simple climatic indices for the tropical atlantic ocean and some applications two indices related to the sea surface temperature sst variability in the tropical atlantic are proposed one index describes the sst averaged over the whole basin 30 n to 20 s 60 w to 15 e and the other illustrates a meridional dipole between the northern and southern hemispheres the computational method for obtaining these indices is intentionally kept simple the objective being to reproduce the signature of the main results previously provided from more complicated statistical analyses monthly time series for both indices are produced from 1964 up to the present time the whole basin index exhibits principally a sustained warming which has intensified since about 1975 and it has a significant periodicity close to that of the quasi biennial oscillation the dipole index exhibits a decadal scale variation and its building up seems to be related to other worldwide climatic changes as for instance el nino southern oscillation extreme episodes rainfall variabilities over the brazilian nordeste and african sahel

impact of the equatorial atlantic on the el nino southern oscillation observations indicate that the atlantic zonal mode influences el nino southern oscillation enso in the pacific as already suggested in previous studies here we demonstrate for the first time using partial coupled experiments that the atlantic zonal mode indeed influences enso the partial coupling experiments are performed by forcing the coupled general circulation model echam5 mpi om with observed sea surface temperature sst in the tropical atlantic but with full air sea coupling allowed in the pacific and indian ocean the ensemble mean of a five member simulation reproduces the observational results well analysis of observations reanalysis and coupled model simulations all indicate the following mechanism sst anomalies associated with the atlantic zonal mode affect the walker circulation driving westward wind anomalies over the equatorial pacific during boreal summer the wind stress anomalies increase the east west thermocline slope and enhance the sst gradient across the pacific the bjerknes positive feedback acts to amplify these anomalies favouring the development of a la nina like anomalies the same mechanisms act for the cold phase of atlantic zonal mode but with opposite sign in contrast to previous studies the model shows that the influence on enso exists before 1970 furthermore no significant influence of the tropical atlantic on the indian monsoon precipitation is found in observation or model

variability of the atlantic meridional mode during the atlantic hurricane season abstract an observational and modeling study is conducted to investigate the structure of the atlantic meridional mode amm during the atlantic hurricane season and the relationship between amm related sst anomalies and environmental conditions that influence seasonal tropical cyclone activity the observational analysis shows that during the atlantic hurricane season the amm exhibits a similar sst and low level wind structure as during boreal spring when the amm is most active observed amm sst variations are accompanied by air temperature and moisture anomalies that are limited to the boundary layer and an anomalous baroclinic circulation structure in the northern subtropical atlantic with an anomalous lower level cyclonic circulation residing under an anomalous upper level anticyclone during a warm phase this baroclinic structure contributes to a reduction in vertical wind shear over the tropical atlantic that is dominated by changes in the upper level flow two sets of model experiments were cond

the influence of atlantic sea surface temperature anomalies on the north atlantic oscillation abstract the influence of atlantic sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic sector during winter is investigated by performing experiments with an atmospheric general circulation model these consist of a 30 yr run with observed sst anomalies for the period 1961 90 confined geographically to the atlantic ocean and of a control run with climatological ssts prescribed globally a third 30 yr integration with observed ssts confined to the south atlantic is made to confirm present findings the simulated interannual variance of 500 hpa wintertime geopotential heights over the north atlantic attains much more realistic values when observed atlantic ssts are prescribed circulation patterns that resemble the positive phase of the north atlantic oscillation nao become more pronounced in terms of the leading eof of winter means and a cluster analysis of daily fields the variance of an interannual nao index increases by fivefold over its control value atl

