regional circulation characteristics associated with a cold surge event over east asia during winter monex abstract a case study is presented of the cold surge over east asia during 9 13 december 1978 using nine vertical levels of winter monex data the surge event is manifested by a rapid meridional mass flow in the lower troposphere from the midlatitudes 30 n to the equator within three days during the period studied the lower tropospheric circulation dramatically changed in extent and intensity with the onset of the surge event the main divergent maximum began shifting from the south china sea to southeast china at the same time the upper tropospheric circulation correspondingly changed in a reversed order from that of the lower troposphere and a direct vertical coupling between flows in the low and high troposphere was observed the time averaged meridional mass circulation between 100 and 126 e reveals a two cell structure the southern cell is located between the northern south china sea and the equator and the northern cell between midlatitudes and the northern south china sea analysis of s

changes in occurrence of cold surges over east asia in association with arctic oscillation 1 it has been newly found that the occurrence of cold surges in east asia is significantly influenced by the arctic oscillation ao in the present study the events of cold surge are objectively determined based on several synoptic criteria and the phase dependency of its occurrences in association with the ao has been revealed during the negative ao phase the frequency of cold surge occurrence is relatively increased than that of neutral and positive ao phases the variation of upper level trough and jet stream over east asia and the siberian high in association of ao are suggested to explain the change of cold surge occurrences

impacts of mjo convection over the maritime continent on eastern china cold temperatures abstractthe present study shows that winter cold events over eastern china can be induced by madden julian oscillation mjo associated anomalous convection over the maritime continent we conduct

precursory signals of east asian winter cold anomalies in stratospheric planetary wave pattern the impacts of the stratospheric polar vortex changes on the tropospheric climate variability have been emphasized in previous studies the present study presents evidence for precursory signals of cold anomalies over east asia in the stratospheric wave pattern during november through march the leading two empirical orthogonal function eof modes of daily 50 hpa geopotential height anomalies along 65 n correspond to changes in the amplitude and phase of the stratospheric planetary wavenumber 1 respectively composite analysis is performed to unravel the temporal evolution of anomalies during 8 phases of 34 events identified based on the second eof mode with a complete life cycle for the period 1979 2016 the surface cold anomalies over eastern china emerge in phase 3 corresponding to negative and positive 50 hpa height anomalies on the north atlantic and russian far east sector respectively and peak in phase 5 corresponding to positive 50 hpa height anomalies over eurasia when the siberian high extends southeastward and the east asian trough deepens with anomalous surface northerly winds downward propagation of stratospheric signal is detected over western europe and western siberia the former is a source region of the tropospheric rossby wave trains propagating along the polar front jet and subtropical jet the downward propagation of stratospheric signal is related to the reflection of stratospheric planetary wavenumber 1 pattern and contributes to the development of the tropospheric rossby wave train that in turn leads to the strengthening of the siberian high and the deepening of the east asian trough

relative contributions of synoptic and intraseasonal variations to strong cold events over eastern china the present study investigates the relative roles of intraseasonal oscillations isos and synoptic variations in strong cold events over eastern china during the boreal winter the isos and synoptic variations explain about 55 and 20 of the total area mean temperature anomaly in eastern china respectively the advection of synoptic winds on synoptic temperature gradients has a leading contribution to the temperature decrease before the cold events and thus the synoptic variations are important in determining the time of peak cold anomalies the isos have a larger role in sustaining the cold events the height anomalies associated with isos and synoptic variations are manifested as rossby wave trains propagating along the polar front jet over the eurasian continent before the cold events they both contribute to the deepening of the east asian trough and the development of cold events compared to the iso wave train the synoptic wave train has a smaller spatial scale and moves faster there are obvious intraseasonal signals in the stratosphere about 1 week before the cold events over eastern china large negative height anomalies associated with the weakening of the polar vortex are observed over the north atlantic these anomalies move eastwards and propagate downwards after reaching the west coast of europe the downward moving stratospheric signal triggers height anomalies in the troposphere over the entrance region of the polar front jet then the anomalies propagate towards east asia along the wave train contributing to the intensification of the siberian high and the east asian trough and the occurrence of cold events over eastern china

