differences in el nino response over the southern hemisphere southern hemisphere sh circulation conditions during austral springs of enso events are examined based on previous knowledge that sst variations over the subtropical south central pacific sscp region are linked to differences among el nino en events a stratification of the springs associated with en events was performed according to sst conditions over the el nino 3 4 sector and over the sscp region the en events associated with cold conditions in the sscp wc exhibit enhanced convection not only in the intertropical convergence zone over the central equatorial pacific but also in the south pacific convergence zone spcz extended south eastward into the subtropical regions the resulting heating forcing intensifies a localized overturning cell which is associated with an anomalous rossby wave source in the central south pacific extratropical region neither the rossby wave source nor the associated wave pattern is evident during en events associated with warm conditions in the sscp and inactive spcz ww the basic features that characterize the differences in the en response over the south pacific can also be identified through the analysis of the spcz activity over the central south pacific the fact that variations in spcz activity lead sst anomaly changes in the sscp would indicate that the differences in the en response over the sh might be mainly driven by atmospheric changes which induces extratropical sst anomalies the differences in the circulation anomalies that characterize both types of en response over the sh were further explored through the analysis of the activity of the three leading modes of circulation variability the combined effect of the three leading patterns describes in some extent the intensification weakening of the cyclonic circulation anomaly observed over the southeastern pacific in wc ww associated with an active inactive spcz in particular the interdecadal variability observed in the pacific by many previous studies influences the circulation response to enso over the sh mainly through changes in the activity of the sh annular mode

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

atmosphere ocean mechanisms of climate anomalies in the angola tropical atlantic sector abstract interannual variations in the large scale atmospheric and oceanic fields over the tropical atlantic are studied in relation to rainfall anomalies on the angola coast departure patterns are constructed by stratification with respect to extremely dry and wet years and by correlation with rainfall in angola which is concentrated in march april the analysis suggests a causality chain of atmospheric oceanic anomalies variations of westward wind stress on the western equatorial atlantic constitute an early link in this chain the annual cycle is characterized by a relaxation of the wind stress from september november to february march anomalous seasonal relaxation of easterly wind stress over the western equatorial atlantic remotely forces the sea surface temperature sst departures in the eastern south atlantic a large relaxation being followed by positive sst departures sea surface temperature modulates the rainfall over downstream angola by controlling the atmospheric moisture and stability

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

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

importance of the indian ocean for simulating rainfall anomalies over eastern and southern africa the relative contributions of the indian ocean and pacific ocean sea surface temperatures ssts to the rainfall variability over eastern central and southern africa during the austral spring summer are examined the variability of african rainfall is statistically related to both oceans but the variability in the two oceans is also related to separate the effects of the indian and pacific oceans a suite of numerical model simulations is presented goga the atmosphere is forced by observed ssts globally ioga the atmosphere is forced by observed ssts only in the indian ocean basin and poga the atmosphere is forced by observed ssts only in the tropical pacific basin while the sst variability of the tropical pacific exerts some influence over the african region it is the atmospheric response to the indian ocean variability that is essential for simulating the correct rainfall response over eastern central and southern africa analyses of the dynamical response s seen in the numerical experiments and in the observations indicate that the pacific and indian oceans have a competing influence over the indian ocean african region this competition is related to the influence of the two oceans on the walker circulation and the consequences of that variability on low level fluxes of moisture over central and southern africa finally given the high correlation found between sst variability in the indian and pacific oceans with the pacific leading by 3 months we speculate on an approach to long lead dynamical climate prediction over central east and southern africa

imprint of the el nino modoki on decadal sea level changes 1 decadal variation in sea level is shown to manifest as higher than normal sea level in the central pacific flanked by lower than normal sea level on either side of the basin during the early 21st century this abnormal condition is evidently aided by frequent occurrences of el nino modoki events and associated wind convergence to the dateline during 2000 2004 the sea level rise in central pacific succeeded a phase of lower than normal sea level associated with la nina modoki events toward the end of 20th century a correlation analysis confirms the dominant influence of el nino la nina modoki on the sea level rise in the central pacific as compared to that of the el nino la nina this influence can even be seen in remote regions such as the coasts of california and mauritius through atmospheric teleconnections

