roles of synoptic to quasi biweekly disturbances in generating the summer 2003 heavy rainfall in east china abstractduring the mei yu season of the summer of 2003 the yangtze and huai river basin yhrb encountered anomalously heavy rainfall and the northern yhrb nyhrb suffered a severe flood because of five continuous extreme rainfall events a spectral analysis of daily rainfall data over yhrb reveals two dominant frequency modes one peak on day 14 and the other on day 4 i e the quasi biweekly and synoptic scale mode respectively results indicate that the two scales of disturbances contributed southwesterly and northeasterly anomalies respectively to the mei yu frontal convergence over the southern yhrb syhrb at the peak wet phase an analysis of bandpass filtered circulations shows that the lower and upper regions of the troposphere were fully coupled at the quasi biweekly scale and a lower level cyclonic anomaly over syhrb was phase locked with an anticyclonic anomaly over the philippines at the synoptic scale the strong northeasterly components of an anticyclonic anomaly with a deep cold

quaternary glaciation of the himalayan tibetan orogen glacial geological evidence from throughout the himalayan tibetan orogen is examined to determine the timing and extent of late quaternary glaciation in this region and its relation to similar changes on a global scale the evidence summarised here supports the existence of expanded ice caps and extensive valley glacier systems throughout the region during the late quaternary however it cannot yet be determined whether the timing of the extent of maximum glaciation was synchronous throughout the entire region or whether the response was more varied the lack of organic material needed for radiocarbon dating has hindered past progress in glacial reconstruction however application of optically stimulated luminescence and terrestrial cosmogenic radionuclide methods has recently expanded the number of chronologies throughout the region limits to the precision and accuracy available with these methods and more importantly geological uncertainty imposed by processes of moraine formation and alteration both conspire to limit the time resolution on which correlations can be made to milankovitch timescales several ka in order to put all studies on a common scale well dated sites have been re evaluated and all the published terrestrial cosmogenic nuclide ages for moraine boulders and glacially eroded surfaces in the himalayan tibetan orogen have been recalculated locally detailed studies indicate that there are considerable variations in the extent of glaciation from one region to the next during a glaciation glaciers throughout monsoon influenced tibet the himalaya and the transhimalaya are likely synchronous both with climate change resulting from oscillations in the south asian monsoon and with northern hemisphere cooling cycles in contrast glaciers in pamir in the far western regions of the himalayan tibet orogen advanced asynchronously relative to the other regions that are monsoon influenced regions and appear to be mainly in phase with the northern hemisphere cooling cycles broad patterns of local and regional variability based on equilibrium line altitudes have yet to be fully assessed but have the potential to help define changes in climatic gradients over time copyright 2008 john wiley sons ltd

quasi biweekly oscillation over the south china sea in late summer propagation dynamics and energetics abstractthe propagation dynamics and energetics of the quasi biweekly oscillation qbwo over the south china sea scs in late summer august september as are investigated in this study the qbwo originates from east of the philippines and has a northwestward propagation after arriving to the east of the scs the qbwo shifts to a westward migration and dominates over the scs the analyses of the vorticity budget suggest that the meridional wind anomaly could control the spatial migration of the vorticity anomaly through the effect term and further influences the movement of the convection anomaly it implies that the meridional wind is a crucial factor to drive the propagation of the qbwo the energetics of the qbwo is investigated to understand the maintenance of the qbwo which indicates that the convection anomaly could affect the circulation anomaly through the energy conversions to maintain the qbwo

simulations of the northern hemisphere through the last glacial interglacial cycle with a vertically integrated and a three dimensional thermomechanical ice sheet model coupled to a climate model

thermo mechanically coupled ice sheet response cold polythermal temperate classical mixture concepts are the appropriate vehicle for describing the dynamics of ice masses containing some water we review and derive respectively the theoretical formulations of cold polythermal and temperate ice masses emphasize the peculiarities of the model equations and point to difficulties that were encountered with the proposed models the focus is both on the adequate physical motivation of the models and the consistency of their mathematical representation

deglaciation of the northern hemisphere at the onset of the eemian and holocene high resolution tims u series dating of sea level events obtained from coral reef complexes suggests that global deglaciation from the saale penultimate glacial to the eem interglacial marine 18o stages 6 5 may have occurred earlier in relation to milankovitch insolation forcing than that from the wisconsinan glacial to the holocene interglacial marine 18o stages 2 1 however the interpretation of these data has been problematic because of the possibility of isotope exchange in order to investigate whether these different lead lag relations between milankovitch forcing and ice volume are feasible from the point of view of large scale ice sheet dynamics and thermodynamics the three dimensional polythermal ice sheet model sicopolis simulation code for polythermal ice sheets is applied to the entire northern hemisphere which gives the major contribution to global ice volume changes due to the relative stability of the antarctic ice sheet and simulations through the last two climatic cycles are conducted the simulations cover the interval from 250 kyr bp until today and are driven by surface temperature reconstructions of deep ice cores grip vostok and simple parameterizations for the change of precipitation with time discussion of the results is focused on the saale eem and the wisconsinan holocene transitions the amount and rate of deglaciation are in good agreement with the specmap record for both cases and the evidence of the data for an early start of the eem interglacial is supported

distinct quasi biweekly features of the subtropical east asian monsoon during early and late summers using global precipitation climatology project daily rainfall and era interim reanalysis data we investigate the distinct characteristic of quasi biweekly variation qbv 12 20 days over east asia ea during early june 10 july 20 and late july 21 august 31 summer the qbv maximum variance is found over the core region of ea 30 40 n 110 130 e which includes eastern china lower reaches of the yellow huaihe and yangtze rivers and the korean peninsula at both its peak wet and dry phases qbv over the core region has a baroclinic structure but with different spatial distributions different lower level prevalent wind anomalies and different upper level major circulation anomalies in the two subseasons meanwhile the two subseasons have different propagating tracks prior to reaching the peak phase and different precursors associated with the local genesis of qbv furthermore during the transition from the peak dry to peak wet phase of qbv the major monsoon circulations have different behaviors that tropical monsoon trough extends eastward in early summer but retreats westward in late summer and the south asia high sah and western north pacific wnp subtropical high move toward away from each other in early late summer the abrupt change of mean state in mid to late july which includes the northward migration of westerly jet sah and wnp and the weakening and broken of westerly jet is considered the root cause of the change in behavior of qbv finally we indicate that the tropical monsoon trough and midlatitude westerly jet are possible sources of qbv over subtropical ea in both subseasons and provide useful guidance for 2 3 week predictions over ea

interannual variations in mixed rossby gravity waves and their impacts on tropical cyclogenesis over the western north pacific abstract the present study investigates the transition from mixed rossby gravity mrg waves to tropical depression td type disturbances and its interannual variations over the western north pacific wnp using ecmwf high resolution data for the years of 1980 2001 as the equatorially trapped mrg waves propagate westward into the wnp the mrg waves transit to td type disturbances because of background flow change interannual variations in the transition of mrg waves are related to monsoon circulation change in response to tropical convective heating over the warm pool wp region when the wp is in a warm state convective heating is enhanced in the western part of the wnp and the monsoon trough retreats westward which induces a westward shift of the wave transition zone in contrast when the wp is in a relatively cold state the eastward penetration of convection and monsoon trough shifts the wave transition to the eastern part of the wnp the zonal wind convergence and shear in the monsoon trough

