thermochronometry reveals headward propagation of erosion in an alpine landscape glacial erosion of mountain ranges produces spectacular alpine landscapes and by linking climate with tectonics influences a broad array of geophysical phenomena although the resultant landforms are easily identified the timing and spatial pattern of topographic adjustment to pleistocene glaciations remain poorly known we investigated topographic evolution in the archetypal glacial landscape of fiordland new zealand using u th he thermochronometry we find that erosion during the past 2 million years removed the entire pre pleistocene landscape and fundamentally reshaped the topography erosion focused on steep valley segments and propagated from trunk valleys toward the heads of drainage basins a behavior expected if subglacial erosion rate depends on ice sliding velocity the fiordland landscape illustrates complex effects of climate on earth s surface morphology

parameterized mesoscale forcing mechanisms for initiating numerically simulated isolated multicellular convection abstract two methods designed to parameterize mesoscale ascent in a three dimensional numerical cloud model via near surface momentum and heat fluxes are presented and compared to the commonly used technique of an initial perturbation placed within the model initial condition the flux techniques use a continuously reinforced thermal or convergent low level wind field to produce upward vertical motion on the order of 10 cm s 1 by which deep moist convection can be initiated the sensitivity of the convective response to the type strength and size of the forcing is evaluated using numerical simulations of a conditionally unstable environment with weak unidirectional shear precipitation free cloud processes are used to further simplify the model response to the forcing the three methods tested produce an initial convective response but only the momentum and heat flux methods are able to produce sustained deep convection that approximately resembles isolated multicellular convection cell regeneration

long lived mesoscale systems in a low convective inhibition environment part i upshear propagation abstractpart ii of this study of long lived convective systems in a tropical environment focuses on forward tilted downshear propagating systems that emerge spontaneously from idealized numerical simulations these systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward tilted circulation with a trailing stratiform region an overturning updraft and a mesoscale downdraft in contrast to this standard mesoscale system the downshear propagating system considered here does not feature a mesoscale downdraft and although there is a cold pool it is of secondary importance to the propagation and maintenance of the system the mesoscale downdraft is replaced by hydraulic jump like ascent beneath an elevated forward tilted overturning updraft with negligible convective available potential energy therefore the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from

textured dust storm activity in northeast amazonis southwest arcadia mars phenomenology and dynamical interpretation abstractdust storms are mars s most notable meteorological phenomenon but many aspects of their structure and dynamics remain mysterious the cloud top appearance of dust storms in visible imagery varies on a continuum between diffuse hazy and textured textured storms contain cellular structure and or banding which is thought to indicate active lifting within the storm some textured dust storms may contain the deep convection that generates the detached dust layers observed high in mars s atmosphere this study focuses on textured local dust storms in a limited area within northeast ne amazonis and southwest sw arcadia planitiae 25 40 n 155 165 w using collocated observations by instruments on board the mars global surveyor mgs and mars reconnaissance orbiter mro satellites in northern fall and winter this area frequently experiences dust storms with a previously unreported ruffled texture that resembles wide mixed layer rolls in earth s atmosphere a resemblance that is supported by h

evaluation of site amplification and site period using different methods for an earthquake prone settlement in western turkey abstract seismic micro hazard zonation for urban areas is the first step towards a seismic risk analysis and mitigation strategy essential here is to obtain a proper understanding of the local subsurface conditions and to evaluate ground shaking effects in this study present and future settlement areas of yenisehir which is located in the earthquake prone marmara region of turkey were evaluated with respect to site amplification and site period borings in conjunction with in situ penetration tests seismic velocity measurements resistivity surveys and microtremor studies were performed and available data from previous investigations were complied to determine the variation of the soil profile as well as the characteristics of the soil layers within the study site in addition new empirical correlations between shear wave velocity v s and number of blows from standard penetration test spt n were also developed to be used for the estimation of amplification factors site amplification was assessed using empirical methods based on estimated values of v s 1 d site response numerical modeling program and microtremor measurements among the three methods employed the numerical technique and microtremor method yielded considerably higher amplification factors when compared to those obtained from the empirical method this situation is considered as a limitation of the empirical methods the survey of site response suggests ground amplification the microzonation map based on soil site amplification suggests amplification factors between 1 6 and 5 in the present settlement while the areas at the north and south of the settlement generally amplify the motion 5 to 9 times the site periods obtained from microtremor studies vary from 0 51 to 0 8 s throughout the settlement in addition the comparison between fundamental site periods and fundamental building periods which were measured in a few buildings and estimated from an empirical expression indicate that prime attention should be paid to resonance phenomena particularly for the northern part of the settlement where high rise buildings are still in construction

