interannual enso and interdecadal enso like variability in the southern hemisphere tropospheric circulation abstract recent work has identified variability in the pacific ocean sst with a structure qualitatively similar to enso but at lower frequencies than enso zhang et al have documented the atmospheric circulation anomalies in the tropics and northern hemisphere that are associated with decadal enso like variability and compared these anomalies to those associated with the interannual enso cycle here the authors extend the study of zhang et al to the southern hemisphere using the national centers for environmental prediction national center for atmospheric research reanalysis data for 1958 96 consistent with previous studies the southern hemisphere circulation anomalies associated with enso display a teleconnection pattern from the central tropical pacific into the far southeastern pacific ocean comparatively larger circulation anomalies are found in the southern hemisphere associated with the decadal enso like variability though aloft the structure of the anomalies emphasizes the polar vortex wit

pacific interdecadal variability in this century s sea surface temperatures analysis of this century s sea surface temperatures over the pacific ocean reveals an interdecadal oscillation with a period of 15 20 years our results show that the well known 1976 77 climate regime shift is not unique but represents one of several phase transitions associated with this interdecadal oscillation also found around 1924 25 1941 42 and 1957 58 the oscillation s striking north south symmetry across the equator implies strong interactions between tropics and extratropics a mode with a period of approximately 70 years and an apparently different spatial pattern is also identified tentatively but has to be evaluated further using longer time series

anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

the vertical structure of temperature in the tropics different flavors of el nino to explore the vertical coherence of the vertical temperature structure in the atmosphere an analysis is performed of the full three dimensional spatial structure of the temperature field monthly mean anomalies from the 40 yr ecmwf re analysis era 40 for a core region of the tropics from 30 n to 30 s with results projected globally the focus is on the first three empirical orthogonal functions eofs two of which have primary relationships to el nino southern oscillation enso and feature rather different vertical structures the second eof 2 also has a weak enso signature but a very complex vertical structure and reflects mainly nonlinear trends some real but also some in large part spurious and associated with problems in assimilating satellite data the dominant pattern eof 1 in its positive sign features highly coherent zonal mean warming throughout the tropical troposphere from 30 n to 30 s that increases in magnitude with height to 300 hpa drops to zero about 100 hpa at the tropopause and has reverse sign to 30 hpa with peak negative values at 70 hpa spatially at low levels it shows warmth throughout most of the tropics although with weak or slightly opposite sign in the western tropical pacific and a strong reversed sign in the pacific subtropics coherent wave structures below 700 hpa at higher latitudes cancel out in the zonal mean however the structure becomes more zonal above about 700 hpa and features off equatorial maxima straddling the equator in the eastern pacific in the upper troposphere with opposite sign at 100 hpa as a signature of a forced rossby wave the corresponding sea level pressure pattern is similar to but more focused in equatorial regions than the southern oscillation pattern the time series highlights the 1997 98 el nino along with those in 1982 83 and 1986 87 and the 1988 89 la nina and correlates strongly with global mean surface temperatures missing however is the prolonged sequence of three successive el nino events in the early 1990s which are highlighted in eof 3 as part of a mainly lower frequency decadal variation that features modest zonal mean warming below 700 hpa cooling from 700 to 300 hpa and warming above 300 hpa peaking at 100 hpa and extending from 40 n to 50 s spatially at the surface this pattern is dominated by southern oscillation wave 1 structures throughout the tropics and especially the subtropics the regional temperature structures are coherent throughout the troposphere with strongest values in the pacific and extending well into the extratropics with a sign reversal at and above 100 hpa strong rossby wave signatures are featured in the troposphere with a distinctive quadrupole pattern that reverses at 100 hpa the vertical coherence of all patterns suggests that they should be apparent in broad layer satellite temperature records but that stratospheric anomalies are not independent the quite different three dimensional structure of these different patterns highlights the need to consider the full structure outside of the pacific and at all vertical levels in accounting for impacts of enso and how they relate to the global mean

interdecadal changes in the enso teleconnection to the caribbean region and the north atlantic oscillation abstract the el nino southern oscillation enso phenomenon and variability in the subtropical north atlantic high sea level pressure slp are known to affect rainfall in the caribbean region an el nino event is associated with drier than average conditions during the boreal summer of year 0 and wetter than average conditions during the spring of year 1 dry conditions during the summer of year 0 of an el nino are associated with the locally divergent surface circulation engendered by the eastward shift of deep convection in the pacific ocean wet conditions during the spring of year 1 of an el nino are associated with the lagged warming of the tropical north atlantic ocean variability in the strength of the north atlantic high is governed mainly by the north atlantic oscillation nao with a positive nao phase implying a stronger than normal high and vice versa the nao is negatively correlated with caribbean rainfall indirectly via anomalous sea surface temperatures sst associated with a