cosmogenic beryllium 10 and neon 21 dating of late pleistocene glaciations in nyalam monsoonal himalayas we present cosmogenic 10be and 21ne chronologies from 21 erratic boulders on three moraine sequences in nyalam county monsoonal himalayas southern margin of the tibetan plateau the surface exposure ages provide evidence for at least two distinct glacial advances during the late stage of the last glacial cycle and for one or more significantly older glaciations the distribution of cosmogenic ages from the three ridges of the old moraine sequence is inconsistent with their stratigraphic order because exposure periods of the erratics prior to deposition on the moraine surface is shown to be small the chronology stratigraphy mismatch suggests that the cosmogenic ages do not date moraine deposition but most likely significant moraine ridge denudation and related boulder exhumation after initial deposition of the moraines during the penultimate glacial cycle or earlier the surface exposure ages based on various currently accepted production rate scaling protocols yield age differences of up to 35 reflecting the poor knowledge of terrestrial cosmogenic production rates at low latitude high altitude sites even within this conservative uncertainty range our results do not yield evidence for late pleistocene glaciations in monsoonal tibet to be asynchronous to those in mid latitudes on both hemispheres there is an urgent need to improve the knowledge of terrestrial cosmogenic nuclide production rates and their scaling to low latitude regions to fully exploit the climate information archived in tropical moraine sequences

the relationship between anomalous presummer extreme rainfall over south china and synoptic disturbances a spectral analysis of daily rainfall data has been performed to investigate extreme rainfall events in south china during the presummer rainy seasons between 1998 2015 excluding 1999 2006 2011 and 2014 the results reveal a dominant frequency mode at the synoptic scale with pronounced positive rainfall anomalies by analyzing the synoptic scale bandpass filtered anomalous circulations 24 extreme rainfall episodes defined as those with a daily rainfall amount in the top 5 are categorized into cyclone 15 and trough 8 types with the remaining events as an anticyclone type according to the the primary anomalous weather system contributing to each extreme rainfall episode the 15 cyclone type episodes are further separated into 11 lower and 4 upper tropospheric migratory anomalies an analysis of their anomalous fields shows that both types could be traced back to the generation of cyclonic anomalies downstream of the tibetan plateau except for two episodes of lower tropospheric migratory anomalies originating over the south china sea however a lower tropospheric cyclonic anomaly appears during all phases in the former type but only in the wettest phase in the latter type with its peak disturbance occurring immediately beneath an upper level warm anomaly the production of extreme rainfall in the trough type episodes is closely related to a deep trough anomaly extending from an intense cyclonic anomaly over north china which in turn could be traced back to a mid latitude rossby wave train passing by the tibetan plateau the results have important implications for understanding the origin structure and evolution of synoptic disturbances associated with the pre summer extreme rainfall in south china

global ice volume variations through the last glacial cycle simulated by a 3 d ice dynamical model abstract a coupled ice sheet ice shelf bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle the mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo mass balance feedback the model is forced by the grip and vostok derived temperature records and by sea level and solar radiation variations which are distributed spatially and seasonally model simulations show that at the last glacial maximum lgm a volume of ice representing about 65 m of sea level equivalent is stored on the eurasian continent whereas north america stores 42 m the other regions greenland tibet south america and antarctica contribute about 17 m to global sea level lowering at the lgm compared to present day sensitivity experiments show that the ice volumes of the eurasian and north american ice sheets are particularly sensitive to summer temperature changes finally the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the eurasian and north american continents ice sheet formation begins at 118 kyr bp in the barents and kara sea region over baffin island and in the high cordilleran range following a 4 c cooling alternating regions of ice sheet expansion by direct snowfall ice flow and grounding of ice shelves can be identified these relate to specific geomorphological traces and may as such help in model validation

retracted the past valley glacier network in the himalayas and the tibetan ice sheet during the last glacial period and its glacial isostatic eustatic and climatic consequences

rossby waves in zonally opposing mean flow behavior in northwest pacific summer monsoon abstract the interactions between monsoon circulations and tropical disturbances in the northwest pacific where the low level mean flow is westerly in the west and easterly in the east are studied with a barotropic model the authors model results suggest that the scale contraction by the confluent background flow the nonlinear dynamics the effect and the large scale convergence are important for the energy and enstrophy accumulation near the region where the zonal flow reverses the energy enstrophy accumulation can be maintained with a continuous rossby wave emanation upstream the largest accumulation occurs when the emanating zonal wavelength is around 2000 km longer rossby waves experience less scale contraction and nonlinear effects while shorter rossby waves cannot hold a coherent structure against dispersive effects the nonlinear energy enstrophy accumulation mechanism is significantly different from previous linear energy accumulation theories in the linear theories this is primarily a

a connection between the tropical pacific ocean and the winter climate in the asian pacific region the impact of the tropical pacific sea surface temperature sst anomaly on the winter mean surface air temperature sat in the asian pacific region is investigated during the period from 1948 to 2008 using both observations and a linear baroclinic model lbm a singular value decomposition svd analysis is conducted between the 500 hpa geopotential height z500 over the northern hemisphere and the sst over the tropical pacific ocean to obtain the large scale atmospheric patterns related to tropical pacific sst focus is given to the second pair of svd mode svd2 which bears some similarities in the z500 field to the arctic oscillation over the north atlantic sector and can impact the sat over a larger area of asian pacific in the winter of a positive svd2 the sat over the midlatitude to high latitude asian continent the arctic ocean the indian ocean and the western subtropical pacific ocean tends to be warmer than normal while the north pacific ocean around the bering strait is abnormally cold and vice versa examination of the associated surface general circulation shows that a positive svd2 tends to shift the siberian high southward and the aleutian low eastward resulting in anomalous weak pressure gradient between the asian continent the north pacific anomalous positive sea level pressure anomalies around japan and southerly wind along the east coast of the asian continent are observed at the same time the east asian trough at midtroposphere becomes weaker than normal and the east asian westerly jet stream is increased in magnitudes and shifted northward the analysis of the wave activity flux and result of idealized numerical experiments show a possible influence of the western tropical pacific sst forcing on the svd2

evolution of the circulation anomalies and the quasi biweekly oscillations associated with extreme heat events in southern china abstractsouthern china located in the tropical subtropical east asian monsoonal region presents a unique anticyclonic cyclonic circulation pattern during extreme heat eh obviously different from the typical anticyclone responsible for eh in many other regions associated with the evolution of eh in southern china the anticyclonic cyclonic anomalies propagate northwestward over the philippines and southern china before the eh onsets the anticyclonic anomaly dominates southern china resulting in stronger subsidence over southern china and stronger southerly southwesterly flow over the western northern margins of southern china the southerly southwesterly flow transports more water vapor to the north of southern china thus together with the local stronger subsidence resulting in drier air condition and accordingly favoring the occurrence of eh conversely after the eh onsets the cyclonic component approaches southern china and offsets the high temperature the oscillations of temperature