relationships between low frequency variability in the southern hemisphere and sea surface temperature anomalies abstract long term trends and interannual variations of circulation anomalies in the southern hemisphere are examined using the national centers for environmental prediction national center for atmospheric research reanalysis from 1949 to 1998 the changes in planetary circulation regimes are linked to global sea surface temperature anomalies sstas empirical orthogonal function eof analysis was performed on 500 hpa height anomalies the leading mode eof1 shows a strong zonal symmetry with a phase reversal between height anomalies in high and midlatitudes apart from zonal symmetry a zonal wavenumber 3 is evident with three centers located in three southern oceans in the low frequency band with fluctuations longer than 60 months eof1 is associated with the second rotated eof mode of sstas with positive loadings over three southern oceans and negative loadings in the north pacific and the north atlantic the next two modes are the pacific south american psa patterns they depict wave 3 patterns in

modulation of the southern africa precipitation response to the el nino southern oscillation by the subtropical indian ocean dipole the climate of southern africa defined as the land area bound by the region 15 s 35 s 12 5 e 42 5 e during the december march rainy season is driven by indo pacific sea surface temperature sst anomalies associated with the el nino southern oscillation enso and the subtropical indian ocean dipole siod the observed december march 1979 2014 southern africa precipitation during the four enso and siod phase combinations suggests that the phase of the siod can disrupt or enhance the southern africa precipitation response to enso here we use a large ensemble of model simulations driven by global sst and enso only sst to test whether the siod modifies the relationship between southern africa precipitation and enso since enso based precipitation forecasts are used extensively over southern africa an improved understanding of how other modes of sst variability modulate the regional response to enso is important enso in the absence of the siod forces an equivalent barotropic rossby wave over southern africa that modifies the regional mid tropospheric vertical motions and precipitation anomalies el nino la nina is related with high low pressure over southern africa that produces anomalous mid tropospheric descent ascent and decreases increases in precipitation relative to average when the siod and enso are in opposite phases the siod compliments the enso related atmospheric response over southern africa by strengthening the regional equivalent barotropic rossby wave anomalous mid tropospheric vertical motions and anomalous precipitation by contrast when the siod and enso are in the same phase the siod disrupts the enso related atmospheric response over southern africa by weakening the regional equivalent barotropic rossby wave anomalous mid tropospheric vertical motions and anomalous precipitation

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

impacts of a pinatubo size volcanic eruption on enso observations and model simulations of the climate responses to strong explosive low latitude volcanic eruptions suggest a significant increase in the likelihood of el nino during the eruption and post eruption years though model results have been inconclusive and have varied in magnitude and even sign in this study we test how this spread of responses depends on the initial phase of el nino southern oscillation enso in the eruption year and on the eruption s seasonal timing we employ the gfdl cm2 1 global coupled general circulation model to investigate the impact of the pinatubo 1991 eruption assuming that in 1991 enso would otherwise be in central or eastern pacific el nino la nina or neutral phases we obtain statistically significant el nino responses in a year after the eruption for all cases except la nina which shows no response in the eastern equatorial pacific the eruption has a weaker impact on eastern pacific el ninos than on central pacific el ninos we find that the ocean dynamical thermostat and to a lesser extent wind changes due to land ocean temperature gradients are the main feedbacks affecting el nino development after the eruption the el nino responses to eruptions occurring in summer are more pronounced than for winter and spring eruptions that the climate response depends on eruption season and initial enso phase may help to reconcile apparent inconsistencies among previous studies

