historical trends in the surface temperature over the oceans based on the coads based on a new and unique compilation of surface ship data over the world ocean the comprehensive ocean atmosphere data set coads the temperature records since 1870 were thoroughly analyzed results for the air and sea surface temperature are presented for the two hemispheres and for individual 10 latitude wide belts the results support most earlier results of a relatively warm period over the oceans in the late 19th century a cool period between about 1905 and 1930 and a warm period from the 1940 s onward of considerable interest and perhaps unique in the historical record are the diverging trends in the midlatitude sea and air temperatures of the two hemispheres during the 1960 s and early 1970 s with relative cooling in the northern hemisphere and relative heating in the southern hemisphere

historical reconstruction of monthly oceanic precipitation 1900 2006 1 an oceanic precipitation reconstruction is developed and evaluated for periods extending back to as early as 1900 large scale monthly oceanic precipitation is reconstructed using the available network of historical gauge data fit to a set of large scale covariance spatial modes based on modern analysis the modern analysis is based on satellite microwave estimates merged with atmospheric reanalysis estimates for 1900 2006 a monthly and 5 spatial product is developed for reconstructing climate scale large scale spatial and inter seasonal and longer timescales variation in pre satellite periods advantages of this study include the use of a homogeneous satellite analysis for computing reconstruction statistics and improved tuning of the reconstruction methods cross validation testing is used to show how much historical variance can be reconstructed with the available sampling in addition reconstructions are performed using several different gauge data sets to evaluate differences due to the choice of gauge data testing shows that that these improved methods produce reconstructions with useful skill in the tropics and northern hemisphere midlatitudes in the southern hemisphere midlatitudes and in polar latitudes in both hemispheres sampling is too sparse to yield much skill the reconstruction is able to resolve large scale modes of variation useful for some diagnostic studies of the 20th century reconstruction efforts will continue as improved satellite and atmospheric reanalyses become available

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

observed nonlinearities of monthly teleconnections between tropical pacific sea surface temperature anomalies and central and eastern north american precipitation abstract most investigations of relationships between tropical pacific sea surface temperature anomaly ssta events and regional climate patterns have assumed the teleconnections to be linear whereby the climate patterns associated with cold ssta events are considered to be similar in structure and morphology but opposite in sign to those linked to warm ssta events in contrast and motivated by early evidence of nonlinearity in the above regard this study identifies characteristic i e composite calendar monthly central and eastern north american precipitation patterns separately for warm and cold ssta events in different regions of the tropical pacific central eastern west central horseshoe far western identified through principal component analysis the precipitation anomaly patterns are computed from an approximately 1 lat long set of monthly station data for 1950 92 their robustness and nonlinearity are established using local regional and field statistical significance tests and a va

a damped decadal oscillation in the north atlantic climate system a simple stochastic atmosphere model is coupled to a realistic model of the north atlantic ocean a north south sst dipole with its zero line centered along the subpolar front influences the atmosphere model which in turn forces the ocean model by surface fluxes related to the north atlantic oscillation the coupled system exhibits a damped decadal oscillation associated with the adjustment through the ocean model to the changing surface forcing the oscillation consists of a fast wind driven positive feedback of the ocean and a delayed negative feedback orchestrated by overturning circulation anomalies the positive feedback turns out to be necessary to distinguish the coupled oscillation from that in a model without any influence from the ocean to the atmosphere using a novel diagnosing technique it is possible to rule out the importance of baroclinic wave processes for determining the period of the oscillation and to show the important role played by anomalous geostrophic advection in sustaining the oscillation

sst assimilation experiments in a tropical pacific ocean model with a simple 3dvar assimilation algorithm a new scheme of assimilating sea surface temperature sst observations is proposed in this paper in this new scheme the linear relation between any two neighboring depths was derived using singular value decomposition technique and then was applied to estimate the temperatures at deeper levels using the temperature analyses at shallower levels the estimated temperatures were assimilated into an ocean model and the procedure was run iteratively at each time step from the surface to a depth of 250 m the oceanic analyses show that the new scheme can more effectively adjust oceanic thermal and dynamical fields and lead to a more realistic subsurface thermal structure when compared with the control

reconstruction of historical sea surface temperatures using empirical orthogonal functions abstract studies of climate variability often rely on high quality sea surface temperature sst anomalies although the high resolution national centers for environmental prediction formerly the national meteorological center optimum interpolation oi sst analysis is satisfactory for these studies the oi resolution cannot be maintained before november 1931 due to the lack of satellite data longer periods of ssts have come from traditional analyses of in situ ship and buoy sst observations alone a new interpolation method is developed using spatial patterns from empirical orthogonal functions e0fs that is a principal component analysis to improve analyses of sst anomalies from 1950 to 1981 the method uses the more accurate oi analyses from 1982 to 1993 to produce the spatial eofs the dominant eof modes which correspond to the largest variance are used as basis functions and are fit in a least squares sense to the in situ data to determine the time dependence of each mode a complete field