topographic effects on spatiotemporal variations of short duration rainfall events in warm season of central north china statistical analyses of the hourly station rainfall observation over the recent 8 years show that rainfalls in the warm season may october of the central north china are dominated by short duration rainfall events lasting less than or equal to 6 h and the southeastward delayed diurnal phases of total rainfall revealed by previous studies are mainly contributed by the propagating short duration rainfall rather than the long duration rainfall as that along the yangtze river valley the spatiotemporal features of rainfall events are highly correlated with elevation heights the largest frequency of short duration rainfall events locates in the southeastern inner periphery of taihangshan and yanshan mountains rainfall over the northwestern mountains often occurs in the afternoon some rainfall events propagate southeastward and influence the rainfall in the southeastern foothills and plain the rainfall with short duration time mainly begins around the late evening in the southeastern plain and even later in coastal regions the understanding of topographic effects to rainfall events is discussed based on reanalysis and station data results indicate that the topography influences the diurnal varied surface or low level temperature moisture and wind fields which benefit rainfall events occurring in the afternoon over the northwestern mountains first and the southeastward propagation afterward

an observational study of the south china sea monsoon during the 1979 summer onset and life cycle abstract the onset and life cycle of the 1979 south china sea summer monsoon were examined in the context of the 30 60 and 12 24 day monsoon modes the former intraseasonal mode formed the northward migrating monsoon trough ridge while the latter intraseasonal mode propagated westward in the south china sea the monsoon in this region exhibited three cycles over the summer may august with the onset taking place about one cycle ahead of the onset of the indian and japanese monsoons climatologically a summer trough line radiated out from the indian monsoon trough region across indochina to the northern south china sea the monsoon onset occurred when the 30 60 day monsoon trough and the 12 24 day low center arrived simultaneously at the northern south china sea close to the climatological summer trough line in the middle of may the breaks occurred when the 30 60 day monsoon ridge lines and the 12 24 day high center met near 15 20 n in the northern south china sea the south china sea monsoon wa

the formation mechanism of the bonin high in august the bonin high is a subtropical anticyclone that is predominant near japan in the summer this anticyclone is associated with an equivalent barotropic structure often extending throughout the entire troposphere although the equivalent barotropic structure of the bonin high has been known for years among synopticians because of its importance to the summer climate in east asia there are few dynamical explanations for such a structure the present paper attempts to provide a formation mechanism for the deep ridge near japan we propose a new hypothesis that this equivalent barotropic ridge near japan is formed as a result of the propagation of stationary rossby waves along the asian jet in the upper troposphere the silk road pattern first the monthly mean climatology is examined in order to demonstrate this hypothesis it is shown that the enhanced asian jet in august is favourable for the propagation of stationary rossby waves and that the regions of descent over the eastern mediterranean sea and the aral sea act as two major wave sources second a primitive equation model is used to simulate the climatology of august the model successfully simulates the bonin high with an equivalent barotropic structure the upper tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hpa when a wave packet arrives sensitivity experiments are conducted to show that the removal of the diabatic cooling over the asian jet suppresses the silk road pattern and formation of an equivalent barotropic ridge near japan while the removal of the diabatic heating in the western pacific does not copyright 2003 royal meteorological society

characteristics and mechanisms of the subseasonal eastward extension of the south asian high abstractthis study investigates the features of eastward extension of the south asian high sah and its connection with diabatic heating and rainfall over eastern asia on subseasonal time scales the causes of sah s eastward extension are examined by potential vorticity pv diagnosis with emphasis on the joint role of diabatic heating feedback and midlatitude wave train the sah s eastward extension features eastward propagation of a wave train across eurasia among the wave train the migration of weak high from the western flank of the tibetan plateau tp to the east of tp contributes to the sah s eastward extension at the early stage when the sah approaches its easternmost position a strong negative pv positive geopotential height center prevails to the east of the tp at 200 hpa the associated anomalies in diabatic heating and rainfall include the anomalous heating and above normal rainfall over the south china sea scs and subtropical western pacific occurring 12 days before the sah s eastern

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

quasi biweekly oscillation over the tibetan plateau and its link with the asian summer monsoon abstract intraseasonal variation isv is especially prominent and unique in the asian summer monsoon region in this work the dominant isv mode over the tibetan plateau tp in the summer monsoon season june august together with its structure and evolution is identified using station observations global precipitation climatology project precipitation data and era interim during 1979 2011 results indicate that quasi biweekly oscillation qbwo is the dominant mode of isv over the tp and is significant in terms of the circulation precipitation and diabatic heating fields in particular the qbwo is closely related to the onset and active break phases of the tp summer monsoon in most cases the qbwo originates from the equatorial western pacific and first propagates northwestward to the bay of bengal and northern india then northward to the southeastern tp and finally eastward to the east asian area showing a clockwise propagation pathway two main mechanisms are responsible for the northward

subseasonal zonal variability of the western pacific subtropical high in summer climate impacts and underlying mechanisms the zonal oscillation of the western pacific subtropical high wpsh significantly influences the weather and climate over east asia this study investigates characteristics and mechanisms of the zonal variability of the wpsh on subseasonal time scales during summer by using a subseasonal wpsh sub wpsh index accompanied with the sub wpsh index strong anticyclonic cyclonic anomalies are found over east asia and coastal region south of 30 n on both 850 hpa and 500 hpa during the positive period of the sub wpsh index the wpsh extends more westward with enhanced precipitation over the yangtze huaihe river basin and suppressed precipitation over the south of the yangtze river in china these precipitation anomalies can last for at least 1 week while the subseasonal zonal variability of the wpsh is found to be closely associated with atmospheric teleconnections and local air sea interaction the mechanisms of the variability are different before and after mid july early and late summer in both early and late summer the east asia pacific eap wave train pattern affects the zonal shift of the wpsh by inducing a low level anomalous anticyclonic cyclonic circulation over the subtropical western pacific and this mechanism is stronger in late summer in constrast the influence of the silk road pattern wave train is more important in the early summer meanwhile in late summer a stronger sst forcing on the atmosphere and a faster cycle of subseasonal variations of the wpsh are observed before the westward stretch of the wpsh which could be related to the colder local sst anomalies the westward stretch of the wpsh is accompanied by stronger anticyclonic anomalies in late summer

tropical cyclone movement and surrounding flow relationships abstract this paper presents results of a comprehensive study of the relationship between the movement of tropical cyclones and the large scale circulation which surrounds them cyclones have been stratified by direction and speed of movement latitude intensity change and size as determined by the radius of the outermost closed surface isobar in three ocean basins the northwest pacific the west atlantic and the australian south pacific region twenty one different stratifications are available in the northwest pacific 13 in the west atlantic and 6 in the australian south pacific area cyclone movement and surrounding flow relationships were studied at different pressure levels and a variety of radii pressure weighted layer averages were also analyzed in search of such relationships results show an important relationship between surrounding large scale flow and tropical cyclone movement for all stratifications the winds in the mid troposphere 500 700 mb at 5 7 latitude radius from the cyclone

