stationary rossby wave propagation in a baroclinic atmosphere observational studies of teleconnections in both soisticial seasons have suggested various patterns of behaviour linked mainly to westerly jets and equatorial westerlies these have been interpreted using barotropic rossby wave theory and simulated using stationary forcing in barotropic models linearized about 300 hpa flows in this paper the relevant propagation behaviour is investigated using a baroclinic model with three dimensional climatological basic states time integrations are performed using localized thermal forcing as a wavemaker the propagation results are qualitatively very similar to those obtained with the barotropic model though there are quantitative differences the westerly jets still act as strong waveguides the shorter wavelengths and smaller wave activity speeds found with the baroclinic model are generally in better agreement with observation propagation into and from the upper tropospheric equatorial westerlies in the east pacific propagation across north america and propagation from europe across the arabian gulf are all found the extent to which upper tropospheric westerlies reach towards the equator influences the propagation into those regions barotropic models can only represent such behaviour if the basic state reflects the near equatorial upper tropospheric zonal wind structure

tropospheric waveguide teleconnections and their seasonality abstractone point correlation maps of the subseasonal variability of 200 hpa meridional wind in nature and an atmospheric general circulation model are systematically analyzed to quantify the impact of the climatological mean jets on tropospheric covariability as a result of the jets acting as waveguides for the propagation of rossby waves as anticipated by linear theory signatures of jet influence are detected in terms of i the geographical position of the strongest teleconnections ii the zonal orientation and extent of prominent patterns of variability and iii the scale of the features that make up those patterns further evidence of jet waveguide influence comes from examining the seasonality of these teleconnection attributes during winter covariability can be essentially circumglobal while during summer it tends to be confined within two separate sectors of the globe where the jets are especially strong experiments with a multilevel linear planetary wave model confirm that the analyzed

an index for tropical temperate troughs over southern africa strong cases of the tropical temperate troughs ttt that are responsible for the most of the summer rainfall over subtropical southern africa are analyzed an index for identifying the ttt is introduced for the first time using anomalies of outgoing longwave radiation olr and the wind the ttt is associated with a ridge trough ridge wave like structure in the lower troposphere over southern africa and the adjoining indian ocean therefore the index considers physical processes that occur over southern africa adjoining the atlantic and indian oceans to depict the variability of the ttt events unusually strong ttt events are identified when the standard deviations of the ttt indices defined by the olr and wind anomalies in the selected regions are above 1 5 and 0 5 respectively after applying this criterion and filtering out consecutive events 55 ttt events are identified during the study period of december january february seasons from 1980 1981 to 2009 2010 from the composite analyses of those 55 events it is found that the ttts evolve with suppressed enhanced convection over the southwest indian ocean adjacent to madagascar southern africa the suppressed convection is in turn found to be associated with the enhanced convection around sumatra in the southeast tropical indian ocean this may explain why more ttt events occur in la nina years as compared to el nino years time evolution of the canonical ttt event shows that it starts 3 days prior to the mature phase of the event suggesting possible predictability after reaching a matured state the system moves east toward the indian ocean and decays within the subsequent couple of days in addition the intertropical convergence zone itcz structure changes over southern africa madagascar during the ttt event and remains similar to climatology over other regions the results indicate that the continental part of the itcz intensifies prior to the ttt event and then spreads southward following the mid latitude influence during and after the event

the british baikal corridor a teleconnection pattern along the summertime polar front jet over eurasia abstractthe british baikal corridor bbc pattern a new teleconnection along the summertime upper tropospheric polar front jet pfj is investigated based on observational and reanalysis datasets

