monsoon fluctuations in two 20 000 yr b p oxygen isotope pollen records off southwest india abstract two marine pollen diagrams for sediments off the southwest coast of india provide a 20 000 yr history of the nearby continental vegetation determined by the monsoon climate within the framework of the isotopic stratigraphy two important phases of the evolution of the monsoon climate are a very arid period about 22 000 18 000 yr b p and a very humid period culminating at 11 000 yr b p the very arid period corresponds to the lowest pollen representation of mangrove vegetation which is used here as an indirect indicator of monsoonal runoff this aridity is due to a very weak southwest airflow a great reduction of summer monsoonal rainfall and reduced runoff of the western ghats rivers the extension of the monsoon over india after the last glacial maximum has been a gradual process following the northward progression of the intertropical convergene zone the very humid period corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall is a climatic response to the maximum summer insolation of the northern hemisphere at 11 000 yr b p

on the connection between benguela and equatorial atlantic ninos and the role of the south atlantic anticyclone for the eastern tropical atlantic two recurring el nino like phenomena with high interannual sst anomalies have been described one centered in the equatorial region as part of the atlantic zonal mode and one off angola referred to as benguela nino both events are supposed to be generated not locally but by a relaxation of the trade winds in the western equatorial atlantic here the connection between sst variations in the two regions is investigated with observational data sets as well as ocean model simulations they are correlated to such an extent that joint events should rather be viewed as one atlantic nino an intriguing feature counterintuitive in view of the remote forcing mechanism is that sst anomalies off angola precede those in the equatorial atlantic we show this behavior to be related to the difference in thermocline depths and a different seasonality of interannual sst variability in the two regions while benguela ninos peak in austral fall due to the angola benguela front being located furthest to the south and high interannual variability in coastal kelvin wave activity warm events at the equator are phase locked to austral winter when the thermocline is shallow perturbation experiments confirm the importance of remote forcing from the equator for sst variability off angola and demonstrate the leading role of wind stress in the generation of sst anomalies in the eastern tropical atlantic these wind stress variations are shown to be linked to fluctuations in the strength of the south atlantic anticyclone a connection that might be important with respect to the predictability of atlantic ninos

mean meridional currents in the central and eastern equatorial atlantic ship based acoustic doppler current profiler adcp velocity measurements collected by several major field programs in the tropical atlantic are averaged and combined with estimates of the mean near surface velocity derived from drifters and argo float surface drifts adcp d to describe the mean cross equatorial and vertical structure of the meridional currents along 23 w and 10 w data from moored adcps and fixed depth current meters a satellite derived velocity product and a global ocean reanalysis were additionally used to evaluate the mean adcp d meridional velocity the dominant circulation features in the long term mean adcp d meridional velocity in the upper 100 m are the tropical cells tcs located approximately between 5 s and 5 n with near surface poleward flow and subsurface equatorward flow that is stronger and shallower in the northern cell compared to the southern cell the thickness of the surface limb of the tcs decreases and the northern cell is found to shift further south of the equator from the central to eastern tropical atlantic analysis of two season means estimated from the ship based adcp near surface drift and moored velocity data as well as the simulated fields indicates that the maximum poleward velocity in the surface limb of the tcs intensifies during december may along 23 w largely due to seasonal compensation between the geostrophic and ageostrophic or wind driven components of the meridional velocity whereas the maximum equatorward flow in the subsurface limb of the northern cell intensifies during june november along both 23 w and 10 w due to the seasonality of the geostrophic meridional velocity

eos microwave limb sounder observations of the antarctic polar vortex breakup in 2004 1 new observations from the microwave limb sounder mls on nasa s aura satellite give a detailed picture of the spring antarctic polar vortex breakup throughout the stratosphere with the first daily global hcl profiles providing an unprecedentedly clear view of transport in the lower stratosphere poleward transport at progressively lower levels filamentation and mixing are detailed in mls hcl n2o h2o and o3 as the 2004 antarctic vortex broke up from the top down in early october through late december improved mls h2o data show the subvortex below the tropical tropopause breaking up almost simultaneously with the lower stratospheric vortex in december vortex remnants persisted in mls tracers for over a month after the breakup in the midstratosphere but no more than a week in the lower stratosphere mls observations show diabatic descent continuing throughout november but weak ascent after late october in the lower stratospheric vortex core our results extend previous observational transport studies and show consistency with mixing and vortex evolution in meteorological analyses and with model studies citation manney g l m l santee n j livesey l froidevaux w g read h c pumphrey j w waters and s pawson 2005 eos microwave limb sounder observations of the antarctic polar vortex breakup in 2004 geophys res lett 32 l12811 doi 10 1029 2005gl022823

equatorial subthermocline currents across the pacific recent sections crossing the equator at nine longitudes from 146 e to 86 w show zonal currents below 400 m similar to those found in a 16 month mean section on 159 w from the pacific equatorial ocean dynamics pequod program in 1982 1983 most of the new measurements were made with a lowered acoustic doppler current profiler eastward current extrema north and south intermediate countercurrents are found in all sections about 2 from the equator in the depth range 500 1500 m with the possible exceptions of 146 e where topography complicates the picture south of the equator and 150 e where the sections extend only from 1 s to 2 n poleward of the intermediate countercurrents westward flow is found near 3 from the equator in most of the sections on the equator from 250 500 m depth a westward equatorial intermediate current is found in many but not all of the sections similarly it is present in the pequod mean but not in all synoptic sections below the intermediate currents and countercurrents an eastward current near 3000 m was found at and south of the equator in the pequod mean and in the new sections from 150 e to 110 w near 4000 m there is westward flow south of the equator in the pequod mean and near the equator in the new sections from 179 e to 135 w geostrophic currents calculated from an 8 year mean hydrographic section at 165 e also resemble the pequod mean although not conclusive the evidence presented here indicates that these currents are basin scale components of the general circulation perhaps involving vigorous horizontal recirculation in a set of basin wide elongated gyres within a few degrees of the equator

zonally asymmetric response of the southern ocean mixed layer depth to the southern annular mode interactions between the atmosphere and ocean are mediated by the mixed layer at the ocean surface the depth of this layer is determined by wind forcing and heating from the atmosphere variations in mixed layer depth affect the rate of exchange between the atmosphere and deeper ocean the capacity of the ocean to store heat and carbon and the availability of light and nutrients to support the growth of phytoplankton however the response of the southern ocean mixed layer to changes in the atmosphere is not well known here we analyse temperature and salinity data from argo profiling floats to show that the southern annular mode sam the dominant mode of atmospheric variability in the southern hemisphere leads to large scale anomalies in mixed layer depth that are zonally asymmetric from a simple heat budget of the mixed layer we conclude that meridional winds associated with departures of the sam from zonal symmetry cause anomalies in heat flux that can in turn explain the observed changes of mixed layer depth and sea surface temperature our results suggest that changes in the sam including recent and projected trends attributed to human activity drive variations in southern ocean mixed layer depth with consequences for air sea exchange ocean sequestration of heat and carbon and biological productivity