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

multi stage onset of the summer monsoon over the western north pacific the climatological summer monsoon onset displays a distinct step wise northeastward movement over the south china sea and the western north pacific wnp 110 160 e 10 20 n monsoon rain commences over the south china sea philippines region in mid may extends abruptly to the southwestern philippine sea in early to mid june and finally penetrates to the northeastern part of the domain around mid july in association three abrupt changes are identified in the atmospheric circulation specifically the wnp subtropical high displays a sudden eastward retreat or quick northward displacement and the monsoon trough pushes abruptly eastward or northeastward at the onset of the three stages the step wise movement of the onset results from the slow northeastward seasonal evolution of large scale circulation and the phase locked intraseasonal oscillation iso the seasonal evolution establishes a large scale background for the development of convection and the iso triggers deep convection the iso over the wnp has a dominant period of about 20 30 days this determines up the time interval between the consecutive stages of the monsoon onset from the atmospheric perspective the seasonal sea surface temperature sst change in the wnp plays a critical role in the northeastward advance of the onset the seasonal northeastward march of the warmest sst tongue sst exceeding 29 5 c favors the northeastward movement of the monsoon trough and the high convective instability region the seasonal sst change in turn is affected by the monsoon through cloud radiation and wind evaporation feedbacks

low frequency equatorial waves in vertically sheared zonal flow part i stable waves abstract the mechanism by which a vertically sheared zonal flow affects large scale low frequency equatorial waves is investigated with two level equatorial plane and spherical coordinates models vertical shears couple barolinic and barotropic components of equatorial wave motion affecting significantly the rossby wave and westward propagating yanai wave but not the kelvin wave this difference results from the fact that the barotropic component is a modified rossby mode and can be resonantly excited only by westward propagating internal waves the barotropic components emanate poleward into the extratropics with a pronounced amplitude while the baroclinic components remain equatorially trapped a westerly vertical shear favors the trapping of rossby and yanai waves in the upper troposphere whereas an easterly shear tends to confine them in the lower troposphere as such their westward propagation is slowed down by both westerly and easterly shears when the strength of the vertical shear varies w

active break cycles diagnosis of the intraseasonal variability of the asian summer monsoon in this study various diagnostics have been applied to daily observed outgoing longwave radiation olr and ecmwf reanalysis era products to provide a comprehensive description of the active break cycles associated with the asian summer monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability 10 20 days and 30 60 days composite analysis of olr based on filtered daily all india rainfall air for the 40 day 30 60 days intraseasonal mode indicates that during active phases convection is significantly enhanced over the indian continent extending over the bay of bengal maritime continent and equatorial west pacific while convection is suppressed over the equatorial indian ocean and northwest tropical pacific resulting in a quadrapole structure over the asian monsoon domain in response to this heating pattern the large scale hadley lateral and the two east west transverse tropical circulations are enhanced there is also a significant impact on the extra tropical circulation through excitation and propagation of rossby waves in contrast the 15 day mode is more regional to the monsoon domain and has a prominent east west orientation in convection only the local hadley circulation over the monsoon region is modulated by this mode the evolution of these two modes as revealed by pop principal oscillation pattern analysis shows that the 40 day mode originates over the equatorial indian ocean once formed it has poleward propagation on either side of the equator and eastward propagation into the equatorial west pacific from the equatorial west pacific northward propagation over the west pacific and westward propagation into the indian longitudes are prominent the propagative features are complex and interactive and are responsible for the quadrapole structure in convection seen from the composites the interannual variability assessed from the pop coefficient time series indicates that the 40 day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic tcz tropical convergence zone the pop analysis of the 15 day mode indicates that this event originates over the equatorial west pacific associated with westward propagating rossby waves amplifies over the northwest tropical pacific and modulates both the continental and oceanic tczs over indian longitudes simultaneously this mode is pronounced during the established phase of the monsoon due to the complexity in the propagational features of both the intraseasonal modes it is concluded that understanding the subseasonal variability of one regional component of the asian summer monsoon asm requires understanding the entire asm system

quasi biweekly oscillation of the asian monsoon rainfall in late summer and autumn different types of structure and propagation this study contrasts two types of quasi biweekly oscillations qbwos over tropical asia in late summer and autumn from august to october using a tracking method to calculate the frequency of qbwo events over the asian monsoon region two types of qbwos in monsoon rainfall are revealed one originates from 110 to 140 e and propagates westward to southern china with a notable impact on the regional rainfall while the other initiates from 160 e to the dateline and does not affect southern china rainfall significantly analysis of the vertical structure of moisture flux shows that the moisture source for type 1 events is dominated by the zonal flux component and that for type 2 the meridional flux component the nature of the moisture flux determines whether the oscillation can propagate across 120 e and affect rainfall over southern china results also show that the strength of the south asian high and the western pacific subtropical high differently modulate the generation of the two types of qbwos specifically mutually stronger weaker highs favor the first second type of the oscillation a close relationship also exists between the qbwos and western pacific sea surface temperature sst anomalies suggesting that the sst anomalies can potentially trigger the qbwos

interaction between the summer monsoons in east asia and the south china sea intraseasonal monsoon modes abstract the summer monsoons in east and southeast asia are characterized respectively by the mei yu in eastern china baiu in japan front mbf and by the monsoon trough stretching from northern indochina to the philippine sea these two major monsoon elements are separated by the north pacific anticyclone as indicated by the 850 mb zonal wind and cumulus convection over some key areas a distinct opposite phase intraseasonal variation exists between the two monsoon elements two approaches are adopted to explore the cause of this opposite phase variation which reflects the coupling between the two monsoon components 1 the correlation coefficient patterns between the 850 mb zonal wind monsoon index and the 850 mb streamfunction field and 2 the composite 850 mb streamline charts and the 120 e zonal wind cross sections it is shown that the opposite phase variation between the two monsoon elements is caused by the anomalous circulation associated with the northward migrating 30 60 day monsoon tr