cold season africa asia multidecadal teleconnection pattern and its relation to the atlantic multidecadal variability a prominent teleconnection pattern of multidecadal variability of cold season november to april upper level atmospheric circulation over north africa and eurasia na ea is revealed by empirical orthogonal function analysis of the twentieth century reanalysis data this teleconnection pattern is characterized by an eastward propagating wave train with a zonal wavenumber of 5 6 between 20 and 40 n extending from the northwest coast of africa to east asia and thus is referred to as the africa asia multidecadal teleconnection pattern aamt one point correlation maps show that the teleconnectivity of aamt is strong and further demonstrate the existence of the aamt the aamt shapes the spatial structure of multidecadal change in atmospheric circulation over the na ea region and in particular the aamt pattern and associated fields show similar structures to the change occurring around the early 1960s a strong in phase relationship is observed between the aamt and atlantic multidecadal variability amv and this connection is mainly due to rossby wave dynamics barotropic modeling results suggest that the upper level rossby wave source generated by the amv can excite the aamt wave train and rossby wave ray tracing analysis further highlights the role of the asian jet stream in guiding the wave train to east asia the aamt acts as an atmospheric bridge conveying the influence of amv onto the downstream multidecadal climate variability the amv is closely related to the coordinated change in surface and tropospheric air temperatures over northwest africa the arabian peninsula and central china which may result from the adiabatic expansion compression of air associated with the aamt

increased summer rainfall in northwest australia linked to southern indian ocean climate variability 1 although annual rainfall over most of australia has followed a continuously decreasing trend over the past 6 decades i e 1948 2007 summer rainfall in northwest australia nwa has followed a pronounced increasing trend with a significant linear trend of 2 65 mm yr this study investigates the causes of increasing rainfall over nwa and focuses on influences originating in the middle to high latitudes i e southern indian ocean climate variability our results indicate that variations in summer rainfall over nwa are related to the concurrent strength of the mascarene high in years with a strong mascarene high in the lower troposphere the cyclonic vorticity over nwa is enhanced and more moisture is transported into nwa simultaneously an anomalous vertical closed circulation forms with an ascending branch over nwa and subsidence over the region occupied by the mascarene high as for the upper troposphere the mascarene high is related to a teleconnection wave train from the southern indian ocean to nwa which in turn influences the circulation over nwa this setting is favorable for enhanced rainfall over nwa analysis of the cause of variations in the mascarene high indicates that underlying external forcing of the high by for example sea surface temperature sst has intensified possibly due to the influence of the southern annular mode sam during the preceding spring this mechanism was further examined using numerical experiments we believe that the strengthening of the mascarene high which is caused by the enhanced sst gradient within the southern indian ocean associated with the preceding upward sam has had a significant influence on the increase in summer rainfall over nwa

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

influence of wintertime large scale circulation on the explosively developing cyclones over the western north pacific and their downstream effects 1 the relationships between large scale wintertime circulation and extratropical cyclones that develop explosively the so called bomb cyclones over the western north pacific are investigated using japanese long term reanalysis project data on a monthly basis the east asian winter monsoon variability strongly modulates the bomb cyclone activity in terms of its geographical distribution when the monsoon is strong the bomb cyclone activity tends to concentrate in the vicinity of the kuroshio current and the kuroshio extension near japan while when the monsoon is weak it disperses over the broader areas the enhancement of the monsoon increases the heat and moisture supply from warm currents facilitating unstable conditions within the atmospheric boundary layer and intensifying baroclinicity in the lower troposphere these factors are believed to play a role in inducing bomb cyclones particularly along the warm currents on submonthly timescales the stationary rossby wave propagation along the south asian waveguide serves as a prominent trigger for the rapid reinforcement of synoptic scale disturbances around japan when a pronounced bomb cyclone comes to its mature stage northeast of japan it is capable of exciting stationary rossby waves downstream from the asian jet exit region as vorticity forcing the stationary wave packets developing southeastward across the north pacific ocean basin induce surface cyclogenesis in the vicinity of the hawaiian islands by leading to the equatorward advection of higher potential vorticity from the midlatitudes bringing about the occurrence of kona storms which cause weather hazards in hawaii