forcing of anomalous sea surface temperature evolution in the tropical atlantic during pacific warm events the seasonal evolution of anomalous interhemispheric sea surface temperature sst gradients in the tropical atlantic from january to april is studied by composites of the 10 warmest warm and 10 coldest cold januaries during 1948 1993 in the equatorial pacific using comprehensive ocean atmosphere data set ship observations in the warm as compared with the cold years an anomalous weakening of the northward sst gradient develops mainly due to anomalous warming in the tropical north atlantic this stems from the combination of three forcings all related to the weakened north atlantic trade winds during pacific warm events most important are the reduced latent heat flux in much of the tropical north atlantic and anomalous downwelling equatorward of 20 n with a further contribution from increased net radiation resulting from the reduced cloudiness due to the diminished convergence in the downstream portion of the north atlantic trades in response to the development of warm anomalies in the tropical north atlantic during january march the cross equatorial northward winds accelerate to april and this leads south of the equator not only to ekman downwelling enhanced divergence reduced cloudiness and increased net radiation but also to enhanced wind speed and evaporation the result is a modest anomalous warming in the western tropical south atlantic increased air temperature over the entire basin presumably due to atmospheric advection from the pacific has little effect on the atlantic sst pattern the anomalous interhemispheric sst gradient controlled primarily by the warm anomaly in the north atlantic has a pivotal role to play in steering the late boreal winter atmospheric circulation in the tropical atlantic sector and thus regional climate anomalies

decadal and interannual sst variability in the tropical atlantic ocean abstract the mechanisms regulating interannual and decadal variations of sea surface temperature sst in the tropical atlantic are examined observed variations of sea surface temperature are typically in the range of 0 3 0 5 c and are linked to fluctuations in rainfall on both the african and south american continents the authors use a numerical model to simulate the observed time series of sea surface temperature for the period 1960 1989 based on the results experiments are conducted to determine the relative importance of heat flux and momentum forcing two dominant timescales for variability of sst are identified a decadal timescale that is controlled by latent heat flux anomalies and is primarily responsible for sst anomalies off the equator and an equatorial mode with a timescale of 2 5 years that is dominated by dynamical processes the interhemispheric gradient of anomalous sst the sst dipole is primarily linked to the former process and thus results from the gradual strengthening and weak

characteristics of low frequency sea surface temperature fluctuations in the tropical atlantic abstract sea surface temperature anomalies in the tropical atlantic ocean are reexamined to investigate an apparent low frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the itcz using principal components rotated by the varimax method and simple correlations of area averaged temperatures we show that during the 1964 88 interval sst anomalies north and south of the itcz are not significantly correlated therefore the low frequency variation with an apparent decadal period observed in the sst gradient across the itcz during 1964 88 does not arise from temporally coherent and out of phase fluctuations in each hemisphere and cannot be characterized as a dipole

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

structure of interannual to decadal climate variability in the tropical atlantic sector abstract a search for coupled modes of atmosphere ocean interaction in the tropical atlantic sector is presented previous studies have provided conflicting indications of the existence of coupled modes in this region the subject is revisited through a rotated principal component analysis performed on datasets spanning the 36 yr period 1958 93 the analysis includes four variables sea surface temperature oceanic heat content wind stress and atmospheric diabatic heating the authors find that the first rotated principal component is associated with fluctuations in the subtropical wind system and correlates with the north atlantic oscillation nao while the second and third modes which are the focus of interest are related to tropical variability the second mode is the atlantic nino mode with anomalous sea surface temperature and anomalous heat content in the eastern equatorial basin wind stress weakens to the west of anomalously warm water while convection is shifted south and eastward surface

analysis of atlantic sst variability factoring interbasin links and the secular trend clarified structure of the atlantic multidecadal oscillation abstract atlantic sst variability in the twentieth century is analyzed factoring the influence of natural sst variability in the pacific basin and the secular change in global ssts the tropical and northern extratropical basins are analyzed together using the extended eof technique which permits extraction of the interannual and multidecadal modes in the pan atlantic basin in a single step the leading mode of pacific uninfluenced sst variability is a multidecadal oscillation focused in the extratropical basin with a period of 70 yr the mode differs from the conventional atlantic multidecadal oscillation amo in the near quiescence of the tropical subtropical basin highlighting the significant influence of the pacific basin on this region in conventional analysis as much as 45 of the regional variance resulting from the conventional amo is due to this influence the second and third modes capture the growth east to west development and decay near simultaneous loss of amplitudes of interannual