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

zonal oscillation of western pacific subtropical high and subseasonal sst variations during yangtze persistent heavy rainfall events abstractthis study examines the relationship between the zonal oscillation of the western pacific subtropical high wpsh and underneath sea surface temperature sst variation on a subseasonal time scale associated with the persistent heavy rainfall phr events over the middle and lower reaches of the yangtze river valley mlyrv in china a total of 76 phr events and 45 break events in the summers of 1979 2011 are first identified over the mlyrv and divided into early and late summer groups during the phr events over the mlyrv for both groups the wpsh stretches more westward accompanied by the positive anomalies of the 500 hpa geopotential height field over east asia and its coastal region south of 30 n and the subseasonal warmer ssts beneath the wpsh western edge the time lagged composites suggest that the wpsh western edge exhibits westward then eastward migration on a subseasonal time scale for the phr events the zonal changes of the wpsh and anomalous circulation and sst anomaly ssta signal

the intraseasonal oscillation of eastern tibetan plateau precipitation in response to the summer eurasian wave train abstractthis study examines the characteristics and mechanisms associated with the dominant intraseasonal oscillation iso that controlled eastern tibetan plateau summer rainfall etpsr over the period 1979 2011 the results of both power and wavelet spectrum analysis reveal that etpsr follows a significant 7 20 day oscillation during most summers the vertical structure of the etpsr iso in the dry phase is characterized by a vertical dipole pattern of geopotential height with a positive center on the eastern tibetan plateau tp and a negative center on the western tp the wet phase shows the opposite characteristics to the dry phase the transitions between the dry and wet phases during an etpsr iso cycle are related to a rossby wave train that presents as large anomalous anticyclonic and cyclonic centers that alternate along the pathway from the eastern atlantic to southern china via the tp it corresponds to the evolution of the phase independent wave activity w which implies an eastward southeastw

intraseasonal variability of the south china sea summer monsoon the objective of this study is to explore based on the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data the intraseasonal variability of the south china sea scs summer monsoon sm in terms of its structure and propagation as well as interannual variations a possible mechanism that is responsible for the origin of the 10 20 day oscillation of the scs sm is also proposed the 30 60 day hereafter the 3 6 mode and 10 20 day hereafter the 1 2 mode oscillations are found to be the two intraseasonal modes that control the behavior of the scssm activities for most of the years both the 3 6 and 1 2 modes are distinct but may not always exist simultaneously in a particular year and their contributions to the overall variations differ among different years thus the interannual variability in the intraseasonal oscillation activity of the scs sm may be categorized as follows the 3 6 category in which the 3 6 mode is more significant in terms of the percentage of variance explained than the 1 2 mode the 1 2 category in which the 1 2 mode is dominant and the dual category in which both the 3 6 and 1 2 modes are pronounced composite analyses of the 3 6 category cases indicate that the 30 60 day oscillation of the scs sm exhibits a trough ridge seesaw in which the monsoon trough and subtropical ridge exist alternatively over the scs with anomalous cyclones anticyclones along with enhanced suppressed convection migrating northward from the equator to the midlatitudes the northward migrating 3 6 mode monsoon trough ridge in the lower troposphere is coupled with the eastward propagating 3 6 mode divergence convergence in the upper troposphere it is also found that for the years in the dual category the scs sm activities are basically controlled by the 3 6 mode but modified by the 1 2 mode composite results of the 1 2 mode category cases show that the 10 20 day oscillation is manifest as an anticyclone cyclone system over the western tropical pacific propagating northwestward into the scs a close coupling also exists between the upper level convergence divergence and the low level anticyclone cyclone it is found that the 1 2 mode of the scs sm mainly originates from the equatorial central pacific although a disturbance from the northeast of the scs also contributes to this mode the flow patterns from an inactive to an active period resemble those associated with a mixed rossby gravity wave observed in previous studies

landscape analysis of the huang he headwaters ne tibetan plateau patterns of glacial and fluvial erosion the large scale geomorphology of the huang he yellow river headwaters centered around the bayan har shan 5267 m asl in the northeastern part of the tibetan plateau is dominated by an uplifted

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

the effects of midlatitude waves over and around the tibetan plateau on submonthly variability of the east asian summer monsoon abstract convective variability at submonthly time scales 7 25 days over the yangtze and huaihe river basins yhrbs and associated large scale atmospheric circulation during the mei yu season were examined using interpolated outgoing longwave radiation olr and ncep ncar reanalysis data for 12 yr having active submonthly convective fluctuation over the yhrbs within the period 1979 2004 correlations between convection anomalies over the yhrbs and upper level streamfunction anomalies at every grid point show two contrasting patterns one pattern exhibits high correlations along the northern to eastern peripheries of the tibetan plateau defined as the net pattern whereas the other has high correlations across the tibetan plateau defined as the at pattern composite analysis of the net pattern shows slow southward migration of convection anomalies from the northeastern periphery of the tibetan plateau to southern china in relation to southward migration of the mei yu front caused by simultaneous am

intraseasonal variations of the yangtze rainfall and its related atmospheric circulation features during the 1991 summer the intraseasonal variations of the yangtze rainfall over eastern china and its related atmospheric circulation characteristics during the 1991 summer are examined based on the gauge observed rainfall and the ncep ncar reanalysis data wavelet analysis shows that during the 1991 summer the active and break sequences of rainfall over the middle and lower yangtze basin are mainly regulated by an oscillatory mode with a period of 15 35 days an investigation of the circulation features suggests that the 15 35 day oscillation is associated with an anomalous low level cyclone anticyclone appearing alternatively over the northern south china sea scs and the philippine sea and related to a northeastward southwestward shift of the western pacific subtropical anticyclone over the scs leading to a lower tropospheric divergence convergence over the yangtze basin in the upper troposphere the 15 35 day oscillation exhibits a dipole anomaly characterized by an anomalous cyclone anticyclone over eastern china and an anomalous anticyclone cyclone over the northern tibetan plateau resulting in a southwestward shrinking northeastward extending of the south asian anticyclone and forming a convergence divergence over eastern china such a coupled anomalous flow pattern between the lower and upper troposphere favors large scale descending ascending motion and hence reduced enhanced rainfall over the yangtze basin dynamically the intraseasonal variations in the yangtze rainfall are mainly determined by the coupling between the low level relative vorticity and the upper level divergence in the middle troposphere the 15 35 day oscillation of the subtropical high is originated over the central north pacific north of hawaii then propagates westward to the scs philippine sea and finally modulates the intraseasonal variations of the yangtze rainfall

anticorrelated intensity change of the quasi biweekly and 30 50 day oscillations over the south china sea 1 over the south china sea the year to year variations in the intensity of the quasi biweekly qbw and 30 50 day oscillations during june july are anti correlated an explanation is offered for the out of phase relationship we found during strong qbw years the june july mean convection and easterly vertical shear are enhanced over the equatorial western central pacific with corresponding low level cyclonic meridional shear to the northwest these conditions concurring with the equatorial eastern pacific warming are favorable for emanation of moist rossby waves from the equatorial western pacific on the other hand the 30 50 day becomes active when the mean convection is enhanced over the eastern indian ocean and maritime continent where this mode stems from and develops which often corresponds to cold western io one of these two large scale settings often occurs in the absence of the other so that when one mode is strong during june july the other mode tends to be weak