the south pacific meridional mode as a thermally driven source of enso amplitude modulation and uncertainty abstractthis study seeks to identify thermally driven sources of enso amplitude and uncertainty as they are relatively unexplored compared to wind driven sources pacific meridional modes are argued to be wind triggers for enso events this study offers an alternative role for the south pacific meridional mode spmm in enso dynamics not as an enso trigger but as a coincident source of latent heat flux lhf forcing of enso ssta that if correctly incorrectly predicted could reduce increase enso prediction errors we utilize a coupled model simulation in which enso variability is perfectly periodic and each el nino experiences identical wind stress forcing differences in el nino amplitude are primarily thermally driven via the spmm when el nino occurs coincidentally with positive phase spmm the positive spmm lhf anomaly counteracts a fraction of the lhf damping of el nino allowing for a more intense el nino if the spmm phase is instead negative the spmm lhf amplifies the lhf damping of el nin

southern hemisphere circulation and relations with sea ice and sea surface temperature abstract relationships on the seasonal timescale between southern hemisphere 500 hpa height sea surface temperature and antarctic sea ice variability have been investigated using ncep ncar reanalyses ncep sea surface temperatures and met office sea surface temperature and sea ice data the dominant region of interannual variability in the southern hemisphere circulation over the southeast pacific ocean is found to be related to enso variability in tropical pacific sea temperatures as shown in a number of earlier papers it is also related to antarctic sea ice variability where an out of phase relationship is found between sea ice extent in the central pacific and in the southwest atlantic ocean sea ice extent is enhanced in one region when the atmospheric flow anomaly is equatorward presumably through a combination of anomalous heat flux and direct advection at the same time the atmospheric flow anomaly in the other region tends to be poleward resulting in a poleward retreat in the sea ice ed

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

relationships between the interannual variability of antarctic sea ice and the southern oscillation abstract a climatology of antarctic sea ice extent based on 20 years of data 1973 1992 is presented including measures of interannual variability and extrema in the first half of the year the greatest variability is found in the western hemisphere particularly in the weddell and ross sea regions while in the second semester the variability displays a considerable degree of zonal symmetry we have used this dataset to explore the possible links between antarctic sea ice extent and the southern oscillation index soi to do this we have calculated their correlation for all pairings of calendar months as well as with the soi taken from the year before and subsequent to that of the time of the sea ice data most of the correlations assume their largest magnitude when the soi leads the anomalies in the sea ice but these differ considerably between the three ocean basins the extent of indian ocean sea ice in the months april through july is positively correlated with the soi during most of the previou

decadal sea level variability in the south pacific in a global eddy resolving ocean model hindcast sea level variability and related oceanic changes in the south pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy resolving ocean general circulation model ogcm for the earth simulator ofes along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992 the first empirical orthogonal function mode of sea level anomalies slas of ofes exhibits broad positive slas over the central and western south pacific the corresponding principal component indicates roughly stable high low and high slas separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s consistent with tide gauge and satellite observations these decadal changes are accompanied by circulation changes of the subtropical gyre at 1000 m depth and changes of upper ocean zonal current and eddy activity around the tasman front in general agreement with previous related studies it is found that sea level variations in the tasman sea can be explained by propagation of long baroclinic rossby waves forced by wind stress curl anomalies if the impact of new zealand is taken into account the corresponding atmospheric variations are associated with decadal variability of el nino southern oscillation enso thus decadal sea level variability in the western and central south pacific in the past three and half decades and decadal enso variability are likely to be connected the sea level rise in the 1990s which attracted much attention in relation to the global warming is likely associated with the decadal cooling in the tropical pacific

multiproxy summer and winter surface air temperature field reconstructions for southern south america covering the past centuries we statistically reconstruct austral summer winter surface air temperature fields back to ad 900 1706 using 22 20 annually resolved predictors from natural and human archives from southern south america ssa this represents the first regional scale climate field reconstruction for parts of the southern hemisphere at this high temporal resolution we apply three different recon struction techniques multivariate principal component regression composite plus scaling and regularized expectation maximization there is generally good

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

late holocene teleconnections between tropical pacific climatic variability and precipitation in the western usa evidence from proxy records decadal to multidecadal fluctuations between drought and relatively more moist conditions are a defining characteristic of precipitation variability in the western usa in an attempt to better understand the forcing mechanisms responsible for producing this variability relationships between proxy indices of tropical climatic variability and precipitation related reconstructions in the western usa are examined the tropical proxies include the o record from the quelccaya ice cap southern subtropical andes and the lacustrine sedimentation record from laguna pallcacocha near equatorial andes the precipi tation related records are tree ring reconstructions of river flow drought severity and precipitation over the contiguo usa one new finding is a consistent relation between decadal variability in el ninno activity and precipitation related proxies through much of the western usa during the past 1200 years surpris ingly the proxy records do not show a systematic link between inferred el ninno activity and precipitation in the interior southwest usa a second new result is the existence of relationships at decadal to multidecadal timescales between fluctuations in quelccaya o precipitation related proxies from the western usa and proxy records from the pacific basin this finding links the quelccaya record to the transhemi spheric pacific decadal scale climatic variability documented from proxy records by villalba et al 2001 and suggests that similar changes in the large scale circulation changes accompany both the decadal and multidecadal signals a composite constructed using gridded proxy precipitation constructed on the basis of decadal scale fluctuations in inferred el ninno activity shows a pattern rather different to ninno based teleconnection maps for the instrumental record in the proxy based composite positive values cover much of the extreme western west central and southeastern usa with negative values in the central mis sissippi valley the interior southwest shows essentially no response a second composite based on multi decadal variability in quelccaya o shows a well developed dipole pattern across the western usa with opposing centres in the interior southwest and northwest it is suggested that this dipole pattern results from multidecadal variability in tropical pacific ssts and resulting changes in the strength of the northeast pacific high and the latitudinal distribution of cool season westerlies across the eastern north pacific and western usa

