a general rule for synoptic eddy feedback onto low frequency flow in this study scale interaction between synoptic eddies and low frequency flow is investigated it is demonstrated here that there is a general rule the left hand rule that describes synoptic eddy feedback onto low frequency flow the rule is that low frequency anomalies systematically stir and deform the transient eddies in such a way that the irrotational eddy vorticity fluxes are directed preferentially about 90 toward the left hand side of the low frequency flow thus this eddy feedback plays a positive role in maintaining and prolonging low frequency flow under the stormy atmosphere similarly we show that the irrotational eddy temperature and moisture fluxes are also directed preferentially about 90 toward the left hand side of the low frequency flow in the northern hemisphere the eddy temperature fluxes and their vertical structure play a positive role in reinforcing the low frequency flow in the low levels the moisture fluxes play a role in enhancing low frequency flow by providing eddy induced moisture convergence and divergence

on the atmospheric response experiment to a blue arctic ocean we demonstrated atmospheric responses to a reduction in arctic sea ice via simulations in which arctic sea ice decreased stepwise from the present day range to an ice free range in all cases the tropospheric response exhibited a negative arctic oscillation ao like pattern an intensification of the climatological planetary scale wave due to the present day sea ice reduction on the atlantic side of the arctic ocean induced stratospheric polar vortex weakening and the subsequent negative ao conversely strong arctic warming due to ice free conditions across the entire arctic ocean induced a weakening of the tropospheric westerlies corresponding to a negative ao without troposphere stratosphere coupling for which the planetary scale wave response to a surface heat source extending to the pacific side of the arctic ocean was responsible because the resultant negative ao like response was accompanied by secondary circulation in the meridional plane atmospheric heat transport into the arctic increased accelerating the arctic amplification

zonal flow stationary wave relationship during el nino implications for seasonal forecasting abstract an analysis of the northern hemispheric zonal mean flow anomalies during el nino is performed and the dynamical effect of such atmospheric flows on the wintertime climatological stationary waves over the pacific north american pna region is assessed only in the subtropical latitudes can one identify a statistically significant zonal flow anomaly during the el ni os of the historical record strong zonal flow anomalies in the midlatitudes are observed during individual el ni o events although these appear to be manifestations of chaotic atmospheric behavior the observational results are confirmed by gcm climate simulations using prescribed ssts for the 1982 93 period the principal sst forced zonal flow signal in these experiments is located on the equatorward flank of the subtropical jet using a linear diagnostic modes the authors find the climatological stationary waves over the pna region to be insensitive to zonal mean flow anomalies in the subtropics on the other hand zonal mean ano

the role of stationary waves in the maintenance of the northern annular mode as deduced from model experiments abstract the influence of stationary waves on the maintenance of the tropospheric annular mode am is examined in a simple global circulation model with perpetual january conditions the presented model experiments vary in the configurations of stationary wave forcing by orography and land sea heating contrasts all simulations display an am like pattern in the lower troposphere the zonal momentum budget shows that the feedback between eddies with periods less than 10 days and the zonal mean zonal wind is generally the dominating process that maintains the am the kinetic energy of the high frequency eddies depends on the stationary wave forcing where orographic forcing reduces and thermal forcing enhances it the ams in the model experiments differ in the superposed anomalous stationary waves and in the strength of the zonally symmetric component if only orographic stationary wave forcing is taken into account the mountain torque decelerates the barotropic wind anomaly and thus acts to weaken the a

eddies and the annular modes of climate variability the dominant modes of month to month varia tion in the troposphere are realistically simulated in a gen eral circulation model whose lower boundary is prescribed with realistic topography and seasonally varying climato logical sea surface temperatures in both hemispheres these internal modes describe a nearly zonally symmetric north south shifting of the zonal jets as anomalous westerlies vac illate between high 50 60 a nd low 30 40 latitudes the eddy structures evolve with the jets and the corre sponding eddy momentum forcings support the shifts in jet position stationary synoptic wave variations mainly ac count for the total eddy forcings in the northern south ern hemisphere pronounced eddy variations occur over the north atlantic sector