a 14kyr record of the tropical andes the lago chungara sequence 18 s northern chilean altiplano abstract high resolution geochemical analyses obtained using an x ray fluorescence xrf core scanner as well as mineralogical data from the lago chungara sedimentary sequence in the northern andean chilean altiplano 18 s provided a detailed reconstruction of the lacustrine sedimentary evolution during the last 14 000 cal yr bp the high resolution analyses attained in this study allowed to distinguish abrupt periods identify the complex structures of the early and mid holocene arid intervals and to compare their timing with titicaca lake and sajama ice records three main components in the lake sediments have been identified a biogenic component mainly from diatoms b volcanics ash layers from the nearby parinacota volcano and c endogenic carbonates the correlation between volcanic input in lago chungara and the total particles deposited in the nevado sajama ice core suggests the parinacota volcano as the common source the geochemical record of lago chungara indicates an increase in siliceous productivity during the early holocene lagging behind the rise in temperatures inferred from the nevado sajama ice core the regional mid holocene aridity crisis can be characterized as a number of short events with calcite and aragonite precipitation in the offshore lake zones

the effect of model bias on the equatorward propagation of extratropical waves the effect of model bias on the equatorward propagation of extratropical waves in a gcm simulation is assessed within the context of simple wave guiding principles the modes representing these waves are identified through the use of empirical orthogonal function analysis performed on the 200 mb zonal wind filtered to retain variations between 6 and 30 days the temporal evolution and vertical structure of these modes are examined through the use of time lagged composite analysis the differences between observed and simulated wave propagation is examined in relationship to the theoretical wave guiding properties associated with the observed and simulated time mean flow the utility of simple wave guiding theory for describing the observed and modeled wave propagation is assessed the model bias in the time mean flow is closely associated with the differences in the propagation of the transient waves the excessively strong wave guiding properties associated with the simulated pacific jet appear to inhibit the proper meridional propagation of wave energy into the tropical central and eastern pacific in the simulation waves that do propagate into the tropical pacific either dissipate or are reflected near the equator while in the observations wave energy propagates into the southern hemisphere on the other hand the wave guiding by the subtropical and midlatitude jets over the atlantic is weaker in the simulation than in the observations in this region wave energy propagates primarily into the tropics in the simulation while some of the observed wave energy is reflected toward the east and northeast over the atlantic and northern africa the locations of the theoretical critical lines and wave guides of the time mean flow although based on many simplifying assumptions are remarkably consistent with the propagation characteristics of these waves

extratropical atmospheric response to equatorial atlantic cold tongue anomalies abstract the extratropical atmospheric response to the equatorial cold tongue mode in the atlantic ocean has been investigated with the coupled ocean atmosphere model speedy ocean speedo similar to the observations the model simulates a lagged covariability between the equatorial cold tongue mode during late boreal summer and the east atlantic pattern a few months later in early winter the equatorial cold tongue mode attains its maximum amplitude during late boreal summer however only a few months later when the itcz has moved southward it is able to induce a significant upper tropospheric divergence that is able to force a rossby wave response the lagged covariability is therefore the result of the persistence of the cold tongue anomaly and a favorable tropical atmospheric circulation a few months later the rossby wave energy is trapped in the south asian subtropical jet and propagates circumglobally before it reaches the north atlantic due to the local increase of the hadley circulation fo

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

afro eurasian intermediate frequency teleconnection and modulation by enso abstractthe afro eurasian intermediate frequency atmospheric teleconnection conveys meteorological signals zonally leads to various atmospheric variations and causes extreme events along its path

relationship between tropical heating and global circulation interannual variability this study examines the relationship between tropical heating and global circulation in the troposphere through singular value decomposition svd analysis and numerical simulations based on a global barotropic spectral model svd analysis was applied to the 200 mbar stream function field and the outgoing longwave radiation olr to extract the most recurrent coupled mode the stream function vector of the first mode indicates an out of phase relationship between the stream function in the northern and southern hemispheres tight gradients in the pattern along the equator suggest a large fluctuation of zonal mean zonal wind associated with this seesaw its eddy component appears to modulate the stationary eddies the major structure of the corresponding olr vector is a dipole near the equator with one center at 120 e and another one at 160 w the first mode exhibits a strong interannual variability and is strongly correlated with the occurrence of el nino and la nina to understand the relationship between the stream function and olr a series of numerical experiments using a barotropic model was carried out specifying rossby wave source associated with differing idealized divergence patterns in the tropics the steady state responses in all experiments exhibit a zonally symmetric structure resembling the stream function vector of the first mode the pattern was mainly forced by the zonal mean component of rossby wave source that is contributed mostly by zonal mean divergent winds under the constraint of zero global mean divergence the same zonal mean forcing is also responsible for the forced eddy stream function perturbations that exhibit similar structures in all experiments