the angola low relationship with southern african rainfall and enso the main states of the angola low al are identified using clustering analysis applied to daily anomalous patterns of 700 hpa wind vorticity over angola and adjacent countries from november to march for the 1980 81 2014 15 period at the daily timescale we examine the extent to which the main states of the al modulate daily rainfall over southern africa at the interannual timescale we assess both the relationship between the occurrence of these al states and el nino southern oscillation enso and the role of the al in explaining enso s failure in driving southern african rainfall at times three reanalyses are considered to account for uncertainties induced by the scarcity of data available for assimilation over southern africa three preferential states of the angola low are identified al state close to its seasonal climatology with slight zonal displacements anomalously weak al state and anomalously strong al state with meridional displacements these different states all significantly modulate daily southern african rainfall near climatological al state promotes wet rainfall anomalies over eastern subtropical southern africa and dry rainfall anomalies over its western part a slight westward shift in the near climatological position of the al leads to reversed zonal gradient in rainfall the remaining regimes significantly modulate the meridional gradient in southern african rainfall anomalously weak and anomalously northward al states promote wet rainfall anomalies over tropical southern africa and dry rainfall anomalies over subtropical southern africa the reverse prevails for anomalously southward al at the interannual timescale enso significantly modulates the seasonal occurrence of most al states in the three reanalyses anomalously weak and southward al states are more strongly correlated with regional rainfall than enso in all reanalyses suggesting that accounting for al variability may improve seasonal forecasts case study analysis of the major 1982 83 and 1997 98 el nino events suggests that the weak rainfall anomalies and strong seasonal al in 1997 98 may result from counteracting effects between enso and indian ocean coupled modes of variability

el nino southern oscillation diversity and southern africa teleconnections during austral summer a wide range of sea surface temperature sst expressions have been observed during the el nino southern oscillation events of 1950 2010 which have occurred simultaneously with different global atmospheric circulations this study examines the atmospheric circulation and precipitation during december march 1950 2010 over the african continent south of 15 circ s a region hereafter known as southern africa associated with eight tropical pacific sst expressions characteristic of el nino and la nina events the self organizing map method along with a statistical distinguishability test was used to isolate the sst expressions of el nino and la nina the seasonal precipitation forcing over southern africa associated with the eight sst expressions was investigated in terms of the horizontal winds moisture budget and vertical motion el nino events with warm sst across the east and central pacific ocean and warmer than average sst over the indian ocean are associated with precipitation reductions over southern africa the regional precipitation reductions are forced primarily by large scale mid tropospheric subsidence associated with anticyclonic circulation in the upper troposphere el nino events with cooler than average sst over the indian ocean are associated with precipitation increases over southern africa associated with lower tropospheric cyclonic circulation and mid tropospheric ascent la nina events with cool sst anomalies over the central pacific and warm sst over the west pacific and indian ocean are associated with precipitation increases over southern africa the regional precipitation increases are forced primarily by lower tropospheric cyclonic circulation resulting in mid tropospheric ascent and an increased flux of moisture into the region

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

water vapour transport from the tropical atlantic and summer rainfall in tropical southern africa an empirical orthogonal functions analysis of the onshore flow of moisture along the west coast of southern africa using ncep doe amip ii re analyses suggests two dominant modes of variability that are linked to a variations in the circulation linked with the south atlantic anticyclone b the intensity of the flow that penetrates from the tropical atlantic the second mode referred as the equatorial westerly mode contributes the most to moisture input from the atlantic onto the subcontinent at tropical latitudes substantial correlations in austral summer between the atlantic moisture flux in the tropics and rainfall over the upper lands surrounding the congo basin suggest the potential role played by this zonal mode of water vapour transport composites for austral summer months when this equatorial westerly mode had a particularly strong expression show an enhanced moisture input at tropical latitudes that feeds into the deep convection occurring over the congo basin sustained meridional energy fluxes result in above normal rainfall east and south of the congo belt during years of reduced equatorial westerly moisture flux a deficit of available humidity occurs in the southern tropics a concomitant eastward shift of deep convection to the southwest indian ocean and southeastern africa leads to below normal rainfall over the uplands surrounding the congo basin

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

a southern hemisphere wave response to enso with implications for southern africa precipitation ensemble gcm simulations with an imposed idealized warming of the eastern pacific ocean reveal two wave anomalies in the southern hemisphere one in the eastern and one in the western hemisphere both are statistically significant at the 99 confidence level application of a steady state linear model and a rossby wave source analysis is used to diagnose the causes of the waves the western hemisphere wave is forced by the advection and stretching of planetary vorticity by the divergent flow from the southern hemisphere component of the central pacific twin anticyclones that straddle the equator during warm events the eastern hemisphere wave is a result of the northeastward shift of the south indian convergence zone sicz that in turn is forced from the upper troposphere by convergence to the north an upper level convergence maximum over the equatorial indian ocean induces divergence to the south encouraging vertical motion and precipitation to the northeast of the sicz s normal position the resulting anomalous upper level convergence in the climatological position of the sicz as well as the anomalous vorticity flux convergence by the transients associated with an equatorward shift of the storm track behind the sicz force the eastern hemisphere rossby wave since a shift of the sicz is a fairly robust observed consequence of enso events these results suggest the mechanism by which drought conditions develop over southern africa at the height of many warm events seasonal prediction capabilities in this region can be improved by monitoring and understanding the details and consequences of the adjustment of the walker circulation near the equator outside of the pacific ocean basin

