oceanic equatorial waves and the 1991 93 el nino abstract equatorial kelvin and rossby waves associated with the 1991 93 el nino warm event were detected in temperature observations made by the tropical atmosphere ocean tao buoy array intraseasonal kelvin waves were a prominent part of equatorial thermocline depth variability and were well represented by a simple model consisting only of first and second mode baroclinic kelvin waves the second mode was essential to properly represent the observed amplitude thermocline depth variability at 5 n and 5 s was dominated by annual and interannual rossby waves which were found to have been largely wind forced in midbasin with little if any signal associated with eastern boundary reflection an evaluation of the wyrtki buildup hypothesis and the delayed oscillator hypothesis in connection with the 1991 93 events showed that a long lag about two years occurred between the arrival of the downwelling signal in the west and the subsequent initiation of el nino this was considerably longer than suggested

the south pacific meridional mode and its role in tropical pacific climate variability abstractthe pacific meridional mode a thermodynamically coupled mode of variability links extratropical pacific oceanic and atmospheric anomalies to the tropical pacific and may give rise to el n

influence of recent stratification changes on enso stability in a conceptual model of the equatorial pacific abstractchanges in the mean circulation of the equatorial pacific ocean partly control the strong decadal modulation of el nino southern oscillation enso this relationship is considered from the linear stability of a conceptual recharge discharge model with parameters tuned from the observed mean state whereas decadal changes in the mean thermocline depth alone are usually considered in conceptual enso models here focus is given to decadal changes in the mean stratification of the entire upper ocean e g the mean thermocline depth intensity and thickness those stratification changes modify the projection of wind stress forcing momentum onto the gravest ocean baroclinic modes their influence on the simulated frequency and growth rate is comparable in intensity to the one of usual thermodynamic and atmospheric feedbacks while they have here a secondary effect on the spatial structure and propagation of sst anomalies this sensitivity is evidenced in particular for the climate shift of the 1970s

why do we have el nino quantifying a diabatic and nonlinear perspective using observations el nino due to its global impact on weather patterns ecosystems agriculture and public health has become as commonly known to the public as the recent global warming but why we have el nino is not yet as well answered as it may have been assumed linear theories have been successful in explaining the transition from the warm phase to the cold phase of the eastern tropical pacific that results from the rise and fall of el nino but failed to explain the asymmetry between the two phases a nonlinear theory for el nino has suggested that there exist two equilibrium states for the tropical pacific one is zonally symmetric or nearly so with the warm pool extending all the way to the eastern pacific and the other is strongly zonally asymmetric with the warm pool confined to the western half of the tropical pacific under this hypothesis enso results from the fact that under the current radiative heating both states are unstable resulting in the apparent wandering behavior in between these two states as seen in the observations to test this hypothesis the authors have obtained the best approximations for the two equilibrium states empirically using updated ocean assimilation data and quantified the stability of these two empirically obtained equilibrium states using two stability analysis methods the results suggest that the two states are unstable offering support for the nonlinear view of why we have el nino

interdecadal change of the structure of the enso mode and its impact on the enso frequency in the late 1970s the enso cycle exhibited frequency change the oscillation period increased from 2 4 yr high frequency during 1962 75 to 4 6 yr low frequency during 1980 93 observations suggest that this frequency change was accompanied by a significant change in the structure of the coupled enso mode in comparison with the high frequency regime the structure of the coupled mode in the low frequency regime shows three distinctive features during the warm phase of enso the eastward shift of the westerly anomalies the meridional expansion of the westerly anomalies and the weaker intensity of the easterly anomalies in the eastern pacific to test the robustness of the relationship between the oscillation period and the structure of the coupled mode the authors designed empirical atmospheric models based on observations and coupled them with the ocean model of zebiak and cane numerical experiments demonstrate that the enso period is sensitive to changes in the wind anomaly pattern in a way much like the observed enso frequency structure relation the increase of the enso period after 1980 is mainly due to the eastward shift of the zonal wind stress with respect to the sst anomalies physical explanations of the dependence of enso frequency on the structure of the coupled mode are provided by diagnosing the relative contributions of the thermocline feedback and zonal advection feedback on enso evolution

