variations of the east asian jet stream and asian pacific american winter climate anomalies in this study the authors apply the ncep ncar reanalysis and other observations to depict the association of the asian pacific american climate with the east asian jet stream eajs with an emphasis on boreal winter seasons and on interannual timescales they analyze the variations of the eajs and their relationships with el nino southern oscillation enso and extratropical north pacific sea surface temperature sst and assess the relative connections of the eajs and enso to the anomalies of atmospheric circulation surface temperature and precipitation in the asian pacific american region it is found that the eajs is coupled to a teleconnection pattern spanning the entire asian pacific american region with the strongest signals over east asia and the western pacific this pattern differs significantly from that associated with enso which influences the earth s climate extensively with a strongest impact on the climate over the central pacific and east a strong eajs is associated with an intensification of the weather and climate systems in asia and over the pacific such as deepening of the east asian trough and the aleutian low and strengthening of the east asian winter monsoon it is linked to colder and drier conditions in east asia and stronger convection over the tropical asia australia sector compared with enso the eajs seems to link to the climate signals of asia and the pacific more strongly an intensified eajs is also associated with anomalies of temperature and precipitation in north america due to the related changes in stationary wave patterns while the eajs does not strongly link to the tropical central eastern pacific sst it is significantly associated with the extratropical north pacific sst more specifically the second most dominant mode of the empirical orthogonal function analysis of the sst in addition a strong weak eajs seems to follow a large small meridional gradient of the western pacific sst associated with warming cooling in the tropics subtropics and cooling warming in the extratropics

connections between wintertime jet stream variability oceanic surface heating and transient eddy activity in the north pacific 1 a set of statistical analyses of the fields from the european center for medium range weather forecasts reanalysis era 40 are carried out to investigate the connections between three selected fields namely the wintertime western pacific jet stream wpjs as represented by the zonal wind at 200 hpa the oceanic surface heating represented by the latent and sensible heat fluxes and the synoptic scale transient eddy activity stea over the north pacific first empirical orthogonal function eof analysis is performed to characterize the wintertime wpjs variability further analyses yield the following conclusions 1 the most dominant relationship among the three selected fields is strongly linked to the el nino southern oscillation enso during enso events anomalous zonal wind at 200 hpa downstream of the wpjs main body shown in the first eof is accompanied by stea anomalies around the region of the anomalous midlatitude zonal wind 2 the strengthening weakening of the wintertime wpjs main body shown in the second eof is connected to the surface heating anomalies in the kuroshio and its extension region as well as to stea anomalies in the region downstream of the wpjs main body 3 the northward southward shift of the wintertime wpjs represented in the third eof is closely related to the south north dipolar structure of the surface heating anomalies in the western north pacific the stea spatial displacement is in conjunction with the shift of the jet stream in the same direction due to the dynamical connection between the winds and the eddies furthermore the stea anomalies in winter may cause the wpjs anomalies on the submonthly timescale as a consequence the northward southward shift of the stea is harmoniously in favor of the similar jet shift

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

zonal jet structure and the leading mode of variability an observational analysis of the northern hemisphere circulation during winter reveals that the leading mode of variability depends on longitude in particular the first eof of the zonal mean circulation differs over the atlantic and pacific sectors these results provide motivation for a series of model runs where a simple gcm is used to investigate the effects of the zonal jet structure on the leading mode of variability in the northern hemisphere model results indicate that the leading mode of variability depends on the distance between the eddy driven and subtropical jets when the jets are well separated the leading mode of variability describes latitudinal shifting of the eddy driven jet however when the two jets are nearly collocated pulsing of the combined jet dominates the variability this change coincides with a weakening of the positive feedback between the eddies and zonal flow anomalies these results provide a possible explanation for the reduced amplitude of the northern annular mode in the pacific sector relative to that in the atlantic sector during northern hemisphere winter

electrical resistivity sounding of the east antarctic ice sheet electrical resistivity soundings using a schlumberger array have been carried out at dome c east antarctica 74 39 s 124 10 e elevation 3400 m to sound the entire 3500 m depth of the ice sheet changes in density and temperature are largely separated in the ice at dome c so activation energies for both firn and ice could be determined we find an activation energy of 0 25 ev in both solid ice and firn between 15 c and 58 c a common value of the activation energy points to a single transport regime in which the charge carriers and conduction paths are the same in firn and ice to evaluate the variation of resistivity with density we have considered five dielectric mixture models that fit the available data on the high frequency dielectric constant of firn only looyenga s equation fits the field data for dc resistivity in the upper 900 m of the ice sheet where impurity concentrations are known from core samples we find no correlation between resistivities and the concentrations of salts or acids instead we find it likely that resistivities are correlated with the crystal size hence with the holocene wisconsin boundary in the ice column a pronounced increase in resistivity to a value comparable with that in temperate glacier ice occurs deep within the ice sheet we attribute this to a large increase in the size and irregularity of the ice crystals which destroys the continuity of the impurity shells surrounding the ice crystals that we believe supply the conduction paths shabtaie and bentley 1994a high resistivity does not imply removal of the impurities from the system moderate concentrations of impurities can be accommodated by locating them in disconnected domains