processes for occurrence of strong cold events over eastern china abstracta strong cold event hit eastern china around 24 january 2016 with surface air temperature reaching more than 10 c below the climatological mean in most regions of eastern china south of 40 n a total of 37 strong cold events similar to the january 2016 event with temperature anomalies over eastern china exceeding 5 c have been identified during the winters from 1979 80 to 2015 16 a comparative analysis of events with surface temperature anomalies of the same intensity but limited to north of 40 n indicates that the southward invasion of cold air to eastern china south of 40 n is related to two factors one is the latitudinal location of the upper level wave train the surface siberian high and the midtropospheric east asian trough over the mid to high latitude eurasian continent the other is a subtropical upper level wave train emanating from the midlatitude north atlantic the emergence of the subtropical wave train is related to the positive phase of the north atlantic oscillation nao wh

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

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

an east asian cold surge case study abstract since a cold surge is a hazardous weather phenomenon in east asia the rapid population increase and economic growth over the past two decades require improvement in forecasting cold surges and their related weather events over this region however without a better understanding of these events this task cannot be accomplished a cold surge with a well defined cold front passing through taiwan was selected to illustrate its impact on the east asian weather system this case is typical of a large portion of surges occurring in the region major findings of this study are as follows coupling with the upper ridge trough structures of the wave train straddling the eastern seaboard of northeast asia cold surges occur sequentially a cold front with a prefront high pressure zone is formed by the new surge outflow interacting with the anticyclone of the aging surge the warm moist air advected northeastward along the cold front assists the development of the new surge s low center while the prefron

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

structure and dynamics of a wave train along the wintertime asian jet and its impact on east asian climate based on observational and reanalysis datasets this study investigates the structure and dynamics of a wave like atmospheric teleconnection pattern along the wintertime asian jet and its influence on east asian climate along the jet the leading empirical orthogonal function eof mode of monthly meridional winds at 250 hpa in winter december january and february is organized as a wave train with maximum anomalies at upper troposphere the wave train propagates northeastward from the north atlantic to europe turns southeastward to the middle east with amplifying amplitude propagates along the jet to south china and reaches japan which is partly induced by sea surface temperature sst anomalies in the equatorial eastern pacific and the north atlantic oscillation over the sector from europe to the middle east the anomalous vortices in the wave train tilt northwestward with height and tilt northeast southwest in horizontal at 250 hpa favoring for extracting available potential energy and kinetic energy from mean flows effectively in addition there exists a positive feedback between transient eddies and the wave train related anomalous circulation over the north atlantic and europe these processes help to maintain and amplify the wave train moreover the wave train can exert significant influences on the wintertime climate in east asia when it is in the phase with a cyclone anticyclone over south china japan rainfall tends to be above normal in south and east china and surface air temperature tends to be above normal around japan and the korea peninsula

intraseasonal variation of the strength of the east asian trough and its climatic impacts in boreal winter abstractthe east asian trough eat is a distinct component of the boreal winter circulation whose strength corresponds to the amplitude of the northern hemispheric stationary waves in this study the mechanism and climatic impacts of the intraseasonal variations of the eat s strength are investigated through composite analysis and dynamical diagnostics the significant roles played by the low frequency rossby wave rw and synoptic transient eddy te are revealed before the peaks of strong eat events an upper tropospheric rw train propagates across northern eurasia and interacts with preexisting surface cold anomalies over central siberia this pattern intensifies the siberian high and causes rw convergence toward the eat leading to 30 of the eat s amplification directly via the rw induced feedback forcing meanwhile rw weakens the background baroclinicity and reduces te activities near the entrance region of the north pacific storm track the te induced feedback forcing leads to another 30 of th