the equatorial undercurrent in the central atlantic and its relation to tropical atlantic variability seasonal to interannual variations of the equatorial undercurrent euc in the central atlantic at 23 w are studied using shipboard observation taken during the period 1999 2011 as well as moored velocity time series covering the period may 2005 june 2011 the seasonal variations are dominated by an annual harmonic of the euc transport and the euc core depth both at maximum during september and a semiannual harmonic of the euc core velocity maximum during april and september substantial interannual variability during the period of moored observation included anomalous cold warm equatorial atlantic cold tongue events during 2005 2008 the easterly winds in the western equatorial atlantic during boreal spring that represent the preconditioning of cold warm events were strong weak during 2005 2008 and associated with strong weak boreal summer euc transport the anomalous year 2009 was instead associated with weak preconditioning and smallest euc transport on record from january to july but during august coldest sst anomalies in the eastern equatorial atlantic were observed the interannual variations of the euc are discussed with respect to recently described variability of the tropical atlantic ocean

is the boreal spring tropical atlantic variability a precursor of the equatorial mode the equatorial mode em governs the tropical atlantic inter annual variability during boreal summer it has profound impacts on the climate of adjacent and remote areas however predicting the em is one of the most challenging and intriguing issues for the scientific community recent studies have suggested a possible connection between the boreal spring meridional mode mm and the em through ocean wave propagation here we use a set of sensitivity experiments with a medium resolution ocean model to determine the precursor role of a mm to create equatorial sst variability our results demonstrate that boreal summer equatorial ssts following a mm are subject to two counteracting effects the local wind forcing and remotely excited oceanic waves for a positive mm the anomalous easterly winds blowing along the equator shallow the thermocline cooling the sea surface via vertical diffusion and meridional advection anomalous wind curl excites a downwelling rossby wave north of equator which is reflected at the western boundary becoming an equatorial kelvin wave kw this downwelling kw propagates eastward deepening the thermocline and activating the thermocline feedbacks responsible for the equatorial warming moreover the local wind forcing and rw reflected mechanism have a significant and comparable impact on the equatorial sst variability changes in the intensity and persistence of these distinct forcings will determine the equatorial sst response during boreal summer our results give a step forward to the improvement of the em predictability

deep atlantic ocean warming facilitated by the deep western boundary current and equatorial kelvin waves abstractincreased heat storage in deep oceans has been proposed to account for the slowdown of global surface warming since the end of the twentieth century how the imbalanced heat at the surface

on the relation between the boreal spring position of the atlantic intertropical convergence zone and atlantic zonal mode abstractprevious studies have talked about the existence of a relation between the atlantic meridional mode amm and atlantic zonal mode azm via the meridional displacement of the intertropical

paleoenvironmental analyses of an organic deposit from an erosional landscape remnant arctic coastal plain of alaska abstract the dominant landscape process on the arctic coastal plain of northern alaska is the formation and drainage of thaw lakes lakes and drained thaw lake basins account for approximately 75 of the modern surface expression of the barrow peninsula the thaw lake cycle usually obliterates lacustrine or peat sediments from previous cycles which could otherwise be used for paleoecological reconstruction of long term landscape and vegetation changes several possible erosional remnants of a former topographic surface that predates the formation of the thaw lakes have been tentatively identified these remnants are characterized by a higher elevation a thick organic layer with very high ground ice content in the upper permafrost and a plant community somewhat atypical of the region ten soil cores were collected from one site and one core was intensively sampled for soil organic carbon content pollen analysis and 14c dating the lowest level of the organic sediments represents the earliest phase of plant growth and dates to ca 9000 cal bp palynological evidence indicates the presence of mesic shrub tundra including sedge birch willow and heath vegetation and microfossil indicators point to wetter eutrophic conditions during this period carbon accumulation was rapid due to high net primary productivity in a relatively nutrient rich environment these results are interpreted as the local response to ameliorating climate during the early holocene the middle holocene portion of the record contains an unconformity indicating that between 8200 and 4200 cal bp sediments were eroded from the site presumably in response to wind activity during a drier period centered around 4500 cal bp the modern vegetation community of the erosional remnant was established after 4200 cal bp and peat growth resumed during the late holocene carbon accumulation rates cars were greatly reduced in response to the combined effects of declining productivity associated with climatic cooling and increased nutrient stress as paludification and permafrost aggradation sequestered mineral nutrients

glacial to holocene fluctuations in hydrography and productivity along the southwestern continental margin of india oxygen isotope and sedimentological records of a sediment core from the southwestern continental margin of india are used to reconstruct the fluctuations in sea surface hydrography and productivity during the last deglaciation the delta o 18 records of globigerinoides ruber and globigerinoides sacculifer exhibit high amplitude oscillations during the early deglaciation and holocene significant variations in delta o 18 during the holocene and a high glacial interglacial amplitude in delta o 18 values delta delta o 18 similar to 2 1 o suggest large fluctuations in sea surface hydrography related to monsoonal precipitation on land our results suggest that although the last deglacial events are coherent in time with the regional and global climatic events fluctuations in sea surface salinity during holocene are unique to this region maximum monsoonal precipitation appears to have occurred after similar to9 8 ka bp unlike the records from the western arabian sea biological productivity was maximum between similar to 18 and 15 ka bp and substantially diminished between similar to 13 and 6 ka bp the increased strength in the winter monsoon during the glacial period could have enhanced convective mixing and nutrient injection leading to high primary production reduced surface productivity during the early holocene may be attributed to the complex dynamics of the circulation system and hydrological cycle along the southwest coast of india c 2001 elsevier science b v all rights reserved

an equatorial extratropical dipole structure of the atlantic nino abstractequatorial atlantic variability is dominated by the atlantic nino peaking during the boreal summer studies have shown robust links of the atlantic nino to fluctuations of the st helena subtropical anticyclone and benguela nino events furthermore the occurrence of opposite sea surface temperature sst anomalies in the eastern equatorial and southwestern extratropical south atlantic ocean sao also peaking in boreal summer has recently been identified and termed the sao dipole saod however the extent to which and how the atlantic nino and saod are related remain unclear here an analysis of historical observations reveals the atlantic nino as a possible intrinsic equatorial arm of the saod specifically the observed sporadic equatorial warming characteristic of the atlantic nino 0 4 k is consistently linked to southwestern cooling 0 4 k of the atlantic ocean during the boreal summer heat budget calculations show that the saod is largely driven by the surface net heat flux anoma

a comparison of the atlantic and pacific bjerknes feedbacks seasonality symmetry and stationarity the bjerknes feedback is the dominant positive feedback in the equatorial ocean basins to examine the seasonality symmetry and stationarity of the pacific and atlantic bjerknes feedbacks we decompose them into three feedback elements that relate thermocline depth sea surface temperature sst and western basin wind stress variability to each other we partition feedback elements into composites associated with positive or negative anomalies using robust regression we diagnose the strength of each composite for the recent period 1993 2012 composites of the pacific bjerknes feedback elements agree well with previous work positive composites are generally stronger than negative composites and all feedback elements are weakest in late boreal spring in the atlantic differences between positive and negative composites are less consistent across feedback elements specifically wind variability seems to play a less important role in shaping atmosphere ocean coupling in the atlantic when compared to the pacific however a clear seasonality emerges feedback elements are generally strong in boreal summer and for the negative composites again in boreal winter the atlantic bjerknes feedback is dominated by subsurface surface coupling applying our analysis to overlapping 25 year periods for 1958 2009 shows that the strengths of feedback elements in both ocean basins vary on decadal time scales while the overall asymmetry of the pacific bjerknes feedback is robust the strength and symmetry of atlantic feedback elements vary considerably between decades our results indicate that the atlantic bjerknes feedback is non stationary on decadal time scales

evidence for the maintenance of slowly varying equatorial currents by intraseasonal variability recent evidence from mooring data in the equatorial atlantic reveals that semi annual and longer time scale ocean current variability is close to being resonant with equatorial basin modes here we show that intraseasonal variability with time scales of 10 s of days provides the energy to maintain these resonant basin modes against dissipation the mechanism is analogous to that by which storm systems in the atmosphere act to maintain the atmospheric jet stream we demonstrate the mechanism using an idealised model set up that exhibits equatorial deep jets the results are supported by direct analysis of available mooring data from the equatorial atlantic ocean covering a depth range of several thousand meters the analysis of the mooring data suggests that the same mechanism also helps maintain the seasonal variability