coherent radar ice thickness measurements over the greenland ice sheet we developed two 150 mhz coherent radar depth sounders for ice thickness measurements over the greenland ice sheet we developed one of these using connectorized components and the other using radio frequency integrated circuits rfics both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice we used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers we operated both radar systems on the nasa p 3b aircraft equipped with gps receivers radar data are tagged with gps derived location information and are collected in conjunction with laser altimeter measurements we have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of program for regional climate assessment parca investigations and the north greenland ice core project radar echograms and derived ice thickness data are placed on a server at the university of kansas http tornado rsl ukans edu greenlanddata htm for easy access by the scientific community we obtained good ice thickness information with an accuracy of 10 m over 90 of the flight lines flown as a part of the parca initiative in this paper we provide a brief description of the system along with samples of data over the interior along the 2000 m contour line in the south and from a few selected outlet glaciers

the linkage between upper level jet streams over east asia and east asian winter monsoon variability abstractthis study investigates the linkage between east asian winter monsoon eawm variability and upper level jets with particular focus on the east asian polar front jet pj and its concurrent variation with the subtropical jet located to the south of the tibetan plateau tsj the winter upper level zonal wind variations over the asian landmass 70 120 e are dominated by two principal modes i e meridional displacement of the pj and out of phase variation in the intensity of the tsj and pj and they are closely linked to the eawm northern mode and southern mode respectively southward shifting of the pj concurs with northwestward displacement of the siberian high sh an enhanced northern east asian trough leading to cold winter in northern east asia meanwhile the simultaneous tsj intensification and pj weakening is linked to an amplified sh a southward shift of the aleutian low al a strengthened southern east asian trough and a wavelike anomaly pattern extending from western barents s

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

why is there an early spring cooling shift downstream of the tibetan plateau abstract the temperature shift over the eastern flank of the tibetan plateau is examined using the last 50 yr of chinese surface station observations it was found that a strong cooling shift occurs in early spring march and april and late summer july august and september in contrast to the warming shift in other seasons the cause of the march april ma cooling is investigated in this study the ma cooling shift on the lee side of the tibetan plateau is found to be not a local phenomenon but rather it is associated with an eastward extension of a cooling signal originating from north africa that is related to the north atlantic oscillation nao in the previous winter the midtropospheric westerlies over the north atlantic and north africa tend to intensify during positive nao phases the enhanced westerlies after passing over the tibetan plateau result in strengthened ascending motion against the lee side of the plateau which favors the formation of midlevel stratiform clouds the increased a

coesite and shocked quartz discovered in the australasian and north american microtektite layers samples from the north american australasian and ivory coast microtektite layers were examined for unmelted impact ejecta 125 m size coesite and shocked quartz identified by x ray diffraction were found at all the sites where a well defined north american microtektite layer had previously been documented coesite and shocked quartz were also foundin seven out of 33 cores from the australasian strewn field however no coesite or shocked quartz was found associated with the ivory coast microtektite layer stishovite was also found at three of the australasian sites all of the australasian cores containing coesite and shocked quartz were taken from within 2000 km of indochina which is believed by most to be the source area for the australasian tektites and microtektites six of the seven cores have the highest concentrations of microtektites ever determined for australasian microtektite bearing cores the seventh core did not contain any microtektites which may be consistent with the hypothesis that the microtektites were deposited in a raylike pattern the discovery of coesite and impact ejecta associated with both the north american and australasian microtektite layers provides further support for the hypothesis of terrestrial impact origin of tektites

