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

a diabatically driven mesoscale vortex in the lee of the tibetan plateau abstract an analysis of a diabatically driven and long lived midtropospheric vortex in the lee of the tibetan plateau during 24 27 june 1987 is presented the large scale conditions were characterized by the westward expansion of the 500 mb western pacific subtropical high and the amplification of a trough in the lee of the plateau embedded within the lee trough three mesoscale convective systems mcss developed a vortex emerged following the dissipation of one mcs with its strongest circulation located in the 400 500 mb layer low level warm advection and surface sensible and latent heating contributed to the convective initiation weak wind and weak ambient vorticity conditions inside the lee trough provided a favorable environment for these mcss and the vortex to develop and evolve the organized vortex circulation featured a coherent core of cyclonic vorticity extending from near the surface to 300 mb with virtually no vertical tilt the air in the vicinity of the vortex was very moist and the

a numerical sensitivity study of the influence of siberian snow on the northern annular mode abstractthe climate version of the general circulation model action de recherche petite echelle grande echelle arpege climat is used to explore the relationship between the autumn siberian snow and the subsequent winter northern annular mode by imposing snow anomalies over siberia as the model presents some biases in the representation of the polar vortex a nudging methodology is used to obtain a more realistic but still interactive extratropical stratosphere in the model free and nudged sensitivity experiments are compared to discuss the dependence of the results on the northern stratosphere climatology for each experiment a positive snow mass anomaly imposed from october to march over siberia leads to significant impacts on the winter atmospheric circulation in the extratropics in line with previous studies the model response resembles the negative phase of the arctic oscillation the well documented stratospheric pathway between snow and the arctic oscillation operates in the nudged experiment

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

impacts of northern tibetan plateau on east asian summer rainfall via modulating midlatitude transient eddies roles of the tibetan plateau tp in forming and changing the seasonal asian climate system have been widely explored however little is known about modulation effects of the tp on extratropical transient eddies tes and subsequent synoptic responses of the east asian rainfall in this study the community atmospheres model version 5 1 coupled with a slab ocean model is employed to highlight the important role of the tp in regulating the upper tropospheric transient wave train comparison between sensitivity experiments with and without the tp shows that the northern tp excites a strong anomalous anticyclone which shifts the upper level east asian westerly jet northward and helps transfer barotropic and baroclinic energy from the mean flow to the synoptic te flow the transient wave train is primarily shifted northward by northern tp and is forced to propagate southeastward along the eastern flank of the tp until reaching eastern china before the strengthening of monsoonal southerlies the tp modulated transient wave train cools the troposphere which decreases the static stability over northern china meanwhile the associated anomalous warm advection induces ascending motion leading to excessive rainfall by releasing unstable energy as the southerly strengthens due to the southeastward propagation of the wave train anomalous heavy rainfall subsequently appears over eastern china from north to south which increases day to day rainfall variation in this region additionally occurrence of this upper tropospheric transient wave train associated with low level southerly peak is substantially increased by northern tp

the tropical extratropical interaction between high frequency transients and the madden julian oscillation abstract the interaction between high frequency transient disturbances and convection and the madden julian oscillation mjo is investigated using ncep ncar reanalysis and satellite outgoing longwave radiation data for 15 northern winters during the phase of the mjo with enhanced convection over the east indian ocean and indonesia and suppressed convection over the south pacific convergence zone both the asian pacific jet and the region of upper tropospheric tropical easterlies over the warm pool are displaced westward these changes in the basic state lead to a weaker or leakier waveguide in the asian pacific jet with a westward displaced forbidden region of tropical easterlies such that high frequency transient waves propagate equatorward into the deep tropics over the central pacific near the date line as these waves induce convection in the region of ascent and reduced static stability ahead of the upper level cyclonic disturbances there is an enhancement of high frequency convective var