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

stratospheric gravity waves generated by multiscale tropical convection abstract the generation of gravity waves by multiscale cloud systems evolving in an initially motionless and thermodynamically uniform environment is explored using a two dimensional cloud system resolving model the simulated convection has similar depth and intensity to observed tropical oceanic systems the convection self organizes into preferred horizontal and temporal scales involving weakly organized propagating cloud clusters the multiscale systems generate a broad spectrum of gravity waves with horizontal scales that range from the cloud system scale up to the cloud cluster scale the gravity waves with the largest horizontal scale play an important role in modifying layered tropospheric inflow and outflow to the cloud systems which in turn influence the multiscale convective organization slower moving short scale gravity waves make the strongest individual contribution to the vertical flux of horizontal momentum and cause a robust peak in the momentum flux spectrum that corresponds to the lif

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

horizontal convective rolls determining the environmental conditions supporting their existence and characteristics abstract data from the convection and precipitation electrification cape project as well as results from numerical simulations are used to study horizontal convective rolls the environmental conditions necessary for sustaining rolls and for influencing the aspect ratio ratio of roll wavelength to convective boundary layer cbl depth and orientation are examined observations and numerical model simulations both suggest that a moderate surface sensible heat flux and some vertical wind shear are necessary for roll existence unlike some previous studies however it is shown that rolls occurred within very low cbl shear conditions 2 10 3 s 1 in addition the low level i e 200 m shear seems to be more important than the shear through the depth of the cbl in roll sustenance the aspect ratio is shown to be proportional to the cbl instability measured in terms of the monin obukhov length the roll orientation is similar to the wind direction at 10 m agl the cbl wind direction the inversio

role of gravity waves in triggering deep convection during toga coare the role of gravity waves in the initiation of convection over oceanic regions during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare experiment is investigated first an autocorrelation method is applied to infrared temperature observations of convective events from satellite images it reveals that new deep convective cells often occur a few hours after a previous intense event at a typical distance of a few hundred kilometers such fast moving modes faster than 15 m s 21 are interpreted as the trace of gravity waves excited by previous convection and contributing to trigger further convection second the specific case of 11 12 december 1992 during which an active squall line is generated after the collapse of a previous mesoscale convective system mcs nearby is analyzed with a nonhydrostatic model the triggering of the second mcs is well reproduced explicitly owing to the use of the two way interactive grid nesting the convective source appears to emit pulses of gravity waves on a wide range of small scales on the contrary the troposphere response to the convective source exhibits a spectral simplicity a slowly evolving mode characterized by an ascent in the pbl and a compensating subsidence in the free troposphere favors shallow convection and inhibits deep convection respectively traveling modes propagating away from the convective source are characterized by a fast mode 50 m s21 and a slower mode 25 ms 21 associated with the convective and stratiform development of the source respectively in agreement with previous studies a budget analysis reveals the different factors leading to the deep convection triggering first an active pbl characterized by strong surface fluxes and mean ascent initiates shallow convection lasting about 2 h inhibited above by the subsiding motions maintaining a dry layer second horizontal advection of moist and cooler air at midlevels and detrainment from cumuli contribute to destroy the dry air layer capping the shallow convective layer finally vertical advection induced by the gravity waves passage modulates the vapor and temperature evolution ascending phases favor moistening and cooling whereas subsiding phases stop these effects delaying the deep convection onset the triggering occurs after a strong subsidence when the ascent phases of deep and shallow modes are combined

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

ground based measurements and dual doppler analysis of 3 d wind fields and atmospheric circulations induced by a meso γ scale inland lake 1 this paper presents a high resolution dual doppler analysis of lake breeze mesoscale circulation induced by an elongated reservoir with a mean width of 2 km and an area of 125 km2 compared to previous meso scale lake breeze studies based on point measurements or aircraft observations the present study provides both a unique quantification and a high resolution spatial and temporal 3 d visualization several hundred meters and 5 min respectively of the kinematic structure of the lake breeze initiation and evolution visible satellite images show a cloud free zone over the lake and adjacent land areas that was promoted by subsidence associated with the lake breeze circulation the background synoptic scale wind flow was almost parallel to the major axis of the lake and distinct lake breeze frontal zones formed along both shorelines spanning the length of the lake dual doppler analyses showed updrafts in the frontal zones perturbation horizontal velocities of 1 5 m s 1 on both sides of the lake and maximum downdrafts of 2 m s 1 centered over the lake vertical vorticity in the boundary layer was produced by differential friction between the smooth lake and adjacent land the circulations are robust and are maintained during the day against a minor change in background wind direction the study shows that the circulations produced by a small lake can generate significant mesoscale circulations that influence local climatology and identifies the importance of including such small mesoscale processes in global forecast models