the mechanical impact of the tibetan plateau on the seasonal evolution of the south asian monsoon the impact of the tibetan plateau on the south asian monsoon is examined using a hierarchy of atmospheric general circulation models during the premonsoon season and monsoon onset april june when westerly winds over the southern tibetan plateau are still strong the tibetan plateau triggers early monsoon rainfalldownstream particularlyoverthebay ofbengalandsouth china the downstreammoist convection is accompanied by strong monsoonal low level winds in experiments where the tibetan plateau is removed monsoon onset occurs about a month later but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase during the mature and decaying phase of monsoon july september when westerly winds over the southern tibetan plateau almost disappear monsoon circulation strength is not much affected by the presence of the tibetan plateau a dry dynamical core with east west oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain in a moist atmosphere the mechanically driven downstream convergence is expected to be associated with significant moisture convergence the authors speculate that the mechanically driven downstream convergence in the presence of the

how ubiquitous is the dipole relationship in tropical atlantic sea surface temperatures several kinds of analysis are applied to sea surface temperature anomalies ssta 1856 1991 to determine the degree to which ssta of opposite sign in the tropical north and south atlantic occur antisymmetric dipole configurations of ssta on basin scales are not ubiquitous in the tropical atlantic unless the data are stratified by both season and frequency inherent dipole behavior cannot be demonstrated upon removing the global el nino southern oscillation signal in ssta which is symmetric between the north and south atlantic from the data the regions north or south of the intertropical convergence zone have qualitatively different temporal variabilities and are poorly correlated dipole configurations do occur infrequently 12 15 of the time but no more so than expected by chance for stochastically independent variables nondipole configurations that imply significant meridional ssta gradients occur much more frequently nearly half of the time cross spectral analysis of seasonally averaged ssta indices for the north and south atlantic show marginally significant coherence with antisymmetric phase in two period bands 8 12 years for the boreal winter spring and 2 3 years for the boreal summer fall antisymmetric coherence is optimal for a small subregion west of angola in the south atlantic with respect to ssta of basin scale in the tropical north atlantic dipole variability even where optimal explains only a small fraction of the total variance in tropical atlantic ssta 7

prediction of tropical atlantic sea surface temperatures using linear inverse modeling the predictability of tropical atlantic sea surface temperature on seasonal to interannual timescales by linear inverse modeling is quantified the authors find that predictability of caribbean sea and north tropical atlantic sea surface temperature anomalies sstas is enhanced when one uses global tropical sstas as predictors compared with using only tropical atlantic predictors this predictability advantage does not carry over into the equatorial and south tropical atlantic indeed persistence is a competitive predictor in those regions to help resolve the issue of whether or not the dipole structure found by applying empirical orthogonal function analysis to tropical atlantic ssts is an artifact of the technique or a physically real structure the authors combine empirically derived normal modes and their adjoints to form influence functions maps highlighting the geographical areas to which the north tropical atlantic and the south tropical atlantic ssts are most sensitive at specified lead times when the analysis is confined to the atlantic basin the 6 month influence functions in the north and south tropical atlantic tend to be of the opposite sign and evolve into clear dipoles within 6 months when the analysis is performed on global tropical ssts the 6 month influence functions are connected

hydrological signatures relating the asian summer monsoon and enso using the ncep ncar reanalysis for the 1950 2000 period differences in the atmospheric hydrological cycle between the extremes of enso i e la nina minus el nino are examined zonal vertically integrated moisture transport vimt across 1008e accounts for about half of the variability in net moisture convergence in the north indian ocean region between enso extremes when all enso events are considered changes in vimt across 1008e are associated with large changes in the strength of the pacific ocean trade wind regime during enso the bulk of the remaining vimt anomalies are from the arabian sea and appear to be associated with sea level pressure variations in the northern and western parts of the indian ocean basin this initial analysis therefore suggests that the interaction between the monsoon and enso may be more complex than the direct modulation of vimt by the pacific ocean trade winds alone the analysis is refined further by comparing the differences of the indian and pacific ocean hydrological cycles between enso extremes when they occur concurrently with anomalous monsoons enso anomalous monsoon years eam and when the monsoon is normal enso normal monsoon years enm for both eam and enm years similar differences exist in vimt across 1008e between enso extremes however major differences are noted in vimt anomalies from the west and south into the north indian ocean region thus the principal difference in moisture convergence in the north indian ocean between eam and enm years is associated primarily with vimt anomalies in the western indian ocean region and not those in the eastern indian or pacific oceans to test the hypothesis that pacific ocean sst anomalies occurring prior to the monsoon may be important in influencing the eventual nature of the monsoon the analysis is extended backward to the spring period while may sst differences in the nino 3 region between enso extremes are found to be similar for both eam and enm years vimt differences in both the indian ocean and the central and western pacific oceans are sig nificantly larger during eam years than enm years may sst differences in the central subtropical pacific ocean are also significantly larger during eam than enm years these results show that the anomalous sst gradient between the eastern equatorial and the central subtropical pacific ocean prior to the monsoon onset together with its associated vimts anomalies may be important factors in determining the degree of connection between monsoon and enso in addition the circulation in the indian ocean prior to and during the monsoon onset shares a strong association with the eventual intensity of the monsoon enso coupling