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

recharge oscillator mechanisms in two types of enso the el ni oscillation enso tends to behave arguably as two different types or flavors in recent decades one is the canonical cold tongue type enso with major sea surface temperature anomalies ssta positionedoverthe easternpacific theotheris awarm pool typeensowith sstacenteredin the central pacific near the edge of the warm pool in this study the basic features and main feedback processes of these two types of enso are examined it is shown that the interannual variability of upper ocean heat content exhibits recharge discharge processes throughout the life cycles of both the cold tongue ct and warm pool wp enso types through a heat budget analysis with focus on the interannual frequency band the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both enso types whereas the zonal advective feedback contributes mainly to their phase transitions the westward shift of the ssta center of the wp enso and the presence of significant surface easterly wind anomalies over the far eastern equatorial pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern pacific ssta nevertheless both the wp and ct enso can be understood to a large extent by the recharge oscillator mechanism

the role of mean state on changes in el nino s flavor recently many studies have argued for the existence of two types of el nino phenomena based on different spatial distributions the conventional el nino or eastern pacific ep el nino and the central pacific cp el nino here we investigate the decadal modulation of cp el nino occurrences using a long term coupled general circulation model simulation focusing in particular on the role of climate state in the regime change between more and fewer cp el nino events the higher occurrence regime of the cp el nino coincides with the lower occurrence regime of ep el nino and vice versa the climate states associated with these two opposite regimes resemble the leading principal component analysis pca modes of tropical pacific decadal variability indicating that decadal change in climate state may lead to regime change in terms of two different types of el nino in particular the higher occurrence regime of cp el nino is associated with a strong zonal gradient of mean surface temperature in the equatorial pacific along with a strong equatorial trade wind over the area east of the dateline in addition the oceanic variables the mixed layer depth and the thermocline depth show values indicating increased depth over the western to central pacific the aforementioned climate states obviously intensify zonal advective feedback which promotes increased generation of the cp el nino frequent cp el nino occurrences are not fully described by oceanic subsurface dynamics and dynamical or thermodynamical processes in the ocean mixed layer and air sea interaction are important contributors to the generation of the cp el nino furthermore the atmospheric response with respect to the ssta tends to move toward the west which leads to a weak air sea coupling over the eastern pacific these features could be regarded as evidence that the climate state can provide a selection mechanism of the el nino type

on the westward shift of tropical pacific climate variability since 2000 a profound westward shift in atmosphere ocean variability in the tropical pacific is observed when 2000 2017 is compared to 1979 1999 this westward displacement is associated with changes in oceanic kelvin wave activity along the equator especially a remarkable reduction in the eastern pacific 175 145 w this coincides with a weakening of low level westerly winds in this region and a westward shift of low level easterly winds in the central and eastern tropical pacific as well as decreased variability of vertical entrainment vertical diffusion in the ocean mixed layer in the eastern pacific the observed enhancement of the zonal contrast of the mean state across the tropical pacific seems to be associated with the westward shift of climate variability along the equator this systematically westward shift of the atmosphere ocean variability in the tropical pacific alters the impact of the tropical pacific on extra tropical climate

the relationship between thermocline depth and sst anomalies in the eastern equatorial pacific seasonality and decadal variations even though the vital role of thermocline fluctuation in el nino southern oscillation enso cycle has been established previously the direct relationship between the thermocline depth and sea surface temperature sst anomalies in the equatorial pacific is yet to be fully understood especially its seasonality thermocline depth anomalies have been found to lead sst anomalies in time with a longitude dependent delay but our study also suggests that the relationship shows considerable seasonal dependency and is strongest weakest during the boreal spring summer over the eastern equatorial pacific where there is least delay compared to that in the western and central pacific the connection between thermocline and sst is the weakest during the boreal spring this feature may be one of causes for enso spring persistence barrier furthermore the thermocline sst connections exhibit significant decadal variations which are remarkably consistent with the decadal changes in the persistence barrier of sst anomalies over the eastern pacific it is also found that the decadal shift in the timing of the thermocline sst connection barrier is caused by the changes in the seasonal cycle of tropical trade winds and thermocline depths