non annular hemispheric signature of the winter north atlantic oscillation sensitivity experiments with an atmospheric general circulation model agcm without a proper stratosphere are performed to locally force a north atlantic oscillation nao like response in order to analyse the tropospheric dynamics involved in its hemispheric extent results show that the circulation anomalies are not confined to the north atlantic basin not even within the first 10 days of integration where the atmospheric response propagates downstream into the westerly jets at this linear stage transient eddy activity dominates the emerging regional nao like pattern while zonal eddy coupling may add on top of the wave energy propagation later at the quasi equilibrium nonlinear stage the atmospheric response emphasizes a wavenumber 5 structure embedded in the westerly jets associated with transient eddy feedback upon the atlantic and pacific storm tracks this agcm waveguided structure rightly projects on the observational nao related circumglobal pattern providing evidence of its non annular character in the troposphere these findings support the view on the importance of the circumglobal waveguide pattern on the development of nao related anomalies at hemispheric level it could help to settle a consensus view of the arctic oscillation which has been elusive so far

structure and characteristics of submonthly scale waves along the indian ocean itcz this study examines wave disturbances on submonthly 6 30 day timescales over the tropical indian ocean during southern hemisphere summer using japanese reanalysis jra25 jcdas products and national oceanic and atmospheric administration outgoing longwave radiation data the analysis period is december february for the 29 years from 1979 1980 through 2007 2008 an extended empirical orthogonal function eeof analysis of daily 850 hpa meridional wind anomalies reveals a well organized wave train pattern as a dominant mode of variability over the tropical indian ocean daily lagged composite analyses for various atmospheric variables based on the eeof result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the indian ocean intertropical convergence zone itcz the wave train is oriented in a northeast southwest direction from sumatra toward madagascar the waves have zonal wavelengths of about 3 000 5 000 km and exhibit westward and southwestward phase propagation individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of sumatra into madagascar meanwhile eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern indian ocean this could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern indian ocean along the mean monsoon westerly flow in addition the waves modulate the itcz convection correlation statistics show the average behavior of the wave disturbances over the tropical indian ocean these statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis the waves appear to be connected to the monsoon westerly flow the waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow this suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical indian ocean the horizontal structure of the wave train may be interpreted as that of a mixture of equatorial rossby waves and mixed rossby gravity wavelike gyres

global view of the intraseasonal oscillation during northern winter abstract in this study svd analysis is applied to a normalized 200 mb streamfunction olr covariance matrix to extract the most recurrent coupled pattern in the northern winter after the removal of the climatological seasonal cycle and seasonal means for each winter the first two singular vectors are on an intraseasonal timescale and the combination of the two forms an oscillation it is characterized by eastward propagation in the indian ocean and the western pacific standing oscillations in both the tropics and the extratropics and the poleward propagation of a zonally symmetric structure although there exists an eastwardly propagating pattern the phase relationship between geopotential wind and streamfunction fields is inconsistent with that of equatorial kelvin waves eastward propagation is most evident in the tropics of the southern hemisphere while the signals in the northern hemisphere are characterized by standing oscillations the distinct characteristics of the northern and southern he

global teleconnections in the 250 mb streamfunction field during the northern hemisphere winter abstract teleconnections of the streamfunction in the global domain based on ecmwf 250 mb winds for the 11 northern winters from 1978 79 through 1988 89 are documented in this study a zonal structure with a node near the equator indicating an out of phase relationship between the streamfunctions in the northern and southern hemisphere appears to mask the fluctuations of the asymmetric components of streamfunction after removing zonal means a global pattern emerges as the dominant structure in the low frequency band this pattern consists of several dipoles straddling either the exit region of midlatitude jets or the equator indicating the existence of teleconnections not only between the midlatitudes and the tropics but also between the northern and southern hemispheres teleconnection patterns in the intermediate frequency band are predominantly wavelike seven waveguides are identified based on the one point lag correlation maps for base points near the maximum teleconnectivity among them are thr