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

lag relationships involving tropical sea surface temperatures abstract a long historical record 100 years of monthly sea surface temperature anomalies from the comprehensive ocean atmosphere data set was used to examined the lag relationships between different locations in the global tropics application of complex principal component cpc analysis revealed that the leading mode captures enso related quasi cyclical warming and cooling in the tropical pacific ocean the dominant features of this mode indicate that sst anomalies in the eastern pacific lead those of the central pacific however a somewhat weaker aspect of this mode also indicates that sst anomalies in the tropical indian and western tropical north atlantic oceans vary roughly in concert with each other but lag behind those in the central and eastern pacific the stability of these lag relationships is indicated by the fact that the leading mode is quite similar in three different 30 year time periods in order to further examine these relationships some simple indexes were formed as the average ov

case studies of extreme climatic events in the amazon basin abstract the mechanisms of climate anomalies in the amazon basin were explored from surface climatological and hydrological series upper air and satellite observations the paper is focused on the march april rainy season peak in the northern portion of amazonia case studies for the moderately wet year 1986 wet showed a relatively far southerly location of the atlantic near equatorial trough and embedded intertropical convergence zone itcz strong ascending motion and vigorous convection over the amazon basin contrasting with pronounced subsidence off the west coast of south america and weak subtropical westerly jets stwj in both hemispheres in contrast the extremely dry el nino year 1983 dry featured a more northward located itcz subsidence over the amazon basin ascending motion and convective rainfall to the west of the andes and strong stwj in synthesis from these analyses some major mechanisms of extreme rainfall events in northern amazonia stand out but only for the late aust

multimodel study of tropical atlantic variability and change 1 interannual variability associated with the zonal and the meridional mode in the tropical atlantic is studied in nine coupled ocean atmosphere models for twentieth century climate conditions tc and the sres a1b scenario for future greenhouse gas concentrations for tc the subtropical part of the meridional mode is reasonably well simulated in contrast to the deep tropical part of the meridional mode and the zonal mode a common model bias is that the onset of the meridional mode is preceded by the presence of a zonal mode in boreal fall that extends towards the western boundary of the atlantic basin and which initiates a wind evaporation sst feedback as a result of this there is a spuriously strong interaction between the zonal and the meridional mode the models that seem to best represent the meridional mode show a weakening for future climate conditions biases in the zonal mode are too strong to assess changes citation breugem w p w hazeleger and r j haarsma 2006 multimodel study of tropical atlantic variability and change geophys res lett 33 l23706 doi 10 1029 2006gl027831

archean komatiite volcanism controlled by the evolution of early continents the generation and evolution of earth s continental crust has played a fundamental role in the development of the planet its formation modified the composition of the mantle contributed to the establishment of the atmosphere and led to the creation of ecological niches important for early life here we show that in the archean the formation and stabilization of continents also controlled the location geochemistry and volcanology of the hottest preserved lavas on earth komatiites these magmas typically represent 50 30 partial melting of the mantle and subsequently record important information on the thermal and chemical evolution of the archean proterozoic earth as a result it is vital to constrain and understand the processes that govern their localization and emplacement here we combined lu hf isotopes and u pb geochronology to map the four dimensional evolution of the yilgarn craton western australia and reveal the progressive development of an archean microcontinent our results show that in the early earth relatively small crustal blocks analogous to modern microplates progressively amalgamated to form larger continental masses and eventually the first cratons this cratonization process drove the hottest and most voluminous komatiite eruptions to the edge of established continental blocks the dynamic evolution of the early continents thus directly influenced the addition of deep mantle material to the archean crust oceans and atmosphere while also providing a fundamental control on the distribution of major magmatic ore deposits

sediment geochronology for bar built estuaries subject to flood deposition and erosion a robust multiproxy approach across an estuarine zone this paper presents a contiguous late anthropocene 210pb sediment geochronology and a late anthropocene flood fire event geochronology for an estuary subject to flood deposition and erosion the procedure used multiple proxies to identify and evaluate flood facies overlying regions of erosion reconstructions of the original baseline sediments were undertaken for the major 210pb geochronological methods only the lower estuary core site which was deficient in inventory of excess 210pb of baseline sediments over the expected atmospheric supply for was chosen to calculate the total amount of erosion erosion as both cumulative mass and thickness was then proportioned across flood events relative to the size of the rp index flood signal the rp index is the product of a simple stepwise thermogravimetric procedure the flood geochronology was constructed by correlating the relative magnitudes of pivotal floods from an existing 100 year rainfall river flow model and correlations in peak sediment char content outside of the flood facies with contemporary fire records overall it was determined that 210pb sediment isotope tomography gave the closest convergence with flood and fire events over those of the constant rate of supply and constant initial concentration methods the agreement signified that around 40 of the original baseline accretion 25 cm had been eroded by floods over the last 83 years and that there was possibly considerably more erosion at the upper site which led to the loss of two flood facies