contrasting thermal evolution of thrust systems an analytical and modeling approach in the front of the western alps in foreland fold and thrust belts the study of the maturity of the organic matter and kinematic and thermal modeling techniques is useful in unraveling the thermal history and maturation of source rocks the case study presented here is the classical example the western alps this work evidences that contrasting thermal evolutions can develop in relatively closely adjacent areas of the same thrust belt analytical results show that the mesozoic rocks have undergone a wide range of temperatures up to 250c locally the higher temperature values are associated with the tectonic emplacement of early widespread allochthonous nappes that were emplaced obliquely in the northern part of the area prior to the thrust tectonics of the subalpine chains folding and offsets of the isomaturity surfaces are observed which implies that in some parts of the thrust belt the thermal peak was reached before fold and thrust deformation erosion rates vary greatly along the thrust front extensive erosion probably more than 4 km 2 5 mi of sediments from the tertiary and the prealpine nappes occurred in the north of the area studied along the bornes transect away from the area of influence of the prealpine nappes numerical modeling shows differences in the timing of maturation of the source rocks according to the area considered maturation was attained either early before thrust tectonics most of the vercors area or during the deposition of the syntectonic flexural series preceding thrust tectonics molasse basin or else during thrust tectonics most of the chartreuse area

integrated palynological organic geochemical and sequence stratigraphic analyses of the middle to upper cenomanian hydrocarbon reservoir source abu roash g member a depositional model in northwestern egypt abstract the current investigation provides further insight into the petroliferous characteristics of the abu roash g member which is regarded as an important rock unit for the egyptian oil industry forty seven samples covering the g member were selected from the bed 14 1 and bed 2 4 wells in the abu gharadig basin and from the abu tunis 1x well in the matruh basin both of which are located in the north western desert an independent dating of the g rocks of bed 2 4 by benthic foraminifera and ostracods in addition to palynological dating suggests a middle late cenomanian age and provides the biochronostratigraphic framework for the sequence stratigraphic analysis analysis of the vertical distribution of particulate organic matter defines three palynofacies types pf pf 1 represents the basal g where shales of the bed wells and calcareous shale of abu tunis 1x were deposited during a relative sea level rise in an outer middle shelf environment that experienced a notable high primary productivity prevailing reducing suboxic anoxic conditions supported preservation of very high amounts of amorphous organic matter aom in pf 1 pf 2 is equated to shales of the middle g of bed 14 1 and bed 2 4 and to calcareous shales and limestone of the upper g in abu tunis 1x pf 2 was deposited during a relative sea level fall in an inner middle shelf setting under better developed suboxic anoxic conditions pf 3 corresponds to the upper g of bed 14 1 and bed 2 4 and represents the shallowest setting where sandy and silty shales were deposited during a pronounced sea level fall in an inner shelf environment the same suboxic anoxic conditions were prevailing during deposition of pf 3 three bioevents were recorded which could be of palaeoecological and or biostratigraphic significance these are senegalinium aenigmaticum dinopterygium cladoides peak dinopterygium cladoides dinopterygium alatum peak and an acme of classopollis brasiliensis sequence stratigraphy of a transect of the four studied sections was carried out to understand the response of the particulate organic matter distribution and depositional system to the sea level changes three third order depositional genetic sequences were recognized and correlated with the global sea level curve kce 2 kce 3 and kce 4 the early highstand systems tract ehst of the genetically related kce 3 in all wells is characterized by relatively rich organic matter where combined remarkably low water circulation and insignificant dilution of organic matter with coarse terrigenous material probably supported good preservation of organic matter spatial distribution of the g rocks shows lateral facies changes this was inferred from sedimentation of an organic poor avg 0 8 toc wt coarse clastic sandy shales facies in the studied area in abu gharadig basin sedimentation changes laterally into a northeast and northwest organic rich finer clastic shale calcareous shales and argillaceous limestone facies in the western matruh basin the robust anoxic conditions and very low dilution of organic matter by terrigenous influx enhanced the organic richness avg 2 4 toc wt of these rocks which resulted in the formation of promising hydrocarbon source rocks thus for a successful hydrocarbon exploration in the north western desert the promising source section of the g member would be associated with shales calcareous shales and argillaceous limestone lithologies its depositional environment is mainly confined to outer middle and inner middle shelf settings that have widespread suboxic anoxic conditions and show ehst pattern in contrast the regressive intervals that are denoted by the lowstand systems tract lst and or the late hst lhst typify the relatively coarse clastics as good quality reservoir rocks that are characterized by poor organic richness due to dilution with terrigenous influx