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

relationship between the arctic oscillation and cold surges over east asia abstract the present study reveals the changes in the characteristics of cold surges over east asia associated with the arctic oscillation ao based on circulation features cold surges are grouped into two general types wave train and blocking types the blocking type of cold surge tends to occur during negative ao periods that is the ao related polarity of the blocking type however the wave train type is observed during both positive and negative ao periods although the wave train features associated with negative ao are relatively weaker the cold surges during negative ao are stronger than those during positive ao in terms of both amplitude and duration the cold surges during positive ao in which the extent of effect is confined to inland china passes through east asia quickly because of weaker siberian high and aleutian low leading to short duration of these cold surges in contrast the cold surge during negative ao characterized by a well organized anticyclone cyclone couplet with high p

geographical dependence of upper level blocking formation associated with intraseasonal amplification of the siberian high abstract intraseasonal amplification events of the surface siberian high in winter are generally associated with blocking ridge formation in the upper troposphere composite analysis applied to the 20 strongest intraseasonal events of upper level anticyclonic anomalies at every grid point over siberia reveals that the blocking formation differs fundamentally between the east and west of the climatological upper level trough over the far east to the west what can be called wave train atlantic origin type is common where a blocking ridge develops from anomalies as a component of a quasi stationary rossby wave train propagating across the eurasian continent under modest feedback forcing from transient eddies to the east of the trough what can be called pacific origin type dominates where a blocking ridge forms in association with westward development of anticyclonic anomalies from the north pacific under stronger feedback forcing from the pacific storm track regardless of a particular type of bl

stratospheric origin of cold surge occurrence in east asia 1 in the present study we have found a precursory signal in the stratospheric circulation prior to the cold surge occurrence in east asia over northern eurasia about one week before the cold surge occurrence strong stratospheric negative potential vorticity anomalies and rising of geopotential height are observed the dynamic linkage between the stratospheric perturbations and the tropospheric adjustment along with initial disturbances for a cold surge occurrence are discussed

a study of the interaction of the north atlantic oscillation with ocean circulation observed patterns of wind stress curl and air sea heat flux associated with the north atlantic oscillation nao are used to discuss the response of ocean gyres and thermohaline circulation to nao forcing and their possible feedback on the nao the observations motivate and are interpreted in the framework of a simple mathematical model that couples ekman layers ocean gyres and thermohaline circulation to the atmospheric jet stream meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres and north south dipoles in air sea flux drive anomalous thermohaline circulation both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence through air sea interaction the overlying jet stream the model which can be expressed in the form of a delayed oscillator with ocean gyres and or thermohaline circulation providing the delay identifies key nondimensional parameters that control whether the ocean responds passively to nao forcing or actively couples it suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales

combined effects of the mjo and the arctic oscillation on the intraseasonal eastern china winter temperature variations abstractthe present study reveals that the madden julian oscillation mjo related temperature anomalies over east asia have notable differences among positive neutral and negative arctic oscilla

the association between stratospheric weak polar vortex events and cold air outbreaks in the northern hemisphere previous studies have identified an association between temperature anomalies in the northern hemisphere and the strength of stratospheric polar westerlies large regions in northern asia europe and north america have been found to cool during the mature and late stages of weak vortex events in the stratosphere a substantial part of the temperature changes are associated with changes in the northern annular mode nam and north atlantic oscillation nao pressure patterns in the troposphere the apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting but only if the temporal and spatial nature of the coupling is known using 51 winters of re analysis data we show that the development of the lower tropospheric temperature relative to stratospheric weak polar vortex events goes through a series of well defined stages including the formation of geographically distinct cold air outbreaks at the inception of weak vortex events a precursor signal in the form of a strong high pressure anomaly over northwest eurasia is associated with long lived and robust cold anomalies over asia and europe a few weeks later near the mature stage of the weak vortex events a shorter lived cold anomaly emerges off the east coast of north america the probability of cold air outbreaks increases by more than 50 in one or more of these regions during all phases of the weak vortex events this shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks as large changes in the frequency of extremes are involved this process is important for the medium range and seasonal prediction of extreme cold winter days three hundred year pre industrial control simulations by 13 coupled climate models corroborate our results copyright 2010 royal meteorological society and crown copyright