numerical study of the 10 january 1998 lake effect bands observed during lake ice abstract this paper presents the results of a series of idealized cloud resolving simulations of the evolution of moist roll convection observed as part of the lake induced convection experiment lake ice that took place during the 1997 98 winter over central lake michigan satellite and radar observations of the roll convection depict striking linear rolls stretching from 10 km off the western shore of the lake across to the eastern shore and then continuing across michigan the spacing of the primary rolls was observed to be 6 km giving a ratio of spacing to depth of about 5 1 which is consistent with theory in addition a longer wavelength 13 km of stationary banding was observed parallel to the shoreline in an earlier study of this case multiply nested simulations of the convective rolls based on real data variable initialization were successful in producing banded structures with similar spacing and location over the water to those observed using fine grid resolution of about 500 m unfortu

rapid glacial erosion at 1 8 ma revealed by 4he 3he thermochronometry alpine glaciation and river incision control the topography of mountain ranges but their relative contributions have been debated for years apatite 4 he 3 he thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern coast mountains of british columbia canada five proximate samples require accelerated denudation of the klinaklini valley initiating 1 8 0 2 million years ago ma at least 2 kilometers of overlying rock were removed from the valley at 5 millimeters per year indicating that glacial valley deepening proceeded 6 times as fast as erosion rates before 1 8 ma this intense erosion may be related to a global transition to enhanced climate instability 1 9 ma

numerical simulation of the interaction between the sea breeze front and horizontal convective rolls part i offshore ambient flow abstract a three dimensional cloud resolving model is used to investigate the interaction between the sea breeze circulation and boundary layer roll convection horizontal convective rolls hcrs develop over land in response to strong daytime surface heating and tend to become aligned parallel to the vertical wind shear vector whereas the land sea heating contrast causes the formation of the sea breeze front sbf along the coastline the ability of hcrs to modulate the along frontal structure of the sbf is examined complementing and extending previous observational and numerical studies three simulations are discussed the first two demonstrating that the model can produce both phenomena independently the third is initialized with offshore mean flow and vertical shear perpendicular to the coastline and results in a sharply defined inland propagating sbf that encounters hcrs aligned perpendicular to it before the interaction takes place the sbf is nearly two dimensional and devoid of along front

stable isotopes reveal high southeast tibetan plateau margin since the paleogene abstract the evolution of the topography of eastern tibet reflects the dynamic interaction between processes at earth s surface and the lower crust reconstruction of its spatio temporal development provides constraints for our understanding of the geodynamics of continental deformation this study examines the topographic evolution of the southeast margin of the tibetan plateau throughout the cenozoic using stable isotope paleoaltimetry of pedogenic carbonates preserved in cenozoic basins extending from the northern to the southern portions of the se margin of the tibetan plateau yunnan province china paleoelevations are calculated using a monte carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the isotopic value of pedogenic carbonate isotope elevation relationships are determined from a modern sampling transect along the modern lancang mekong river and an estimated eocene rayleigh fractionation model that was randomly resampled calculated elevations indicate the se margin of tibet was at its present elevation as early as the late eocene with elevations of 3 3 km as far south as the northern third of china s yunnan province this result expands the extent of the eocene tibetan plateau more than 1000 km east of that previously known and precludes surface uplift via lower crustal flow in the area of sw sichuan and northern yunnan as a driver for drainage reorganization and an observed middle to late miocene pulse of rapid exhumation elevation estimates from the southern two thirds of the study area parallel to the red river fault suggest approximately 1 km of post late miocene surface uplift consistent with estimates from previous studies

gravity wave influences on mesoscale divergence an observational case study characteristics of tropospheric low frequency gravity waves are diagnosed in radiosonde soundings from the tropicalwarm pool international cloud experiment near darwin australia the waves have typical vertical wavelengths of about 4 km horizontal wavelengths of about 600 km and intrinsic periods of about 12 hr these scales match those of the vertical horizontal and temporal variability found in area averaged horizontal wind divergence over the same domain vertical profiles of divergence show wave like structures with variability of the order of 2 10 5 s 1 in the free troposphere the results for darwin are similar to previously reported observed mesoscale patterns of divergence convergence over the tropical atlantic the findings imply that tropical divergence on spatial scales of a few hundred kilometers which is known to influence the organization of convection may be forced by gravity waves

scale selection in locally forced convective fields and the initiation of deep cumulus abstract deep cumulus dynamics has often been treated as an initial value problem where the long time effect of surface energy fluxes are neglected initiation is often assumed to follow from a strong localized deformation of the flow field which is elsewhere quiescent in nature however the atmosphere is rarely found in an undisturbed condition just prior to the inception of deep growth one likely cause of widespread motions is the natural modal response of the environment to surface energy fluxes which results in a field of disturbances evidence is presented in this paper for the possible existence of a class of solutions when deep convection is allowed to evolve in the context of a thermally forced field of shallow convection this class of solutions is neglected when one visualizes the growth of severe local storms in term of buoyant bubbles in an otherwise tranquil atmosphere considering deep cumulus initiation as a field problem severely limits the concept of an isolated cloud individual clou