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

influence of the barotropic mean flow on the width and the structure of the atlantic equatorial deep jets a representation of an equatorial basin mode excited in a shallow water model for a single high order baroclinic vertical normal mode is used as a simple model for the equatorial deep jets the model is linearized about both a state of rest and a barotropic mean flow corresponding to the observed atlantic equatorial intermediate current system we found that the eastward mean flow associated with the north and south intermediate counter currents nicc and sicc respectively effectively shields the equator from off equatorial rossby waves the westward propagation of these waves is blocked and focusing on the equator due to beta dispersion is prevented this leads to less energetic jets along the equator on the other hand the westward barotropic mean flow along the equator reduces the gradient of absolute vorticity and hence widens the cross equatorial structure of the basin mode increasing lateral viscosity predominantly affects the width of the basin modes kelvin wave component in the presence of the mean flow while the rossby wave is confined by the flanking nicc and sicc independent of the presence of the mean flow the application of sufficient lateral mixing also hinders the focusing of off equatorial rossby waves which is hence an unlikely feature of a low frequency basin mode in the real ocean

structure of the atlantic ocean equatorial deep jets the equatorial deep jets in the atlantic ocean are described using vertical strain jz estimated from all available deep ctd stations in the region wavelet analysis reveals a distinct energy peak around 661 sdbar vertical wavelength 1232 dbar pressure and 61 58 latitude from the equator this high vertical wavenumber and off equatorial maximum coupled with previously published velocity data that show nodes in zonal velocity near 61 58 is grossly consistent with the structure of first meridional mode equatorial rossby waves however the meridional scale obtained from the observations exceeds by about 1 5 the theoretical meridional scale for these waves the jets are strong with zonal velocities similar in magnitude to the kelvin wave phase speed for their vertical wavelength harmonics of jz at vertical wavelengths of 1 2 1 4 and perhaps 1 8 that of the primary peak provide evidence of a large amplitude structure although sparse available phase data at the 661 sdbar vertical wavelength suggest downward and westward phase propagation assuming sinusoidal character in time and longitude gives estimates of a 5 61 yr period and a 708 6608 zonal wavelength these vertical temporal and zonal scales are roughly consistent with first meridional mode equatorial rossby wave dynamics however although vertical and zonal phase propagation are discernible there is no obvious signature of upward energy propagation in the variance vertical maxima which is problematic for a simple linear rossby wave interpretation

deep velocity measurements in the western equatorial indian ocean abstract vertical profiles of horizontal current collected in april and june 1979 in the western indian ocean revealed the presence of short vertical scale 150 300 m deep zonal jets trapped to within 1 of the equator meridional velocity records displayed in general higher temporal and spatial variability and significantly less energy at the larger vertical scales as compared with zonal records vertical wavenumber spectra of velocity showed no statistically significant peaks the conspicuous alternating zonal jets were identified with the slightly more energetic as compared to background levels 500 429 stretched meter sm wavelengths for most vertical wavenumbers zonal currents were not significantly coherent at distances greater than 400 km downstream at shorter zonal separations phase lags were indistinguishable from zero on the equator there is an indication of upward shift of approximately 100 sm over the 500 429 sm band also on the equator zonal current u and vertical displacement

seasonal and regional variability of upper ocean diapycnal heat flux in the atlantic cold tongue sst variability within the atlantic cold tongue act region is of climatic relevance for the surrounding continents a multi cruise data set of microstructure observations is used to infer regional as well as seasonal variability of upper ocean mixing and diapycnal heat flux within the act region the variability in mixing intensity is related to the variability in large scale background conditions which were additionally observed during the cruises the observations indicate fundamental differences in background conditions in terms of shear and stratification below the mixed layer ml for the western and eastern equatorial act region causing critical froude numbers fr to be more frequently observed in the western equatorial act the distribution of critical fr occurrence below the ml reflects the regional and seasonal variability of mixing intensity turbulent dissipation rates e at the equator 2 n 2 s are strongly increased in the upper thermocline compared to off equatorial locations in addition e is elevated in the western equatorial act compared to the east from may to november whereas boreal summer appears as the season of highest mixing intensities throughout the equatorial act region coinciding with act development diapycnal heat fluxes at the base of the ml in the western equatorial act region inferred from e and stratification range from a maximum of 90 wm 2 in boreal summer to 55 wm 2 in september and 40 wm 2 in november in the eastern equatorial act region maximum values of about 25 wm 2 were estimated during boreal summer reducing to about 5 wm 2 towards the end of the year outside the equatorial region inferred diapycnal heat fluxes are comparably low rarely exceeding 10 wm 2 integrating the obtained heat flux estimates in the ml heat budget at 10 w on the equator accentuates the diapycnal heat flux as the largest ml cooling term during boreal summer and early autumn in the western equatorial act elevated meridional velocity shear in the upper thermocline contributes to the enhanced diapycnal heat flux within this region during boreal summer and autumn the elevated meridional velocity shear appears to be associated with intra seasonal wave activity

response of equatorial oceans to periodic forcing oscillating wind with a period p induce variability with the following characteristics in the upper few hundred meters of the equatorial zone 5 sup 0 n to 5 sup 0 s of the ocean 1 p 10 days these winds fluctuate too rapidly to generate strong currents and excite primarily waves 2 10 days 150 days the amplitude of variability is almost independent of frequency an equilibrium response which is in phase with the forcing and which corresponds to a succession of steady states is approached asymptotically these time scales are for a basin 5000 km wide if the width of the basis exceeds 5000 km then the 150 daytime scale increases in the deep ocean below the thermocline motion corresponds to propagating waves generated by the divergence of the nonlinear currents in the upper ocean