drivers of reduced enso variability in mid holocene in a coupled model the drivers of el nino southern oscillation enso intensity change during the mid holocene mh are investigated through employing a coupled model that exhibits excellent performance in simulating the present day enso behaviors the model shows a 28 decrease in enso intensity in the mh simulation compared to the pre industrial pi simulation showing an agreement with the ranges indicated by the paleo proxies based on quantitative analyses we reveal that the changes in the oceanic dynamic processes including the thermocline zonal advection and ekman feedback terms in the order from being most to least important were the major drivers of the reduced enso intensity in the mh further diagnosis analyses show that the weakening in all three oceanic dynamic terms could be traced back to the weakened thermocline response to zonal wind stress anomaly in the mh compared to that in the pi such weakened thermocline response was due to the relatively flattened meridional structure of enso related interannual anomaly field e g zonal wind stress anomaly field in the mh which arose from the strengthening of the mean meridional overturning circulation namely the mean pacific subtropical cell stc the process oriented analyses throughout this study suggest a critical linkage between enso intensity change and mean stc change in the mh through documenting how the mean stc change altered the oceanic dynamic processes and thus drove the enso intensity change

investigating the role of the tibetan plateau in enso variability abstractthe role of the tibetan plateau tp in el nino southern oscillation enso variability is investigated using coupled model experiments with different topography setups removing the tp res

critical considerations when assessing hydrocarbon plays using rock eval pyrolysis and organic petrology data data quality revisited abstract the dramatic increase in exploration for unconventional hydrocarbon resources has inherently fuelled the need for new source rock geochemical data the need for new data comes along with an increasing number of new users many of whom do not possess the background to interpret accurately and evaluate the quality of data sets generated by different geochemical screening techniques e g rock eval pyrolysis vitrinite reflectance here datasets from rock eval pyrolysis vitrinite reflectance and leco toc analyses are scrutinized and compared to show how failing to recognize good vs bad datasets can dramatically change interpretations during prospect or play appraisals detector saturation contamination of the sample with drilling fluid and suppression of both tmax and vitrinite reflectance are examples of complications that could compromise the validity of the results and the play or prospect reviews derived from them in addition misconceptions such as leco toc is better than rock eval 6 toc expressed by many users are a consequence of the lack of understanding of how different screening techniques and instrumentation work a solid understanding of these pitfalls and limitations can provide inexperienced geoscientists and engineers with the required support to improve risk maps for hydrocarbon charge analysis and source rock evaluations when using classic guidelines for interpreting results

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

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

assessing the twenty first century shift in enso variability in terms of the bjerknes stability index abstracta decadal change in the character of enso was observed around year 2000 toward weaker amplitude higher frequency events with an increased occurrence of central pacific el ninos here these changes are assessed in terms of the bjerknes stability index bj index which is a measure of the growth rate of enso related sst anomalies the individual terms of the index are calculated from ocean reanalysis products separately for the time periods 1980 99 and 2000 10 the spread between the products is large but they show a robust weakening of the thermocline feedback due to a reduced thermocline slope response to anomalous zonal wind stress as well as a weakened wind stress response to eastern equatorial pacific sst anomalies these changes are consistent with changes in the background state of the tropical pacific cooler mean sst in the eastern and central equatorial pacific results in reduced convection there together with a westward shift in the ascending branch of the walker circulation this shif

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

interannual and interdecadal variability of ocean temperature along the equatorial pacific in conjunction with enso in this paper the leading modes of ocean temperature anomalies ota along the equatorial pacific ocean are analyzed and their connection with el nino southern oscillation enso and interdecadal variation is investigated the first two leading modes of ota are connected with the different phases of the canonical enso and display asymmetric features of enso evolution the third leading mode depicts a tripole pattern with opposite variation of ota above the thermocline in the central pacific to that along the thermocline in the eastern and western pacific this mode is found to be associated with so called enso modoki insignificant correlations of this mode with the first two leading modes suggest that enso modoki may be a mode that is independent to the canonical enso and also has longer time scales compared with the canonical enso the fourth mode reflects a warming cooling tendency above below the thermocline since 2000 both the first and second modes have a large contribution to the interdecadal change in thermocline during 1979 2012 also the analysis also documents that both enso and ota shifted into higher frequency since 2000 compared with that during 1979 1999 interestingly the enso modoki related ota mode does not have any trend or significant interdecadal shift during 1979 2012 in addition it is shown that first four eof modes seem robust before and after 1999 2000 suggesting that the interdecadal shift of the climate system in the tropical pacific is mainly a frequency shift and the changes in spatial pattern are relatively small although the mean states over two periods experienced some significant changes