the effect of mesoscale heterogeneity on the genesis and structure of mesovortices within quasi linear convective systems abstract this study examines the structure and evolution of quasi linear convective systems qlcss within complex mesoscale environments convective outflows and other mesoscale features appear to affect the rotational characteristics and associated dynamics of these systems thus real data numerical simulations of two qlcs events have been performed to i identify and characterize the various ambient mesoscale features that modify the structure and evolution of simulated qlcss and then to ii determine the nature of interaction of such features with the systems with an emphasis on the genesis and evolution of low level mesovortices significant low level mesovortices develop in both simulated qlcss as a consequence of mechanisms internal to the system consistent with idealized numerical simulations of mesovortex bearing qlcss and not as an effect of system interaction with external heterogeneity however meso scale order of 10 km heterogeneity in the form of a convective outflow boundary is su

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

timing and rate of exhumation along the litang fault system implication for fault reorganization in southeast tibet the litang fault system that crosses the litang plateau a low relief surface at high elevation 4200 4800 m above sea level that is not affected by regional incision provides the opportunity to study exhumation related to tectonics in the se tibetan plateau independently of regional erosion combining apatite and zircon fission track with apatite u th he thermochronologic data we constrain the cooling history of the litang fault system footwall along two transects apatite fission track ages range from 4 to 16 ma ahe ages from 2 to 6 ma and one zircon fission track age is 99 ma these data imply a tectonic quiet period sustained since at least 100 ma with a slow denudation rate of 0 03 km ma interrupted at 7 to 5 ma by exhumation at a rate between 0 59 and 0 99 km ma we relate that faster exhumation to the onset of motion along the left lateral normal litang fault system that onset is linked to a lower miocene important kinematic reorganization between the xianshuihe and the red river faults with the eastward propagation of the xianshuihe fault along the xiaojiang fault system and the formation of the zhongdian fault such strike slip faults allow the sliding to the east of a wide continental block with the litang fault system accommodating differential motion between rigid blocks the regional evolution appears to be guided by the strike slip faults with different phases of deformation which appears more in agreement with an hidden plate tectonic model rather than with a lower channel flow model

a numerical investigation of boundary layer quasi equilibrium despite the large energy input from surface evaporation the moist static energy mse of the tropical boundary layer remains relatively constant on large spatial and temporal scales due to lifting of vapor by cloudy updrafts and the addition of dry air from the layers above arakawa and schubert 1974 suggested that drying is due mainly to clear air turbulent entrainment between cloudy updrafts while raymond 1995 described drying due mainly to convective downdrafts we used cloud resolving numerical simulations to investigate the transport of mse into the boundary layer and found turbulent entrainment between clouds to be the dominant process

significant increase in relief of the european alps during mid pleistocene glaciations the effect of expanded glaciation on the relief of mountain ranges is debated chronometric and model data from the european alps suggest that relief in the rhone valley was enhanced as a result of the increased incision of the valley following the mid pleistocene climate transition

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

propagation of surface uplift lower crustal flow and cenozoic tectonics of the southeast margin of the tibetan plateau surface uplift of the southeast margin of the tibetan plateau is interpreted to have progressed from the northwest near the tibetan border to the southeast in the red river region of the central yunnan province china this interpretation is based on existing thermochronologic data and new mapping and sedimentologic and paleobotanic data demonstrating incision in the headwaters of the red river in pliocene time or later together with previously published data demonstrating surface uplift and a gradient in crustal thickness in the absence of upper crustal shortening this is strong evidence for growth of the southeast margin of the tibetan plateau through lower crustal flow displacement along the ailao shan red river shear zone slowed or ceased in early pliocene time and the xianshuihe xiaojiang fault system initiated accommodating diffuse deformation and rotation around the eastern himalayan syntaxis we suggest a kinematic link between the change in mode of deformation and the introduction of a weak crustal layer through lower crustal flow