seasonal dependence of surface wind stress variability on sst and precipitation over the tropical pacific the dependence of interannual variability of surface zonal and meridional wind stresses x and y on sea surface temperature sst and precipitation over the tropical pacific is examined using observed data a strong seasonality in the dependence is found in january the largest sst and precipitation anomalies are located in the central to eastern and central tropical pacific respectively x anomalies in the southern central tropical pacific and y anomalies in the northern tropical pacific are highly correlated to both the sst and precipitation anomalies in contrast during july the largest sst and precipitation anomalies are located at the eastern and western tropical pacific respectively east of the dateline x anomalies present little dependence on the sst anomalies west of the dateline x anomalies depend strongly on the precipitation anomalies that are not linked to the leading modes of sst

robustness of low frequency circulation patterns derived from eof and rotated eof analyses abstract the robustness of low frequency circulation patterns defined by unrotated and rotated empirical orthogonal functions e0fs are compared based on the northern hemisphere 10 day low pass filtered wintertime 500 hpa height field the pacific north american pattern and the north atlantic oscillation are the most prominent modes of low frequency variability in the data the reproducibility of the spatial patterns derived from eof and rotated eof analysis is assessed by repeating the analysis on 50 subsets of the data each comprised of the maps belonging to 22 randomly selected winters from the 44 winters in the total record the results indicate that rotated spatial patterns are less sensitive to sampling fluctuations than their unrotated counterparts

winter to winter recurrence of sea surface temperature salinity and mixed layer depth anomalies abstract the mean seasonal cycle of mixed layer depth mld in the extratropical oceans has the potential to influence temperature salinity and mixed layer depth anomalies from one winter to the next temperature and salinity anomalies that form at the surface and spread throughout the deep winter mixed layer are sequestered beneath the mixed layer when it shoals in spring and are then re entrained into the surface layer in the subsequent fall and winter here we document this re emergence mechanism in the north pacific ocean using observed ssts subsurface temperature fields from a data assimilation system and coupled atmosphere ocean model simulations observations indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during winter recurs in the following winter the model simulation with mixed layer ocean physics reproduced the winter to winter recurrence while model simulations with observed ssts specified in the tropical pacific and a 50 m slab in the north pacific did not this difference between the model results indicates that the winter to winter sst correlations are the result of the re emergence mechanism and not of similar atmospheric forcing of the ocean in consecutive winters the model experiments also indicate that sst anomalies in the tropical pacific associated with el nino are not essential for re emergence to occur the recurrence of observed sst and simulated sst and sss anomalies are found in several regions in the central north pacific and are quite strong in the northern 50 n part of the basin the winter to winter autocorrelation of sss anomalies exceed those of sst since only the latter are strongly damped by surface fluxes the re emergence mechanism also has a modest influence on mld through changes in the vertical stratification in the seasonal thermocline

experiments in reconstructing twentieth century sea levels abstract one approach to reconstructing historical sea level from the relatively sparse tide gauge network is to employ empirical orthogonal functions eofs as interpolatory spatial basis functions the eofs are determined from independent global data generally sea surface heights from either satellite altimetry or a numerical ocean model the problem is revisited here for sea level since 1900 a new approach to handling the tide gauge datum problem by direct solution offers possible advantages over the method of integrating sea level differences with the potential of eventually adjusting datums into the global terrestrial reference frame the resulting time series of global mean sea levels appears fairly insensitive to the adopted set of eofs in contrast charts of regional sea level anomalies and trends are very sensitive to the adopted set of eofs especially for the sparser network of gauges in the early 20th century the reconstructions appear especially suspect before 1950 in the tropical pacific while this limits some applications of the sea level reconstructions the sensitivity does appear adequately captured by formal uncertainties all our solutions show regional trends over the past five decades to be fairly uniform throughout the global ocean in contrast to trends observed over the shorter altimeter era consistent with several previous estimates the global sea level rise since 1900 is 1 70 0 26 mm yr 1 the global trend since 1995 exceeds 3 mm yr 1 which is consistent with altimeter measurements but this large trend was possibly also reached between 1935 and 1950