a synoptic and dynamical characterization of wave train and blocking cold surge over east asia through an agglomerative hierarchical clustering method cold surges over east asia are classified into two distinct types based on the spatial pattern of the geopotential height anomalies at 300 hpa one is the wave train type that is associated with developing large scale waves across the eurasian continent the other is the blocking type whose occurrence accompanies subarctic blocking during the wave train cold surge growing baroclinic waves induce a southeastward expansion of the siberian high and strong northerly winds over east asia blocking cold surge on the other hand is associated with a southward expansion of the siberian high and northeasterly winds inherent to a height dipole consisting of the subarctic blocking and the east asian coastal trough the blocking cold surge tends to be more intense and last longer compared to the wave train type the wave train cold surge is associated with the formation of a negative upper tropospheric height anomaly southeast of greenland approximately 12 days before the surge occurrence further analysis of isentropic potential vorticity reveals that this height anomaly could originate from the lower stratosphere over the north atlantic cold surge of the blocking type occurs with an amplifying positive geopotential and a negative potential vorticity anomaly over the arctic and the northern eurasia in stratosphere these anomalies resemble the stratospheric signature of a negative phase of the arctic oscillation this stratospheric feature is further demonstrated by the observation that the blocking type cold surge occurs more often when the arctic oscillation is in its negative phase

mechanisms of intraseasonal amplification of the cold siberian high mechanisms of intraseasonal amplification of the siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over siberia at each location the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere over central and western siberia what may be called wave train atlantic origin type is common where a blocking ridge forms as a component of a quasi stationary rossby wave train propagating across the eurasian continent a cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the tibetan plateau it is found through the potential vorticity pv inversion technique that interaction between the upperlevel stationary rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high upper level pv anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal rossby waves the surface cold anomalies thus intensified in turn act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train the baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies which may be interpreted as dissipative destabilization of the incoming external rossby waves

on the three dimensional propagation of stationary waves abstract a locally applicable nonzonally averaged conservation relation is derived for quasi geostrophic stationary waves on a zonal flow a generalization of the eliassen palm relation the flux which appears in this relation constitutes it is argued a useful diagnostic of the three dimensional propagation of stationary wave activity this is illustrated by application to a simple theoretical model of a forced rossby wave train and to a northern hemisphere winter climatology results of the latter procedure suggest that the major forcing of the stationary wave field derives from the orographic effects of the tibetan plateau and from nonorographic effects diabatic heating and or interaction with transient eddies in the western north atlantic and north pacific oceans and siberia no evidence is found in the data for wave trains of tropical origin forcing by the orographic effects of the rocky mountains seems to be of secondary importance

interannual variation of the east asian cold surge activity abstract the occurrence frequency of the east asian cold surge exhibits an interannual variation in concert with the el nino southern oscillation enso cycle that is the cold surge occurs more less frequently during warm cold enso winters because the cold surge high low dipoles are coupled with the upper level synoptic short waves any mechanism modulating the activity of these waves would affect the cold surge activity the streamfunction budget analysis in the short wave regime indicates that the development of the cold surge short wave train over east asia and the northwest pacific is modulated by the north pacific enso short wave train due to the coupling between the upper level cold surge short wave train and the surface cold surge dipole it is inferred from this streamfunction budget analysis that the interannual variation of the cold surge occurrence frequency is a result of this modulation

an analysis of the large scale climate anomalies associated with the snowstorms affecting china in january 2008 abstract extraordinarily frequent and long lasting snowstorms affected china in january 2008 causing above normal precipitation below normal temperature and severe icing conditions over central southern china these snowstorms were closely linked to the change in the middle east jet stream mejs which intensified and shifted southeastward the change in mejs was accompanied by southeastward shifts of the ridge and the trough over europe and western asia the intensified mejs also strengthened the trough embedded in the southern branch of the subtropical westerlies over the southern tibetan plateau enhancing the water vapor transport from western asia and the bay of bengal to china in the meantime the subtropical western pacific high swph was stronger and its ridgeline was farther north than normal the anomalous high slowed down the eastward propagation of weather systems to the pacific and favored convergence of water vapor over central southern china the mejs is usually strong when the arctic