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

quasi biweekly impact of the atmospheric heat source over the tibetan plateau on summer rainfall in eastern china we investigated the intraseasonal relationship between the atmospheric heat source over tibetan plateau tp and summer rainfall in eastern china a quasi biweekly oscillation qbwo is the common dominant periodicity over both the tp and eastern china crucially the tp heat source qbwo leads rainfall qbwo over its downstream region by 2 8 days the qbwo over the tp shows a significant eastward propagation phase composite further identified the specific propagation pathway tp qbwo first propagates eastward to central china southward to southern china and then northeastward to the lower reaches of the yangtze river with a zigzag propagating pathway mechanistically the eastward propagation of the upper level divergence caused by the movement of the 200 hpa jet core and south asian high contributes to the eastward propagation of the rainfall qbwo simultaneously the eastward westward shift in the western north pacific subtropical high causes deepening flattening of the monsoon trough and the occurrence of an anomalous cyclone anticyclone over the western north pacific an anomalous anticyclonic cyclonic circulation around the tp appears with the wet to dry dry to wet phase transition of the tp qbwo together they play a crucial part in the southward northeastward movement of the qbwo further dynamic analysis indicates that the horizontal moisture advection acts on the whole eastward propagating process of the qbwo whereas the horizontal vorticity advection is only significant when qbwo is over the tp this study shows that the fluctuations in tp heat source are important indicators in extended forecasts of summer rainfall in eastern china

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

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

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

influence of low arctic sea ice minima on anomalously cold eurasian winters 1 influence of low arctic sea ice minima in early autumn on the wintertime climate over eurasia is investigated observational evidence shows that significant cold anomalies over the far east in early winter and zonally elongated cold anomalies from europe to far east in late winter are associated with the decrease of the arctic sea ice cover in the preceding summer to autumn seasons results from numerical experiments using an atmospheric general circulation model support these notions the remote response in early winter is regarded as a stationary rossby wave generated thermally through an anomalous turbulent heat fluxes as a result of anomalous ice cover over the barents kara seas in late autumn which tends to induce an amplification of the siberian high causing colder conditions over the far east the late winter cold anomalies over eurasia are also reproduced in our experiment which is associated with the negative phase of the north atlantic oscillation

generation processes of mesoscale convective systems following midlatitude troughs around the sichuan basin 1 the generation processes of mesoscale convective systems mcss that occurred over the sichuan basin in china were revealed in the early 2008 monsoon season mcs occurrences detected in meteosat geostational satellite images are associated with the traveling of midlatitude troughs after the onset of the indian monsoon three episodes of large scale mcss were generated under synoptic conditions of merging southwesterly low level monsoon flows with a northerly midlatitude air mass following the trough in the leeward of the tibetan plateau without direct migration of the vortex generated from the plateau surface numerical simulations using a weather research and forecast wrf model showed that the mcs was triggered in the evening by strengthening of the low level wind convergences with horizontal shear between the southerly monsoon flow with large convective available potential energy and the northerly dry intrusion a sudden increase in the northerly winds was confirmed by sonde observation data in the western basin and the winds were simulated as intrusions passing over the qinling mountains when the daytime clouds over the mountain were diminished sensitivity experiments by a wrf simulation revealed that the topography of the sichuan basin was able to capture the dry intrusion at the bottom to prevent the propagation of disturbances from the plateau and to cause the sudden onset of mcss apart from the plateau with a heavy precipitation zone

causes of intraseasonal diabatic heating variability over and near the tibetan plateau in boreal summer the structure and evolution features of the first two leading modes of the intraseasonal diabatic heating variability over the tibetan plateau tp during northern summer are investigated using reanalysis and observational data both of the leading modes present a dominant 10 30 day intraseasonal oscillation iso the first mode is characterized by a perturbation center over the southern tp stp which remains quasi stationary and is closely related to the low latitude iso the associated low latitude iso is originated from the tropical western pacific wp and propagates westward northwestward toward northwestern india along the mean monsoon trough the westward propagation near the south china sea is mainly attributed to anomalous meridional vorticity advection and the advection of the planetary vorticity by iso flow the stationary feature of the perturbation over the stp is ascribed to the topographical features around the stp the intraseasonal heating variability over the stp is attributed to the alternation of anticyclonic and cyclonic flow associated with the westward propagating iso perturbation originated from the tropical wp the second leading mode is characterized by an east west asymmetric structure over the tp the intraseasonal diabatic heating anomaly propagates clockwise from the northwestern to eastern tp while a heating anomaly with an opposite sign propagates from the southeastern to western tp the mid latitude rossby wave trains play an essential role in forming the dipole structure the wave trains propagate southeastward before reaching the tp and then eastward as they cross the tp the source of anomalous water vapor over the tp is originated from lower latitudes the upper and lower level wave trains are well coupled over the tp exhibiting a baroclinic structure