aeolian particles in marine cores as a tool for quantitative high resolution reconstruction of upwelling favorable winds along coastal atacama desert northern chile upwelling areas play a major role in ocean biogeochemical cycles and ultimately in global climate especially in higly productive regions as the south eastern pacific this work is based on the analysis of the aeolian lithic particles accumulated in laminated sediments off mejillones 23 s in the eastern boundary humboldt current system it proposes a high resolution quantitative reconstruction of the upwelling favorable southerly wind strength in the past 250 years comparing its variability with changes in organic carbon export preserved changes to the sea bottom the increase of the intensity and variability in fluxes of particles larger than 35 m and 100 m since the second half of the 19th century and during the 20th century confirms a general strengthening of southerly winds in the region spectral analysis on the complete time series of yearly depositional fluxes indicates that sedimentary variability can be explained by a combination of interannual enso to decadal pdo oscillations similar to the ones yielded by the analysis of the interdecadal pacific oscillation index however when applied separately to the lithic fluxes of the first and last centuries of the time series the method shows that relative to the one of the interannual mode of variability the influence of the decadal mode has increased in the recent period based on the presence absence of particles with sizes larger than 35 100 m each year of the time series is classified as a low wind 12 m s year from the ad 1754 1820 period to the ad 1878 1998 one the proportion of low and intermediate wind years decreased from 12 and 74 to 3 and 68 respectively whereas the proportion of strong wind years increased from 14 to 29 for these periods the mean organic carbon also increased 22 stating the strong relation between export preservation productivity rate and southerly wind intensity in the recent period from ad 1950 on for which the oceanic nino index is available the strong wind years ad 1982 1983 1994 and 1997 correspond to large values of this index suggesting that constructive interferences that result from the interplay between interannual and decadal oscillations modes might explain in part the reinforcement of the winds along the north chilean coast

a central tropical pacific coral demonstrates pacific indian and atlantic decadal climate connections while instrumental and proxy based climate records describe significant decadal scale climate variabil ity throughout the tropical pacific indian and atlantic oceans the processes responsible for these variations and their interactionsare not readily apparent from the obs er vations a new 112 yr coral based sea surface temperature sst reconstruction from palmyra island in the central tropical pacific ctp exhibitss trong decadal variability with an amplitude of roughly 0 3 c a 12 13yr period sig nal in thiscoral record ishighly coherent with long equa torial atlantic and indian ocean climate records implying a unified phenomenon the atlantic pattern suggests that it may fall under direct influence of anomaloussst in the ctp as it does over interannual timescales while the in dian ocean pattern exhibits maximum response during the switch between warm cold states in the tropical pacific the results demonstrate that the ctp has played a significant role in determining the expression of global decadal climate variability over the twentieth century

enso like and enso induced tropical pacific decadal variability in cgcms abstractoutputs from coupled general circulation models cgcms are used in examining tropical pacific decadal variability tpdv and their relationships with el nino southern oscillation enso herein tpdv is classified as either enso induced tpdv eit or enso like tpdv elt based on their correlations with a decadal modulation index of enso amplitude and spatial pattern eit is identified by the leading eof mode of the low pass filtered equatorial subsurface temperature anomalies and is highly correlated with the decadal enso modulation index this mode is characterized by an east west dipole structure along the equator elt is usually defined by the first eof mode of subsurface temperature of which the spatial structure is similar to enso generally this mode is insignificantly correlated with the decadal modulation of enso eit closely interacts with the residuals induced by enso asymmetries both of which show similar spatial structures on the other hand elt is controlled by slowly varying oc

the southern oscillation part vi anomalies of sea level pressure on the southern hemisphere and of pacific sea surface temperature during the development of a warm event abstract the paper shows the discrete mean three month anomalies of sea level pressure on the southern hemisphere during the year before and the year of a warm event in the southern oscillation together with associated anomalies of sea surface temperature in the south pacific 0cean the two sets anomalies develop in a parallel and physically logical sequence over the south pacific ocean in conjunction with changes in the south pacific convergence zone nearly all of the southern hemisphere responds to the southern oscillation but the response is largest in the australia south pacific sector large anomalies of sea level pressure form well ahead of any on the northern hemisphere and this observation together with the conspicuous anomalies in the region of australia and the south pacific suggest that the origin of the southern oscillation must be sought in this region