intraseasonal variations of the british baikal corridor pattern abstractthe british baikal corridor bbc pattern is the dominant waveguide mode trapped along the summertime polar front jet over northern eurasia it consists of four geographically fixed centers

decadal relationship between the north atlantic oscillation and cold surge frequency in taiwan 1 the close decadal relationship between the north atlantic oscillation nao and the cold surge frequency in northern taiwan is identified the cold surge frequency was higher lower in 1957 1977 1981 2001 which corresponded to the negative positive phase of the nao the teleconnection pattern associated with the nao suggests that the siberian high the ridge upstream of lake baikal and the east asian trough which are well known circulation characteristics favorable for cold surge occurrences were enhanced in the negative nao phase a weakened upper level convergence over the mediterranean sahara occurring in the negative nao phase was associated with a wave like pattern spreading toward east asia along the subtropical jet stream barotropic modeling results suggest that the suppressed upper level convergence in the mediterranean sahara region may force a wave train emanating toward east asia along the subtropical jet stream which acts as a rossby waveguide the barotropic wave pattern may result in a stronger low level northerly over subtropical east asia and create a favorable background for the further southward penetration of cold air and therefore more frequent cold surge occurrence the same process may be applied to the period when the nao is in the positive phase

rotational atmospheric circulation during north atlantic european winter the influence of enso the dominant variability modes of the north atlantic european rotational flow are examined by applying a principal component analysis pca eof to the 200 hpa streamfunction mid winter anomalies jan feb monthly means the results reveal that when this norm is used the leading mode eof1 does not correspond to the traditional north atlantic oscillation nao which appears in our analysis as the second leading mode eof2 but is the local manifestation of the leading hemispheric streamfunction eof the regression of this regional mode onto the global sst field exhibits a clear el nino signature with no signal over the atlantic while the associated upper height anomalies resemble the tropical northern hemisphere tnh pattern east of north america this tnh like wavetrain produces a meridional dipole like pattern at lower levels although in some ways this pattern resembles the nao eof2 the dynamics of these two modes are very different in that only eof2 is associated with a latitudinal shift of the north atlantic stormtrack thus the choice of the streamfunction norm in the eof analysis allows the separation of two different phenomena that can produce similar dipolar surface pressure anomalies over the north atlantic but that have different impact on european climate these two modes also differ on their contribution to variability at lower levels while nao eof2 is mostly confined to the north atlantic tnh eof1 has a more annular global character at upper levels nao eof2 also produces a global pattern but with no annular structure reminiscent of the circumglobal teleconnection

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

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

global extratropical response to diabatic heating variability of the asian summer monsoon abstract global teleconnections associated with the asian summer monsoon convective activities are investigated based on monthly data of 29 northern hemisphere summers defined as june september jjas two distinct teleconnection patterns are identified that are associated respectively with variabilities of the indian summer monsoon and the western north pacific summer monsoon the indian summer monsoon convective activity is associated with a global pattern that has a far reaching connection in both hemispheres whereas the western north pacific summer monsoon convective activity is connected to a southern hemisphere wave train that influences the high latitude south pacific and south america a global primitive equation model is utilized to assess the cause of the global circulation anomalies the model responses to anomalous heatings of both monsoon systems match the general features of the observed circulation anomalies well and they are mainly controlled by linear processes the response patterns ar

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

arctic sea ice patterns driven by the asian summer monsoon abstractthe fluctuation of arctic sea ice concentration sic has been associated with changes in ocean circulation ecology and northern hemisphere climate prediction of sea ice melting patterns is of great societal interest but such prediction remains difficult because the factors controlling year to year sea ice variability remain unresolved distinct monsoon arctic teleconnections modulate summer arctic sic largely by changing wind forced sea ice transport east asian monsoon rainfall produces a northward propagating meridional rossby wave train extending into the siberian arctic the indian summer monsoon excites an eastward propagating circumglobal teleconnection along the subtropical jet reaching the north atlantic before bifurcating into the arctic the remote asian monsoon variations induce a dominant dipole sea ice melt pattern in which the north atlantic european arctic contrasts with the siberian north american arctic the monsoon related sea ice variations are complementary and comparable