the importance of atmospheric dynamics in the northern hemisphere wintertime climate response to changes in the earth s orbit milankovitch proposed that variations in the earth s orbit cause climate variability through a local thermodynamic response to changes in insolation this hypothesis is tested by examining variability in an atmospheric general circulation model coupled to an ocean mixed layer model subjected to the orbital forcing of the past 165 000 yr during northern hemisphere summer the model s response conforms to milankovitch s hypothesis with high low insolation generating warm cold temperatures throughout the hemisphere however during northern hemisphere winter the climate variations stemming from orbital forcing cannot be solely understood as a local thermodynamic response to radiation anomalies instead orbital forcing perturbs the atmospheric circulation in a pattern bearing a striking resemblance to the northern annular mode the primary mode of simulated and observed unforced atmospheric variability the hypothesized reason for this similarity is that the circulation response to orbital forcing reflects the same dynamics generating unforced variability these circulation anomalies are in turn responsible for significant fluctuations in other climate variables most of the simulated orbital signatures in wintertime surface air temperature over midlatitude continents are directly traceable not to local radiative forcing but to orbital excitation of the northern annular mode this has paleoclimate implications during the point of the model integration corresponding to the last interglacial eemian period the orbital excitation of this mode generates a 1 2 c warm surface air temperature anomaly over europe providing an explanation for the warm anomaly of comparable magnitude implied by the paleoclimate proxy record the results imply that interpretations of the paleoclimate record must account for changes in surface temperature driven not only by changes in insolation but also by perturbations in atmospheric dynamics

the key role of lower level meridional shear in baroclinic wave life cycles a series of idealized nonlinear life cycle experiments is performed to compare changes in life cycle behavior caused by upper level and near surface meridional shear of the initial zonal wind it is shown that both the eddy kinetic energy and the zonal flow accelerations produced during a cycle of growth and equilibration respond primarily to the meridional shear of the zonal wind near the surface and only weakly to shear near the tropopause near the critical shear for transition from anticyclonic to cyclonic life cycle behavior the zonal flow accelerations are minimized and the eddy persistence is maximized above this critical shear eddy breaking on the poleward side of the jet increases and strong cyclonic zonal wind shears are generated the influence of baroclinic shears is minimized by using dipolar wind anomalies that are zero near the center of a basic baroclinic jet and by taking advantage of the fact that the life cycle response is very sensitive to small changes in the magnitude of initial meridional shear the small baroclinic shears contribute to the differences in the sense that a cyclonic shear decreasing with height is slightly more effective in inducing cyclonic behavior than is a barotropic cyclonic shear with the same surface value upper tropospheric eddy momentum fluxes by linear normal modes are also much more sensitive to lower tropospheric meridional shear than to upper tropospheric meridional shear the primary response of normal modes to lower tropospheric meridional shear is to change the momentum flux at all levels

on the zonal structure of the north atlantic oscillation and annular modes abstract the zonal structure and dynamics of the dipolar patterns of intraseasonal variability in the extratropical atmosphere namely the north atlantic oscillation nao and the so called annular modes of variability are investigated in an idealized general circulation model particular attention is focused on the relationships linking the zonal structure of the stationary waves synoptic variability i e the storm tracks and the zonal structure of the patterns of intraseasonal variability large scale topography and diabatic anomalies are introduced to modify and concentrate the synoptic variability establishing a recipe for a localized storm track comparison of the large scale forcing synoptic variability and patterns of intraseasonal variability suggests a nonlinear relationship between the large scale forcing and the variability it is found that localized nao like patterns arise from the confluence of topographic and diabatic forcing and that the patterns are more localized than one would e

a model to interpret driftwood transport in the arctic abstract driftwood is frequently used to estimate past changes of sea ice extent and circulation in the arctic nevertheless driftwood observations are difficult to interpret because of the potentially complex relation with climate change in order to determine the origin of the observed changes we built a driftwood transport model dtm simulating the driftwood trajectories from the boreal forest to arctic coasts the model is driven by three main variables which are the sea ice velocity concentration and the sea surface current velocity that can be derived from observations or climate model outputs e g from a general climate model gcm overall the dtm model agrees with the observations although this comparison needs to be taken with caution because of the sparse data and the uncertainties of driftwood provenance through simulations performed with the dtm model we confirm the strong influence of the variability of the atmospheric circulation on the spatial driftwood distribution model simulations of the mid holocene period driven by six gcms show that small local changes in sea ice circulation a westward shift in the transpolar drift and a reduced beaufort gyre during the mid holocene compared to the present period suffice to explain the driftwood landing change during the mid holocene with a non negligible contribution from reduced sea ice concentration consequently a change in driftwood deposit should not be directly interpreted as large modifications in atmospheric circulation and the complexity of the response of driftwood trajectories to past climate changes clearly highlights the interest of using a model to interpret driftwood records