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

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

atmosphere sea ice low frequency variability with a simple model of the southern hemisphere summary a simple primitive equation general circulation model sgcm is used as a representation of an aquaplanet with no orography to model constant southern hemisphere winter conditions the statistical signie cance of the decadal and quasi biennial variability is erst assessed in a long time sgcm run by means of a frequencydomain statistical decomposition the modelled long wave atmospheric pattern is then associated with the observed southern hemisphere annular mode as suggested by previous studies using the same sgcm a simple linear relationship between the low level wind and the ice velocity is then introduced into the sgcm to investigate the feedbacks between the sea ice cover and the baroclinic waves the zonal mean state reached by the sea ice cover in a long coupled run a few hundred years exhibits characteristics similar to the observations investigation of the low frequency variability in the coupled simulation leads to the following results 1 statistically signie cant variability is observed on interdecadal decadal interannual and quasi biennial time scales 2 interdecadal decadal and quasi biennial signals are associated with the atmospheric annular mode that forces changes in the northward extent of the sea ice cover at all southern ocean longitudes 3 the interannual signal 3 6 year period exhibits spatio temporal patterns and propagation speed similar to the wellknown antarctic circumpolar wave

southern hemisphere origins of the 1976 climate shift 1 observations from the tropical pacific ocean identify an abrupt climate shift in 1976 with surface temperatures changing from cooler than normal to warmer than normal in the span of about 1 year model results show that this climate shift originates with subsurface temperature anomalies in the south tropical pacific ocean which propagate first to the western boundary then northward to the equator and finally eastward along the equator to 140 w where they rise to the surface the results suggest that changes in the north pacific respond to changes in the tropical pacific

low frequency variability of the antarctic circumpolar wave this study evaluates the antarctic circumpolar wave acw variability in the southern ocean using a 27 year series of sea surface temperature sst and sea level pressure slp from a cross covariance analysis we find that the strongest covariation between the extratropical wavenumber 2 in sst and in slp is during the austral summer in the south pacific ocean examination of the time series reveals two timescales of variability a wavenumber 2 structure in sst and slp anomalies correlates well at interannual ia timescales when enso driven teleconnections seem to energize the acw moreover in the 1973 1999 epoch the acw has been modulated by interdecadal id variability possibly related to the southern oscillation

austral spring southern hemisphere circulation and temperature changes and links to the spcz abstractsignificant austral spring trends have previously been observed in west antarctica and antarctic peninsula temperatures and in atmospheric circulation across the southern pacific and atlantic here physical mechanisms for the observed trends are investigated through analysis of monthly circulation and temperatures from the era interim dataset and outgoing longwave radiation olr data the negative pressure trend over the south pacific during spring is strongest in september while the positive pressure trend over the south atlantic is strongest in october pressure trends in november are generally nonsignificant the authors demonstrate that a significant september trend toward increased convection reduced olr in the poleward portion of the south pacific convergence zone spcz is statistically related to rossby wave like circulation changes across the southern oceans the wave response is strongest over the south pacific in september and propagates eastward to the south atlantic in october o

weather regimes in the south american sector and neighbouring oceans during winter we classified 34 years of winter daily 500 hpa geopotential height patterns over the eastern south pacific south america south atlantic region using the k means clustering method we found a significant classification into five weather regimes wrs defined as the most frequent large scale circulation anomalies wr1 trough centred downstream of the drake passage wr2 trough over the sw pacific and ridge downstream wr3 ridge over the se pacific and nw se trough downstream wr4 trough over the se pacific and nw se ridge downstream and wr5 weak ridge to the west of southern south america we also analysed their persistence and temporal evolution including transitions between them and development around onsets and breaks of each regime the preferred transitions wr1 wr3 wr2 wr4 wr1 and also wr1 wr3 wr2 wr1 suggest the progression of a rossby wave like pattern in which each of the regimes resemble the pacific south america modes significant influence of the wrs on local climate over argentina was found the preferred transitions wr1 wr3 and wr3 wr2 induce sustained cold conditions over patagonia and over northern argentina respectively the most significant change in precipitation frequency is found for wr3 with wetter conditions over all the analysed regions finally the interannual to interdecadal significant variations in the occurrence of these regimes were discussed wr1 and wr3 are more frequent and wr2 is less frequent during el nino and wr2 and wr5 are more frequent and wr1 is less frequent during la nina a significant decrease in wr2 and increase of wr4 and wr5 during the 1970s and early 1980s were found

dominant covarying climate signals in the southern ocean and antarctic sea ice influence during the last three decades abstracta composite dataset comprising geopotential height sea surface temperature zonal and meridional surface winds precipitation cloud cover surface air temperature latent plus sensible heat fluxes and sea ice concentration has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013 three covarying climate signals associated with variations in the sea ice distribution around antarctica have been detected through the application of the multiple taper method with singular value decomposition mtm svd features of the established patterns of variation over the southern hemisphere extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations the climate patterns considered here are the southern annular mode sam the pacific south american psa teleconnection the semiannual oscillation sao and the zonal wavenumber 3 zw3 mode it is shown that most of the sea ice temporal variance i