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

circulations of the west pacific jet stream abstract the jet stream of the west pacific is a very steady feature of the winter circulation with almost continuousintensification over east china and japan and weakening in the central pacific in this study the national meteorological center spectral forecast model with normal mode initialization is used as a tool to provide diagnostic elements in a region of nonstandard data sources cross sections transverse to the jet stream in its intensification zone show a deep single celled direct solenoidal circulation around a single frontal zone to be producing large increases of kinetic energy farther east in the central pacific a strong indirect solenoidal circulation produces a strong decrease of kinetic energy the irrotational wind components at jet stream levels are suggestive of an inertial cycle as part of the jet stream dynamics a simple model of a modified inertial cycle is integrated in which the geostrophicwind is allowed to vary as a function of the ageostrophic flow transverse to the jet a

bedrock topography and wind erosion sites in east antarctica observations from the 2002 us itase traverse ice stratigraphy from deep penetrating radar data collected during the 2002 us international trans antarctic scientific expedition us itase traverse shows evidence of a significant erosion surface and drift filled basin related to a previously undiscovered 1400 m subglacial mountain between hercules dome 87842 0 s 1088 w and south pole the 3 mhz radar profile crosses three subglacial mountains at approximately 458 to the ice flow direction cross cutting reflectors in the top 500 m of ice stratigraphy are interpreted as angular unconformities resulting from wind erosion as the ice deforms over the mountain tops the unconformities correlate locally with zones of high radarsat reflectivity several nearby sites with similar relatively high radarsat reflectivity adjacent to the traverse indicate that active wind erosion may be taking place at these locations as well based on the local correlation between surface wind scour and subglacial topography we interpret the nearby cluster of bright radarsat reflectivity to indicate the presence of a small range of subglacial mountains the ability to trace isochronal stratigraphy associated with scour sites using shallow and deep radar to nearby dated ice cores presents the possibility of exploiting wind scour zones to access well dated older ice with shallow coring equipment

the different configurations of the east asian polar front jet and subtropical jet and the associated rainfall anomalies over eastern china in summer abstractto investigate the concurrent impacts of the east asian polar front jet eapj and subtropical jet easj on the summer rainfall over eastern china positive strengthened eapj with weakened easj and negative weakened eapj with strengthened easj configurations are identified in the positive configuration rainfall decreases in the northern part of eastern china and increases in the southern part vice versa in the negative configuration the possible mechanisms maintaining the two jet configurations are further proposed from the perspectives of sea surface temperature sst and synoptic scale transient eddy activities stea in the positive configuration meridional distributed cold warm sst anomalies over the eastern north pacific may induce regional circulation and meridional temperature gradient anomalies which can strengthen the eapj and weaken the easj the central pacific la nina like sst anomalies are related with the arctic vortexlike anomalies in the stratosphere which may strength

snow megadunes in antarctica sedimentary structure and genesis 1 megadune fields occupy large areas in the interior of the east antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes they therefore are important to surface mass balance and ice core interpretation field observations gps gpr and surface measurements have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area located 200 km east of dome c a combination of remote sensing analysis using landsat and satellite radar altimetry and field measurements indicate that slope in the prevailing wind direction spwd and climatic conditions play a crucial role in megadune genesis the megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds the megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation ranging between 25 leeward faces to 120 windward faces of the accumulation in adjacent nonmegadune areas leeward faces are characterized by glazed sastrugi free surfaces and extensive depth hoar formation windward faces are covered by large rough sastrugi up to 1 5 m in height

characterizing midlatitude jet variability lessons from a simple gcm abstract fluctuations in the tropospheric zonal jet are often characterized using anomaly patterns or empirical orthogonal functions representing deviations of the zonal mean flow from climatology in previous studies the leading anomaly pattern has been interpreted as representing north south jet movements while the second anomaly pattern has been interpreted as representing independent fluctuations in jet strength and width here it is shown that these leading anomaly patterns are in fact dependent and together represent north south movements of the jet fluctuations in jet strength which are approximately inversely proportional to jet width superimpose upon these dominant north south meanderings the distinction between the usual anomaly pattern perspective and this new perspective may have important implications in the interpretation of tropospheric zonal jet variability

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

trapping of synoptic scale disturbances into the north pacific subtropical jet core in midwinter 1 over the northwestern nw pacific a subtropical jet stream develops at 30 n in midwinter as the east asian winter monsoon intensifies eddies with subweekly periods propagating through the midlatitude tropopause into the nw pacific storm track tend to be trapped into the jet core 1000 km away from a surface baroclinic zone at 40 n while lifted up by 3 km the trapping appears to weaken the interaction of the upper level eddies with the baroclinic zone thus acting against eddy amplification and thereby contributing to the midwinter minimum in the eddy activity as observed before the late 1980s since then under the reduced trapping effect by the weakened jet upper level eddies tended to propagate right above the surface baroclinic zone while strongly interacting it even in midwinter as in fall and spring this midwinter tendency acted to enhance the eddy amplification that led to the recent disappearance of the activity minimum

storm tracks and zonal mean flow variability a comparison between observed and simulated data a statistical technique is used to analyze the relation between monthly mean zonal flow and storm tracks activity in the observations and numerical simulations echam4 model the singular value decomposition technique svd has been used to correlate storm tracks and monthly mean wintertime anomaly fields the analysis has been performed on data from january 1980 to december 1989 nmc analyses and on an ensemble of agcm simulations with prescribed sst for the same period separately in the euro atlantic and pacific sectors we found good correlation between storm tracks activity and zonal flow in both regions in both data and simulations the dominant svd modes show that the storm tracks spatial displacement is in conjunction with jet shifts in the same direction our analysis suggests that the model is highly sensitive to the equatorial ocean forcing although the model produces an excessive response to el nino and la nina phases it shows good capability of simulating the dynamical connection between storm tracks and jet