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

indices of the southern hemisphere zonal wind abstract the time and spatial variation of the southern hemisphere 500 hpa zonal wind has been examined using spectral analysis bandpass filtering and empirical orthogonal function eof analysis applied to a 15 year sample of australian hemispheric analyses spectral analysis of the entire 15 year record of the 500 hpa zonal mean westerly wind shows significant peaks only on the seasonal and interannual time scales the mean segmented spectra for each season failed to show any additional significant peaks at higher frequencies or any significant differences between seasons the primary pattern of variation revealed by eof analysis shows similar behavior on synoptic to seasonal time scales with compensating departures occurring at intervals of 20 latitude the first eof has opposing peaks near 40 and 60 s and shows an equivalent barotropic pattern when correlated with individual grid point values at 500 hpa and mean sea level pressure correlations of the zonal pattern with regional anomalies reveal

analysis and modeling of the arctic oscillation using a simple barotropic model with baroclinic eddy forcing abstract in this study a numerical simulation of the arctic oscillation ao is conducted using a simple barotropic model that considers the barotropic baroclinic interactions as the external forcing the model is referred to as a barotropic s model since the external forcing is obtained statistically from the long term historical data solving an inverse problem the barotropic s model has been integrated for 51 years under a perpetual january condition and the dominant empirical orthogonal function eof modes in the model have been analyzed the results are compared with the eof analysis of the barotropic component of the real atmosphere based on the daily ncep ncar reanalysis for 50 yr from 1950 to 1999 according to the result the first eof of the model atmosphere appears to be the ao similar to the observation the annular structure of the ao and the two centers of action at pacific and atlantic are simulated nicely by the barotropic s model therefore the atmospheric low frequency variabilities

propagation of planetary waves between the troposphere and stratosphere abstract the propagation of planetary waves between the troposphere and stratosphere is investigated using a linear time dependent primitive equation model it is found that the tropopause acts like a valve for the propagation of planetary waves the key parameters controlling the valve are the vertical gradient of buoyancy frequency and the vertical shear of the zonal winds at the tropopause for a given wind profile smaller gradient of buoyancy frequency enhances the propagation of planetary waves for a given profile of buoyancy frequency the larger the shear the more the wave activity is trapped in the troposphere and therefore there is less left to propagate into the stratosphere the transmission across the tropopause is however not sensitive to zonal winds in the upper stratosphere the propagation of planetary waves is very sensitive to transience more transient waves propagate more vertically within the troposphere and for more transient waves more wave activity is transferred into the

northern hemisphere teleconnection patterns during extreme phases of the zonal mean circulation abstract regional climate anomalies associated with year to year changes in the tropospheric zonal mean zonal wind are examined this study focuses on the wintertime northern hemisphere extratropics and compares seasonal mean anomalies associated with to those associated with the el nino southern oscillation during the 1947 94 period dynamical model experiments indicate that a single zonal index characterized by out of phase anomalies at 35 and 55 n is of primary importance for zonal flow stationary wave interactions in the northern hemisphere extratropies such fluctuations in the zonal mean zonal flow are shown to occur independently of tropical sst variability consistent with earlier studies dynamical model experiments and regression analyses of the historical data indicate that such a zonal index explains a significant fraction of the wintertime stationary wave variability in several regions the principal centers of action reside within wave trains over the north pacific north american

on the composite response of the mlt to major sudden stratospheric warming events with elevated stratopause based on a climate chemistry model constrained by reanalyses below 50 km the zonal mean composite response of the mesosphere and lower thermosphere mlt to major sudden stratospheric warming events with elevated stratopauses demonstrates the role of planetary waves pws in driving the mean circulation in the presence of gravity waves gws helping the polar vortex recover and communicating the sudden stratospheric warming ssw impact across the equator with the ssw onset strong westward pw drag appears above 80 km primarily from the dissipation of wave number 1 perturbations with westward period of 5 12 days generated from below by the unstable westward polar stratospheric jet that develops as a result of the ssw the filtering effect of this jet also allows eastward propagating gws to saturate in the winter mlt providing eastward drag that promotes winter polar mesospheric cooling the dominant pw forcing translates to a net westward drag above the eastward mesospheric jet which initiates downwelling over the winter pole as the eastward polar stratospheric jet returns this westward pw drag persists above 80 km and acts synergistically with the return of westward gw drag to drive a stronger polar downwelling that warms the pole adiabatically and helps reform the stratopause at an elevated altitude with the polar wind reversal during the ssw onset the westward drag by the quasi stationary pw in the winter stratosphere drives an anomalous equatorial upwelling and cooling that enhance tropical stratospheric ozone along with equatorial wind anomalies this ozone enhancement subsequently amplifies the migrating semidiurnal tide amplitude in the winter midlatitudes