analysis of the non linearity in the pattern and time evolution of el nino southern oscillation in this study the observed non linearity in the spatial pattern and time evolution of el nino southern oscillation enso events is analyzed it is shown that enso skewness is not only a characteristic of the amplitude of events el ninos being stronger than la ninas but also of the spatial pattern and time evolution it is demonstrated that these non linearities can be related to the non linear response of the zonal winds to sea surface temperature sst anomalies it is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive el nino versus negative la nina and strong versus weak events exist which is mostly describing the difference between central and east pacific events central pacific events tend to be weak el nino or strong la nina events in turn east pacific events tend to be strong el nino or weak la nina events a rotation of the two leading empirical orthogonal function modes illustrates that for both el nino and la nina extreme events are more likely than expected from a normal distribution the bjerknes feedbacks and time evolution of strong enso events in observations as well as in coupled model simulations also show strong asymmetries with strong el ninos being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by la nina events in turn strong la nina events are preceded by el nino events and are more strongly forced by thermocline depth anomalies than by wind anomalies further the zonal wind response to sea surface temperature anomalies during strong el nino events is stronger and shifted to the east relative to strong la nina events supporting the eastward shifted el nino pattern and the asymmetric time evolution based on the simplified hybrid coupled rechoz model of enso it can be shown that the non linear zonal wind response to sst anomalies causes the asymmetric forcings of enso events this also implies that strong el ninos are mostly wind driven and less predictable and strong la ninas are mostly thermocline depth driven and better predictable which is demonstrated by a set of 100 perfect model forecast ensembles

variability in the south atlantic anticyclone and the atlantic nino mode sea surface temperature sst anomalies in the eastern equatorial atlantic are connected to modulations in the strength of the south atlantic subtropical high pressure system referred to as the south atlantic anticyclone saa using ocean and atmosphere reanalysis products we show here that the strength of the saa from february to may impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial atlantic eea via anomalous tropical wind power this modulation of the timing and amplitude of the seasonal cold tongue development manifests as anomalous sst events peaking between june and august the timing and impact of this connection is not completely symmetric for warm and cold events for cold events an anomalously strong saa in february and march leads to positive wind power anomalies from february to june resulting in an early cold tongue onset and subsequent cold sst anomalies in june and july for warm events the anomalously weak saa persists until may generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm sst anomalies mechanisms by which saa induced wind power variations south of the equator influence eea sst are discussed including ocean adjustment via rossby and kelvin wave propagation meridional advection and local intraseasonal wind variations

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

basin wavelength equatorial deep jet signals across three oceans equatorial deep jets edjs are equatorially trapped stacked zonal currents that reverse direction every few hundred meters in depth throughout much of the water column this study evaluates their structure observationally in all three oceans using new high vertical resolution argo float conductivity temperature depth ctd instrument profiles from 2010 to 2014 augmented with historical shipboard ctd data from 1972 to 2014 and lower vertical resolution argo float profiles from 2007 to 2014 the vertical strain of density is calculated from the profiles and analyzed in a stretched vertical coordinate system determined from the mean vertical density structure the power spectra of vertical strain in each basin are analyzed using wavelet decomposition in the indian and pacific oceans there are two distinct peaks in the power spectra one kelvin wave like and the other entirely consistent with the dispersion relation of a linear first meridional mode equatorial rossby wave in the atlantic ocean the first meridional mode rossby wave signature is very strong and dominates in all three ocean basins rossby wave like signatures are coherent across the basin width and appear to have wavelengths the scale of the basin width with periods of about 5 yr in the indian and atlantic oceans and about 12 yr in the pacific ocean their observed meridional scales are about 1 5 times the linear theoretical values their phase propagation is downward with time implying upward energy propagation if linear wave dynamics hold

vortex dynamics and the evolution of water vapour in the stratosphere of the southern hemisphere the seasonal evolution of water vapour in the stratosphere of the southern hemisphere is studied by using water vapour measurements made by the microwave limb sounder on the upper atmosphere research satellite this evolution is interpreted with the aid of meteorological fields produced at the uk meteorological office by data assimilation the processes governing the distribution of water vapour are clarified by focusing on the physical and dynamical conditions in and around the stratospheric polar vortex sustained diabatic descent in the vortex causes isopleths of water vapour mixing ratio to dip down markedly in the polar vortex strengthening radial gradients of water vapour in the westerly jet while stretching and folding of material lines in anticyclones adjacent to the polar vortex leads to a widening zone of weak horizontal gradients of water vapour the circulation is discussed in terms of the dynamics of interacting vortices two different flow regimes are identified a mid and late southern winter with a strong polar vortex and one or more eastward travelling anticyclone and b spring with a relatively weak polar vortex and a quasi stationary anticyclone the phenomenon of merger of anticyclones already observed in the stratosphere of the northern hemisphere is documented for the southern hemisphere a detailed study of the tracer transport during merger is made by computing the isentropic advection of many thousands of particles a comparison is made of the seasonal evolution of water vapour in the stratosphere of the southern and northern hemispheres

multiple causes of interannual sea surface temperature variability in the equatorial atlantic ocean the tropical atlantic ocean shows sea surface temperature variability on interannual timescales observational and model data suggest that some of this variability can be attributed to the advection of anomalously warm northern subtropical waters toward the equator

the bjerknes feedback in the tropical atlantic in cmip5 models coupled state of the art general circulation models still perform relatively poorly in simulating tropical atlantic ta climate to investigate whether lack of air sea interaction might be responsible for their biases we investigate the bjerknes feedback bf in the ta the driver of the dominant interannual variability in that region first we analyse this mechanism from reanalysis data then we compare our findings to model output from the coupled model intercomparison project phase 5 the feedback is subdivided into three components the first one consists of the influence of eastern equatorial sea surface temperature anomalies sst on zonal wind stress anomalies tau u in the western basin the second component is the influence of wind stress anomalies in the western ta on eastern equatorial oceanic heat content anomalies hc the third component is the local response of overlying sst to hc in the eastern ta all three components are shown to be present in era interim and oras4 reanalysis by correlating the two variables of each component with each other the obtained patterns are compared to the ones from model output via pattern correlation per component while the models display errors in the annual cycles of sst tau u and hc as well as in the seasonality of the feedback the impact of sst on wind stress and the impact of wind stress on hc are simulated relatively well by most of the models this is especially the case when correcting for the error in seasonality the third component of the bf the impact of hc on sst in the eastern part of the basin deviates from what we find in reanalysis we find an influence of hc anomalies on overlying ssts in the eastern equatorial ta but it is weaker than in the reanalysis and it is not strongly confined to the equator longitude depth cross sections of equatorial temperature variance and correlation between subsurface temperature anomalies and sst in the cold tongue region show that flawed simulation and slow adjustment of the subsurface ocean are responsible for this

el nino and la nina sea surface temperature anomalies asymmetry characteristics associated with their wind stress anomalies 1 the asymmetric nature of el nino and la nina sea surface temperature sst anomalies is investigated by the use of national centers for environmental prediction reanalysis data and various ocean and atmosphere models it is demonstrated that the relatively weak sst anomalies during la nina compared with those of el nino are related to the westward shift of wind stress anomalies by 10 15 the asymmetric characteristics of atmospheric responses are confirmed by the general circulation model experiments with the two different sst anomalies which have equal amplitude but are of opposite sign from each other the experiments with an intermediate ocean model and a hybrid coupled model clearly show that the sst anomalies over the equatorial pacific become weaker as the zonal wind stress shifts to the west not only the amplitude but also the oscillation timescale of the sst anomaly is shown to be sensitive to the location of wind stress anomalies the duration of la nina which is rather shorter than that of el nino is also related to the longitudinal displacement of the wind stress anomaly

anomalous tropical ocean circulation associated with la nina modoki 1 el nino modoki is a variant of el nino characterized by warming around the dateline flanked by anomalous cooling in the east and west however the opposite phase la nina modoki has received little attention because the prominent cooling of sea surface temperature sst during major la nina events is observed in the central pacific and thus it is difficult to define the two different types of cold events from the sst anomaly pattern here we demonstrate that cold events in 2000 and 2008 can be clearly distinguished from traditional la nina events using surface currents derived from satellite observations during 2000 and 2008 anomalous zonal currents in the equatorial pacific demonstrate divergence with westward currents west of the dateline and eastward currents east of it these currents are opposite to the circulation pattern during the 2004 el nino modoki event an empirical orthogonal function eof analysis of surface currents for the period 1993 2009 shows a circulation anomaly pattern similar to that in 2000 2004 and 2008 in the second eof the first eof is consistent with traditional el nino la nina events and does not exhibit a current reversal along the equator our results also indicate that strong cyclonic anticyclonic circulation anomalies occur in the tropical western pacific around 5 n 15 n during the 2004 2000 and 2008 el nino la nina modoki events and during the strong traditional el nino la nina events of 1997 1998 these circulation anomalies are related to an sst gradient in the western and central pacific