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

modification of the southern african rainfall variability enso relationship since the late 1960s analysis of 149 raingauge series 1946 1988 shows a weak positive correlation between late summer rainfalls january march in tropical southern africa and the southern oscillation index soi the correlation coefficients have been unstable since world war ii they were close to zero before 1970 and significant thereafter before 1970 southern african late summer rainfalls were more specifically correlated with regional patterns of sea surface temperature sst mainly over the southwestern indian ocean after 1970 teleconnections with near global sst anomaly patterns i e over the central pacific and indian oceans dominate the regional connections the increase in the sensitivity of the southern african rainfall to the global so related circulation anomalies is simultaneous with the correlation between soi and more extensive sst anomalies particularly over the southern indian ocean this feature is part of longer term decadal global sst variability as inferred from statistical analyses numerical experiments using the meteo france general circulation model arpege climat are performed to test the impact of the observed sst warming in the southern indian and extratropical oceans during el nino southern oscillation enso events on southern african rainfall simulated results show that enso events which occurred in the relatively cold background of the pre 1970 period in the southern oceans had a little effect on southern africa climatic conditions and atmospheric circulation by contrast more recent enso events with warmer sst over the southern oceans lead to a climatic bipolar pattern between continental southern african and the western indian ocean which is characterized by reduced enhanced deep convection and rainfall over the subcontinent the western indian ocean a weaker subtropical high pressure belt in the southwestern indian ocean is also simulated along with a reduced penetration of the moist southern indian ocean trade winds over the southern african plateau these results are consistent with the strong droughts observed over all southern africa during enso events since 1970

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

role of cross equatorial waves in maintaining long periods of low convective activity over southern africa abstractperiods of low convective activity over southern africa during the peak rainy season from december to february are known to be due to the northeastward displacement of the tropical temperate trough ttt systems from the landmass in this study using interim european centre for medium range weather forecasts ecmwf re analysis era interim data the authors show that the displacement of the ttt systems during long periods of low convective activity has origins in the northern hemisphere using standardized area averaged outgoing longwave radiation olr daily anomalies over southern africa long periods of low convective activity are defined as periods of positive olr anomalies lasting consecutively for 5 or more days with a standard deviation of 1 or more an eddy streamfunction anomaly composite of the periods of low convective activity shows an upper level anomalous wave originating in the northern hemisphere and extending to southern africa from the eastern pacific and displacing the tropic

the impact of enso on southern african rainfall in cmip5 ocean atmosphere coupled climate models we study the ability of 24 ocean atmosphere global coupled models from the coupled model intercomparison project 5 cmip5 to reproduce the teleconnections between el nino southern oscillation enso and southern african rainfall in austral summer using historical forced simulations with a focus on the atmospheric dynamic associated with el nino overestimations of summer rainfall occur over southern africa in all cmip5 models abnormal westward extensions of enso patterns are a common feature of all cmip5 models while the warming of the indian ocean that happens during el nino is not correctly reproduced this could impact the teleconnection between enso and southern african rainfall which is represented with mixed success in cmip5 models large scale anomalies of suppressed deep convection over the tropical maritime continent and enhanced convection from the central to eastern pacific are correctly simulated however regional biases occur above africa and the indian ocean particularly in the position of the deep convection anomalies associated with el nino which can lead to the wrong sign in rainfall anomalies in the northwest part of south africa from the near surface to mid troposphere cmip5 models underestimate the observed anomalous pattern of pressure occurring over southern africa that leads to dry conditions during el nino years