a pan atlantic decadal climate oscillation sea surface temperature sst variabilities on time scales of 10 14 years have been documented in various parts of the atlantic ocean here we present observational evidence that these regional variabilities are part of a coherent pan atlantic decadal oscillation pado characterized by zonal bands of sst and wind anomalies stacked in the meridional direction with alternate polarities from the south atlantic all the way to greenland we propose that the interaction of wind evaporation and sst is key to establishing this interhemispherical pado based on results from a new ocean atmosphere coupling model forced by extratropical wind forcing the model successfully reproduces the observed decadal oscillation in both sst and wind velocity over the tropics this decadal extratropical forcing of the tropics is in sharp contrast to the well known tropics to extratropics teleconnection that operates on interannual time scales in association with el nino southern oscillation enso

observed decadal midlatitude and tropical atlantic climate variability two common indicators of atlantic climate variability viz the north atlantic oscillation nao and the cross intertropical convergence zone itcz sea surface temperature sst gradient are examined for their frequency characteristics and midlatitude tropical links sst anomalies north and south of the itcz are found to be uncorrelated on all time scales while the sea level pressure slp fluctuations associated with the nao display a coherent seesaw between iceland and the azores this out of phase relationship spans a broad range of time scales but is particularly strong in the 5 10 year period band strong broadband coherence between the nao and the tropical atlantic cross itcz sst difference is found in the 8 20 year period band suggesting a significant midlatitude tropical interaction moreover tropical atlantic ssts on both sides of the itcz separately exhibit significant coherence with the nao index and slp variability over iceland and the azores based on these findings we hypothesize that the tropical atlantic ta ocean atmosphere interaction is affecting north atlantic climate variability

variability of the tropical ocean surface temperatures at decadal multidecadal timescales part i the atlantic ocean abstract gridded time series from the global ocean surface temperature atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical atlantic sea surface temperature sst variations at decadal timescales and to develop physical interpretations of statistical patterns of decadal sst variations each time series was 110 yr 1882 1991 long the tropical atlantic sst variations were compared with decadal variations in a 74 yr long 1912 85 north nordeste brazil rainfall time series and a 106 yr long 1886 1991 tropical atlantic cyclone activity index time series the tropical atlantic sst variations were also compared with decadal variations in the extratropical atlantic sst multiyear to multidecadal variations in the cross equatorial dipole pattern identified as a dominant empirical pattern of the tropical atlantic sst variations in earlier and present studies are shown to be variations in the approximately north south gradient of sst anomalies

circulation mechanisms related to northeast brazil rainfall anomalies this study explores the role of the upper ocean for circulation anomalies in the overlying atmosphere with focus on the late boreal winter and extreme climatic events in northeast brazil data sources comprise rainfall records in the nordeste surface ship observations of the sea surface temperature sst pressure and wind fields coads period 1948 1990 satellite observations of tropical convection hrc 1971 1988 and upper air analyses of the european centre for medium range weather forecasts ecmwf 1980 1991 all for the tropical atlantic sector interhemispheric sst gradients are most strongly associated with north south contrasts in pressure and the meridional wind component whereas the inverse sst pressure relations in situ are less close enhanced northward temperature increase in the tropical atlantic is accompanied by steeper meridional pressure gradient and accelerated southerly wind component which is representative of a northward displaced intertropical convergence zone itcz with the latter in turn leading to drought in northeast brazil interhemispheric contrasts in the 850 1000 mbar layer mean temperature are similar to those of sst and account for most of the meridional surface pressure gradient during wet as compared to dry years in northeast brazil the tropical north atlantic is cooler and the south atlantic warmer and accordingly the lower tropospheric thickness is reduced to the north but inflated to the south of the equator resulting in increased reduced surface pressure over the north south atlantic as well as reduced southerly surface wind stronger subsidence over the outer tropics of the northern hemisphere and intensified ascending motion and convective activity over the nordeste related to a southward displaced near equatorial convection belt the surface and upper air evidence thus indicates the ways in which the interhemispheric sst gradients exert a hydrostatic control on the lower tropospheric thickness pattern and thus force the south north surface pressure gradients and the surface meridional wind component and hence modulate the latitude position of the itcz and nordeste rainfall