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

interannual atmospheric variability forced by the deep equatorial atlantic ocean climate variability in the tropical atlantic ocean is determined by large scale ocean atmosphere interactions which particularly affect deep atmospheric convection over the ocean and surrounding continents1 apart from influences from the pacific el nino southern oscillation2 and the north atlantic oscillation3 the tropical atlantic variability is thought to be dominated by two distinct ocean atmosphere coupled modes of variability that are characterized by meridional4 5 and zonal6 7 sea surface temperature gradients and are mainly active on decadal and interannual timescales respectively8 9 here we report evidence that the intrinsic ocean dynamics of the deep equatorial atlantic can also affect sea surface temperature wind and rainfall in the tropical atlantic region and constitutes a 4 5 yr climate cycle specifically vertically alternating deep zonal jets of short vertical wavelength with a period of about 4 5 yr and amplitudes of more than 10 cm s 1 are observed in the deep atlantic to propagate their energy upwards towards the surface10 11 they are linked at the sea surface to equatorial zonal current anomalies and eastern atlantic temperature anomalies that have amplitudes of about 6 cm s 1 and 0 4 c respectively and are associated with distinct wind and rainfall patterns although deep jets are also observed in the pacific12 and indian13 oceans only the atlantic deep jets seem to oscillate on interannual timescales our knowledge of the persistence and regularity of these jets is limited by the availability of high quality data despite this caveat the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical atlantic deep jet generation and upward energy transmission through the equatorial undercurrent warrant further theoretical study

revisiting the cause of the eastern equatorial atlantic cold event in 2009 an extreme cold sea surface temperature event occurred in the atlantic cold tongue region in boreal summer 2009 it was preceded by a strong negative atlantic meridional mode event associated with north westerly wind anomalies along the equator from march to may although classical equatorial wave dynamics suggest that westerly wind anomalies should be followed by a warming in the eastern equatorial atlantic an abrupt cooling took place in the literature two mechanisms meridional advection of subsurface temperature anomalies and planetary wave reflection are discussed as potential causes of such an event here for the first time we use in situ measurements in addition to satellite and reanalysis products to investigate the contribution of both mechanisms to the 2009 cold event our results suggest that meridional advection is less important in cold events than in corresponding warm events and in particular did not cause the 2009 cold event argo float data confirm previous findings that planetary wave reflection contributed to the onset of the 2009 cold event additionally our analysis suggests that higher baroclinic modes were involved

temporal and spatial structure of the equatorial deep jets in the pacific ocean abstract the spatial and temporal structure of the equatorial deep jets edjs in the pacific ocean is investigated using ctd station data taken on the equator from 1979 through 2001 the edjs are revealed in profiles of vertical strain z estimated from the ctd data in a stretched vertical coordinate system the majority of synoptic meridional sections were occupied over an 8 yr span west of the date line two decade equatorial time series are available at both 110 w and 140 w analysis shows the expected equatorial trapping of z but yields little new detailed information about the edj meridional structure analysis of the equatorial data yields novel results the edjs are most easily seen in the eastern pacific at and east of 140 w there they may be isolated from the influence of higher frequency rossby waves generated by surface forcing spectral analysis of equatorial z profiles shows a significant and coherent peak at 400 sdbar vertical wavelength with no 1 56 10 3 s 1 from 95 w to 142

gps tec response to the 22 july 2009 total solar eclipse in east asia 1 the longest total solar eclipse of this century occurred in east and south asia on 22 july 2009 the eclipse was accompanied with a medium magnetic storm whose main phase onset occurred 27 min after the passage of the moon s umbral shadow using tec data from 60 gps stations we construct differential tec maps to investigate the ionosphere response to the solar eclipse in central china in the range of 26 n 36 n 108 e 118 e i e the magnetic latitude 15 n 25 n during the eclipse s totality a shadow in the ionosphere shown as tec depletion area was formed 100 km south of the moon s umbral path with a maximum decrease of 5 tecu the tec depletion area moved eastward following the movement of the totality area with a time lag of 10 min enhancements of tec due to the storm are observed after the main phase onset the relative drop of tec due to the solar eclipse is evidently larger at lower latitudes than that at higher ones and around noontime than that in the morning by modeling work we find that the latitudinal dependence of the tec response may result from latitudinal variation of magnetic inclination which influences the diffusion of ionization among different layers besides the local time dependence of tec response is closely related to the local time variation of background atmosphere density which affects the electron loss efficiency in the ionosphere

deep intraseasonal variability in the central equatorial atlantic besides the zonal flow that dominates the seasonal and long term variability in the equatorial atlantic energetic intraseasonal meridional velocity fluctuations are observed in large parts of the water column 15 years of full depth velocity data from an equatorial mooring at 23 w are used to investigate intraseasonal variability and specifically the downward propagation of intraseasonal energy from the surface into the deep ocean near the surface 20 to 50 m intraseasonal variability at 23 w peaks at periods between 30 to 40 days it is associated with westward propagating tropical instability waves which undergo an annual intensification in august enhanced energy levels of equatorial intraseasonal variability are observed down to about 2000 m a frequency vertical mode decomposition shows that meridional velocity fluctuations are more energetic than the zonal ones for periods 50 days the energy peak at 30 to 40 days and vertical modes 2 to 5 excludes equatorial rossby or gravity waves and suggests yanai waves to be associated with the observed intraseasonal energy yanai waves that are considered to be generated by tropical instability waves propagate their energy from near the surface west of 23 w down and eastward to eventually reach the mooring location the distribution of intraseasonal energy depends largely on the dominant frequency and the time depth and longitude of excitation with the dominant vertical mode of the yanai waves playing only a minor role observations also indicate the presence of weaker intraseasonal variability at 23 w below 2000 m that is not associated with tropical instability waves

on the width of the equatorial deep jets the equatorial deep jets edj are a striking feature of the equatorial ocean circulation in the atlantic ocean the edj are associated with a vertical scale of between 300 and 700 m a time scale of roughly 4 5 years and upward energy propagation to the surface it has been found that the meridional width of the edj is roughly 1 5 times larger than expected based on their vertical scale here we use a shallow water model for a high order baroclinic vertical normal mode to argue that mixing of momentum along isopycnals can explain the enhanced width a lateral eddy viscosity of 300 m2 s 1 10 is found to be sufficient to account for the width implied by observations