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

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

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

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

distinguishing interannual variations of the northern and southern modes of the east asian winter monsoon abstractthe east asian winter monsoon eawm related climate anomalies have shown large year to year variations in both the intensity and the meridional extent the present study distinguishes the interannual variations of the low latitude and mid to high latitude components of the eawm to gain a better understanding of the characteristics and factors for the eawm variability through composite analysis based on two indices representing the northern and southern components modes of the eawm variability the present study clearly reveals features unique to the northern and southern mode the northern mode is associated with changes in the mid to high latitude circulation systems including the siberian high the aleutian low the east asian trough and the east asian westerly jet stream whereas the southern mode is closely related to circulation changes over the global tropics the north atlantic and north america a strong northern mode is accompanied by positive negative and positive surface temp

the development mechanism for tibetan plateau warm vortices abstract the low level cyclonic vortices which form over the tibetan plateau in the summer monsoon season are major rain producing systems and have the potential to trigger cyclogenesis on the lee side when they move off the plateau two cases of the plateau vortices which occurred in july 1979 are studied the characteristics of the vertical structure in their developing stage and the circulation condition favorable for the eastward movement in the mature stage are diagnosed and presented by use of fgge iiib datasets numerical simulations with real data were performed using the gfdl limited area mesoscale simulation model results suggest that the latent heating is an essential driving force for the development of the vortices studied here the analysis of a continuous cisk model with a basic state resembling that actually observed over the summer plateau shows that the predicted unstable mode has a preferred scale growth rate and vertical structure all of which are qualitatively comparable to observ

seasonal prediction of the northern and southern temperature modes of the east asian winter monsoon the importance of the arctic sea ice previous research work found that two distinct surface air temperature sat modes the northern n and the southern s modes dominate the east asian winter monsoon eawm region the inter annual variations of these two modes were mainly attributed to preceding siberian snow cover anomalies and el nino southern oscillation enso observed evidence in this study shows that sea ice anomalies on barents kara bk and laptev seas and those on chukchi beaufort cb sea in autumn have co mingled effects on the two abnormal eawm modes if negative sea ice anomalies appear in the bk and northern cb sea in september october so the following winter sat anomaly over east asia is featured by an obvious cooling north of 40 n which highly resembles the sat n mode of eawm if negative sea ice anomalies occur in bk laptev sea but positive anomalies in the southern cb sea the east asia winter sat anomaly exhibits a salient cold condition over the south of 40 n and corresponds to the eawm s mode the above results indicate that autumn arctic sea ice can provide another predictability source for the eawm besides siberian snow cover and enso to further verify its contribution to seasonal prediction of the eawm a series of physical empirical models are established using the combinations of so arctic sea ice autumn siberian snow cover and enso hindcast experiment output shows when adding autumn arctic sea ice into the predictors the cross validated prediction skill is significantly improved the possible physical mechanisms on how preceding arctic sea ice anomalies impact on the n and s modes are also discussed

another look at interannual to interdecadal variations of the east asian winter monsoon the northern and southern temperature modes abstract this study investigates the causes of interannual to interdecadal variability of the east asian ea 0 60 n 100 140 e winter monsoon eawm over the past 50 yr 1957 2006 the winter mean surface air temperature variations are dominated by two distinct principal modes that together account for 74 of the total temperature variance the two modes have notably different circulation structures and sources of variability the northern mode characterized by a westward shift of the ea major trough and enhanced surface pressure over central siberia represents a cold winter in the northern ea resulting from cold air intrusion from central siberia the southern mode on the other hand features a deepening ea trough and increased surface pressure over mongolia representing a cold winter south of 40 n resulting from cold air intrusion from western mongolia the cold northern mode is preceded by excessive autumn snow covers over southern siberia mongolia whereas the cold southern mode is preceded b