effect of alpha damage annealing on apatite u th he thermochronology recent data on he diffusion challenge the temperature sensitivity of apatite u th he thermochronology the damage induced by recoil of u and th decay series during emission of particles recoil damage has been proposed to modify he diffusion properties through time however we propose that annealing of these irradiation defects may be an important phenomenon and may be significant in case of slowly cooled or reheated basement rocks to test this hypothesis we developed a quantitative model including an explicit treatment of recoil damage annealing and their effect on he diffusion kinetics and calibrate it against literature data our model is based on two hypotheses 1 helium is in equilibrium between an apatite crystal and its defects and 2 alpha recoil damage annealing can be described analogously to fission track annealing this model has been embedded into a monte carlo simulation of helium production ejection diffusion and applied to data from the french massif central a complex slowly cooled terrain with burial reheating where the thermal history has been constrained by previous fission track ft data including ft length distributions u th he ages are close to the ft ages from the same samples and are generally reproducible among replicates but some samples present he age dispersion that is not correlated with crystal size our model reproduces the massif central data very well except for three samples where he ages are older than corresponding ft ages we show that annealing of irradiation damage has an important impact on retentivity of helium and that the he content he is only a rough approximation of the damage level in particular our results show that independence of he ages on crystal sizes in case of reheated samples is a clear indication of the higher he retentivity induced by recoil defects and that an explicit treatment of defect annealing is required for a correct interpretation of u th he ages in such a case more generally a correlation with the crystal size can bring information on the thermal path only if the age of defects well represented by the fission track age is available due to the dependence of the partial retention zone on damages conversely in case of rapid cooling or for samples having low u and th contents damage effects can be ignored without significant effects on he ages

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

direct influence of gravity waves on surface layer stress during a cold air outbreak as shown by synthetic aperture radar abstract synthetic aperture radar sar images of oceans and the great lakes have provided a highly detailed means of observing atmospheric boundary layer phenomena such as convection land breezes and internal gravity waves this is possible because the backscattered radiation detected by sar can be dominated by scattering from wind driven capillary waves whose spatial variation is visible as patterns in the sar images in this paper we present two case studies in which sar images taken over lake superior demonstrate spatial variability in the surface wind stress created over the lake by coincident gravity waves and boundary layer convection during cold air outbreaks of particular interest is the direct influence of the gravity waves on the lake surface stress despite the intervening highly convective atmosphere as well as the detailed view of the fetch dependence of that stress

distorted drainage basins as markers of crustal strain east of the himalaya extensive lithospheric deformation on the eastern margin of the india eurasia collision has brought three major rivers into exceptionally close proximity for over 300 km the salween mekong and yangtze rivers are only tens of kilometers apart 10 times closer than rivers of comparable length elsewhere in the world we view deeply incised river valleys as displacement markers that move with the underlying crust over time scales of at least tens of millions of years accordingly the close spacing of these major rivers and their nearly parallel trends reflect the large crustal strains near the eastern himalayan syntaxis these river characteristics are consistent with two primary phases of deformation in this tectonic setting ne sw shortening of 0 5 oriented radially from the eastern syntaxis followed by dextral shear strain of 6 1 along a north trending zone pervasive shearing of this magnitude throughout the 150 km wide region of anomalous drainage would account for 1000 km of northward motion of india relative to southern china directly east of this region another 1000 km of northward motion is likely to have been accommodated by pervasive shearing through a zone hundreds of kilometers wide finally we draw attention to the remarkable accord between the arcuate paths of each of the three great rivers in the broader southeastern tibet region and small circles that curve around the eastern himalayan syntaxis

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

spatially variable exhumation rates in orogenic belts an andean example abstract the cordillera real of the bolivian andes is a large tectonically active mountain range that dominates sediment influx into the amazon basin but rates of exhumation in the orogen are poorly known we present 20 new apatite fission track ages from two valleys in the cordillera real to constrain patterns of mountain range exhumation over 106 107 yr we interpret these and previously published data from a third valley using a 2 d thermal model that accounts for topographic and advective influences on measured cooling ages exhumation rates in the cordillera real are 0 2 0 6 mm yr comparable to rates in parts of denali the washington cascades the olympic mountains and the european alps and an order of magnitude slower than rates in taiwan nanga parbat the greater himalaya of nepal and the southern alps of new zealand three to fourfold cooling age variations in the cordillera real imply at least twofold exhumation rate variations within and between valleys over distances of only tens of ki

correlation of himalayan exhumation rates and asian monsoon intensity although most data suggest that the india eurasia continental collision began 45 55 myr ago the architecture of the himalayan tibetan orogen is dominated by deformational structures developed in the neogene period 23 myr ago the stratigraphic record and thermochronometric data indicate that erosion of the himalaya intensified as this constructional phase began and reached a peak around 15 myr ago it remained high until 10 5 myr ago and subsequently slowed gradually to 3 5 myr ago but then began to increase once again in the late pliocene and pleistocene epochs here we present weathering records from the south china sea bay of bengal and arabian sea that permit asian monsoon climate to be reconstructed back to the earliest neogene these indicate a correlation between the rate of himalayan exhumation as inferred from published thermochronometric data and monsoon intensity over the past 23 myr we interpret this correlation as indicating dynamic coupling between neogene climate and both erosion and deformation in the himalaya although the india eurasia collision initiated 50 myr ago major deformation and exhumation of the himalaya did not begin until the early neogene 23 myr ago this coincides with the increased intensity of the asian monsoons as indicated by weathering records from the south china sea bay of bengal and arabian sea and hints at a dynamic coupling between climate and both erosion and deformation in the himalaya

space time structure of rain rate fields information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems in this study rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of taylor s hypothesis for relating their spatial and temporal statistics weather radar derived rain rate maps were employed to obtain one and two dimensional spatial power spectra azimuthally averaged two dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two dimensional turbulence driven by the input of energy over a narrow band of wave numbers one dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data temporal spectra from the gage time series were nearly identical in shape to the one dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate themore temporal and spatial scales for spectra corresponding to longer durations a match could not be made less