influence of the pacific japan pattern on indian summer monsoon rainfall abstractthis study discusses the impact of the pacific japan pj pattern on indian summer monsoon ism rainfall and its possible physical linkages through coupled and uncoupled pathways empirical orthogonal function analysis of 850 hpa relative vorticity over the western north pacific wnp is used to extract the pj pattern as the leading mode of circulation variability the partial correlation analysis of the leading principal component reveals that the positive pj pattern which features anticyclonic and cyclonic low level circulation anomalies over the tropical wnp and around japan respectively enhances the rainfall over the southern and northern parts of india the northwestward propagating rossby waves in response to intensified convection over the maritime continent reinforced by low level convergence in the southern flank of westward extended tropical wnp anticyclone increase rainfall over southern peninsular india meanwhile the anomalous moisture transport from the warm bay of bengal due t

the antarctic circumpolar wave a combination of two signals abstract a simplified view of the possible mechanisms behind the antarctic circumpolar wave acw interannual variability is provided by a frequency domain decomposition of several observed atmospheric and oceanic variables two significant interannual signals with different temporal and spatial characteristics are identified in the southern ocean and most of the variance of the acw in the interannual band can be accounted for by a linear combination of them the first signal has a period of oscillation of around 3 3 yr and a zonal wavenumber 3 structure across the southern ocean it involves self sustained fluctuations inherent in the southern ocean and driven by coupled air sea interactions in which the atmosphere and the ocean mutually force one another this signal is represented by an atmospheric standing oscillation with centers at fixed locations around antarctica and a propagating oceanic pattern in which the surface antarctic circumpolar current plays an essential role the second signal has a

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

the signature of enso in global temperature and precipitation fields derived from the microwave sounding unit abstract global temperature anomalies associated with enso are investigated making use of a 13 year record of gridded temperature and precipitation data from the microwave sounding unit msu the warm phase of the enso cycle during this period was characterized by an overall warming of the tropical troposphere superimposed upon a distinctive equatorially symmetric dumbbell shaped pattern straddling the equator near 140 w accompanied by negative anomalies along the equator over the western pacific by means of singular value decomposition svd analysis it is shown that this pattern fluctuated in phase with the displacements of convective activity over the equatorial pacific as reflected in the anomalies in outgoing longwave radiation olr and msu precipitation fields fluctuations in mean tropical tropospheric temperature lagged the olr anomalies and the related temperature pattern by about 3 months the same dumbbell shaped pattern was evident with reversed polarity in the lower stratosphere tog

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

interdecadal dynamics of the north pacific ocean abstract an isopycnal ocean model forced by ncep ncar reanalysis wind stresses and heat fluxes is used to study the interdecadal variability of the pacific ocean in the 1958 97 period a reasonable agreement is found between the model s modes of variability and those obtained by other researchers from both 100 years of observations and theoretical predictions in agreement with previous observational work decadal and interdecadal timescales have different descriptions and from this study it is suggested that they indeed have different dynamics this study focuses on the dynamics of the ocean s interdecadal variability that is of timescales of about 20 yr the decadal timescale that is 10 yr is briefly outlined and compared with previous studies it is found that atmospheric heat fluxes play a key role in establishing the interdecadal sst pattern in the midlatitudinal north pacific these fluxes would excite a high baroclinic mode igniting a series of events that move around the basin in midlatitu

dynamics of sea surface temperature anomalies in the southern ocean diagnosed from a 2d mixed layer model we analyze the processes responsible for the generation and evolution of sea surface temperature anomalies observed in the southern ocean during a decade based on a 2d diagnostic mixed layer model in which geostrophic advection is prescribed from altimetry anomalous air sea heat flux is the dominant term of the heat budget over most of the domain while anomalous ekman heat fluxes account for 20 40 of the variance in the latitude band 40 60 s in the acc pathway lateral fluxes of heat associated with anomalous geostrophic currents are a major contributor dominating downstream of several topographic features reflecting the influence of eddies and frontal migrations a significant fraction of the variability of large scale sst anomalies is correlated with either enso or the sam each mode contributing roughly equally the relation between the heat budget terms and these climate modes is investigated showing in particular that anomalous ekman and air sea heat fluxes have a co operating effect with regional exceptions hence the large sst response associated with each mode it is further shown that enso or sam locked anomalous geostrophic currents generate substantial heat fluxes in all three basins with magnitude comparable with that of atmospheric forcings for enso and smaller for the sam except for limited areas enso locked forcings generate sst anomalies along the acc pathway and advection by mean flows is found to be a non negligible contribution to the heat budget exhibiting a wavenumber two zonal structure characteristic of the antarctic circumpolar wave by contrast sam related forcings are predominantly zonally uniform along the acc hence smaller zonal sst gradients and a lesser role of mean advection except in the southwest atlantic while modeled sst anomalies are significantly correlated with observations over most of the southern ocean the analysis of the data model discrepancies suggests that vertical ocean physics may play a significant role in the nonseasonal heat budget especially in some key regions for mode water formation