extratropical atmospheric response to the atlantic nino decaying phase abstract the atlantic nino or atlantic equatorial mode em is the dominant coupled variability phenomenon in the tropical atlantic basin during boreal summer from the 1970s the mode has changed evolving in time from east to west and without persisting until the following winter in a previous observational work the authors have studied the atmospheric response to the em during the 1979 2005 period proposing three main issues along the decaying phase of this mode 1 the continuous confinement of the anomalous deep convection over northeastern brazil following the thermal forcing decay 2 an increasing dipole like precipitation anomaly with dry conditions in the florida gulf of mexico region and 3 the excitation of rossby waves forced by the remaining upper tropospheric divergence that are trapped into the subtropical jet but do not show a robust impact on the european sector in this work a 10 member ensemble simulation for the recent em with the university of california los angeles agcm model

on the dynamical basis for the asian summer monsoon rainfall el nino relationship abstract the dynamical basis for the asian summer monsoon rainfall el nino linkage is explored through diagnostic calculations with a linear steady state multilayer primitive equation model the contrasting monsoon circulation during recent el nino 1987 and la nina 1988 years is first simulated using orography and the residually diagnosed heating from the thermodynamic equation and the uninitialized but mass balanced ecmwf analysts as forcings and then analyzed to provide insight into the importance of various regional forcings such as the el nino related heating anomalies over the tropical indian and pacific oceans the striking simulation of the june august 1987 1988 near surface and upper air tropical circulation anomalies indicates that tropical anomaly dynamics during northern summer is essentially linear even at the 150 mb level the vertical structure of the residually diagnosed heating anomaly that contributes to this striking simulation differs significantly from the specified canonic

holocene and deglacial ocean temperature variability in the benguela upwelling region implications for low latitude atmospheric circulation 1 mg ca analyses of g bulloides and abundances of n pachyderma left coiling from ocean drilling program odp leg 175 hole 1084b in the benguela coastal upwelling system document lower sea surface temperatures during the last glacial maximum lgm younger dryas mid holocene and little ice age in the southeastern atlantic taking into consideration the possible effects of differential carbonate dissolution the mg ca data indicate younger dryas temperatures 2 3 c cooler than those of the early holocene and lgm temperatures 4 5 c cooler than those of the early holocene the cool interval during the deglacial period at hole 1084b matches the timing of younger dryas shifts in cariaco basin and greenland ice sheet records and that of a nearby alkenone record comparison of mid holocene cooling at hole odp1084b with other high resolution records of holocene and last deglacial sea surface temperatures from the tropical atlantic implies consistent basin wide changes in atmospheric circulation a brief period of 1 5 2 c cooling between 17 8 and 17 2 ka if related to heinrich event 1 is consistent with a previously hypothesized tropical origin of all heinrich climate change events

warm events in the tropical atlantic abstract sea surface temperature in the eastern equatorial atlantic ocean undergoes anomalous warming events of 1 2 c every few years the warm anomalies reach their maximum strength in northern hemisphere summer when equatorial upwelling normally brings cold thermocline water to the surface by compositing surface observations from a 28 year record we are able to identify consistent features in anomalies of sst and winds the composites show that the sst anomalies in northern summer are confined to the eastern equatorial region with reduced zonal winds to the west and reduced northward trade winds to the east accompanying these changes in winds are enhanced convection near the equator caused by a southward shift and intensification of the intertropical convergence zone later in the year sst south of the equator becomes elevated as a result by spring of the year following the equatorial anomaly convection in the western side of the basin is much higher than normal to understand the ocean dynami