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

mesoscale thermodynamic influences on convection initiation near a surface dryline in a convection permitting ensemble abstractin this study the authors examine initiation of severe convection along a daytime surface dryline in a 10 member ensemble of convection permitting simulations results indicate that the minimum buoyancy bmin of pbl air parcels must be small bmin 0 5 c for successful deep convection initiation ci to occur along the dryline comparing different ensemble members reveals that cape magnitudes allowing for entrainment and the width of the zone of negligible bmin extending eastward from the dryline act together to influence ci since pbl updrafts that initiate along the dryline move rapidly northeast in the vertically sheared flow as they grow into the free troposphere a wider zone of negligible bmin helps ensure adequate time for incipient storms to mature which itself is hastened by larger cape local bmin budget calculations and trajectory analysis are used to quantify physical processes responsible for the reduction of negative buoyancy prior to ci here the grid resolved forcing and fo

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

spatial and temporal pattern of erosion in the three rivers region southeastern tibet convergence and collision between india and eurasia have produced the tibetan plateau which stands 5 km high over a region of 3 million km2 its southeastern margin lies in the restraining bend between the sichuan basin and the eastern himalayan syntaxis in this region three parallel rivers the salween the mekong and the yangtze carve gorges up to 3 km deep along the longitudinal profiles large scale knickzones defined by very high steepness correspond to the gorges of the salween and mekong the yangtze instead has a nearly linear profile upstream from its first big bend new low temperature thermochronometric data reveal a complex pattern of erosion in the three rivers region from the salween in the west to the yangtze in the east the magnitude and rate of erosion decrease from south to north erosion rates exhibit variable gradients in space and time along the salween and the mekong a northward increase of erosion rate is followed by a decrease with additional distance to the north variations of erosion rate in time are characterized by a deceleration along the salween and a general deceleration with local acceleration along the mekong this pattern together with river profile analysis is best explained by active coupling between tectonics and river incision related to the indentation and northward migration of the corner of the indian continent

large river offsets and plio quaternary dextral slip rate on the red river fault yunnan china using multispectral spot images and 1 100 000 topographic data we present an improved map of the active red river fault zone between midu yunnan china and hanoi vietnam the fault zone is composed of parallel strands one of which the yuanjiang fault was previously undetected there also appears to be a component of extension all along the fault zone such extension increases toward the se from yunnan to the south china sea coast and the vector describing the motion of south china relative to indochina points within the n45 135 e quadrant we attempt to assess the plio quaternary dextral slip rate on the red river fault rrf by restoring large river offsets and searching for the largest plausible one across much of yunnan the fault is perpendicular to local catchments that drain into the red river from precise mapping of the river courses on spot satellite images and on 1 100 000 topographic maps numerous multiple offsets along the fault can be detected and reconstructed the lack of correlation between the apparent offsets and the lengths of the rivers upstream from the fault suggests either that the drainage system was in large part established prior to the onset of dextral slip along the fault or that frequent captures have occurred we thus try to find the best fit between series of river channels upstream and downstream from the fault by progressively restoring the dextral displacement in increments of 500 m up to an offset of 50 km for each increment we measure the misfits root mean squares rms between the upstream and downstream channels the best fit and smallest rms are obtained for an offset of 25 0 5 km that we interpret to represent the clearest large right lateral displacement recorded in the geomorphology along the active red river fault since dextral motion is likely to have started around 5 myr the most probable average plio quaternary slip rate on the fault is of order of 5 mm yr we attribute the apparent lack of seismic activity on a large stretch of the fault to millennial recurrence times between great earthquakes our study shows that relatively small drainage systems can keep a good record of fairly large cumulative fault offsets