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

forced planetary waves in the northern hemisphere winter wave coupled orographic and thermal forcings abstract a more complete and new formulation of the orographic forcing and new thermal forcings are included in a steady state model of the northern hemisphere planetary waves when both forcings are included the simulation produces excellent results which are compared in detail with observations in particular the siberian high the tropospheric east asian trough and subtropical tropospheric east asian jet stream maxima are well reproduced even though the forcing is primarily extratropical in origin the modes uses a lower boundary condition in which the orographic forcing is determined by the effects of the total flow not just the zonal mean basic state consequently the net orographic forcing changes when thermal forcing is added and the tow solution is not equal to the linear sum of the solutions with orographic and thermal forcings separately the thermally induced orographic forcing is found to be very significant and in the troposphere there is strong interaction between the two forcings with

the winter concurrent meridional shift of the east asian jet streams and the associated thermal conditions abstractin this study the concurrent meridional shift of the east asian polar front jet eapj and the east asian subtropical jet easj and the associated thermal conditions have been investigate

unconformable stratigraphy in east antarctica part ii englacial cosets and recrystallized layers complex unconformable englacial stratigraphy including a segment of distinctive cosets of bed sequences occurs throughout the thickness of a 3 2 mhz ice sheet radar profile we acquired across the upper byrd glacier east antarctica catchment some cosets span 10 km are 100 m thick and are delineated by distinct horizons at 40 90 m depth in firn comparisons between 200 mhz and specially processed 3 2 mhz profiles reveal that the delineating horizons result from density modified layers produced by decades to millennia of subaerial exposure as detailed in our related paper part i these comparisons together with reflected waveforms at depth also reveal that the modified layers retain their chemical stratification and therefore the original unconformable surface two profile segments show high amplitude transverse folds spanning much of the ice sheet thickness the parallel nature of most of them suggests basal sliding beneath long term up ice flow accumulation zones which we identify in satellite images as the likely sources for the cosets the unconformable stratigraphy at depths greater than 2000 m shows that antidunal deposition and intense firn recrystallization zones have persisted for tens of thousands of years in this region of east antarctica

interdecadal variations of the east asian winter monsoon and their association with quasi stationary planetary wave activity abstract interdecadal variations of the east asian winter monsoon eawm and their association with the quasi stationary planetary wave activity are analyzed by using the 40 yr european centre for medium range weather forecasts re analysis dataset and the national centers for environmental prediction national center for atmospheric research reanalysis dataset it is found that the eawm experienced a significant weakening around the late 1980s that is the eawm was strong during 1976 87 and became weak after 1988 this leads to an obvious increase in the wintertime surface air temperature as well as a decrease in the frequency of occurrence of cold waves over east asia the dynamical process through which the eawm is weakened is investigated from the perspective of quasi stationary planetary waves it is found that both the propagation and amplitude of quasi stationary planetary waves have experienced obvious interdecadal variations which are well related to those of the eawm compared to the period 1976

fast flow signature in the stagnated kamb ice stream west antarctica among the major ice streams that drain west antarctica kamb ice stream formerly called ice stream c is unique in that it stagnated 150 yr ago but its former fast flow conditions are virtually unknown here we presentsurface based radar profiles of the ice stream s undulating internal stratigraphy which records these conditions our analysis of the profiles indicates that pre stagnation flow velocities averaged over a period 740 yr exceeded 350 m yr 1 in the trunk of the ice stream this velocity constraint would be lower if the ice had been thickening higher if thinning but suggests mass loss from the ice stream catchment that is of sufficient magnitude to reverse the gain estimated for today s siple coast region analysis of other ice streams would allow comparison of velocities over millennial time scales with observations of present day velocities useful for evaluating how west antarctic ice drainage has evolved