dynamics of the indian monsoon and enso relationships in the sintex global coupled model this paper uses recent gridded climatological data and a coupled general circulation model gcm simulation in order to assess the relationships between the interannual variability of the indian summer monsoon ism and the el nino southern oscillation enso the focus is on the dynamics of the ism enso relationships and the ability of the state of the art coupled gcm to reproduce the complex lead lag relationships between the ism and the enso the coupled gcm is successful in reproducing the ism circulation and rainfall climatology in the indian areas even though the entire ism circulation is weaker relative to that observed in both observations and in the simulation the ism rainfall anomalies are significantly associated with fluctuations of the hadley circulation and the 200 hpa zonal wind anomalies over the indian ocean a quasi biennial time scale is found to structure the ism dynamical and rainfall indices in both cases moreover ism indices have a similar interannual variability in the simulation and observations the coupled model is less successful in simulating the annual cycle in the tropical pacific a major model bias is the eastward displacement of the western north pacific inter tropical convergence zone itcz near the dateline during northern summer this introduces a strong semiannual component in pacific walker circulation indices and central equatorial pacific sea surface temperatures another weakness of the coupled model is a less than adequate simulation of the southern oscillation due to an erroneous eastward extension of the southern pacific convergence zone spcz year round despite these problems the coupled model captures some aspects of the interannual variability in the tropical pacific enso events are phase locked with the annual cycle as observed but are of reduced amplitude relative to the observations wavelet analysis of the model nino34 time series shows enhanced power in the 2 4 year band as compared to the 2 8 year range for observations during the 1950 2000 period the ism circulation is weakened during enso years in both the simulation and the observations however the model fails to reproduce the lead lag relationship between the ism and nino34 sea surface temperatures ssts furthermore lag correlations show that the delayed response of the wind stress over the central pacific to ism variability is insignificant in the simulation these features are mainly due to the unrealistic interannual variability simulated by the model in the western north pacific the amplitude and even the sign of the simulated surface and upper level wind anomalies in these areas are not consistent with observed patterns during weak strong ism years the ism and western north pacific itcz fluctuate independently in the observations while they are negatively and significantly correlated in the simulation this isolates the pacific walker circulation from the ism forcing these systematic errors may also contribute to the reduced amplitude of enso variability in the coupled simulation most of the unrealistic features in simulating the indo pacific interannual variability may be traced back to systematic errors in the base state of the coupled model

a physical basis for the interannual variability of rainfall in the sahel a major factor in rainfall variability over sahelian west africa is the latitudinal location of the tropical rainbelt when it is displaced abnormally far northward the sahel experiences a wet year an anomalous southward displacement results in drought in this paper we examine the question of what controls the location during the boreal summer hypothesizing that inertial instability plays a role an analysis of surface pressure and temperature fields wind fields divergence and vertical motion show that the criteria for inertial instability are satisfied in wet augusts but not in dry ones the key determinant appears to be the surface pressure gradient between the continent and the equatorial atlantic when this is large inertial instability results in the development of a low level westerly jet the presence of this jet enhances the horizontal and vertical shear and displaces the african easterly jet northwestward associated with this situation is strong vertical motion over the sahel and subsidence over the guinea coast producing dry conditions over the latter the result is a rainfall dipole one of two major modes of variability over west africa important factors include sea surface temperatures ssts in the equatorial atlantic and pressure in the south atlantic the first of these factors suggests a link with the atlantic nino mode of tropical atlantic variability while the second suggests a possible link with the pacific and the extratropical south atlantic overall our study relates the well known sst influence on sahel rainfall to atmospheric dynamics over the continent copyright 2007 royal meteorological society

small scale convection in the subduction zone mantle wedge abstract small scale convection in the upper mantle can appreciably influence large scale mantle dynamics and has important implications for geophysical observables such as seismic anisotropy and surface heat flow we develop numerical models to evaluate the likelihood of small scale convection in the mantle wedge above subducting slabs the characteristics of small scale convection are analyzed using the 3 d single mode approximation in which one characteristic wavenumber represents small scale convective motions with rotational axes parallel to the convergence direction numerical simulations are run for a range of characteristic wavenumbers rayleigh numbers and subduction parameters e g slab dip angle convergence velocity and downgoing plate age for each simulation we quantify the excitation due to small scale convection and determine under what conditions and characteristic wavenumbers this excitation is maximized we find that of the parameters examined mantle wedge viscosity plays the most significant role in dictating the occurrence and strength of small scale convective motions in the mantle wedge numerical models run with subduction parameters similar to that of northeast japan where it has been proposed that small scale convection may be occurring in the mantle wedge require a mantle wedge viscosity of 10 18 pa s for significant small scale convection to occur

wintertime variability in the euro atlantic region in observations and in ecmwf seasonal ensemble experiments an empirical orthogonal function eof decomposition of monthly mean analyses of 500 hpa height 1949 94 is used to describe the interannual variability of the large scale flow in the euro atlantic region during winter the first four eofs resemble low frequency variability patterns identified in previous studies such as the north atlantic oscillation and the eastern atlantic and eurasian teleconnection patterns the second eof and fourth eof eof4 are associated with the occurrence of el nino like sea surface temperature sst anomalies according to an observational analysis for eof4 correlations with sst anomalies in the west pacific are also important indications of an influence of tropical sst anomalies on the blocking like third eof emerging from the european centre for medium range weather forecasts ecmwf re analysis era data are not confirmed by a longer sst record a negligible correlation exists between the first eof and el nino indices during the era period although a link may be detected in earlier decades in the second part of the paper a 14 winter set of seasonal ensemble simulations performed with the ecmwf atmospheric model forced by observed sst is validated by comparing the projection of era data onto the four leading euro atlantic eofs with those of ensemble experiments and computing composite anomalies of analyses and model fields the performance of the model is uneven and depends on the large scale pattern considered model biases and flow dependent errors affect the simulations of some of the eofs in particular the model has strong problems reproducing the occurrence of european blocks the best correlation 69 between the time series of analysis and ensemble mean principal components is obtained for eof4 which seems to be forced by sst anomalies in the west pacific associated with el nino southern oscillation enso events the effects of this forcing are felt on the zonal wind structure over eurasia and are reasonably reproduced by the ecmwf model conversely the propagation into the atlantic region of planetary waves originating in the east pacific is poorly simulated thus degrading the model performance in predicting euro atlantic anomalies during some strong enso events