in situ low relief landscape formation as a result of river network disruption the relict landscapes of southeast tibet are being formed in situ as a result of river drainage reorganization that renders rivers unable to balance tectonic uplift so these landscapes may not provide an unaltered record of past geomorphic conditions high elevation low relief surfaces or relict landscapes are generally thought to be uplifted old landscapes that preserve past tectonic and environmental conditions rong yang et al have tested current models of landscape evolution using digital topographic analysis of so called relict landscapes in southeast tibet and yunnan province china dramatic scenery boasting up to 3 km of relief encompassing the gorges of the yangtze mekong and salween rivers they find that the region may not provide an unaltered record of past geomorphic conditions rather these landscapes form in situ as a result of river drainage reorganization that renders rivers unable to balance tectonic uplift landscapes on earth retain a record of the tectonic environmental and climatic history under which they formed landscapes tend towards an equilibrium in which rivers attain a stable grade that balances the tectonic production of elevation and with hillslopes that attain a gradient steep enough to transport material to river channels equilibrium low relief surfaces are typically found at low elevations graded to sea level however there are many examples of high elevation low relief surfaces often referred to as relict landscapes1 2 or as elevated peneplains3 these do not grade to sea level and are typically interpreted as uplifted old landscapes preserving former more moderate tectonic conditions4 here we test this model of landscape evolution through digital topographic analysis of a set of purportedly relict landscapes on the southeastern margin of the tibetan plateau one of the most geographically complex climatically varied and biologically diverse regions of the world we find that in contrast to theory the purported surfaces are not consistent with progressive establishment of a new steeper river grade and therefore they cannot necessarily be interpreted as a remnant of an old low relief surface we propose an alternative model supported by numerical experiments in which tectonic deformation has disrupted the regional river network leaving remnants of it isolated and starved of drainage area and thus unable to balance tectonic uplift the implication is that the state of low relief with low erosion rate is developing in situ rather than preserving past erosional conditions

investigation of short period gravity waves with the lindenberg 482 mhz tropospheric wind profiler during four consecutive days in may 2001 convectively forced short period 6 45 min gravity waves were observed with a 482 mhz wind profiler which is continuously operated by the deutscher wetterdienst german weather service at the lindenberg observatory 60 km south east of berlin the objective of this campaign was to investigate onset and development of convectively forced gravity waves in the lower and middle troposphere the wave character could be unambiguously identified by simultaneous vertical wind and temperature measurements and their respective phase shift of 2 in accordance with previous findings convection waves were found to be generated at the top of the convective boundary layer they propagate predominantly horizontally with a slow but clearly recognizable vertical increase of wave activity the layer with significant wave activity reached the upper detection range at 7 0 km within a couple of hours on each of the observational days gravity wave activity started to decay after 16 utc with a slower rate than the simultaneously decaying forcing convection some wave activity remained during the night but at low amplitude levels the vertical wind energy component of the free atmosphere was found to be about 30 of the corresponding convective boundary layer cbl energy which is much more than previously reported values from numerical simulations the wavelet analysis of highly resolved wind profiler vertical velocity data t 16 s z 250 m in the boundary layer and free troposphere gives new insights into the temporal and vertical development of very short period convection waves through the troposphere at the cbl top a broad spectrum of wave scales with intrinsic periods between 6 and 45 min is generated with increasing height shorter scales t 13 min disappear and only longer ones remain wave trapping which is confirmed by vertically orientated phase lines is an important mechanism here copyright 2004 royal meteorological society

convective initiation at the dryline a modeling study abstract a nonhydrostatic three dimensional version of the colorado state university regional atmospheric modeling system csu rams is used to deduce the processes responsible for the formation of drylines and the subsequent initiation of deep moist dryline convection a range of cumuliform cloud types are explicitly simulated along drylines on 15 16 and 26 may 1991 in accordance with observations in the simulations narrow convergence bands along the dryline provide the lift to initiate deep moist convection the thermally direct secondary convective boundary layer cbl circulations along the dryline are frontogenetic and solenoidally forced maximum updrafts reach 5 m s 1 and the bands are 3 9 km wide and 10 100 km or more in length the updrafts penetrate and are decelerated by the overlying stable air above the cbl reaching depths of about 2000 m in the cases studied moisture convergence along the mesoscale updraft bands destabilizes the local sounding to deep convection while simultaneously

numerical simulation of the interaction between the dryline and horizontal convective rolls abstract the results of high resolution simulations of an idealized dryline environment are discussed the use of a single high resolution domain combined with accurate advection numerics and minimized numerical filtering allows the explicit resolution of large horizontal convective roll hcr circulations and their daytime evolution the horizontal convective rolls are oriented in the direction of the lower planetary boundary layer pbl wind shear by midafternoon a north south oriented dryline develops near the center of the simulation domain with the pbl circulations from both sides intersecting the dryline at multiple locations west of the dryline the hcr bands evolve into open convective cell occ structures having stronger and deeper vertical circulations compared to the occs and hcrs to the east the occs and hcrs east of the dryline impact the dryline and convective cloud location by modulating the low level moisture and upslope easterly flow the interaction between occ and hcr circulations