meridional circulation and the surface pressure change associated with the southern annular mode comparison with the arctic oscillation 1 eddy forced meridional circulation and corresponding surface pressure change associated with the month to month variability of the southern annular mode sam are examined in the framework of the eulerian mean dynamics and they are compared with those of the arctic oscillation ao effect of wave forcings on the surface pressure was diagnosed by means of a zonal mean quasi geostrophic model on the sphere it is found that the surface pressure change associated with the sam is mainly produced by the meridional circulation driven by mechanical and thermal eddy forcings of zonal wave number 1 and mechanical forcing by high frequency transient eddies this contrasts with the surface pressure change associated with the ao which is produced by the mechanical forcing by zonal wave number 2 or 3 and high frequency transient eddies close relationship between the meridional circulation and surface pressure was found not only for the month to month variability but also for the decadal variability as also observed for the ao

importance of midlatitude oceanic frontal zones for the annular mode variability interbasin differences in the southern annular mode signature abstracta midlatitude oceanic frontal zone is a confluent region of warm and cool ocean currents characterized by a strong meridional gradient in both sea surface temperature sst and surface air temperature sat while recent observational and modeling studies indicate potential impacts of midlatitude oceanic fronts on the extratropical climatological circulation including storm tracks and eddy driven westerlies their impacts on the atmospheric dominant low frequency variability i e the annular mode still remain to be understood this study explores possible impacts of midlatitude oceanic frontal zones on annular mode signatures in the wintertime southern hemisphere sh to mimic the sh sets of idealized aquaplanet experiments are conducted with zonally symmetric distributions of sst prescribed globally at the lower boundary of an atmospheric general circulation model by systematically changing the latitude of frontal gradient in the sst profile the experiments reveal that the characteristic

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

barotropic and baroclinic annular variability in the southern hemisphere abstractthe leading patterns of large scale climate variability in the southern hemisphere are examined in the context of extratropical kinetic energy it is argued that variability in the southern hemisphere extratropical flow can be viewed in the context of two distinct and largely independent structures both of which exhibit a high degree of annularity 1 a barotropic structure that dominates the variance in the zonal mean kinetic energy and 2 a baroclinic structure that dominates the variance in the eddy kinetic energy the former structure corresponds to the southern annular mode sam and has been extensively examined in the literature the latter structure emerges as the leading principal component time series of eddy kinetic energy and has received seemingly little attention in previous work the two structures play very different roles in cycling energy through the extratropical troposphere the sam is associated primarily with variability in the meridional propagation of wave activity has a s

decadal changes in the southern hemisphere sea surface temperature in association with el nino southern oscillation and southern annular mode the spatial structure of el nino southern oscillation enso and the southern annular mode sam which are the two most important climate modes affecting sea surface temperature sst variability in the southern hemisphere sh appear to have changed since 1999 the characteristic features of the enso and sam related atmospheric and oceanic variability in the sh are compared between two sub periods 1979 1998 and 1999 2012 using cyclostationary empirical orthogonal function analysis during the earlier period of 1979 1998 the enso is characterized by conventional eastern pacific type in which the signals in the sh constitute the pacific south america teleconnection pattern in contrast due to a shift of the active center of enso to the central pacific in the later period 1999 2012 atmospheric circulation and sst variability over the sh significantly vary moreover the sam related sst variability also shows remarkable differences before and after 1998 1999 this difference is primarily attributed to differences in the non annular spatial component of the sam between the two periods due to the changes in the spatial structure of the sam as well as those of the enso sst variability in the sh displays a marked change between the two periods detailed descriptions of the decadal changes of the sh sst in terms of interaction in the oceanic and atmospheric variability are presented along with the possible implications of this change

coupled ocean atmosphere ice response to variations in the southern annular mode abstract the coupled ocean atmosphere ice response to variations in the southern annular mode sam is examined in the national center for atmospheric research ncar community coupled climate model version 2 the model shows considerable skill in capturing the predominantly zonally symmetric sam while regional deviations between model and observation sam winds go a long way in explaining the generally small differences between simulated and observed sam responses in the ocean and sea ice systems vacillations in the position and strength of the circumpolar winds and the ensuing variations in advection of heat and moisture result in a dynamic and thermodynamic forcing of the ocean and sea ice both meridional and zonal components of ocean circulation are modified through ekman transport which in turn leads to anomalous surface convergences and divergences that strongly affect the meridional overturning circulation and potentially the pathways of intermediate water ventilation a heat budget analysis de