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

enhanced multidecadal climate variability in the seventeenth century from coral isotope records in the western indian ocean 1 the slowly growing coral diploastreaheliopora affords a novel opportunity to obtain multicentury records of paleoclimate including details of the interannual rhythms associated with the el nino southern oscillation enso system we examine climate variability in an enso teleconnected region using new oxygen isotope records from d heliopora spanning most of the twentieth 1896 1998 and seventeenth 1622 1722 centuries from the mafia archipelago tanzania the modern record demonstrates coherency with relevant instrumental and proxy time series documents twentieth century warming and displays significant power at enso periodicities the seventeenth century record lacks any trend exhibits interannual variance comparable to the modern record and displays a pronounced interdecadal signal not evident in the twentieth century that correlates with other tropical and hemispheric climate records we find no clear evidence of solar irradiance influence on interannual variability in the western indian ocean during these intervals although the mean sea surface temperature appears to vary inversely with insolation

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

decadal variation of the annual cycle in the australian dataset abstract during the 1970s and 1980s elements of the atmospheric circulation over the southern hemisphere changed markedly from their state in the two previous decades the change was evident in the zonal asymmetry especially in the zonal harmonic wave 3 at higher latitudes and in the semiannual wave in pressure and wind the semiannual wave changed in the same sense in all three southern oceans but by the largest amount in the south pacific ocean the second harmonic in a 12 month series by which we describe the semiannual wave dominates the shape of the long term mean annual curve of sea level pressure in mid and high latitudes this harmonic weakened during the period and its midlatitude peak disappeared in the south pacific ocean as part of the low frequency changes during the 18 years from 1972 to 1988 the central pressure in the subantarctic trough fell the trough moved northward and the subtropical ridge moved south the meridional movement of the trough and the ridge and the concurrent

the interconnected global climate system a review of tropical polar teleconnections abstractthis paper summarizes advances in research on tropical polar teleconnections made roughly over the last decade elucidating el nino southern oscillation enso impacts on high latitudes has remained an important focus along different lines of inquiry tropical to polar connections have also been discovered at the intra seasonal timescale associated with madden julian oscillations mjo on the timescale of decades changes in mjo phases can result in temperature and sea ice changes in the polar regions of both hemispheres moreover the long term changes in sst of the western tropical pacific tropical atlantic and north atlantic ocean have been linked to the rapid winter warming around the antarctic peninsula while sst changes in the central tropical pacific have been linked to the warming in west antarctica rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal timescales enso related tropical sst anomal

statistics and dynamics of persistent anomalies abstract persistent anomalies with recurrent spatial patterns play an important role in the atmosphere s low frequency variability we establish a connection between statistical and dynamical methods of description and prediction of persistent anomalies this is done by computing and analyzing the empirical orthogonal functions eofs in a simple deterministic model on the one hand and in southern hemisphere geopotential heights on the other the dynamical model is governed by the fully nonlinear equivalent barotropic vorticity equation on the sphere with simplified forcing dissipation and topography model solutions exhibit persistent anomalies identifiable with blocked zonal and wave train anomalies in northern hemisphere atmospheric data flow structures similar to the patterns above occur as high variance eofs of this nonlinear model the southern hemisphere data we analyze consist in gridded daily maps of 500 mb heights from june 1972 to july 1983 two types of persistent anomalies appear in t

a diatom inferred record of lake variability during the last 900 years in lutzow holm bay east antarctica decadal centennial scale climate variability in coastal antarctica remains poorly understood due to the limited number of highly resolved well dated records we present a 900 year decadal scale reconstruction based on sedimentary diatoms from lake abi in lutzow holm bay east antarctica hydrological change is inferred from diatom ecological preferences in conjunction with an existing regional training set and implies that lake water specific conductivity depth and nitrogen availability are the key drivers of diatom assemblage change lake abi underwent a series of subtle environmental changes related to these environmental variables possibly driven by changes in catchment snow melt and the duration of seasonal ice cover ordination is used to trace the major patterns of change in the diatom community with notable shifts identified between 470 and 400 and at 350 cal a bp where present ce 1950 the frequency of environmental variability at lake abi is broadly consistent with a record of the interdecadal pacific oscillation during the last millennium but contrasts with the apparent climate stability elsewhere in eastern antarctica further research is required to constrain the limnological and ecological responses of lakes in coastal antarctica to obtain more rigorous palaeoclimate reconstructions from these sites of immense potential