wind stress curl and enso discharge recharge in the equatorial pacific discharge and recharge of the warm water volume wwv above the 20 c isotherm in an equatorial pacific ocean box extending across the pacific from 156 e to the eastern ocean boundary between latitudes 5 s and 5 n are key variables in enso dynamics a formula linking wwv anomalies zonally integrated wind stress curl anomalies along the northern and southern edges of the box and flow into the western end of the box is derived and tested using monthly data since 1993 consistent with previous work a wwv balance can only be achieved if the 20 c isotherm surface is not a material surface that is warm water can pass through it for example during el nino part of the wwv anomaly entering the box is cooled so that it is less than 20 c and therefore passes out of the bottom of the box the 20 c isotherm surface the observations suggest that the anomalous volume passing through the 20 c isotherm is approximately the same as t the anomalous wwv entering the western end of the box therefore the observed wwv anomaly can be regarded as being driven by the anomalous wind stress curl along the northern and southern edges of the box the curl anomaly changes the wwv both by divergent meridional flow at the edges of the box and vortex stretching that is the sverdrup balance does not hold in the upper ocean a typical amplitude for the rate of change of wwv for the 5 s 5 n box is 9 6 sv sv 10 6 m 3 s 1 the wind stress curl anomaly and the transport anomaly into the western end of the box are highly correlated with the el nino index nino 3 4 the average sea surface temperature anomaly ssta over the region 5 s 5 n 170 120 w and nino 3 4 leads minus the wwv anomaly by one quarter of a cycle based on the preceding results a simple discharge recharge coupled enso model is derived only water warmer than about 27 5 28 c can give rise to deep atmospheric convection so unlike past discharge recharge oscillator models the west central rather than eastern equatorial sstas are emphasized the model consists of two variables t the ssta averaged over the region of strong enso air sea interaction in the west central pacific equatorial strip 5 s 5 n 156 e 140 w and d the 20 c isotherm depth anomaly averaged over the

weakened interannual variability in the tropical pacific ocean since 2000 abstractan interdecadal shift in the variability and mean state of the tropical pacific ocean is investigated within the context of changes in el nino southern oscillation enso compared with 1979 99 the interannual variability in the tropical pacific was significantly weaker in 2000 11 and this shift can be seen by coherent changes in both the tropical atmosphere and ocean for example the equatorial thermocline tilt became steeper during 2000 11 which was consistent with positive negative sea surface temperature anomalies increased decreased precipitation and enhanced suppressed convection in the western central and eastern tropical pacific which reflected an intensification of the walker circulation the combination of a steeper thermocline slope with stronger surface trade winds is proposed to have hampered the eastward migration of the warm water along the equatorial pacific as a consequence the variability of the warm water volume was reduced and thus enso amplitude also decreased

area length and thickness conservation dogma or reality abstract the basic assumption of quantitative structural geology is the preservation of material during deformation however the hypothesis of volume conservation alone does not help to predict past or future geometries and so this assumption is usually translated into bed length in 2d or area in 3d and thickness conservation when subsurface data are missing geologists may extrapolate surface data to depth using the kink band approach these extrapolations preserving both thicknesses and dips lead to geometries which are restorable but often erroneous due to both disharmonic deformation and internal deformation of layers first the bolivian sub andean zone case is presented to highlight the evolution of the concepts on which balancing is based and the important role played by a decoupling level in enhancing disharmony second analogue models are analyzed to test the validity of the balancing techniques chamberlin s excess area approach is shown to be on average valid however neither the length nor the thicknesses are preserved we propose that in real cases the length preservation hypothesis during shortening could also be a wrong assumption if the data are good enough to image the decollement level the chamberlin excess area method could be used to compute the bed length changes