20 50 day oscillation of summer yangtze rainfall in response to intraseasonal variations in the subtropical high over the western north pacific and south china sea the spatio temporal variability in summer rainfall within eastern china is identified based on empirical orthogonal function eof analysis of daily rain gauge precipitation data for the period 1979 2003 spatial coherence of rainfall is found in the yangtze basin and a wavelet transform is applied to the corresponding principal component to capture the intraseasonal oscillation iso of yangtze rainfall the ensemble mean wavelet spectrum representing statistically significant intraseasonal variability shows a predominant oscillation in summer yangtze rainfall with a period of 20 50 days a 10 20 day oscillation is pronounced during june and july this finding suggests that the 20 50 day oscillation is a major agent in regulating summer yangtze rainfall composite analyses reveal that the 20 50 day oscillation of summer yangtze rainfall arises in response to intraseasonal variations in the western north pacific subtropical high wnpsh which in turn is modulated by a rossby wave like coupled circulation convection system that propagates northward and northwestward from the equatorial western pacific when an anomalous cyclone associated with this rossby wave like system reaches the south china sea scs and philippine sea the wnpsh retreats northeastward due to a reduction in local pressure under these conditions strong monsoonal southwesterlies blow mainly toward the scs philippine sea while dry conditions form in the yangtze basin with a pronounced divergent flow pattern in contrast the movement of an anomalous anticyclone over the scs philippine sea results in the southwestward extension of the wnpsh consequently the tropical monsoonal southwesterlies veer to the northeast over the scs and then converge toward the yangtze basin producing wet conditions therefore the 20 50 day oscillation of yangtze rainfall is also manifest as a seesaw pattern in convective anomalies between the yangtze basin and the scs philippine sea a considerable zonal shift in the wnpsh is associated with extreme dry wet episodes in the yangtze basin with an abrupt eastward westward shift in the wnpsh generally leading the extreme negative positive yangtze rainfall anomaly by a 3 8 period of the 20 50 day oscillation this finding may have implications for improving extended range weather forecasting in the yangtze basin

subseasonal intensity variation of the south asian high in relationship to diabatic heating observation and cmip5 models this study investigates the subseasonal intensity variation of south asian high sah and the dynamic linkage with precipitation induced diabatic heating during the summer of 1979 2005 based on the observation and 18 models from the coupled model intercomparison project cmip5 the sah s intensity variation with a period of approximately 10 36 days is identified both in the observation and 18 models by performing an empirical orthogonal function eof analysis on the standardized subseasonal anomalies in geopotential height at 100 hpa over the sah s main body region with the observed strengthening of the sah an enhanced rainfall belt between 70 120 e migrates northward from the equatorial region the northward propagating rainfall belt occupies almost the whole indian subcontinent indochina peninsula and subtropical east asian regions between 20 40 n when the sah reaches the strongest the relative vorticity diagnosis reveals the dynamical linkage between the subseasonal sah s intensity variation and the precipitation anomalies over the asian monsoon region 1 the observed northward propagating rainfall band forms a horizontal gradient of diabatic heating favoring an enhancement of the sah over its southern part 2 when the rainfall band approaches the regions of south and east asia between 20 40 n the increased vertical gradient of diabatic heating in the upper level contributes significantly to the intensification of the sah 3 the horizontal advection process favors the westward expansion of the sah the observation to model comparisons indicate that the model s capacity to reproduce the sah s intensity variation is highly associated with simulations of the anomalous rainfall band and its northward propagation a realistic reproduction of precipitation anomalies is fundamental to simulating the dynamical processes related to diabatic heating and thus the simulation of the sah s subseasonal intensity variation

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

results from the ice sheet model intercomparison project heinrich event intercomparison ismip heino results from the heinrich event intercomparison heino topic of the ice sheet model intercomparison project ismip are presented ismip heino was designed to explore internal large scale ice sheet instabilities in different contemporary ice sheet models these instabilities are of interest because they are a possible cause of heinrich events a simplified geometry experiment reproduces the main characteristics of the laurentide ice sheet including the sedimented region over hudson bay and hudson strait the model experiments include a standard run plus seven variations nine dynamic thermodynamic ice sheet models were investigated one of these models contains a combination of the shallow shelf ssa and shallow ice approximation sia while the remaining eight models are of sia type only seven models including the sia ssa model exhibit oscillatory surges with a period of 1000 years for a broad range of parameters while two models remain in a permanent state of streaming for most parameter settings in a number of models the oscillations disappear for high surface temperatures strong snowfall and small sediment sliding parameters in turn low surface temperatures and low snowfall are favourable for the ice surge cycles we conclude that further improvement of ice sheet models is crucial for adequate robust simulations of cyclic large scale instabilities

paleoglaciological reconstructions for the tibetan plateau during the last glacial cycle evaluating numerical ice sheet simulations driven by gcm ensembles abstract the tibetan plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate however the glacial history of the tibetan plateau is more poorly constrained than that of most other formerly glaciated regions such as in north america and eurasia on the basis of some field evidence it has been hypothesized that the tibetan plateau was covered by an ice sheet during the last glacial maximum lgm abundant field and chronological evidence for a predominance of local valley glaciation during the past 300 000 calendar years that is 300 ka coupled to an absence of glacial landforms and sediments in extensive areas of the plateau now refute this concept this furthermore calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence surprisingly the robustness of such numerical ice sheet model results has not been widely queried despite potentially important climate ramifications we simulated the growth and decay of ice on the tibetan plateau during the last 125 ka in response to a large ensemble of climate forcings 90 members derived from global circulation models gcms using a similar 3d thermomechanical ice sheet model as employed in previous studies the numerical results include as extreme end members as an ice free tibetan plateau and a plateau scale ice sheet comparable in volume to the contemporary greenland ice sheet we further demonstrate that numerical simulations that acceptably conform to published reconstructions of quaternary ice extent on the tibetan plateau cannot be achieved with the employed stand alone ice sheet model when merely forced by paleoclimates derived from currently available gcms progress is however expected if future investigations employ ice sheet models with higher resolution bidirectional ice sheet atmosphere feedbacks improved treatment of the surface mass balance and regional climate data and climate reconstructions

event based extreme precipitation in central eastern china large scale anomalies and teleconnections event based extreme precipitation eep defined as an extreme precipitation event no less than 1 mm for continuous days having at least one daily precipitation exceeding the 90th percentile are categorized into three types according to the time distribution pattern tdp of extreme precipitation daily intense precipitation appearing only at the first half of event tdp1 at both the first and second halves tdp2 and only at the second half of event tdp3 this study focuses on the tdp1 and tdp2 types which occur much more frequently in the central eastern china and investigates associated distinguishing large scale teleconnection patterns the tdp1 events dominantly occur in mid to late spring which are associated with the silk road pattern srp wave train manifested from western europe to northwest pacific along the subtropical westerly jet the tripolar sea surface temperature sst anomalous pattern over the north atlantic ocean i e low sst anomalies in the azores islands two high sst anomalies over the greenland and subtropical north atlantic are mainly attributed to force the srp wave meanwhile the enhanced northwestward moisture transport from the south china converges with the southeastward moisture transport related to the srp from the north china resulting in the tdp1 extreme precipitation events over the central eastern china the tdp2 events are closely conjunction with the meiyu precipitation in the yangtze huai river basin in summer during the tdp2 events the east asia pacific eap teleconnection is exhibited along the east asia coasts which is triggered by the anomalous convection in the western north pacific an anomalous anticyclone related to the eap teleconnection contributes to the westward stretch of the western pacific subtropical high providing significant enhanced moisture transportation toward the yangtze huai river basin correspondingly the meridional gradient of the equivalent potential temperature theta e is intensified and favored of forming meiyu front precipitation this study highlights the definition of eep event emphasizing the tdp of extreme precipitation and distinguished features of occurring seasons and large scale circulations associated with the two dominant types of eep events