deformation behavior during blind thrust translation as a function of fault strength deformation partitioning between translation and distortion for a thrust sheet and for the roof sequence above a moving thrust horse were analyzed in terms of the role of fault strength using finite element models greater frictional resistance on the thrust decollement decreased fault translation increased distortion of the thrust sheet and roof sequence and increased the ratio of backthrusting to forethrusting for the roof sequence in all models with weak decollements 0 35 the ratio of tip line propagation to thrust displacement is very high during initial thrust movement but decreases significantly during later fault motion this observation supports interpretations in natural thrust systems where thrust faults propagate large distances before accumulating significant displacements the tip lines for weak decollements also propagated into the foreland well in advance of the distortion front in the overlying thrust sheet or roof sequence this result does not support interpretations from natural systems for the existence of ductile beads in front of propagating thrusts but rather suggests that recent models for fault arrest or displacement gradient folds may be mechanically valid in addition no model for roof sequences yielded a simple end member response of only backthrusting or forethrusting suggesting that the many blind thrust belts where only one response has been interpreted may need to be re examined finally in those cases where more than one thrust flat moves simultaneously in the models partitioning of displacement and distortion in space and time changes significantly this result supports interpretations from natural systems where more than one thrust is thought to move at once

the effects of the indo pacific warm pool on the stratosphere sea surface temperature sst in the indo pacific warm pool ipwp plays a key role in influencing east asian climate and even affects global scale climate change this study defines ipwp nino and ipwp nina events to represent the warm and cold phases of ipwp sst anomalies respectively and investigates the effects of these events on stratospheric circulation and temperature results from simulations forced by observed sst anomalies during ipwp nino and nina events show that the tropical lower stratosphere tends to cool during ipwp nino events and warm during ipwp nina events the responses of the northern and southern polar vortices to ipwp nino events are fairly symmetric as both vortices are significantly warmed and weakened however the responses of the two polar vortices to ipwp nina events are of opposite sign the northern polar vortex is warmed and weakened but the southern polar vortex is cooled and strengthened these features are further confirmed by composite analysis using reanalysis data a possible dynamical mechanism connecting ipwp sst to the stratosphere is suggested in which ipwp nino and nina events excite teleconnections one similar to the pacific north america pattern in the northern hemisphere and a rossby wave train in the southern hemisphere which project onto the climatological wave in the mid high latitudes intensifying the upward propagation of planetary waves into the stratosphere and in turn affecting the polar vortex

the great atacama flood of 2001 and its implications for andean hydrology in february 2001 widespread flooding occurred throughout the atacama desert of northern chile and southern peru it was particularly severe in the rio loa basin where roads and bridges were disrupted and the town of calama inundated the instantaneous peak flow in the rio salado a tributary of the rio loa reached 310 m3 s 1 an order of magnitude higher than any previously recorded event the flood is estimated to have a return period of 100 200 years and is shown to have been caused by intense long duration rainfall in the western cordillera associated with la nina the surface water response is typical of arid areas and highly dependent on antecedent conditions but is quite different in perennial and ephemeral catchments ephemeral flood flows suffer high transmission losses recharging phreatic aquifers perennial rivers have lower runoff coefficients but baseflow levels remained high after the event for several months due to bank storage rebound and interflow extremely high energies of 3000 w m 2 were generated by the floods in the cordillera becoming less in the precordillera and downstream erosion and sediment transport were consequently highest in the upper and middle reaches of the rivers with mixed erosion deposition in the lowest reach the new insights gained from the interpretation and quantification of this event have important implications for palaeoenvironmental analysis hazard management water resource evaluation and the palaeohydrological evolution of the andes copyright 2005 john wiley sons ltd

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

a 700 year record of southern hemisphere extratropical climate variability annually dated ice cores from west and east antarctica provide proxies for past changes in atmospheric circulation over antarctica and portions of the southern ocean temperature in coastal west and east antarctica and the frequency of south polar penetration of el nino events during the period ad 1700 1850 atmospheric circulation over the antarctic and at least portions of the southern hemisphere underwent a mode switch departing from the out of phase alternation of multi decadal long phases of eof1 and eof2 modes of the 850 hpa field over the southern hemisphere as defined in the recent record by thompson and wallace 2000 thompson and solomon 2002 that characterizes the remainder of the 700 year long record from ad 1700 to 1850 lower tropospheric circulation was replaced by in phase behavior of the amundsen sea low component of eof2 and the east antarctic high component of eof1 during the first phase of the mode switch both west and east antarctic temperatures declined potentially in response to the increased extent of sea ice surrounding both regions at the end of the mode switch west antarctic coastal temperatures rose and east antarctic coastal temperatures fell respectively to their second highest and lowest of the record polar penetration of el nino events increased during the mode switch the onset of the ad 1700 1850 mode switch coincides with the extreme state of the maunder minimum in solar variability late 20th century west antarctic coastal temperatures are the highest in the record period and east antarctic coastal temperatures close to the lowest since ad 1700 extratropical regions of the southern hemisphere have experienced significant climate variability coincident with changes in both solar variability and greenhouse gases