modulation of the qbo on the mjo related surface air temperature anomalies over eurasia during boreal winter previous studies have indicated the modulation of the madden julian oscillation mjo by the quasi biennial oscillation qbo and the influence of the mjo on surface temperature over eurasia during boreal winter the present study reveals that the mjo related circulation anomalies are different in easterly and westerly qbo years leading to distinct surface temperature anomaly patterns over eurasia during the easterly qbo years the surface air temperature anomalies over eurasia display a meridional dipole pattern in mjo phase 2 associated with the mid latitude surface anticyclonic anomalies the development of surface anomalous anticyclone is attributed to a combined effect of negative north atlantic oscillation nao related mid latitude wave train and stronger mjo convection triggered poleward propagation of rossby wave train the negative nao is related to the easterly qbo through the holton tan relationship the anomalous overturning circulation excited by the stronger mjo convection in easterly qbo years also contributes to the development and eastward extension of anomalous anticyclone the anticyclonic anomalies induce the meridional temperature anomaly pattern by horizontal advection during the westerly qbo years the surface air temperature anomalies over eurasia show a zonal alternating pattern in mjo phase 3 which corresponds to the development of mid latitude rossby wave train associated with positive nao with a stronger mjo nao connection in westerly qbo years the mjo convection induces upper level divergent wind anomalies contributing partially to the development of the rossby wave source and helping the building of the mid latitude wave train the zonal temperature anomalies over eurasia are also contributed by the horizontal advection associated with surface cyclonic anomalies

interannual variability of the east asian winter monsoon and related modulations of the planetary waves abstractinterannual variability of the east asian winter monsoon is investigated through composite analysis applied to observational data for 50 recent years although the monsoon activity itself is confined into the lower troposphere its midwinter variability tends to accompany upper tropospheric geopotential height anomalies similar to the eurasian eu and western pacific wp teleconnection patterns the eu like pattern is characterized by a wavy signature over the eurasian continent and the north atlantic with surface temperature anomalies over the far east and north america in the wp like pattern a meridional dipole of upper level height anomalies is evident over the far east these anomaly patterns related to the anomalous winter monsoon activity are found to accompany marked modulations of the climatological development of the upper tropospheric planetary waves from late autumn to midwinter enhanced monsoon activity in january associated with the wp like pattern involves anomalous seasonal

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

early jurassic rifting of the arabian passive continental margin of the neo tethys field evidence from the lurestan region of the zagros fold and thrust belt iran

another look at influences of the madden julian oscillation on the wintertime east asian weather 1 as one of the major predictability sources on an intraseasonal time scale the madden julian oscillation mjo exerts a profound influence on the subseasonal forecast of the east asian ea surface air temperature sat and precipitation in this study we examine the direct link of the mjo with the ea sat and precipitation and its dynamical mechanism to represent the mjo we perform an empirical orthogonal function eof analysis on pentad outgoing longwave radiation olr over 20 s 20 n 60 e 150 w the eof1 mode is mostly characterized by a single convection center near the maritime continent 90 150 e whereas the eof2 mode has an east west dipole structure with enhanced convection over the eastern indian ocean and suppressed convective activities over the tropical western pacific at the same pentad of a positive eof1 phase large areas of cold anomalies with reduced precipitation emerge in the ea region north of 20 n and persist through two pentads later at the same pentad of a positive eof2 phase sat and precipitation exhibit a zonal dipole pattern with cold and dry anomalies covering the ea region west of 120 e and warm and wet anomalies to the east these dipole anomalies in sat and precipitation systematically move eastward in the next two pentads a linearized global primitive equation model is utilized to assess the cause of the intraseasonal variability in sat and precipitation over east asia associated with the tropical heating of the mjo the model responses to heating sources that mimic the eof1 and eof2 olr patterns match well the general features of the observed circulation anomalies under forcing of a positive phase of the eof1 pattern strengthened local hadley cell or monsoon circulations within 90 e 150 e are reproduced with anomalous northerly winds and dry anomalies prevailing in the lower troposphere over east asia the processes that influence east asia are mainly associated with intraseasonal changes in local hadley circulation and the northern hemisphere branch of the equatorially trapped rossby wave gyres forced by the mjo heating