rossby wave propagation into the tropics in two gfdl general circulation models during the northern winter the eastern pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres theoretical and simple modeling studies suggest that such a region should favor the penetration of rossby waves into the tropics from higher latitudes observational results by kiladis and weickmann using 200 mb data indicate that rossby waves do indeed propagate freely into the tropical eastern pacific during the northern winter from the asian jet exit region they also confirmed that cross equatorial dispersion of energy from the northern into the southern hemisphere occurs frequently the present study examines these interactions in climatological runs of two gfdl gcms the northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical pacific despite the relative weakness of the asian jet and wave activity with respect to observations propagation of rossby waves into the tropics is present in both models and these waves are strongly positively tilted as seen in the observations a momentum budget of the zonal wind and e vector diagnostics over the tropical pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

topographic effects on the eastward propagation and initiation of the madden julian oscillation abstract this study investigates the relationship between deep convection and heating anomaly in the madden julian oscillation mjo and the tropical topography the eastward propagation of the deep heating anomalies is confined to two regions the indian ocean and the western pacific warm pool superimposed on the eastward propagation is a series of quasi stationary deep heating anomalies that occur sequentially and discretely downstream in a leapfrog manner in the central indian ocean the maritime continent tropical south america and tropical africa the deep heating anomaly usually preceded by near surface moisture convergence and shallow heating anomalies tends to occur on the windward side of the tropical topography in these regions except the central indian ocean under the prevailing surface easterly anomaly of the mjo it is suggested that the lifting and frictional effects of the tropical topography and landmass induce the near surface moisture convergence anomaly which in turn triggers

the sequence stratigraphy of fluvial depositional systems the role of floodplain sediment storage abstract the currently used model for alluvial sequence stratigraphy has been criticised miall 1991 and an alternative model is offered here in this model alluviation mainly takes place during transgressive and not highstand phases when accommodation space allows sediment storage the high capacity for some river systems to store floodplain sediments is a critical consideration the effects of climatic and intrinsic geomorphic changes during fluvial deposition are likely to greatly complicate simple base level controlled sequence models and recognising higher order fourth and fifth order cycles will be particularly difficult

enso induced tropical convection variability over the indian and western pacific oceans during the northern winter as revealed by a self organizing map 1 the dominant low frequency patterns of outgoing longwave radiation over the tropical indian and western pacific oceans in response to el nino southern oscillation enso during the northern winter are investigated using the nonlinear classification method of the self organizing map som additionally aided by an empirical orthogonal function eof analysis there are at least two different air sea coupled phenomena in the tropical indian ocean i e the indian ocean dipole iod mode in late summer and fall and the wind evaporation sea surface temperature wes feedback driven mode in the winter and spring the som results exhibit that the phase of wes becomes positive negative at the el nino la nina phase which indicates a linear linkage of wes with enso in contrast few combined patterns of the negative iod and the la nina event can be extracted although the reversed pattern is prominent suggesting a nonlinear like relationship between iod and enso since the enso induced convective forcing over the tropical indian and western pacific oceans has strong asymmetric features with respect to the enso phase the remote response of the east asian winter monsoon to enso becomes complicated at the el nino event the monsoon circulation in the southern part of east asia tends to be attenuated in late winter through the dominance of the western north pacific anticyclone in the lower troposphere but at the la nina event the monsoon circulation over korea and japan is enhanced in early winter through the downstream development of stationary rossby wave packets along the south asian waveguide