gravity waves above a convective boundary layer a comparison between wind profiler observations and numerical simulations wind profiler observations and three dimensional numerical modelling are used to investigate gravity waves generated over convectively active boundary layers on 12 and 13 may 2001 at lindenberg germany the results illustrate the importance of changes in the background wind and stability profile in influencing the vertical propagation of the gravity waves the resultant changes in vertical propagation cause the dominance of relatively long wavelength long period waves at high levels and the dominance of relatively short wavelength short period waves near the top of the convective boundary layer there are important differences between the two days in the wave propagation characteristics due to subtle changes in the background flow conditions copyright 2007 royal meteorological society

quantifying landscape differences across the tibetan plateau implications for topographic relief evolution 1 we quantify the bulk topographic characteristics of the tibet qinghai plateau with specific focus on three representative regions northern central and southeastern tibet quantitative landscape information is extracted from shuttle radar topography mission digital elevation models we find that the morphology of the tibetan plateau is nonuniform with systematic regional differences the northern and central parts of the plateau are characterized by what we suggest to call positive topography i e a topography in which elevation is positively correlated with relief and mean slope a major change from the internally drained central part of tibet to the externally drained part of eastern tibet is accompanied by a transition from low to high relief and from positive to negative topography i e a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope relief in eastern tibet is largest along rivers as they cross an ancient eroded plateau margin at high angle to the major strike slip faults the yalong yulong thrust belt implying strong structural control of regional topography we propose that the evolution of river systems and drainage efficiency the ability of rivers to transport sediments out of the orogen coupled with tectonic uplift is the simplest mechanism to explain systematic regional differences in tibetan landscapes basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief this mode of smoothing started concurrently with tectonic construction of the relief as most clearly illustrated today in the qilian shan qaidam region of the northeastern plateau in the interior of tibet further passive filling due to internal drainage only continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening thus diachronous beveling at high elevation produced the low relief surface of the high plateau in southeast tibet headward retreat of external drainages brought back in the global ocean base level first disrupting then interrupting the relief reduction process it produced a transitional topography by dissecting the old remnant plateau surface which introduced younger and steeper incision of this hitherto preserved high base level this provides a unifying mechanism for the formation of the low relief plateau interior and for the origin of the high elevation low relief relict surface in southeastern tibet our analysis brings forth the importance of surface processes in particular drainage efficiency in shaping plateau morphology and landscape relief such key processes appear to have been mostly ignored in numerical models of plateau deformation our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift low relief surface first formed at low elevation extending all the way to the south china sea shore before being warped upward in the late miocene pliocene by lower crustal channel flow

late neogene structural inversion around the northern gulf of tonkin vietnam effects from right lateral displacement across the red river fault zone continental extrusion may take up much of the deformation involved in continental collisions major strike slip zones accommodate the relative extrusion displacement and transfer deformation away from the collision front the red river fault zone rrfz accommodated left and right lateral displacements when indochina and south china were extruded during the indian eurasian collision the northern song hong basin onshore and offshore in the gulf of tonkin delineates the direct extension of the rrfz and thus records detailed information on the collision induced continental extrusion we assess the rapidly evolving kinematics of the fault zone buried within the basin based on seismic analysis contrary to previous studies we do not identify indications for latest miocene left lateral motion across the rrfz we tentatively consider the shift from left to right lateral motion to have occurred already during the middle late miocene as indicated by inversion of ne sw striking faults in the bach long vi area right lateral displacement terminated around the end of the miocene in the song hong basin however continued inversion in the bach long vi area and nnw sse striking normal faulting suggests a stress regime compatible with right lateral motion across the onshore part of the rrfz continuing to the present inversion around the bach long vi island may have accommodated up to a few kilometers of right lateral displacement between the indochina and south china blocks comparable ne sw striking fault zones onshore may have accommodated a larger fraction of the right lateral slip across the rrfz thus accounting for the restricted transfer of lateral displacement to the offshore basins

impact of a front dryline merger on convection initiation near a mountain ridge in beijing abstracta case study is presented of convection initiation ci resulting from the merger of a cold front with a dryline in southwestern beijing china on the afternoon of 11 june 2011 this process is analyzed with s band doppler radar data surface automatic weather station data and mesoscale numerical simulation results the formation of this dryline is analogous to that on the great plains of the united states and it is conducive to ci with mesoscale updrafts generated from the baroclinic frontogenesis and with favorable instability immediately on the moist side prior to the front dryline merger as the cold front approached the observed boundary layer convergence line or the simulated meso scale secondary dryline ci occurred ahead of the cold front with little contribution from frontogenetic baroclinity of the dryline the cold front then merged with the dryline and the baroclinity of the dryline was enhanced by the associated convergence to a degree comparable to that caused by frontogene