reconstructing tropical pacific sea level variability for the period 1961 2002 using a linear multimode model monthly mean sea level anomalies in the tropical pacific for the period 1961 2002 are reconstructed using a linear multi mode model driven by monthly mean wind stress anomalies from the ncep ncar and era 40 reanalysis products overall the sea level anomalies reconstructed by both wind stress products agree well with the available tide gauge data although with poor performance at kanton island in the western central equatorial pacific and reduced amplitude at christmas island the reduced performance is related to model error in locating the pivot point in sea level variability associated with the so called tilt mode we present evidence that the pivot point was further west during the period 1993 2014 than during the period 1961 2002 and attribute this to a persistent upward trend in the zonal wind stress variance along the equator west of 160 w throughout the period 1961 2014 experiments driven by the zonal component of the wind stress alone reproduce much of the trend in sea level found in the experiments driven by both components of the wind stress the experiments show an upward trend in sea level in the eastern tropical pacific over the period 1961 2002 but with a much stronger upward trend when using the ncep ncar product we argue that the latter is related to an overly strong eastward trend in zonal wind stress in the eastern central pacific that is believed to be a spurious feature of the ncep ncar product

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

a three region conceptual model for central pacific el nino including zonal advective feedback abstractthe simple zonal two region framework of the recharge paradigm can accurately manifest the traditional eastern pacific ep type of el nino southern oscillation enso as its major warming

el nino variability in simple ocean data assimilation soda 1871 2008 1 a new ocean reanalysis that covers the period from 1871 to 2008 is used to explore the time evolving characteristics of el nino the new reanalysis assimilates all available hydrographic and sea surface temperature data into a model of the global ocean forced with surface boundary conditions from an atmospheric reanalysis that also covers the period from 1871 through 2008 using traditional measures of el nino our reanalysis shows that the timing of el nino events is in agreement with sea surface temperature reconstructions but el nino in the reanalysis is stronger particularly from 1871 to 1920 a new index based on the first moment of the temperature anomaly is introduced the new index is used to characterize the strength and location of el nino events and has the advantage that it is independent of the location of el nino using the new index el nino in the reanalysis shows prominent decadal variability of strength but relatively little long term trend el nino events were strong in the last part of the 19th century and first part of the 20th century and again in the latter part of the 20th century with weak el nino events in the middle of the 20th century the location of el nino also varies considerably ranging from the western to the eastern pacific near the coast of south america however the null hypothesis that the location of el nino can be represented as a random distribution about a central longitude of about 140 w cannot be rejected

variability of the meridional overturning in the north atlantic from the 50 year gecco state estimation abstract the german partner of the consortium for estimating the circulation and climate of the ocean gecco provided a dynamically consistent estimate of the time varying ocean circulation over the 50 yr period 1952 2001 the gecco synthesis combines most of the data available during the entire estimation period with the ecco massachusetts institute of technology mit ocean circulation model using its adjoint this gecco estimate is analyzed here for the period 1962 2001 with respect to decadal and longer term changes of the meridional overturning circulation moc of the north atlantic a special focus is on the maximum moc values at 25 n over this period the dynamically self consistent synthesis stays within the error bars of h l bryden et al but reveals a general increase of the moc strength the variability on decadal and longer time scales is decomposed into contributions from different processes changes in the model s moc strength are strongly influenced by the southward communication of d

changes in tropical pacific thermocline depth and their relationship to enso after 1999 abstractthe characteristics of el nino southern oscillation enso variability have experienced notable changes since the late 1990s including a breakdown of the zonal mean upper ocean heat content as a precursor for enso these changes also initiated a debate on the role of thermocline variations on the development of enso events since the beginning of the twenty first century in this study the connection between thermocline variations and el nino and la nina events is examined separately for the 1980 98 and 1999 2012 periods the analysis highlights the important role of thermocline variations in modulating enso evolutions in both periods it is found that thermocline variation averaged in the central tropical pacific including both equatorial and off equatorial regions is a good precursor for enso evolutions before and after 1999 while the traditional basinwide mean of equatorial thermocline variation is a good precursor only before 1999 the new precursor including both high frequency variabili