extratropical forcing of tropical wave disturbances along the indian ocean itcz the role of extratropical waves in the excitation of tropical waves on submonthly timescales is explored along the indian ocean intertropical convergence zone itcz during the austral summer using japanese reanalysis products and noaa outgoing longwave radiation data the analysis period is december february of 1979 1980 to 2008 2009 the submonthly tropical waves are regarded as a type of rossby wave propagating along the mean monsoon westerly flow they play an important role in modulating the indian ocean itcz convection the linkage between the tropical and extratropical waves which is responsible for the formation and strengthening of tropical waves is examined composite analysis results linked to the tropical wave train development show that the midlatitude rossby wave train progresses eastward and northeastward from the south atlantic into the subtropical indian ocean as a trough and ridge that form part of the midlatitude wave train approach the southern africa southwest indian ocean swio region a southwest northeast oriented wave train is subsequently established originating from this feature and is strengthened across the tropical indian ocean the midlatitude wave propagation toward the subtropics induces the growth of the trough and ridge over the swio wave activity flux diagnostics indicate that the amplified trough and ridge over the swio act as an energy source for northeastward amplification of the tropical waves through the wave energy dispersion process the results suggest that the propagation of the midlatitude wave toward the swio is the fundamental mechanism behind the development of the tropical waves along the indian ocean itcz

remote response of the east asian winter monsoon to tropical forcing related to el nino southern oscillation 1 the mechanism of the east asian winter monsoon variability in response to el nino southern oscillation enso related tropical forcing is investigated using japanese long term reanalysis project data additionally aided by the japan meteorological agency climate data assimilation system there are at least two different responses zonally symmetric and asymmetric of the asian jet over south asia to the enso related tropical convective forcing during the northern hemisphere winter the zonally symmetric response induced by zonally extended anomalous convection from the philippine sea through southern india and sri lanka is pronounced at the mature phase of enso the zonally asymmetric response is intimately associated with anomalous convection localized in the vicinity of the philippine and south china seas accompanied by an anomalous walker circulation cell between the maritime continent and tropical indian ocean when this asymmetric response is prominent enso related anomalous convection can give rise to a change in the east asian winter monsoon system through stationary rossby wave propagation along the south asian waveguide the north atlantic oscillation nao related extratropical forcing is also a crucial factor and contributes not only to the downstream development of subpolar teleconnections across northern eurasia but also to the reinforcement of the zonally asymmetric pattern of the asian jet over south asia resulting in a significant effect on the east asian winter monsoon circulation a combination of the enso and nao related forcing plays a vital role in triggering the occurrence of extraordinary anomalous monsoon circulations such as extremely heavy snowfall in the 2005 2006 winter in japan

persistent severe drought in southern china during winter spring 2011 large scale circulation patterns and possible impacting factors 1 severe drought persisted in southern china from january to may in 2011 in this study a statistical analysis is carried out to discuss the multiple possible impacting factors including la nina the north atlantic oscillation nao and the thermal condition of the tibetan plateau tp the la nina event in 2010 11 excited a lower tropospheric anomalous cyclone over the northwestern pacific weakening the northwestern pacific subtropical high and caused an eastward shift of the high as a result transportation of wet and warm moisture from tropical oceans to southern china decreased the la nina event also strengthened the upper tropospheric east asian jet stream and deepened the east asian trough favoring a southward intrusion of dry northerly flow from the siberia the la nina condition in the previous two seasons also seemed to provide precursory signals for the drought moreover in january may 2011 the nao was in a positive phase and it tended to excite stationary rossby waves that were distributed along the sub polar and subtropical waveguides respectively the sub polar one induced an anomalous anticyclone over the siberia favoring a southward intrusion of high latitude northerly flow to southern china the subtropical one associated possibly with the enhanced convection over the broad region from the mediterranean to sahara was favorable for an influence of upper tropospheric flow on southern china the tp might also exert an influence on the drought by weakening the westerly flow to the southern flank of tp and reducing water vapor transport from the bay of bengal to southern china

the large scale modulation of subtropical cyclogenesis in the central and eastern pacific ocean abstract an analysis of the composite large scale circulation associated with periods of enhanced active or diminished inactive cyclogenesis in the subtropical central and eastern pacific ocean is presented composites were constructed using surface and tropospheric analyses from the ecmwf tropical ocean global atmosphere toga dataset for 10 northern hemisphere cool seasons 1986 96 active periods of subtropical cyclogenesis were defined to be periods in which two or more cyclones developed in close succession to each other while inactive periods were defined to be periods of at least 10 days duration during which no cyclones with a subtropical origin were present in the pacific basin the analysis revealed that the occurrence of subtropical cyclones in the central and eastern pacific ocean is strongly linked to the strength and location of the asian jet with active periods characterized by a weaker zonally retracted asian jet while inactive periods are characterized by a stronger zonally elon