fossil palm beetles refine upland winter temperatures in the early eocene climatic optimum eocene climate and associated biotic patterns provide an analog system to understand their modern interactions the relationship between mean annual temperatures and winter temperatures temperature seasonality may be an important factor in this dynamic fossils of frost intolerant palms imply low eocene temperature seasonality into high latitudes constraining average winter temperatures there to 8 c however their presence in a paleocommunity may be obscured by taphonomic and identification factors for macrofossils and pollen we circumvented these problems by establishing the presence of obligate palm feeding beetles chrysomelidae pachymerina at three localities a fourth tentatively in microthermal to lower mesothermal early eocene upland communities in washington and british columbia this provides support for warmer winter eocene climates extending northward into cooler canadian uplands

modelling the precipitation response over southern africa to the 2009 2010 el nino using a stretched grid global atmospheric model the 2009 2010 el nino event was a moderately strong central pacific type enso and as such expected to lead to a substantial drought over southern africa during austral summer however many parts of the region experienced average to well above average rainfall during this season given that seasonal forecasting skill tends only to be good during enso seasons and many parts of the sub continent rely on rain fed agriculture understanding why the rainfall was so anomalous during this el nino event is important to this end a global stretched grid atmospheric general circulation model with relatively high horizontal resolution of 0 5 0 5 is applied over the region with observed and idealised sst forcing in the latter experiments ssts are kept as observed over one ocean basin e g pacific and as climatology over the other two basins e g atlantic indian or as climatology over one basin and as observed over the other two basins in order to help understand which of these three basins may have contributed most to the observed rainfall anomalies in summer 2009 2010 it is found that pacific ocean forcing contributed to the summer rainfall anomalies over most regions of southern africa with the atlantic acting to oppose the effects of the pacific however over mozambique and to some extent zimbabwe the indian ocean was more important with the atlantic again acting in opposition the increased rainfall over most of southern africa appears mainly due to a stronger angola low circulation system and to anomalously strong moisture flux from the tropical western indian ocean and to lesser extent the tropical south east atlantic ocean

the south indian convergence zone and interannual rainfall variability over southern africa abstract the south indian convergence zone sicz is identified in this paper as a region of enhanced precipitation extending off the southeast coast of southern africa during austral summer unlike the south pacific convergence zone the sicz is a land based convergence zone lbcz with position and intensity at least partially determined by surface conditions over southern africa an idealized gcm simulation is used to explore the basic dynamics of lbczs in the tropics and subtropics output from a realistic gcm simulation and the national centers for environmental prediction national center for atmospheric research 40 year reanalysis are analyzed to apply this basic dynamical framework to the case of the sicz in contrast to the intertropical convergence zone where column moisture convergence is primarily due to meridional wind convergence in the moist environment precipitation within the sicz and the lbczs in general is also supported by zonal wind convergence moisture convergence by transient eddy

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

subtropical indian ocean sst dipole events and southern african rainfall an atmospheric general circulation model agcm is used to examine how the regional atmospheric circulation and rainfall over southern africa respond to a recently observed dipole in subtropical sea surface temperature sst over the south indian ocean observations suggest that when sst is warm to the south of madagascar and cool off western australia increased summer rains occur over large areas of southeastern africa the model results suggest that this sst pattern leads to increased rainfall via enhanced convergence of moister than average air over the region increased evaporation occurs over the warm pole in the south west indian ocean and this moist air is advected towards mozambique and eastern south africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow

potential sources of decadal climate variability over southern africa abstractpotential sources of decadal climate variability over southern africa are examined by conducting in depth analysis of available datasets and coupled general circulation model cgcm experiments the observational data in recent decades show a bidecadal variability noticeable in the southern african rainfall with its positive phase of peak during 1999 2000 it is found that the rainfall variability is related to anomalous moisture advection from the southwestern indian ocean where the anomalous sea level pressure slp develops the slp anomaly is accompanied by anomalous sea surface temperature sst both slp and sst anomalies slowly propagate eastward from the south atlantic to the southwestern indian ocean the analysis of mixed layer temperature tendency reveals that the sst anomaly in the southwestern indian ocean is mainly due to eastward advection of the sst anomaly by the antarctic circumpolar current the eastward propagation of slp and sst anomalies are also confirmed in the 270 yr outp