how are heat waves over yangtze river valley associated with atmospheric quasi biweekly oscillation over yangtze river valley yrv where heat wave hw events most frequently occur in china during 1979 2014 30 out of 57 hw events nearly 55 in july and august is found to be related with the dry phases of atmospheric quasi biweekly oscillation qbwo when a significant low level anticyclonic anomaly laa associated with qbwo appears over yrv temperature rises sharply according to the adiabatic heating caused by subsidence and the enhanced downward solar radiation due to decreased clouds the laa with subsidence over yrv is primarily generated by quasi biweekly atmospheric waves which are classified to three types through case by case categorization named as mid latitude wavetrain wnp western north pacific wavetrain and double wavetrains respectively the mid latitude wavetrain qbwo causes the laa through subsidence induced by upper level cyclonic vorticity which is associated with an eastward southeastward migrating wave train from eastern europe to wnp in the upper troposphere the wnp wavetrain qbwo forms laa through a northwestward migrating lower tropospheric wave train emanating from tropical wnp to southeastern china the double wavetrains qbwo triggers laa through both the low level shear anticyclonic vorticity provided by a low level northwestward westward propagating wave train from tropical wnp to south china sea and the upper level positive vorticity associated with an eastward southeastward migrating wave train from eastern europe to southeastern china in the upper troposphere in all cases south asian high extends eastward and wnp subtropical high extends westward during hw events tracing these distinct precursory circulation anomalies may facilitate better understanding and short medium range forecast of hw

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

quaternary glaciation of gurla mandhata naimon anyi abstract the quaternary glaciation of gurla mandhata naimona nyi an impressive isolated dome shaped massif situated in a remote region of southern tibet was examined using glacial geomorphic methods and dated using 10 be terrestrial cosmogenic nuclides the oldest moraines representing an expanded ice cap that stretched 5 km into the foreland of the gurla mandhata massif likely formed during marine isotope stage mis 10 or an earlier glacial cycle another glacial expansion of coalescing piedmont type occurred during the early part of the last glacial cycle or the penultimate glacial cycle after which glaciers became restricted to entrenched valley types impressive latero frontal moraines at the mouths of most valleys date to the early part of the last glacial cycle and mis 3 a succession of six sets of moraines within the valleys and up to the contemporary glaciers show that glaciers advanced during the lateglacial early holocene neoglacial and possibly little ice age the change of style of glaciation throughout the latter part of the quaternary from expanded ice caps to deeply entrenched valley glaciers might reflect 1 climatic controls with reduced moisture supply to the region over time and or 2 tectonic controls reflecting increase basin subsidence due to detachment faulting and enhanced valley incision

characterizing two types of transient intraseasonal oscillations in the eastern tibetan plateau summer rainfall during summer the intraseasonal disturbances over the eastern tibetan plateau etp can initiate development of severe weather system downstream previous studies yielded inconsistent results on the intraseasonal variability isv of summer rainfall in terms of periodicity genesis process and propagation pathway over the ept based on small samples in this study we detected two dominant peaks of transient isv centered on quasi biweekly 12 24 days qbw and quasi 9 8 11 days using daily rainfall data over the etp during the period of 1992 2012 composite analysis revealed that the two isvs were predominantly associated with the non stationary wave trains which traveled along different pathways for the qbw its mid latitude wave train featured a upper level southeastward migration originating in northern europe and traveling via the east european plain the ural mountains lake balkhash lake baikal the mongolian plateau and then continued southward to the etp and south asia and its tropical wave train was characterized with a northwestward northward migration in low level starting from the philippine sea ps south china sea scs region moving over northern bay of bengal scs region and arriving over the southern fridge of tp and southern china in contrast for quasi 9 day the most significant mid latitudes variability featured an eastward propagating upper level wave train originating from western europe passing across the mediterranean the black and caspian seas arriving over the tp and moving towards east asia and the most evident tropical variability exhibited a clear northwestward westward migration of a low level wave train originating from ps passing over taiwan and subsequently moving towards southeastern china their different spatiotemporal features of associated wave trains caused their distinct linkages with eastern china rainfall anomalies a meridional pattern with a giant ural mountain ridge was the most remarkable precursory signals in upstream region before the qbw wet phase occurrence which was different from the quasi 9 day the major processes generating the local wet spells for the two modes were commonly linked to the preceding boundary warming the upper level negative vorticity and low level prevalent winds which triggered the ascending anomaly and lower tropospheric pre moistening we also discussed the co variation of the wave trains between mid latitudes and low latitudes the distinct evolution related with the two isvs over the etp described here may provide a useful guidance for 2 3 weeks extended range forecasts over the etp and its downstream regions

the eismint benchmarks for testing ice sheet models we present a series of benchmark experiments designed for testing and comparing numerical ice sheet models following the outcome of two eismintworkshops organized to intercompare large scale ice sheet models currently in operation model benchmark experiments are described for ice sheets underfixed and moving margin conditions these address both steady state and time dependent behavior under schematic boundary conditions and with prescribedphysics a comparison was made of each model s prediction of basic geophysical variables such as ice thickness velocity and temperature consensusachieved in the model intercomparison provides reference solutions against which the accuracy and consistency of ice sheet modeling codes can be assessed

coordinated influences of the tropical and extratropical intraseasonal oscillations on the 10 30 day variability of the summer rainfall over southeastern china this study explores the spatial variations and physical mechanisms of 10 30 day rainfall anomalies over southeastern china based on daily station observed rainfall data for the period 1979 2015 empirical orthogonal function analysis shows that the dominant spatial distribution of 10 30 day rainfall anomalies is a monopole pattern over the south of the middle and lower reaches of the yangtze river valley smly lead lag composites reveal that the evolution of such a monopole pattern depends on the coordinated influences of 10 30 day atmospheric intraseasonal oscillations isos from the tropics and mid high latitudes in the upper troposphere the southeastward propagating rossby wave train from the mid high latitudes which presents as anomalous anticyclones and cyclones alternating over eastern europe to southeastern coastal area of china induces strong ascents descents over the smly via vorticity advection circulation anomalies associated with tropical iso over east asia western north pacific trigger a vertical cell with strong updraft downdraft over the smly and downdraft updraft to the south further enhancing the ascents descents over the smly forming the wet dry phases of 10 30 day rainfall anomalies moreover due to the meridional non uniformity of iso related diabatic heating along the indian ocean longitudes an anticyclone cyclone is generated over the central indian northern bay of bengal which tends to anchor the anomalous ascents descents over the smly through its interaction with the intraseasonal rossby wave from mid high latitudes thus favoring the persistence of wet dry phases of the 10 30 day smly rainfall anomalies