the non tropical coral cladocora caespitosa as the new climate archive for the mediterranean high resolution weekly trace element systematics abstract high resolution weekly laser ablation icp ms trace element analyses b sr u mg ba are reported for the scleractinian coral cladocora caespitosa collected from the northern adriatic sea geochemical ratios sr ca b ca mg ca u ca ba ca were measured in a 38 mm long 10 years growth external coralline portion wall region and generally exhibit a close relationship with the in situ measured weekly fortnightly data on sea surface temperature sst available for the last 6 years in particular b ca ratios tuned to fine scale variations in sst show a high degree of correlation r 0 856 n 136 with sst and indicate that coral calcification only occurs above a minimum temperature threshold of 14 16 c in addition the ranges of trace element variability are larger than those typically recorded in tropical corals consistent with the large seasonal variations in sst of the adriatic this study thus demonstrates the feasibility of extracting and exploiting high resolution geochemical records from non tropical corals such as c caespitosa as a proxy for sst

interannual variability of summer monsoon onset over the western north pacific and the underlying processes climatological summer monsoon onset over the south china sea scs and the western north pacific wnp defined as the region of 108 208n 1208 1608e displays three distinct stages around mid may monsoon rain commences in the scs and the philippines in early to mid june the monsoon rain extends to the southwestern philippine sea after mid july the rainy season starts in the northeastern part of the wnp the onset anomaly however displays an in phase interannual variation across the entire wnp domain the standard deviation of the onset date increases eastward from 3 pentads in the scs to 5 pentads in the northeastern part of the domain the large onset variability in the wnp is mainly attributed to large year to year changes of the seasonal cycle

the thermal oceanographic signal of el nino reconstructed from a kiritimati island coral central equatorial pacific sea surface temperature sst anomaly is a critical predictor of basin wide oceanographic and atmospheric effects of the el nino southern oscillation enso phenomenon we employ two geochemical thermometers measured on coralline aragonite to reconstruct an independent proxy based measure of central equatorial pacific sea surface temperature anomaly in addition we assess the observational error associated with extraction of large scale sst anomalies from 18o and sr ca measurements on the basis of paired data for the 1981 1987 period rms error for the estimation of sst from kiritimati coral 18o is about 0 4 c assuming no seawater 18o influence for sr ca the observational error is about 0 5 c singular spectrum analysis of the 18o time series suggests that 1 3 of the variance is explained by sst anomaly and that this variance may be separated from other signals in the frequency domain the interannual component of the 18o record shares 70 variance with the interannual component of local sst anomaly estimates 0 84 and correlates as highly with nino3 region 150 w 90 w 5 n 5 s sst anomaly estimates comparison of annual averages of the 18o data with analyzed sst for 55 years suggests that the error in deriving annually averaged sst anomalies at kiritimati is about 0 4 c a global sst correlation analysis suggests significant correlation with the rest of the pacific basin and the tropical indian and atlantic sectors the ocean wide level of correlation achieved using the coral data is indistinguishable from that achieved using the nino3 sst anomaly index and suggests that a few well located coral reconstructions with low observational error may be sufficient to reconstruct the global sst anomaly field associated with enso activity

local coupled equatorial variability versus remote enso forcing in an intermediate coupled model of the tropical atlantic the relative roles played by the remote el nino southern oscillation enso forcing and the local air sea interactions in the tropical atlantic are investigated using an intermediate coupled model icm of the tropical atlantic the oceanic component of the icm consists of a six baroclinic mode ocean model and a simple mixed layer model that has been validated from observations the atmospheric component is a global atmospheric general circulation model developed at the university of california los angeles ucla in a forced context the icm realistically simulates both the sea surface temperature anomaly ssta variability in the equatorial band and the relaxation of the atlantic northeast trade winds and the intensification of the equatorial westerlies in boreal spring that usually follows an el nino event the results of coupled experiments with or without pacific enso forcing and with or without explicit air sea interactions in the equatorial atlantic indicate that the background energy in the equatorial atlantic is provided by enso however the time scale of the variability and the magnitude of some peculiar events cannot be explained solely by enso remote forcing it is demonstrated that the peak of ssta variability in the 1 3 yr band as observed in the equatorial atlantic is due to the local air sea interactions and is not a linear response to enso seasonal phase locking in boreal summer is also the result of the local coupling the analysis of the intrinsic sustainable modes indicates that the atlantic el nino is qualitatively a noisedriven stable system such a system can produce coherent interdecadal variability that is not forced by the pacific or extraequatorial variability it is shown that when a simple slab mixed layer model is embedded into the system to simulate the northern tropical atlantic nta sst variability the warming over nta following el nino events have characteristics location and peak phase that depend on air sea interaction in the equatorial atlantic in the model the interaction between the equatorial mode and nta can produce a dipolelike structure of the ssta variability that evolves at a decadal time scale the results herein illustrate the complexity of the tropical atlantic ocean atmosphere system whose predictability jointly depends on enso and the connections between the atlantic modes of variability