behavior of one to two week summertime subtropical wind maxima over the south pacific during an enso cycle abstract the behavior of subtropical jet streaks over the australian south pacific region is investigated for four consecutive 6 month summer seasons november to april during the period 1985 89 the study is an extension of a recent one by ko and vincent hereafter referred to as kv in which jet streaks during the summer season of 1984 85 were examined ko and vincent found that the upper tropospheric zonal wind behaved in a quasi periodic manner with maxima recurring over the western south pacific at intervals between one and two weeks in the present study wind maxima are found to exhibit a 1 2 week periodic oscillation over the south pacific in all four years thus substantiating the finding by kv in addition a second set of jet streaks with a similar periodicity is found over the southern australian region it is also seen that the mean summertime position of the south pacific jet and its accompanying jet streaks are much farther cast during the el nino event of 1986 87 than they are in the

synoptic scale rossby waves and the geographic distribution of lateral transport routes between the tropics and the extratropics in the lower stratosphere atmospheric transport between the tropics and the extratropics in the lowest part of the stratosphere during northern hemisphere winter is investigated the role of synoptic scale disturbances that propagate laterally into the tropics is examined using the middle atmosphere version of the national center for atmospheric research community climate model version 3 general circulation model in the lower stratosphere synoptic scale rossby waves propagate vigorously from the northern i e winter extratropics through two westerly ducts where the westerly zonal mean winds near the equator are favorable to rossby wave propagation the waves break in the westerly ducts and modify the mean potential vorticity pv structure to connect subtropical and equatorial regions of sharp pv gradients frequent wave breaking and the wave induced pv structure create distinct routes where transport occurs vigorously between the tropics and the northern extratropics interhemispheric transport also occurs through regions associated with the westerly ducts in the southern summer hemisphere lower stratosphere synoptic scale disturbances propagate mainly as tongues of pv elongated from extratropical disturbances the transport between the tropics and the southern extratropics has a strong geographic preference but is dominated by the monsoon circulation as was shown for the upper troposphere by chen 1995 pv tongues and other transient anomalies are of secondary importance

equatorial windows and barriers for stationary rossby wave propagation abstractrossby waves can cross the equator and connect the northern hemisphere nh and southern hemisphere sh or be blocked in the vicinity of the equator this work explores the windows and ba

blocking and rossby wave breaking on the dynamical tropopause in the southern hemisphere abstract rossby wave breaking on the dynamical tropopause in the southern hemisphere the 2 pvu surface is investigated using the era 40 dataset the indication of wave breaking is based on reversal in the meridional gradient of potential temperature and persistent large scale wave breaking is taken as a strong indication that blocking may be present blocking in the midlatitudes is found to occur predominantly during wintertime in the pacific and is most vigorous in the east pacific while during summertime the frequency of blocking weakens and its extent becomes confined to the west pacific the interannual variability of blocking is found to be high wave breaking occurs most frequently on the poleward side of the polar jet and has some but not all of the signatures of blocking so it is referred to as high latitude blocking in general cyclonic wave breaking occurs on the poleward side of the polar jet otherwise anticyclonic breaking occurs however at least in wintertime wave breaking in th

dynamics of an interhemispheric teleconnection across the critical latitude through a southerly duct during boreal winter abstractin this study an interhemispheric teleconnection pattern across the critical latitude from southern africa through south asia to the north pacific was revealed in boreal winter monthly averaged 250 hpa streamfunction fields obtained from both the 40 yr ecmwf re analysis era 40 and the ncep ncar reanalysis data from 1957 58 to 2001 02 classical rossby wave theory for zonally varying flow in which the effects of the basic state meridional wind are ignored predicts that stationary rossby waves cannot propagate across easterlies to elucidate the underlying mechanisms responsible for this interhemispheric teleconnection the theoretical basis for stationary wave propagation across the critical latitude is considered taking into account meridional ambient flow the theoretical results suggest that the southerly flow over east africa the western indian ocean and south asia creates a path for the northward propagation of stationary waves across the critical latitude stationary wavenumber and grou