel to the direction of shear are able to deviate from a plane as a fault spreads like dislocations that cross slip in a crystal it is explained how deviations from planar shear can bifurcate fault surfaces and create en echelon faults the residual stresses produced by such deviations are tensions and compressions in the direction of shear

the basse normandie duplex boulonnais n france evidence for an out of sequence thrusting overprint abstract the thrust sheets outcropping in the basse normandie quarry near the hydrequent village boulonnais n france represents an exceptionally well exposed section of the nw european variscan thrust front these structures developed in the footwall of the main hydrequent thrust have been often described as a classic example of a duplex structure only the lower part of the structure satisfies however the geometric and kinematic criteria defining a duplex and more precisely an intraformational hinterland dipping duplex the upper thrust sheets of the imbricate stack exhibit a much more complex pattern of deformation than a simple piggy back duplication of the same rock sequence restoration of these thrust sheets based upon the definition of two marker beds as well as the analyses of fold thrust relationships and strain markers argues for a late ne verging thrust event that progressed within the thrust system from the tip of the upper thrust sheets towards the hydrequent thrust in a local break back style of thrust propagation this out of sequence thrusting event induced refolding and cross cutting of the forelimb of a hangingwall anticline developed previously above the footwall ramp of the nne verging basal thrust of the structure within the whole thrust system the lower duplex represents only a minor structure developed during the initial phase of thrusting in the foreland of the major anticline as a frontal second order duplex the structural data presented in this paper illustrate the tectonic processes acting within the deformed zones lying in the footwall of major thrusts and emphasize the out of sequence style of thrust migration that arises from the sequential blocking of thrust propagation towards the foreland

vortex encounter rates with fixed barometer stations comparison with visual dust devil counts and large eddy simulations abstracta phenomenological model is developed wherein vortices are introduced at random into a virtual arena with specified distributions of diameter core pressure drop longevity and translation speed and the pressure history at a fixed station is generated using an analytic model of vortex structure only a subset of the vortices present are detected as temporary pressure drops and the observed peak pressure drop distribution has a shallower slope than the vortex core pressure drops field studies indicate a detection rate of about two vortex events per day under favorable conditions for a threshold of 0 2 mb 1 mb 1 hpa this encounter rate and the observed falloff of events with increasing pressure drop can be reproduced in the model with approximately 300 vortices per square kilometer per day rather more than the highest visual dust devil counts of approximately 100 devils per square kilometer per day this difference can be reconciled if dust lifting typically only occurs in the field above a

structural development of an archean orogen western point lake northwest territories the point lake orogen in the central archean slave province of northwestern canada preserves more than 10 km of structural relief through an eroded antiformal thrust stack and deeper anastomosing midcrustal mylonites fault restoration along a 25 km long transect requires a minimum of 69 km slip and 53 km horizontal shortening in the western part of the orogen the basal decollement places mafic plutonic volcanic rocks over an ancient tonalitic gneiss complex ten kilometers to the east in the keskarrah bay area slices of gneiss unroofed on brittle thrusts shed molasse into several submerged basins conglomerates and associated thinly bedded sedimentary rocks are interpreted as channel levee and overbank facies of this thrust related sedimentary fan system the synorogenic erosion surface at the base of the conglomerate truncates premetamorphic or early metamorphic thrust faults formed during foreland propagation while other thrusts related to hinterland progressing imbrication displace this unconformity tightening of synorogenic depositional troughs resulted in the conglomerates present localization in synclines to the west of associated thrust faults and steepening of structural dips eastern parts of the orogen consist of isoclinally folded graywackes composed largely of mutti and ricci lucchi turbidite facies b c and d interpreted as submarine fan deposits eroded from a distant volcanic arc thrust faults in the metasedimentary terrane include highly disrupted slate horizons with meter scale duplex structures and recrystallized calcmylonites exhibiting sheath folds and boudin trains with very large interboudin distances the sequence of fabric development and the overall geometry of this metasedimentary terrane strongly resembles younger forearc accretionary prisms conditions of deformation along the thrusts parallel the regional metamorphic zonation amphibolite facies in the basal decollement through greenschist facies shear zones to cataclastic crush zones in the region of emergent thrusts in keskarrah bay depth differences can account for only half of the metamorphic gradient thermal profiles which increased downwards in obducted greenstone belts and synthrusting plutonism explains other high metamorphic gradients a tectonic model involving the collision of an accretionary prism with a continental margin best explains the structural and sedimentological evolution of the orogen