interactions between enso transient circulation and tropical convection over the pacific abstract the interannual variability of transient waves and convection over the central and eastern pacific is examined using 30 northern winters of ncep ncar reanalyses 1968 69 1997 98 and satellite outgoing longwave radiation data starting in 1974 there is a clear signal associated with the el nino southern oscillation such that differences in the seasonal mean basic state lead to statistically significant changes in the behavior of the transients and convection with periods less than 30 days which then feed back onto the basic state during a warm event el nino phase the northern hemisphere subtropical jet is strengthened over the central pacific the region of upper tropospheric mean easterlies over the tropical western pacific expands eastward past the date line and the upper tropospheric mean westerly duct over the tropical eastern pacific is weakened the transients tend to propagate along the almost continuous waveguide of the subtropical jet equatorward propagation into the westerly

interannual variability of surface air temperature over mid high latitudes of eurasia during boreal autumn this study analyzes the dominant modes of interannual variability of surface air temperature sat during boreal autumn over the mid high latitudes of eurasia and investigates their associations with snow cover atmospheric circulation and sea surface temperature sst the first second and third empirical orthogonal function eof mode of autumn sat anomalies displays same sign distribution an east west dipole pattern and a south north dipole pattern respectively analysis of surface heat fluxes indicates that snow changes explain only small patches of sat anomalies related to the first two eofs via altering surface shortwave radiation atmospheric circulation anomalies have important contributions to the formation of sat anomalies southerly northerly wind anomalies generally favor positive negative sat anomalies via bringing warmer colder air from lower higher latitudes the atmospheric circulation anomalies related to the first eof mode are attributed to a combination of the arctic oscillation ao and the scandinavia pattern and those related to the second eof mode have a close relation with the east atlantic west russian eawr and circumglobal teleconnection cgt patterns formation of the atmospheric circulation anomalies related to the third eof mode is partly related to the arctic sea ice change around the barents kara seas sst anomalies have little contribution to the atmospheric circulation anomalies associated with the first three eof modes of eurasian autumn sat interannual variations hindcast skill of the sat anomalies related to the first second eof mode is improved when taking both the ao and scandinavia eawr and cgt patterns into account

linkage between interannual variation of the east asian intraseasonal oscillation and mei yu onset abstractthe mei yu onset over the middle to lower reaches of the yangtze river valley mlyrv varies considerably from early june to mid july which leads to large interannual changes in rainy seas

study of a heavy rain vortex formed over the eastern flank of the tibetan plateau abstract a case of the heavy rain vortex which occurred during the period 14 15 july 1979 is studied using a limited area mesoscale numerical model this is a representative example of a group of warm southwest vortices that often form over the eastern flank of the tibetan plateau after the onset of the summer indian monsoon some common features of the dynamic structures exhibited both by the simulation and by observations are discussed the developing vortex is noticeably detached from the polar frontal zone a 180 phase shift exists between the upper and lower layer vorticity fields in the boundary layer a pronounced northward transport of mass and moisture is connected with an intense upward motion near and to the east of the 700 mb vortex center whole the southward cold advection is insignificant the vortex originated and rapidly developed in a stagnation region on the lee side of the plateau the presence of the stagnation region not only removes local dynamical energy sources from the environm

eurasian snow cover variability and northern hemisphere climate predictability we present observational evidence demonstrating dynamic interactions and feedbacks between multi seasonal snow cover and winter time circulation anomalies over mid high latitudes the cooling effect of snow cover is associated with a strengthened and more expansive siberian high with more frequent topographically constrained intrusions west and north early season snow cover variability leads to altered general circulation patterns consistent with the dominant mode of winter variability observed in the northern hemisphere troposphere the implications of the surface atmosphere coupling for seasonal to interannual predictability are also discussed