a linear tendency correction technique for improving seasonal prediction of sst tropical atlantic sector using an agcm coupled to a slab ocean by construction the model has systematic biases in its deterministic dynamics because the slab ocean has no ocean dynamics we show that the linear correction procedure successfully corrects the model biases in the regions where ocean dynamics are expected to be important 4 in a recent study chang et al 2003 hereafter csj show that sst anomalies in the tropical north atlantic tna can be predicted two seasons in advance using an agcm coupled to a slab ocean owing to the combined effect of the remote enso influence and local thermodynamic air sea feedbacks but in the tropical south and equatorial atlantic the simple coupled model revealed poor skills and under performed the persistence forecast here we use csj s results as a reference with the exception that the prediction and verification period is expanded from 1959 to 2000 we focus on february may the peak months of the gradient mode of variability in the tropical atlantic chiang et al 2002 allowing us to investigate the importance of ocean dynamics in its evolution

characteristics of winter precipitation variation over northern central eurasia and their connections to sea surface temperatures over the atlantic and pacific oceans abstract this study reveals spatial and temporal characteristics of precipitation variability and their teleconnections to sea surface temperatures ssts over the atlantic and pacific oceans by analyzing 68 yr of recent precipitation records over the former soviet union in addition to a general increasing trend of about 0 4 mm yr 1 or 6 decade 1 over much of the study region three major modes of precipitation variation are identified a quasi biennial variation of 2 3 yr is found over the region surrounding the caspian and aral seas an el nino timescale precipitation variation of 4 5 yr is present over southern central siberia and is associated with eastern tropical pacific ssts a quasi decadal timescale variation of about 11 12 yr is evident over central european russia this quasi decadal precipitation variation is closely linked to a major sst anomaly pattern of alternating latitudinal belts over the atlantic and sst variations over the equatorial pacific ocean these associations to ssts are str

the response of a coupled model of enso to observed estimates of stochastic forcing in this work the role that observed intraseasonal atmospheric variability may play in controlling and maintaining enso variability is examined to this end an asymptotically stable intermediate coupled model of el nino southern oscillation enso is forced with observed estimates of stochastic forcing which are defined to be the part of the atmospheric variability that is apparently independent of the ocean circulation the stochastic forcing sf was estimated from 51 yr 1950 2000 of ncep ncar reanalyses of surface winds and net surface heat flux 32 yr 1950 81 of reconstructed sea surface temperatures sst and 19 yr 1982 2000 of reynolds sst in the tropical pacific the deterministic component of the surface wind and heat flux anomalies that can be linearly related to sst anomalies was estimated using the singular value decomposition of the covariance between the anomaly fields and was then removed from the atmospheric anomaly fields to recover the stochastic component of the ocean surface forcing principal component analysis reveals that the stochastic component has no preferred mode of variability exhibits decorrelation times of a few days and has a spectrum that is indis tinguishable from red noise a 19 yr stochastically forced coupled model integration qualitatively shows some similarities with the observed equatorial sst the robustness of this result is checked by performing different sensitivity experiments the model mostly exhibits a linear and nonnormal response to the low frequency tail of sf using the ideas of generalized linear stability theory the dynamically important contributions of the sf are isolated and it is shown that most of the variability in the stochastically forced model solution is produced by stochastically induced kelvin waves forced in the western and central pacific moreover the two most dynamically important patterns of stochastic forcing which account for 71 of the expected variance in the model response describe eastward propagation of the forcing similar to the mjo the results of this study support the hypothesis that a significant fraction of enso variability may be due to sf and suggest that a better understanding of the influence of sf on the ocean surface in the western central pacific may be required in order to understand the predictability of enso

reconstructing sea level using cyclostationary empirical orthogonal functions 1 cyclostationary empirical orthogonal functions derived from satellite altimetry are combined with historical sea level measurements from tide gauges to reconstruct sea level fields from 1950 through 2009 previous sea level reconstructions have utilized empirical orthogonal functions as basis functions but by using cyclostationary empirical orthogonal functions and by addressing other aspects of the reconstruction procedure an alternative sea level reconstruction can be computed the procedure introduced here is capable of capturing the annual cycle and el nino southern oscillation enso signals back to 1950 with correlations between the reconstructed enso signal and common enso indices found to be over 0 9 the regional trends computed from the new reconstruction show good agreement with the trends obtained from the satellite altimetry but some discrepancies are seen when comparing with previous sea level reconstructions over longer time periods the computed rate of global mean sea level rise from the reconstructed time series is 1 97 mm yr from 1950 to 2009 and 3 22 mm yr from 1993 to 2009