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

nonmodal growth of atmospheric disturbances relevant to the east asian pressure surge in boreal winter significant events of east asian pressure surge are identified based on sea level pressure for boreal winters of the period 1979 2016 these events typically grow from a high pressure anomaly over northern europe and the northwestern russia and attain their peak over siberia around ten days after the initiation the structure of the pressure surge at its peak intensity mimics that of the semi permanent siberian high with a two level quasi geostrophic qg model a nonmodal instability analysis of the winter climatological flow reveals that one of the most rapidly amplifying optimal disturbances with an optimization time of 2 days resembles the structure of the east asian pressure surge this optimal disturbance originates from small scale precursor disturbances over northern europe and the barents sea such initial disturbances grow in magnitude via siberia towards east asia forming a low level ridge extending to around 50 n the optimal disturbance successfully captures the temporal and spatial scales and the overall structure of the circulation anomaly associated with the pressure surge albeit with varying degrees of accuracy of the location of individual trough ridge of the surge anomaly additional experiments suggest that 1 adding damping effect to the two level qg model extends the low level ridge further south to around 40 n and 2 the upper level wave train feature associated with pressure surge can be captured even in a barotropic model by optimal disturbances with an optimization time of 4 days

the changing relationship between interannual variations of the north atlantic oscillation and northern tropical atlantic sst abstractthe relationship between interannual variations of boreal winter north atlantic oscillation nao and northern tropical atlantic nta sea surface temperature sst experienced obvious interdecadal changes during 1870 2012 similar interdecadal changes are observed in the amplitude of nta sst anomalies the mean nta sst change may be a plausible reason for several changes in the nao nta sst connection under a higher mean nta sst nta sst anomalies induce larger wind anomalies over the north atlantic that produce a tripole sst anomaly pattern and amplify nta sst anomalies comparison of the evolution of anomalies between 1970 86 and 1996 2012 unravels changing roles of el nino southern oscillation enso and extratropical atmospheric disturbances in the formation of nta sst anomalies during 1970 86 enso events play a key role in initiating nta sst anomalies in the preceding spring through atmospheric circulation changes with the decay of enso sst anomalies in the midlatitude north atlantic wea

arctic climate and atmospheric planetary waves analysis of a fifty year record 1946 1995 of monthly averaged sea level pressure data provides a link between the phases of planetary scale sea level pressure waves and arctic ocean and ice variability results of this analysis show 1 a breakdown of the dominant wave 1 pattern in the late 1960 s 2 shifts in the mean phase of waves 1 and 2 since this breakdown 3 an eastward shift in the phases of both waves 1 and 2 during the years of simulated cyclonic arctic ocean circulation relative to their phases during the years of anticyclonic circulation 4 a strong decadal variability of wave phase associated with simulated arctic ocean circulation changes finally the arctic atmospheric circulation patterns that emerge when waves 1 and 2 are in their extreme eastern and western positions suggest an alternative approach for determining significant forcing patterns of sea ice and high latitude variability

combined effect of el nino southern oscillation and pacific decadal oscillation on the east asian winter monsoon using long term observational data and numerical model experiments the combined effect of the el nino southern oscillation enso and pacific decadal oscillation pdo on the variability of the east asian winter monsoon is examined in the observations it is found that when the enso and pdo are in phase combinations i e el nino positive pdo phase and la nina negative pdo phase a negative relationship between enso and east asian winter monsoon is significantly intensified in other words when el nino la nina occurs with positive negative pdo phase anomalous warm cold temperatures are dominant over the east asian winter continent on the other hand there are no significant temperature anomalies when the enso and pdo are out of phase combinations i e el nino negative pdo phase and la nina positive pdo phase further analyses indicate that the anticyclone over the western north pacific including the east asian marginal seas plays an essential role in modulating the intensity of the east asian winter monsoon under the changes of enso pdo phase relationship long lasting high pressure and warm sea surface temperature anomalies during the late fall winter and following spring over the western north pacific which appear as the el nino occurs with positive pdo phase can lead to a weakened east asian winter monsoon by transporting warm and wet conditions into the east asian continent through the southerly wind anomalies along the western flank of the anomalous high pressure and vice versa as the la nina occurs with negative pdo phase in contrast the anomalous high pressure over the western north pacific does not show a prominent change under the out of phase combinations of enso and pdo numerical model experiments confirm the observational results accompanying dominant warm temperature anomalies over east asia via strong anticyclonic circulation anomalies near the philippine sea as the el nino occurs with positive pdo phase whereas such warming is weakened as the el nino occurs with negative pdo phase this result supports the argument that the changes in the east asian winter monsoon intensity with enso are largely affected by the strength of the anticyclone over the western north pacific which significantly changes according to the enso pdo phase relationship