dynamics of distinct intraseasonal oscillation in summer monsoon rainfall over the meghalaya bangladesh western myanmar region covariability between the tropics and mid latitudes detailed spatiotemporal structures for the submonthly scale 7 25 days intraseasonal oscillation iso in summer monsoon rainfall and atmospheric circulation were investigated in south asia using high quality rainfall and reanalysis datasets the meghalaya bangladesh coast of the western myanmar mbwm region is the predominant area of submonthly scale iso in the asian monsoon regions the distinct rainfall iso is caused by a remarkable alternation of low level zonal wind between westerly and easterly flows around the gangetic plain on the same timescales in the active iso phase of the mbwm a strong low level westerly southwesterly flows around the plain and a center of cyclonic vorticity appears over bangladesh hence a local southerly flows toward the meghalaya plateau and there is strong southwesterly flow towards the coast along southeastern bangladesh and western myanmar resulting in an increase in orographic rainfall rainfall also increases over the lowland area of the mbwm due to the low level convergence in the boundary layer under the strong cyclonic circulation the submonthly scale low level wind fluctuation around the mbwm is caused by a westward moving n 1 equatorial rossby er wave when the anticyclonic cyclonic anomaly related to the er wave approaches the bay of bengal from the western pacific humid westerly southwesterly easterly southeasterly flows enhance around the gangetic plain on the northern fringe of the anticyclone cyclone and in turn promote reduce rainfall in the mbwm simultaneously robust circulation signals are observed over the mid latitudes in the active phase cyclonic anomalies appear over and around the tp having barotropic vertical structure and also contributing to the enhancement of low level westerly flow around the gangetic plain in the upper troposphere an anticyclonic anomaly is also observed upstream of the cyclonic anomaly over the tp having wavetrain structure the mid latitude circulation around the tp likely helps to induce the distinct iso there in conjunction with the equatorial waves thus the distinct iso in the mbwm is strongly enhanced locally 500 km by the terrain features although the atmospheric circulation causing the iso has a horizontal scale of 6 000 km or more extending across the whole asian monsoon system from the tropics to mid latitudes

influence of the background state on rossby wave propagation into the great lakes region based on observations and model simulations abstractthe authors investigate the relationship between hydrology in the great lakes basin namely overlake precipitation and transient rossby waves using the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data and historical output from phase 3 of the coupled model intercomparison project cmip3 the preferred path of observed rossby wave trains associated with overlake precipitation on lake superior depends strongly on season and appears to be related to the time mean upper level flow during summer and fall the northern hemisphere extratropical jet is relatively narrow and acts as a waveguide such that rossby wave trains traversing the great lakes region travel along the extratropical pacific and atlantic jets during other months the pacific jet is relatively broad which allows more wave activity originating in the tropics to penetrate into the midlatitudes and influence lake superior precipitation analysis is extended to cmip3 mod

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

how autumn eurasian snow anomalies affect east asian winter monsoon a numerical study previous studies have found that snow eurasian anomalies in autumn can affect east asian winter monsoon eawm but the mechanisms remain controversial and not well understood the possible mechanisms by which eurasian autumn snow anomalies affect eawm are investigated by numerical experiments with a coupled general circulation model and its atmospheric general circulation model component the leading empirical orthogonal function mode of the october november mean eurasian snow cover is characterized by a uniform anomaly over a broad region of central eurasia 40 n 65 n 60 e 140 e however the results from a 150 ensemble mean simulation with snow depth anomaly specified in october and november reveal that the mongolian plateau and vicinity mpv 40 55 n 80 120 e is the key region for autumn snow anomalies to affect eawm the excessive snow forcing can significantly enhance eawm and the snowfall over the northwestern china and along the eawm front zone stretching from the southeast china to japan the physical process involves a snow monsoon feedback mechanism the excessive autumn snow anomalies over the mpv region can persist into the following winter and significantly enhance winter snow anomalies which increase surface albedo reduce incoming solar radiation and cool the boundary layer air leading to an enhanced mongolian high and a deepened east asian trough the latter in turn strengthen surface northwesterly winds cooling east asia and increasing snow accumulation over the mpv region and the southeastern china the increased snow covers feedback to eawm system through changing albedo extending its influence southeastward it is also found that the atmosphere ocean coupling process can amplify the delayed influence of eurasian snow mass anomaly on eawm the autumn surface albedo anomalies however do not have a lasting memory effect only if the albedo anomalies are artificially extended into december and january will the eawm be affected in a similar way as the impacts of autumn snow mass anomalies