nonlinear interdecadal changes of the el nino southern oscillation nonlinear interdecadal changes in the el nino southern oscillation enso phenomenon are investigated using several tools a nonlinear canonical correlation analysis nlcca method based on neural networks a hybrid coupled model and the delayed oscillator theory the leading nlcca mode between the tropical pacific wind stress ws and sea surface temperature sst reveals notable interdecadal changes of enso behaviour before and after the mid 1970s climate regime shift with greater nonlinearity found during 1981 99 than during 1961 75 spatial asymmetry for both sst and ws anomalies between warm el nino and cool la nina events was significantly enhanced in the later period during 1981 99 the location of the equatorial easterly anomalies was unchanged from the earlier period but in the opposite enso phase the westerly anomalies were shifted eastward by up to 25 according to the delayed oscillator theory such an eastward shift would lengthen the duration of the warm events by up to 45 but leave the duration of the cool events unchanged supporting evidence was found from a hybrid coupled model built with the lamont dynamical ocean model coupled to a statistical atmospheric model consisting of either the leading nlcca or cca mode

artificial intelligence reconstructs missing climate information historical temperature measurements are the basis of global climate datasets like hadcrut4 this dataset contains many missing values particularly for periods before the mid twentieth century although recent years are also incomplete here we demonstrate that artificial intelligence can skilfully fill these observational gaps when combined with numerical climate model data we show that recently developed image inpainting techniques perform accurate monthly reconstructions via transfer learning using either 20cr twentieth century reanalysis or the cmip5 coupled model intercomparison project phase 5 experiments the resulting global annual mean temperature time series exhibit high pearson correlation coefficients 0 9941 and low root mean squared errors 0 0547 c as compared with the original data these techniques also provide advantages relative to state of the art kriging interpolation and principal component analysis based infilling when applied to hadcrut4 our method restores a missing spatial pattern of the documented el nino from july 1877 with respect to the global mean temperature time series a hadcrut4 reconstruction by our method points to a cooler nineteenth century a less apparent hiatus in the twenty first century an even warmer 2016 being the warmest year on record and a stronger global trend between 1850 and 2018 relative to previous estimates we propose image inpainting as an approach to reconstruct missing climate information and thereby reduce uncertainties and biases in climate records an artificial intelligence based method may infill gaps in historical temperature data more effectively than conventional techniques application of this method reveals a stronger global warming trend between 1850 and 2018 than estimated previously

interdecadal changes of surface temperature since the late nineteenth century we present global fields of decadal annual surface temperature anomalies referred to the period 1951 1980 for each decade from 1881 1890 to 1981 1990 and for 1984 1993 in addition we show decadal calendar seasonal anomaly fields for the warm decades 1936 1945 and 1981 1990 the fields are based on sea surface temperature sst and land surface air temperature data the ssts are corrected for the pre world war ii use of uninsulated sea temperature buckets and incorporate adjusted satellite based ssts from 1982 onward our results extend those published in the 1990 intergovernmental panel on climate change scientific assessment and its 1992 supplement we assess the impact of various sources of error in the fields despite poor data coverage initially and around the two world wars the generally cold end of the nineteenth century and start to the twentieth century are confirmed together with the substantial warming between about 1920 and 1940 slight cooling of the northern hemisphere took place between the 1950s and the mid 1970s although slight warming continued south of the equator recent warmth has been most marked over the northern continents in winter and spring but the 1980s were warm almost everywhere apart from greenland the northwestern atlantic and the midlatitude north pacific parts of the middle to high latitude southern ocean may also have been cool in the 1980s but in this area the 1951 1980 climatology is unreliable the impact of the satellite data is reduced because the record of blended satellite and in situ sst is still too short to yield a climatology from which to calculate representative anomalies reflecting climatic change in the southern ocean however we propose a method of using existing satellite data in a step toward this target the maps are condensed into global and hemispheric decadal surface temperature anomalies we show the sensitivity of these estimated anomalies to alternative methods of compositing the spatially incomplete fields running decadal zonal means and annual global and hemispheric time series are also shown finally we discuss some salient features in terms of observed atmospheric circulation changes and of the results of climate model integrations with increasing atmospheric greenhouse gases

reemergence areas of winter sea surface temperature anomalies in the world s oceans 1 using datasets of sea surface temperature sst surface heat flux upper ocean thermal data and climatological temperature and salinity profiles we try to detect reemergence areas of winter sst anomalies in the world s oceans and describe characteristics of these areas in terms of mixed layer depth mld annual mean heat flux and properties of waters formed in winter mixed layer eventually seven reemergence areas are found four in the northern hemisphere and three in the southern hemisphere all areas have a large seasonal variation of mld and are the regions where annual mean heat fluxes are relatively small except for two regions in the northern hemisphere in the viewpoint of water properties it is found that these areas correspond to the mode water formation regions subtropical mode waters of the indian ocean south pacific south atlantic north pacific and north atlantic and north pacific central and north atlantic subpolar mode waters