causes of the el nino and la nina amplitude asymmetry in the equatorial eastern pacific abstract the amplitude asymmetry between el nino and la nina is investigated by diagnosing the mixed layer heat budget during the enso developing phase by using the three ocean assimilation products simple ocean data assimilation soda 2 0 2 soda 1 4 2 and the global ocean data assimilation system godas it is found that the nonlinear zonal and meridional ocean temperature advections are essential to cause the asymmetry in the far eastern pacific whereas the vertical nonlinear advection has the opposite effect the zonal current anomaly is dominated by the geostrophic current in association with the thermocline depth variation the meridional current anomaly is primarily attributed to the ekman current driven by wind stress forcing the resulting induced anomalous horizontal currents lead to warm nonlinear advection during both el nino and la nina episodes and thus strengthen weaken the el nino la nina amplitude the convergence divergence of the anomalous geostrophic mixed layer currents dur

on the motion of air through the stratospheric polar vortex abstract trajectory calculations using horizontal winds from the u k meteorological office data assimilation system and vertical velocities from a radiation calculation are used to simulate the three dimensional motion of air through the stratospheric polar vortex for northern hemisphere nh and southern hemisphere sh winters since the launch of the upper atmosphere research satellite throughout the winter air from the upper stratosphere moves poleward and descends into the middle stratosphere in the sh lower to middle stratosphere strongest descent occurs near the edge of the polar vortex with that edge defined by mixing characteristics the nh shows a similar pattern in late winter but in early winter strongest descent is near the center of the vortex except when wave activity is particularly strong strong barriers to latitudinal mixing exist above about 420 k throughout the winter below this the polar night jet is weak in early winter so air descending below that level mixes between pola

a comparative stability analysis of atlantic and pacific nino modes abstractel nino southern oscillation enso in the pacific and the analogous atlantic nino mode are generated by processes involving coupled ocean atmosphere interactions known as the bjerknes feedback it has been argued that the atlantic nino mode is more strongly damped than enso which is presumed to be closer to neutrally stable in this study the stability of enso and the atlantic nino mode is compared via an analysis of the bjerknes stability index this index is based on recharge oscillator theory and can be interpreted as the growth rate for coupled modes of ocean atmosphere variability using observational data an ocean reanalysis product and output from an ocean general circulation model the individual terms of the bjerknes index are calculated for the first time for the atlantic and then compared to results for the pacific positive thermocline feedbacks in response to wind stress forcing favor anomaly growth in both basins but they are twice as large in the pacific compared to the atlanti

ventilation of the equatorial atlantic by the equatorial deep jets equatorial deep jets edjs are a prominent flow feature of the equatorial atlantic below the equatorial undercurrent down to about 3000 m here we analyze long term moored velocity and oxygen observations as well as shipboard hydrographic and current sections acquired along 23 degree sign w and covering the depth range of the oxygen minimum zones of the eastern tropical north and south atlantic the moored zonal velocity data show high baroclinic mode edj oscillations at a period of about 4 5 years equatorial oxygen observations which do not resolve or cover a full 4 5 yr edj cycle nevertheless reveal large variability with oxygen concentrations locally spanning a range of more than 60 mol kg 1 we study the effect of edjs on the equatorial oxygen concentration by forcing an advection diffusion model with the velocity field of the gravest equatorial basin mode corresponding to the observed edj cycle the advection diffusion model includes an oxygen source at the western boundary and oxygen consumption elsewhere the model produces a 4 5 yr cycle of the oxygen concentration and a temporal phase difference between oxygen concentration and eastward velocity that is less than quadrature implying a net eastward oxygen flux the comparison of available observations and basin mode simulations indicates that a substantial part of the observed oxygen variability at the equator can be explained by edj oscillations the respective role of mean advection edjs and other possible processes in shaping the mean oxygen distribution of the equatorial atlantic at intermediate depth is discussed key points equatorial deep jets strongly affect oxygen distribution variability mean oxygen ditribution in the equatorial atlantic at intermediate depth gravest equatorial basin mode forces an advection diffusion model

characteristics of atmospheric wave induced laminae observed by ozonesondes at the southern tip of south america articulo publicado en la revista journal of geophysical research atmospheres no 123 p 1 19 2018

forcing of the atlantic equatorial deep jets derived from observations the equatorial deep jets edjs are an ubiquitous feature of the equatorial oceans in the atlantic ocean they are the dominant mode of interannual variability of the zonal flow at intermediate depth on the basis of more than 10 years of moored observations of zonal velocity at 23 w the vertically propagating edjs are best described as superimposed oscillations of the 13th to the 23th baroclinic modes with a dominant oscillation period for all modes of 1650 days this period is close to the resonance period of the respective gravest equatorial basin mode for the dominant vertical modes 16 and 17 it is argued that since the equatorial basin mode is composed of linear equatorial waves a linear reduced gravity model can be employed for each baroclinic mode driven by spatially homogeneous zonal forcing oscillating with the edj period the fit of the model solutions to observations at 23 w yields a basin wide reconstruction of the edjs and the associated vertical structure of their forcing from the resulting vertical profile of mean power input and vertical energy flux on the equator it follows that the edjs are locally maintained over a considerable depth range from 500 2500 m with the maximum power input and vertical energy flux at 1300 m the strong dissipation closely ties the apparent vertical propagation of energy to the vertical distribution of power input and together with the edjs prevailing downward phase propagation require the phase of the forcing of the edjs to propagate downward

variability at intermediate depths at the equator in the atlantic ocean in 2000 06 annual cycle equatorial deep jets and intraseasonal meridional velocity fluctuations time series of high vertical resolution current meter measurements between 600 m and 1800 m depths on the equator in the atlantic were obtained at two locations 10 and 23 w the measurements have a time span of almost 7 years 2000 06 and provide insights into the temporal scales and vertical structure of variability at intermediate depths variability in the zonal velocity component records is dominated by semiannual annual and interannual fluctuations at semiannual and annual periodicities vertical scales are large on the order of 2000 stretched meters sm and show upward phase propagation in contrast interannual variability is associated with small vertical scale flows called equatorial deep jets edjs presenting downward phase propagation most of the time fitting a plane wave to these small vertical scale flows leads to velocity amplitude vertical scale and temporal scale estimates of 8 normalized cm s 1 440 sm and 4 4 yr however this plane wave cannot explain all the variability presenting small vertical scales indeed the data suggest that along with a seasonal cycle of much larger vertical scale different features with edj vertical scale coexist with the possibility of a semipermanent eastward jet at around 1500 sm variability in the meridional velocity component is dominated by intraseasonal fluctuations in addition at 23 w the meridional component shows low frequency flows that may be due to the interaction of zonal fluctuations with the mid atlantic ridge

physical processes associated with the tropical atlantic sst gradient during the anomalous evolution in the southeastern ocean abstract this work is focused on the evolution of the dominant air sea coupled mode in the equatorial and southeastern tropical atlantic and the associated physical processes it is shown that in june august jja the evolution of the dominant mode is mainly dynamically driven and displays a coherent warming or cooling pattern extending from the angola coast toward the equator in the gulf of guinea for anomalies peaking in jja the warming cooling is initiated near the angola coast in march may it is suggested that sst anomalies along the coast and near the equator are physically connected the air sea interaction along the coast may be a major factor in triggering the development of sst anomalies near the equator which is intensified by local positive feedbacks that may include bjerknes and ekman processes in return the warming or cooling near the equator weaken the sst anomalies along the coast by changing the direction of anomalous wind slow westward rossby wave propagation may also play a role