intraseasonal teleconnection between the summer eurasian wave train and the indian monsoon this study investigated the most recurrent coupled pattern of intraseasonal variability between midlatitude circulation and the indian summer monsoon ism the leading singular vector decomposition svd pattern reveals a significant coupled intraseasonal variation between a rossby wave train across the eurasian continent and the summer monsoon convection in northwestern india and pakistan hereafter referred to as nism the wave train associated with an active phase of nism rainfall displays two high pressure anomalies one located over central asia and the other over northeastern asia they are accompanied by increased rainfall over the western siberia plain and northern china and decreased rainfall over the eastern mediterranean sea and southern japan the circulation of the wave train shows a barotropic structure everywhere except the anomalous central asian high located to the northwest of india where a heat induced baroclinic circulation structure dominates the time lagged svd analysis shows that the midlatitude wave train originates from the northeastern atlantic and traverses europe to central asia the wave train enhances the upper level high pressure and reinforces the convection over the nism region meanwhile it propagates farther toward east asia along the waveguide provided by the westerly jet after an outbreak of nism convection the anomalous central asian high retreats westward composite analysis suggests a coupling between the central asian high and the convective fluctuation in the nism the significance of the midlatitude ism interaction is also revealed by the close resemblance between the individual empirical orthogonal functions and the coupled svd modes of the midlatitude circulation and the ism it is hypothesized that the eastward and southward propagation of the wave train originating from the northeastern atlantic contributes to the intraseasonal variability in the nism by changing the intensity of the monsoonal easterly vertical shear and its associated moist dynamic instability on the other hand the rainfall variations over the nism reinforce the variations of the central asian high through the monsoon desert mechanism thus reenergizing the downstream propagation of the wave train the coupling between the eurasian wave train and nism may be instrumental for understanding their interaction and can provide a way to predict the intraseasonal variations of the indian summer monsoon and east asian summer monsoon

characteristics and origin of quasi biweekly oscillation over the western north pacific during boreal summer 1 this study investigates the structure energetic and origin of quasi biweekly oscillation qbwo over the western north pacific wnp using ncep reanalyses for the years 2000 2007 in the context of vorticity there appears to be a significant qbwo mode over the wnp during the summer qbwo emerges from the equatorial region and propagates northwestward its horizontal structure exhibits a slight southwest northeast tilt but mainly longitudinal elongation in the vertical the qbwo has a northwest tilt with height that gives rise to a structure of the first baroclinic mode the centers of vorticity and vertical motion near the equator show a phase lag of about one quarter wavelength consistent with the characteristics of equatorial waves whereas the cyclonic circulation is tightly coupled with anomalous convection as the wave moves away from the equator energetic analysis of the qbwo reveals that diabatic heating in the tropics and baroclinic processes in the subtropics play important roles in the generation of eddy available potential energy eape in turn the conversion from eape to eddy kinetic energy eke and the barotropic conversion are major sources for eke to compensate the loss by eke redistribution and dissipation tracing the qbwo to equatorial disturbances our results show some features of equatorially trapped n 1 rossby mode such as phase speed and group velocity this mode is generally characterized by a zonal planetary wave number of about 6 and nearly symmetric circulation about the equator a typical case from 2002 is chosen to illustrate that the origin of the qbwo is closely associated with the theoretical equatorial rossby wave

biweekly and 21 30 day variations of the subtropical summer monsoon rainfall over the lower reach of the yangtze river basin abstract the lower reach of the yangtze river basin lyrb is located at the central region of the mei yu and baiu front which represents the subtropical east asian ea summer monsoon based on the newly released daily rainfall data two dominant intraseasonal variation isv modes are identified over the lyrb during boreal summer may august with spectral peaks occurring on day 15 the biweekly mode and day 24 the 21 30 day mode these two modes have comparable intensities and together they account for above about 57 of the total intraseasonal variance both isv modes exhibit baroclinic structures over the lyrb at their extreme phases however the genesis and evolutions associated with the two modes are different considering the genesis of their extreme wet phases over the lyrb the biweekly mode is initiated by a midlatitude jet stream vorticity anomaly moving southeastward while the 21 30 day mode is primarily associated with a low level westward propagation of an anticyclonic anomaly from

ice the paradigm of wild plasticity ice plasticity has been thoroughly studied owing to its importance in glaciers and ice sheets dynamics in particular its anisotropy easy basal slip has been suspected for a long time then fully characterized 40 years ago more recently emerged the interest of ice as a model material to study some fundamental aspects of crystalline plasticity an example is the nature of plastic fluctuations and collective dislocation dynamics twenty years ago acoustic emission measurements performed during the deformation of ice single crystals revealed that plastic flow proceeds through intermittent dislocation avalanches power law distributed in size and energy this means that most of ice plasticity takes place through few very large avalanches thus qualifying associated plastic fluctuations as wild this launched an intense research activity on plastic intermittency in the material science community the interest of ice in this debate is reviewed from a comparison with other crystalline materials in this context ice appears as an extreme case of plastic intermittency characterized by scale free fluctuations complex space and time correlations as well as avalanche triggering in other words ice can be considered as the paradigm of wild plasticity

structure genesis and scale selection of the tropical quasi biweekly mode the quasi biweekly mode qbm and the 30 60 day mode are two major intraseasonal oscillations isos in the tropics the qbm is known to have a major influence in determining the active and break conditions of the indian monsoon during the northern summer a westward propagating equatorial rossby wave with quasi biweekly period influences the australian monsoon during the northern winter universality between the summer and winter qbm is established through analysis of daily circulation and convection data for 10 years it is shown that the mean spatial structure of the qbm in circulation and convection resembles that of a gravest meridional mode equatorial rossby wave with wavelength of about 6000 km and westward phase speed of approximately 4 5 m s 1 however the maximum zonal wind occurs at around 5 n 5 s during the northern summer winter the wave structure appears to be translated northward southward by about 5 during the northern summer winter the relationship between outgoing long wave radiation and circulation data indicates that the mode is driven unstable by coupling with moist convection similarity in temporal and spatial characteristics of the mode during the two seasons leads us to propose that the same mechanism governs the genesis and scale selection of the mode in both the seasons an acceptable mechanism for genesis and scale selection of the qbm has been lacking in the present study a mechanism for genesis and scale selection of the observed qbm is proposed a simple 2 layer model that includes a steady ekman boundary layer bl formulation incorporating effect of entrainment mixing is constructed for the convectively coupled equatorial waves without influence of the background mean flow moist feedback in the presence of frictional bl convergence drives the gravest meridional mode equatorial rossby wave unstable with observed wavelength and period but with zonal winds symmetric about the equator potential temperature perturbation associated with the rossby wave is in phase with relative vorticity perturbation at low level the bl drives moisture convergence in phase with the relative vorticity at the top of the bl release of latent heat associated with the bl convergence enhances the potential temperature leading to a positive feedback the mean flow over the indian ocean and western pacific at low levels is such that the zero ambient absolute vorticity or the dynamic equator shifts to around 5 n 5 s during summer winter and results in a shift of the unstable rossby waves towards the north south by about 5 the resulting structure of the unstable rossby mode resembles the observed structure of the biweekly mode it is shown that neither evaporation wind feedback nor vertical shear of the mean flow is crucial for the existence of the mode however these processes marginally modify the growth rate and make the structure of the unstable wave more realistic