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

the sensitivity of stationary waves to variations in the basic state zonal flow abstract a linear primitive equation stationary wave model having high vertical and meridional resolution is used to examine the sensitivity of orographically forced primarily by himalayas stationary waves at middle and high latitudes to variations in the basic state zonal wind distribution we find relatively little sensitivity to the winds in high latitude but remarkable sensitivity to small variations in the subtropical jet fluctuations well within the range of observed variability in the jet can lead to large variations in the stationary waves of the high latitude stratosphere and to large changes even in tropospheric stationery waves implications for both sudden warmings and large scale weather are discussed

a general circulation model study of the atmospheric response to extratropical sst anomalies observed in 1950 79 abstract a 30 year experiment with an atmospheric general simulation model has been performed the lower boundary condition at all oceanic grid points between 38 s and 60 n has been prescribed to follow the observed month to month variation of the sea surface temperature sst field during the 1950 79 period much of the model diagnosis presented here pertains to the midlatitude atmospheric response to recurrent sst patterns in the north pacific and north atlantic in winter the principal modes of variability of the seasonally averaged 515 mb height and sst fields have been identified using rotated principal component rpc analysis the extrema of the first atmospheric mode reside over the north atlantic and eurasia whereas the second mode is associated with height anomalies in the north pacific north american sector cross correlation analysis reveals that these two atmospheric modes am linked to leading patterns of the sst field in the north atlantic and north pacific respectively it is also demonst

wave maintained annular modes of climate variability abstract the leading modes of month to month variability in the northern and southern hemispheres are examined by comparing a 100 yr run of the geophysical fluid dynamics laboratory gcm with the ncep ncar reanalyses of observations the model simulation is a control experiment in which the ssts are fixed to the climatological annual cycle without any interannual variability the leading modes contain a strong zonally symmetric or annular component that describes an expansion and contraction of the polar vortex as the midlatitude jet shifts equatorward and poleward this fluctuation is strongest during the winter months the structure and amplitude of the simulated modes are very similar to those derived from observations indicating that these modes arise from the internal dynamics of the atmosphere dynamical diagnosis of both observations and model simulation indicates that variations in the zonally symmetric flow associated with the annular modes are forced by eddy fluxes in the free troposphere while

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

left hand rule for synoptic eddy feedback on low frequency flow 1 in this study scale interaction between synoptic eddies and low frequency flow is investigated the synoptic eddy feedback is a key process in sustaining the low frequency flow we show clear evidence using ncep reanalysis data that there is a general underlying rule the left hand rule governing the synoptic eddy feedback onto low frequency flow this rule states that eddy vorticity fluxes are directed preferentially about 90 degrees toward their left hand side so that they converge into cyclonic flow and diverge from anticyclonic flow therefore the eddy vorticity flux plays a positive role in reinforcing low frequency flow citation kug j s and f f jin 2009 left hand rule for synoptic eddy feedback on low frequency flow geophys res lett 36 l05709 doi 10 1029 2008gl036435

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

observed evidence of an impact of the antarctic sea ice dipole on the antarctic oscillation abstracta lagged maximum covariance analysis mca is applied to investigate the linear covariability between monthly sea ice concentration sic and 500 mb geopotential height z500 in the southern hemisphere sh the dominant signal is the atmospheric forcing of sic anomalies throughout the year but statistically significant covariances are also found between austral springtime z500 and prior sic anomalies up to four months earlier the mca pattern is characterized by an antarctic dipole adp like pattern in sic and a positively polarized antarctic oscillation aao in z500 such long lead time covariance suggests the forcing of the aao by persistent adp like sic anomalies the leading time of sic anomalies provides an implication for skillful predictability of springtime atmospheric variability

zonal flow vacillation and eddy forcing in a simple gcm of the atmosphere abstract zonal flow vacillation with very long time scales is observed in a 3070 day simple gcm simulation with zonally symmetric forcing the long lasting zonal wind anomalies suggest that zonal flow vacillation is self maintained wave mean flow interactions are investigated by composite analysis and transform eulerian momentum budget analysis nonlinear life cycle simulations are conducted to demonstrate that each extreme phase of the zonal flow vacillation is a quasi stable state and is self maintained by the embedded synoptic eddies the firm eof mode of zonal mean wind shows an out of phase relation between anomalies at 60 s and at 40 s with a barotropic structure this structure is similar to the dominant vacillation pattern observed in the southern hemisphere the composite jet stream in the high low index phase of zonal flow vacillation shifts poleward equatorward from the time mean location and becomes broader narrower and weaker stronger composite eddies in the high index phase tilt nw