seasonal southern hemisphere multi variable reflection of the southern annular mode in atmosphere and ocean reanalyses variations of southern hemisphere sh climate variables are often linked to the southern annular mode sam variability we examined such linkage by seasons using state of the art atmosphere and ocean sea ice reanalyses the associated sam related anomaly sra fields of the climate variables denoting anomalies corresponding to the same variation in sam are overall consistent across the reanalyses among the atmospheric products 20crv2 differs from era interim and cfsr in the sea level pressure sras over the amundsen sea resulting in less warming over the antarctic peninsula among the ocean reanalyses orap5 and c glors exhibit the largest consistency the major difference between them and the lower resolution cfsr and soda reanalyses is deeper penetration of anomalous meridional currents compared to the other ocean reanalyses cfsr exhibits stronger and spatially more coherent surface current sras resulting in greater sras of sea ice motion and ice thickness along the ice edges the sras of sensible and total surface heat fluxes are reduced in cfsr due to ocean atmosphere coupling significant sea ice concentration sras are present on the west side of peninsulas along the east antarctica coast in spring and winter most notably in orap5 and c glors implying changes in new ice production and shelf water formation most atmosphere and ocean variables manifest an annular sra pattern in summer and a non annular pattern in the other seasons with a wavenumber 3 structure strongest in autumn and weakest in summer the wavenumber 3 structure should be related to the zonal wave three pattern of the sh circulation the relation of which to sam needs further exploration

a seasonal climatology of effective diffusivity in the stratosphere a 7 year 1992 1998 seasonal climatology of effective horizontal diffusivity is presented for the stratosphere 350 1900 k as in previous studies the diagnosis is based on the equivalent length of a test tracer advected on isentropic surfaces in this case using the van leer flux limiting scheme driven by the united kingdom meteorological office assimilated winds although the magnitude of equivalent length is resolution dependent its structure is shown to be reasonably robust for quantifying the inhomogeneous mixing in the stratosphere the van leer calculation agrees well with a more expensive spectral transform calculation at a comparable resolution suggesting that the diagnostic is not sensitive to the advection scheme or subgrid representation of the models a first attempt is also made at estimating the implicit numerical diffusion of the van leer scheme which is necessary to convert equivalent length to effective diffusivity compared with the spectral calculations with a constant diffusion coefficient the van leer results show notably greater diffusivity within the winter polar vortices despite the comparable equivalent lengths suggesting that the scheme may be overdiffusing in the vicinities of mobile tracer extrema the climatology of equivalent length is then presented and the seasonal evolution is discussed in detail for the lower middle and upper stratosphere the major mixing barriers winter and summer polar vortices and tropical eddy transport barrier are easily identified as well as the strong mixing regions surf zones generally equivalent length tends to be small in regions of strong zonal wind and large in regions of weak wind large values of equivalent length are observed in the summer lower stratosphere and in the middle stratosphere during the breakup of the polar vortices interhemispheric asymmetry is observed both after the winter polar vortex breakup where in the middle stratosphere the southern hemisphere shows much larger equivalent lengths and in the summer tropical region where larger equivalent lengths are observed in the northern hemisphere likely related to the monsoon circulation a monthly averaged equivalent length climatology is presented and implications for two dimensional stratospheric chemistry transport modeling are discussed

eos microwave limb sounder observations of frozen in anticyclonic air in arctic summer a previously unreported phenomenon a frozen in anticyclone friac after the 2005 arctic spring vortex breakup was discovered in earth observing system eos microwave limb sounder mls long lived trace gas data a tongue of low latitude high n 2 o low h 2 o air was drawn into high latitudes and confined in a tight anticyclone then advected intact in the summer easterlies through late august a similar feature in o 3 disappeared by early april as a result of chemical processes the friac was initially advected upright at nearly the same speed at all levels from 660 to 1300 k 25 45 km increasing vertical wind shear after early june tilted the friac and weakened it at higher levels the associated feature in pv disappeared by early june transport calculations fail to reproduce the remarkable persistence of the friac suggesting deficiencies in summer high latitude winds the historical pv record suggests that this phenomenon may have occurred several times before the lack of a persistent signature in o 3 or pv along with its small size and rapid motion make it unlikely that a friac could have been reliably identified without hemispheric daily long lived trace gas profiles such as those from eos mls

symmetry of the atlantic nino mode el nino southern oscillation enso in the pacific is asymmetric for warm and cold events with respect to amplitude spatial patterns and temporal evolution here the symmetry of the atlantic nino mode which many previous studies have argued is governed by atmosphere ocean dynamics similar to those of enso is investigated using two different ocean reanalysis products calculation of bjerknes feedback terms for the pacific reveals a pronounced asymmetry between warm and cold events though unlike most previous studies the largest asymmetry is found in the relationship between eastern pacific thermocline depth and sst anomalies for the atlantic cold events are effectively mirror images of warm events with bjerknes feedbacks of similar strength the analysis supports not only the conclusion that atlantic ninos are more symmetric than enso but the hypothesis itself that the bjerknes feedback is operative in the atlantic given the strength of the relationship between the key variables involved

some overlooked features of tropical atlantic climate leading to a new nino like phenomenon abstract the atlantic nino an equatorial zonal mode akin to the pacific el nino southern oscillation enso is phase locked to boreal summer when the equatorial easterly winds intensify and the thermocline shoals in the gulf of guinea a suite of satellite and in situ observations reveals a new mode of tropical atlantic variability that displays many characteristics of the zonal mode but instead peaks in november december nd this new mode is found to be statistically independent from both the atlantic nino in the preceding summer and the pacific enso the origin of this nd zonal mode lies in an overlooked aspect of the seasonal cycle in the equatorial atlantic in november the equatorial easterly winds intensify for the second time increasing upwelling and lifting the thermocline in the gulf of guinea an analysis of high resolution climatological data shows that these dynamical changes induce a noticeable sst cooling in the central equatorial atlantic the shoaling thermocline and increased upwelli

stacked jets in the deep equatorial atlantic ocean 1 middepth current measurements in the equatorial atlantic are characterized by elevated levels of energy contained in zonal flows of high baroclinic mode number these alternating zonal flows often called equatorial stacked jets have amplitudes up to 20 cm s 1 and vertical wavelengths of 600 m the jets are most pronounced in the depth range between 500 and 2500 m repeated direct velocity observations at 35 w indicate that the jets are coherent within 1 of the equator individual jets can persist for 1 2 years but they appear and decay rather irregularly the equatorial stacked jets are also found in realistic general circulation model simulations the features grow in amplitude with increasing horizontal and vertical model resolution however even at very high model resolutions their amplitudes are still underestimated in all model simulations high levels of energy related to the stacked jets are found in the vicinity of the western boundary currents wbcs depth range and strength of the wbcs in different experiments are related to depth range and strength of the jets in the interior stacked jets are characterized by eastward wave propagation suggesting that high baroclinic mode kelvin waves radiate energy generated in the wbc into the interior and form the stacked jets