rossby wave propagation and teleconnection patterns in the austral winter abstract observational evidence of and theoretical support for the northern and southern hemisphere teleconnection patterns in the austral southern hemisphere winter are examined through an upper troposphere streamfunction teleconnectivity map and time lag cross correlation analysis using ecmwf initialized analysis 2oo hpa winds for the 11 june august periods from 1979 to 1989 as was previously found for the northern hemisphere winter the regions of strong teleconnectivity particularly in the winter hemisphere tend to he oriented in the zonal direction and coincide with the location of the major jet streams although equatorward propagation from the northern and southern hemispheres is observed little evidence of cross equatorial propagation has been found for comparison the response of a barotropic model linearized about a climatological 300 hpa june august time mean flow to localized forcing is determined it is found that the activity tends to be trapped inside each of the southern hemisphere

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

inescapable slow slip on the altyn tagh fault 1 gps surveys conducted in 1994 1998 and 2002 on the central portion of the altyn tagh fault confirm left lateral slip rates of 9 4 mm yr significantly slower than geological estimates of slip rate for the past several thousand years the measurements were obtained on a 300 km long profile between 88 and 91 e within one fault dimension of the mw 7 6 and mw 7 8 kunlun earthquakes of 1997 and 2001 the inferred elastic displacements from these events are incorporated into the interpreted 1994 2002 velocity field the recent serendipitous occurrence of these two large earthquakes on a sub parallel fault system suggests that slip on the kunlun fault may have recently accelerated thereby reducing the slip rate on the altyn tagh fault however geodetic data from northern tibet prior to the 2001 earthquake indicate present day rates similar to long term rates this suggests that systematic errors may be present in published geologic slip rate estimates for the altyn tagh fault

two distinct patterns of spring eurasian snow cover anomaly and their impacts on the east asian summer monsoon 1 the eurasian snow cover anomaly in spring has been considered as one of the important factors affecting east asian summer monsoon easm the spring snow cover data for the period from 1972 to 2004 are used to extract dominant spatial patterns over the eurasian region and to examine their impacts on the easm through empirical orthogonal function eof analysis the first eof mode is generally characterized by a continent wide snow cover anomaly over the whole eurasian region while the second eof mode is dominated by an east west dipole structure over eurasia our study indicates that the variability of dipole pattern snow cover is more closely related to the easm rainfall than that of continent wide snow cover a strong dipole pattern with positive negative snow cover anomalies over western eurasia and negative positive snow cover anomalies over eastern eurasia signifies enhanced reduced summer rainfall over east asia and the eurasian wave train pattern is apparent an important implication of these results is that the spring snow cover anomaly over eurasia provides a complementary precursor for easm variability

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

low quaternary slip rate reconciles geodetic and geologic rates along the altyn tagh fault northwestern tibet for more than two decades the slip rate along the active left slip altyn tagh fault of northwestern tibet has been disputed with millennial rates reported to be as much as three times faster than those determined geodetically this problem is significant because the total offset plate boundary length and age of the altyn tagh fault make it the most important single structure accommodating india asia convergence north of the himalayas here we show that the central altyn tagh fault slipped at only 14 9 mm a over the past 4 6 ka by tightly bracketing the age of a displaced fluvial terrace riser at yuemake 88 51 e 38 19 n this result contradicts previous latest quaternary rates and is consistent with those derived from geodetic paleoseismic and geologic measurements and thus resolves the long standing dispute over the latest quaternary slip rate along the longest active strike slip fault in tibet