anomalous winter climate conditions in the pacific rim during recent el nino modoki and el nino events present work compares impacts of el nino modoki and el nino on anomalous climate in the pacific rim during boreal winters of 1979 2005 el nino modoki el nino is associated with tripole dipole patterns in anomalies of sea surface temperature precipitation and upper level divergent wind in the tropical pacific which are related to multiple boomerangs of ocean atmosphere conditions in the pacific zonal and meridional extents of those boomerangs reflect their independent influences which are seen from lower latitudes in the west to higher latitudes in the east in the central pacific more moisture is transported from the tropics to higher latitudes during el nino modoki owing to displacement of the wet boomerang arms more poleward toward east discontinuities at outer boomerang arms manifest intense interactions between tropical and subtropical extratropical systems the pacific north american pattern and related climate anomalies in north america found in earlier studies are modified in very different ways by the two phenomena the seesaw with the dry north and the wet south in the western usa is more likely to occur during el nino modoki while much of the western usa is wet during el nino the moisture to the southwestern usa is transported from the northward shifted itcz during el nino modoki while it is carried by the storms traveling along the southerly shifted polar front jet during el nino the east asian winter monsoon related anticyclone is over the south china sea during el nino modoki as compared to its position over the philippine sea during el nino causing opposite precipitation anomalies in the southern east asia between the two phenomena

remote effects of el nino and modoki events on the austral summer precipitation of southern africa abstractremote effects modulating the austral summer precipitation over southern africa during el nino el nino modoki events are investigated by analyzing the observed events during december february of the years from 1982 83 to 2010 11 based on the composite analyses it is found that southern africa experiences significantly below normal precipitation during el nino events compared to el nino modoki events during these latter events precipitation anomalies are not so significant although southern africa as a whole receives below normal precipitations the differences in the spatial distribution of precipitation over southern africa are seen to be related to the sea surface temperature sst anomalies of the equatorial pacific through atmospheric teleconnections the low level 850 hpa matsuno gill response to anomalously high precipitation over the pacific during el nino events results in an anomalous anticyclone extending from the equatorial to the subtropical south indian ocean these anomalous ant

recurrent daily olr patterns in the southern africa southwest indian ocean region implications for south african rainfall and teleconnections a cluster analysis of daily outgoing longwave radiation olr anomalies from 1979 to 2002 over the southern africa southwest indian ocean swio region for the november to february season reveals seven robust and statistically well separated recurrent patterns of large scale organized convection among them are three regimes indicative of well defined tropical temperate interactions linking the hinterland parts of southern africa to the mid latitudes of the swio preferred transitions show a tendency for an eastward propagation of these systems analysis of daily rainfall records for south africa shows that six of the olr regimes are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country atmospheric anomalies from the ncep doe ii reanalysis dataset show that the olr regimes are associated with either regional or near global adjustments of the atmospheric circulation the three regimes representative of tropical temperate interactions being in particular related to a well defined wave structure encompassing the subtropical and temperate latitudes featuring strong vertical anomalies and strong poleward export of momentum in the lee of the location of the cloud band the time series of olr regimes seasonal frequency are correlated to distinctive anomaly patterns in the global sea surface temperature field among which are shown to be those corresponding to el nino and la nina conditions the spatial signature of el nino southern oscillation s enso influence is related to the combination of an increased decreased frequency of these regimes it is shown in particular that the well known dipole in convection anomalies contrasting southern africa and the swio during enso events arises as an effect of seasonal averaging and is therefore not valid at the synoptic scale this study also provides a framework to better understand the observed non linearities between enso and the seasonal convection and rainfall anomalies over the region

on the likelihood of tropical extratropical cloud bands in the south indian convergence zone during enso events abstractthe southern hemisphere subtropical convergence zones are important regions of rainfall in the subtropics the south indian ocean convergence zone sicz has the strongest seasonality and exhibits substantial interannual variability in strength and position during austral summer on synoptic time scales the sicz is a preferred region for the formation of tropical extratropical te cloud bands with local maxima over the southern african mainland and madagascar this study investigates how the seasonality in satellite observed cloud band frequency emerges from the interplay between the asynchronous seasonal cycles in convective instability and upper level flow as represented by reanalysis data these atmospheric mean states are diagnosed with a gross convective instability metric and a method to distinguish between subtropical and eddy driven jet axes month by month analysis of these diagnostics elucidates how mean state perturbations during enso events modify cloud band likelihood typically 1