energetics of the tropical atlantic zonal mode sea surface temperature in the central eastern equatorial atlantic has a seasonal cycle far bigger than that of the pacific but interannual anomalies smaller than those of the pacific given the amplitude of seasonal sst variability one wonders whether the seasonal cycle in the atlantic is so dominant that it is able to strongly influencetheevolutionofitsinterannualvariability inthisstudy interannualupper oceanvariabilitywithinthe tropical atlanticis viewed from an energetics perspective and the role ofocean dynamics in particularthe role ofoceanmemory withinzonalmodeeventsisinvestigated unlikeinthepacificwhereseasonalandinterannual variability involve distinctly different processes the results suggest that the latter is a modulation of the former

equatorial atlantic interannual variability role of heat content 1 the dynamics of the equatorial atlantic zonal mode are studied using observed sea surface height ssh sea surface temperature sst and heat flux and reanalysis wind stress and upper ocean temperature principal oscillation pattern pop analysis shows that the zonal mode is an oscillatory normal mode of the observed coupled system obeying the delayed action recharge oscillator paradigm for el nino southern oscillation variations in equatorial averaged ssh a proxy for upper ocean heat content precede sst anomalies in the cold tongue by 4 5 months about a quarter of the pop period positive subsurface temperature anomalies appear in the west as a delayed response to the preceding cold event these propagate eastward where due to the shallow thermocline they can influence sst leading to the next warm event although sst variations exhibit weak westward propagation during some zonal mode events pop analysis indicates that to first order there is no zonal propagation in sst net surface heat flux anomalies generally act to damp sst anomalies the zonal mode explains a large amount 70 of sst variability in the east and a significant fraction 19 of equatorial variability thus the predictability potential in the equatorial atlantic on seasonal time scales may be considerably higher than currently thought

using multiple passive tracers to identify the importance of the north brazil undercurrent for atlantic cold tongue variability the use of multiple passive tracers in a dynamical ocean model is presented as a method to study water mass origins the multiple passive tracer method is successfully applied to determine the origin regions of the atlantic cold tongue act using 31 passive tracers at the time of the act minimum in sea surface temperature 38 3 of the surface water in the central equatorial atlantic is found to originate in the western side of the basin with only 11 2 originating in the east conversely for the act surface cooling off the west coast of africa only 2 1 is from the west of the atlantic basin with 71 7 from the east the region of the north brazil undercurrent is found to be the most important origin region for the central atlantic act region for a 6 8 month lead time using the met office en4 observational dataset of ocean temperatures correlations are found between january temperatures in the north brazil undercurrent region and both the act mean temperature and act spatial extent in july august significant at the 0 95 level this suggests that the 6 month lead time predictability of the act may be increased by improved knowledge of the north brazil undercurrent temperature results from previous studies suggest that such increased predictability of the act could potentially help improve predictions of the west african monsoon

variability of the atlantic off equatorial eastward currents during 1993 2010 using a synthetic method 1 we have developed validated and applied a synthetic method to monitor the off equatorial eastward currents in the central tropical atlantic this method combines high density expendable bathythermograph xbt temperature data along the ax08 transect with altimetric sea level anomalies slas to estimate dynamic height fields from which the mean properties of the north equatorial countercurrent necc the north equatorial undercurrent neuc and the south equatorial undercurrent seuc and their variability can be estimated on seasonal to interannual timescales on seasonal to interannual timescales the synthetic method is well suited for reconstructions of the necc variability reproduces the variability of the neuc with considerable skill and less efficiently describes variations of the seuc which is located in a region of low sla variability a positive correlation is found between interannual variations of the necc transport and two indices based on an interhemispheric sea surface temperature sst gradient and southeasterly wind stress in the central tropical atlantic the neuc is correlated on interannual timescales with ssts and meridional wind stress in the gulf of guinea and zonal equatorial wind stress this study shows that both altimetry and xbt data can be effectively combined for near real time inference of the dynamic and thermodynamic properties of the tropical atlantic current system

annual and semiannual cycle of equatorial atlantic circulation associated with basin mode resonance seasonal variability of the tropical atlantic circulation is dominated by the annual cycle but semi annual variability is also pronounced despite weak forcing at that period here we use multi year full depth velocity measurements from the central equatorial atlantic to analyze the vertical structure of annual and semi annual variations of zonal velocity a baroclinic modal decomposition finds that the annual cycle is dominated by the 4th mode and the semi annual cycle by the 2nd mode similar local behavior is found in a high resolution general circulation model this simulation reveals that the annual and semi annual cycles of the respective dominant baroclinic modes are associated with characteristic basin wide structures using an idealized linear reduced gravity model to simulate the dynamics of individual baroclinic modes it is shown that the observed circulation variability can be explained by resonant equatorial basin modes corollary simulations of the reduced gravity model with varying basin geometry i e square basin versus realistic coastlines or forcing i e spatially uniform versus spatially variable wind show a structural robustness of the simulated basin modes a main focus of this study is the seasonal variability of the equatorial undercurrent euc as identified in recent observational studies main characteristics of the observed euc including seasonal variability of transport core depth and maximum core velocity can be explained by the linear superposition of the dominant equatorial basin modes as obtained from the reduced gravity model

mechanism and geochemical implications of the late holocene organic carbon burial event an example from the southwest coast of india carbonaceous clay found in the palaeo deposits of meenachil river basin was analysed for the total organic carbon nitrogen and textural characters radiocarbon dating of this clay formation and the embedded carbonized wood fragments was also done the values obtained for the organic carbon nitrogen and c n ratio of the carbonaceous clay exhibited a very remarkable range suggestive of different environmental conditions of formation it is evident from the present study that since the lignin and cellulose are the dominant components of terrestrial higher plants allochthonous and submerged organic matter have high c n ratio the radio carbon dating of the sediment and wood samples suggested that the palaeo deposits of meenachil river basin were formed as result of many transgrassive regressive episodes which had started even before the formation of vembanad lake the formation of carbonaceous clay as found sandwiched in palaeo deposits was due to the global eustatic sea level fluctuations and tectonism

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

the role of ocean dynamics in the interaction between the atlantic meridional and equatorial modes this study examines a mechanism of the interaction between the tropical atlantic meridional and equatorial modes to derive robust heat content hc variability the ensemble mean hc anomalies hca of six state of the art global ocean reanalyses for 1979 2007 are analyzed compared with previous studies characteristic oceanic processes are distinguished through their dominant time scales using the ensemble empirical mode decomposition eemd method the hc fields are first decomposed into components with different time scales the authors analysis shows that these components are associated with distinctive ocean dynamics thehigh frequency firstthree componentscanbecharacterizedastheequatorialmodes whereas the low frequency the fifth and sixth components are featured as the meridional modes in between the fourth component on the time scale of 3 4 yr demonstrates mixed characteristics of the meridional and equatorial modes because of an active transition from the predominant meridional to zonal structures on this time scale physically this transition process is initiated by the discharge of the off equatorial hca which is first accumulated as a part of the meridional mode into the equatorial waveguide which is triggered by the breakdown of the equilibrium between the cross equatorial hc contrast and the overlying wind forcing and resultsinamajorheattransportthroughtheequatorialwaveguideintothesoutheasterntropicalatlantic itis

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