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

opposing effects of reflective and nonreflective planetary wave breaking on the nao planetary wave breaking pwb over the subtropical north atlantic is observed over 45 winters december 1958 arch 2003 using ncep ncar reanalysis data pwb is manifested in the rapid large scale and irreversible overturning of potential vorticity pv contours on isentropic surfaces in the subtropical upper troposphere as breaking occurs over the subtropical north atlantic an upper tropospheric pv tripole anomaly forms with nodes over the subtropical midlatitude and subpolar north atlantic the northern two nodes of this tripole are quite similar to the spatial structure of the north atlantic oscillation nao with positive polarity nonlinear reflection is identified in approximately a quarter of all pwb events following breaking two distinct circulation regimes arise one in response to reflective events and the other in response to nonreflective events for reflective events anomalies over the north atlantic rapidly propagate away from the breaking region along a poleward arching wave train over the eurasian continent the quasi stationary wave activity flux indicates that wave activity is exported out of the atlantic basin at the same time the regional poleward eddy momentum flux goes through a sign reversal as does the polarity of the nao for nonreflective events the dipole anomaly over the north atlantic amplifies diagnostics for nonreflective events suggest that wave activity over the azores gets absorbed allowing continued enhancement of both the regional poleward eddy momentum flux and the positive nao

observed antarctic interannual climate variability and tropical linkages abstractthis study reviews the mechanisms associated with antarctic tropical climate linkages and presents new analyses of the seasonality and spatial patterns of tropical climate signals in the antarctic for the late 1950s to the present tropical climate signals are primarily communicated to the antarctic via the pacific south america psa pattern and the southern annular mode sam the impacts of these circulation patterns and their tropical linkages are evident in regressions of seasonally stratified antarctic station temperature data and annually resolved ice core records on global fields of sea surface temperature sea level pressure and precipitation temperature and ice core anomalies in the antarctic peninsula region and adjoining areas of west antarctica are significantly impacted by the psa interpreted as a rossby wave train driven by anomalous tropical deep convection during enso events this pattern is most evident in the austral spring consistent with recent studies suggesting that atm

zonal eddy dynamics of the north atlantic oscillation abstract this research is an attempt to understand the dynamical mechanisms that drive the wintertime north atlantic oscillation nao on monthly and longer timescales in an earlier work by deweaver and nigam the authors showed that momentum fluxes from stationary waves play a large role in maintaining the zonal mean zonal wind u perturbations associated with the nao in this paper a linear stationary wave model is used to show that zonal mean flow anomalies in turn play a large role in maintaining the nao stationary waves a strong two way coupling thus exists between u and the stationary waves in which each is both a source of and a response to the other when forced by zonal eddy coupling terms terms that represent the interaction between nao covariant zonal mean zonal wind anomalies and the climatological eddy flow together with heating and transient fluxes the model produces a realistic simulation of the observed stationary wave pattern zonal eddy coupling terms make the largest contribution

a pv view of zonal flow vacillation abstract it is suggested here that the zonal flow vacillation of the southern hemisphere is caused by a mutual interaction between the barotropic shear of the zonal flow and the evolution of baroclinic eddies during the later stages of their lifecycle an index of the zonal wind anomaly difference between 40 and 60 s is defined for a 13 yr record of european centre for medium range weather forecasts ecmwf analyses periods are selected during which the zonal flow is at the extremes of its characteristic vacillation which are distinguished by a broad westerly jet with minor maxima near 30 and 60 s and a narrower jet peaked near 40 s the narrower 40 s jet has stronger cyclonic shear across the baroclinic zone these changes are accompanied by shifts in poleward eddy momentum flux on the 500 hpa surface and potential vorticity fluxes on the theta surfaces that lie in the midtroposphere which are both consistent with the maintenance of the zonal wind anomalies against friction series of synoptic maps