concurrent variation between the east asian subtropical jet and polar front jet during persistent snowstorm period in 2008 winter over southern china 1 the concurrent variation features between the east asian subtropical jet and polar front jet were investigated during persistent snowstorm period in 2007 2008 winter over southern china the east asian subtropical jet was divided into two parts 1 the plateau jet located along the southern side of the tibetan plateau and 2 the ocean jet situated at the southeastern japan island the concurrent intensity variation among the polar front jet plateau jet and ocean jet and the associated atmospheric anomalous signals were examined a possible mechanism for concurrent variation among the three jets was also investigated from a perspective of synoptic scale transient eddy activities stea the enhanced plateau jet was simultaneously correlated with the weakened polar front jet while the variation of the ocean jet lagged the variation of the plateau jet polar front jet about 5 days the concurrent variation between the plateau jet and the polar front jet acted as an important bridge that linked the snowstorm to the atmospheric anomalous signals associated with the cold and warm air activities due to the opposite trends of stea variation over the southern and northern sides of the tibetan plateau the plateau jet and the polar front jet exhibited a significant concurrent variation feature the stea anomalies over the plateau jet and polar front jet regions propagated downstream to the east asian coast as a wave train along the southern and northern sides of the tibetan plateau respectively resulting in a 5 day lag variation relationship between the ocean jet and the plateau jet polar front jet

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

seasonal variations of the synoptic scale transient eddy activity and polar front jet over east asia abstract seasonal variations of the synoptic scale transient eddy activity stea and the jet streams over east asia are examined through analysis of the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data extracted from the 6 hourly upper level wind fields the distribution of the jet core numbers exhibits a distinct geographical border for the east asian subtropical jet easj and the east asian polar front jet eapj at the latitudes of the northern tibetan plateau tp in the cool seasons two branches of the stea and low level baroclinicity exist over the east asian landmass accompanied by the two jet state of the easj and eapj in the warm seasons a single jet pattern of the easj along the north flank of the tp is accompanied by the weakened stea over the mid to high latitudes of east asia further analysis shows two distinct features of the seasonal variations of the stea over east asia compared with that over the north pacific first during the transit

surface winds over the antarctic continent a review surface winds over antarctica often classified as katabatic are intimately related to the orientation and steepness of the underlying ice terrain such flows result primarily from the strong radiational cooling of the sloping ice surface which creates a downslope directed horizontal pressure gradient force it is possible to diagnose the time averaged near surface streamline patterns of cold air drainage currents using recently compiled detailed antarctic ice topography maps and appropriate estimates of the strength of the surface temperature inversion the resulting streamlines agree with available observations and illustrate the high degree of nonuniformity of gravity driven flows off the ice sheets in certain interior sections negatively buoyant air from a large catchment area drains through a restricted section of coastline such confluence zones represent regions of enhanced supplies of cold air and are shown to be related to anomalously strong katabatic winds implications for sea ice formation are discussed

seasonal evolution of the upper tropospheric westerly jet core over east asia the location change of the westerly jet core at upper troposphere in june and july is investigated by using the ncep ncar reanalysis data the results show that the location of the westerly jet core changes rapidly from 140 e to 90 e during 35th 39th pentads which corresponds to the plum rain period over east asia the location change of the jet core is actually the relative intensity change of the different westerly jet centers the meridional temperature contrast in the troposphere is associated with the rapid location change of the jet core the diabatic heating changes are the primary factor determining the seasonal evolution of the westerly jet core over east asia

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

concurrent variations in the location and intensity of the asian winter jet streams and the possible mechanism this study investigates the concurrent variations in the location and intensity of the east asian subtropical jet easj and polar front jet eapj with a focus on the relationship between the variations and the atmospheric circulation in the mid latitude region the possible mechanisms for the concurrent variations of the easj and eapj are explored the wintertime upper level zonal wind variation over the landmass 50 100 e is characterized by two principal modes i e the out of phase variations in the intensity and the meridional displacements of the easj eapj the easj and eapj are intensified weakened when they are located close to far away from each other corresponding to a weakened intensified east asian trough over the northern pacific region and a decreased increased geopotential height in the mid latitude over central asia the spatial pattern of 500 hpa geopotential height anomaly is similar to the eurasian teleconnection pattern while the pattern of sea level pressure anomaly shows a feature similar to the arctic oscillation analyses of related thermal dynamical processes indicate that the increased decreased diabatic heating and horizontal heat transport lead to a larger smaller meridional temperature gradient over the easj eapj regions which subsequently intensifies weakens the east asian jets severe weak convective activities accompanied with warmer colder sst in the tropics also contribute to the intensification weakening of the easj and eapj dynamically the strong weak divergence of the eddy vorticity flux along the northern tibetan plateau and that of the eliassen palm flux of the synoptic scale stationary waves are favorable for the intensification weakening of zonal winds through the wave mean flow interactions as a result the easj and eapj are intensified weakened