forcing of the antarctic circumpolar wave by el nino southern oscillation teleconnections we address several issues regarding the antarctic circumpolar wave acw these include the extent to which the acw is related to el nino southern oscillation enso cycles and the need to reconcile differences between the observed zonal wavenumber 2 pattern and the wavenumber 3 pattern found in coupled ocean atmosphere models in the present study we revisit the sea surface temperature sst signal of the observed acw we find that the associated sst variations may be decomposed into several empirical orthogonal functions eofs that are linearly independent the first four eofs describe 84 of the total variance on timescales of 3 7 years and superposition of sst signals of the four eofs reproduces sst signals of the observed acw given that eof analysis can only describe standing oscillations we then employ complex eof ceof analysis suitable for studying propagating waves the first two ceofs denoted ceofsst1 and 2 account for 70 of the total variance and the sst variability reconstructed from them again reproduces the observed acw the real part of ceofsst1 44 of the total variance is similar to the first real eof eofsst1 both eofsst1 and ceofsst1 may be identified with enso and have a wavenumber 2 zonal pattern in the southern middle to high latitudes ceofsst1 is the major constituent of the acw in the period of 1981 1997 the associated atmospheric circulation displays a pacific south america psa pattern statistical analyses demonstrate that the psa pattern teleconnected to enso is the major mechanism that forces this principal constituent of the acw ceofsst2 26 of the total variance has a zonal wavenumber 3 pattern in the same latitude band similar to that simulated by several coupled models we suggest that if enso is not adequately resolved in coupled models but structures with zonal wavenumber 3 pattern are then the modeled acw would appear to have a zonal wavenumber 3 pattern

nonstationary impacts of the southern annular mode on southern hemisphere climate abstract the temporal stability of the southern annular mode sam impacts on southern hemisphere climate during austral spring is analyzed results show changes in the typical hemispheric circulation pattern associated with sam particularly over south america and australia between the 1960s 70s and 1980s 90s in the first decades the sam positive phase is associated with an anomalous anticyclonic circulation developed in the southwestern subtropical atlantic that enhances moisture advection and promotes precipitation increase over southeastern south america sesa on the other hand during the last decades the anticyclonic anomaly induced by the sam s positive phase covers most of southern south america and the adjacent atlantic producing weakened moisture convergence and decreased precipitation over sesa as well as positive temperature anomaly advection over southern south america some stations in the australia new zealand sector and africa exhibit significant correlations between the sam and prec

on the functioning of the southern oscillation in the south american sector part i surface climate abstract the functioning of the southern oscillation so over south america and the surrounding tropical atlantic and eastern pacific oceans is studied through analyses of bimonthly patterns of correlation between an so index and the fields of pressure wind temperature and rainfall hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation most pronounced is the anomalously low pressure over the eastern pacific during the negative so phase defined by anomalously low high pressure at tahiti darwin consistently positive so pressure correlations over the eastern tropical pacific extend eastward into the north atlantic region and southern south america during the respective winter semester during the austral winter the tendency for anomalously abundant rainfall in central chile during the negative so phase appears related to an anomalously weak and northward displaced south pacific subtropical high while relativ

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract the role of tephras in the nz intimate project is a critical one because most high resolution palaeoclimatic records are linked and dated by one or more tephra layers in this review first we document eruptive distributional and compositional fingerprinting data both mineralogical and geochemical for 22 key marker tephras erupted since 30 000 years ago to facilitate their identification and correlation we include new glass compositional data the selected marker tephras comprise 10 from taupo and nine from okataina volcanoes rhyolitic one from tuhua volcano peralkaline rhyolitic and one each from tongariro and egmont volcanoes andesitic second we use four approaches to develop 2 age models for the tephras youngest to oldest 1 calendar ages for kaharoa and taupo y were obtained by wiggle matching log derived tree ring sequences dated by 14c 2 whakaipo v was dated using an age depth model from peat 3 14 tephras in the montane kaipo peat sequence waimihia s unit k whakatane tuhua mamaku rotoma opepe e poronui c karapiti b okupata konini waiohau rotorua rerewhakaaitu were dated by simultaneously wiggle matching stratigraphic position and 51 independent 14c age points against intcal04 using bayesian probability methods via both oxcal and bpeat and 4 the five oldest tephras erupted before ca 18 000 cal yr bp were dated by calibrating limited numbers of 14c ages using intcal04 okareka or comparison curves of the expanded cariaco basin sequence te rere kawakawa oruanui poihipi okaia kawakawa oruanui tephra the most widely distributed marker tephra was erupted probably ca 27 097 957 cal yr bp potential dating approaches for the older tephras include their identification in antarctic ice cores if present or annually laminated sediments for which robust calendar age models have been constructed high precision ams 14c dating on appropriate material from environmentally stable sites systematic luminescence dating or new radiometric techniques e g u th he if suitable minerals are available and errors markedly reduced further application of bayesian age modelling to stratigraphic sequences of 14c ages possibly augmented with luminescence ages may help refine age models for pre holocene tephras with the largest errors finally we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the new zealand region which is a key objective of australasian and southern hemisphere intimate projects