observed evidence of an impact of the antarctic sea ice dipole on the antarctic oscillation abstracta lagged maximum covariance analysis mca is applied to investigate the linear covariability between monthly sea ice concentration sic and 500 mb geopotential height z500 in the southern hemisphere sh the dominant signal is the atmospheric forcing of sic anomalies throughout the year but statistically significant covariances are also found between austral springtime z500 and prior sic anomalies up to four months earlier the mca pattern is characterized by an antarctic dipole adp like pattern in sic and a positively polarized antarctic oscillation aao in z500 such long lead time covariance suggests the forcing of the aao by persistent adp like sic anomalies the leading time of sic anomalies provides an implication for skillful predictability of springtime atmospheric variability

nonlinear modes of north american winter climate variability derived from a general circulation model simulation abstract nonlinear principal component analysis nlpca via a neural network nn approach was applied to an ensemble of six 47 yr simulations conducted by the canadian centre for climate modelling and analysis cccma second generation atmospheric general circulation model agcm2 each simulation was forced with the observed sea surface temperature from the global sea ice and sea surface temperature dataset gisst from january 1948 to november 1994 the nlpca modes reveal nonlinear structures in both the winter 500 mb geopotential height z500 anomalies and surface air temperature sat anomalies over north america with asymmetric spatial anomaly patterns during the opposite phases of an nlpca mode only during its negative phase is the first nlpca mode related to the el nino southern oscillation enso the positive phase is related to a weakened jet stream spatial patterns of the nlpca mode for the z500 anomalies generally agree with those for the sat anomalies nonlinear canonical correlation

the dependence of caribbean rainfall on the interaction of the tropical atlantic and pacific oceans abstract seasonally stratified analyses of rainfall anomalies over the intra americas sea and surrounding land areas and of onset and end dates of the central american rainy season show that the variability of the tropical atlantic sea surface temperature anomaly ssta is more strongly associated with rainfall over the caribbean and central america than is tropical eastern pacific ssta seasonal differences include the importance of antisymmetric configurations of tropical atlantic ssta in the dry season but not in the rainy season both oceans are related to rainfall but the strength of the rainfall response appears to depend on how ssta in the tropical atlantic and eastern pacific combine the strongest response occurs when the tropical atlantic is in the configuration of a meridional dipole antisymmetric across the itcz and the eastern tropical pacific is of opposite sign to the tropical north atlantic when the tropical north atlantic and tropical pacific are of the same sign the rainfall respons

upper eocene ejecta of the new jersey continental margin reveal dynamics of chesapeake bay impact evidence for the chesapeake bay crater as the source for new jersey continental margin ejecta is provided by fine grained tektites and coarse grained unmelted ejecta the upper eocene ejecta deposit now demonstrated to be part of the north american strewn field occurs on the new jersey continental margin at ocean drilling program odp sites 904 and 903 the mineralogy major oxide composition of the ejecta materials and biostratigraphic age of the enclosing sediments link the origin of these ejecta to the recently recognized chesapeake bay impact crater located only 330 km away sediments associated with the ejecta provide information about the dynamics of impact events the 35 cm thick ejecta bearing layer can be subdivided into three subunits that indicate a sequence of events bottom subunit iii documents sediment failure and deposition of gravel sized fragments middle subunit ii records deposition of abundant sand sized ejecta by gravity settling and upper subunit i contains a 12 cm thick sedimentary deposit containing rare silt sized tektites and evidence of waning currents these events are interpreted by linking sediment deposition to seismic ground motion and subsequent tsunami waves triggered by both the chesapeake bay impact and slope failures

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

a comparative study of sea level reconstruction techniques using 20 years of satellite altimetry data sea level reconstructions extend spatially dense data sets such as those from satellite altimetry by decomposing the data set into basis functions and fitting those functions to in situ tide gauge measurements with a longer temporal record we compare and evaluate two methods for reconstructing sea level through an idealized study the compared sea level reconstruction methods differ in the technique for calculating basis functions i e empirical orthogonal functions eofs versus cyclostationary eofs cseofs reconstructions are created using archiving validation and interpretation of satellite oceanographic aviso satellite altimetry data and synthetic tide gauges synthetic tide gauge records are simulated using historical distributions and real high frequency signal to test reconstruction skill the cseof reconstructions show high skill in reproducing variations in global mean sea level gmsl and ocean climate indices and are affected less by both limited tide gauge distribution and added high frequency tide gauge signal than eof reconstructions typically cseof reconstructions slightly underestimate sea level amplitudes while eof reconstructions overestimate sea level amplitudes in some cases significantly both of these results are accentuated with decreasing quality of the synthetic tide gauge data set additionally we investigate how the reconstructions differ when reconstructing with more of the variance retained in the basis functions increasing the variance explained by the basis functions from 70 to 90 reduces the efficacy of an eof reconstruction to reproduce common ocean indices when noise is included in the tide gauge data sets these results show that in the idealized comparative cases examined the cseof method of sea level reconstruction creates more robust reconstructions especially when less than ideal tide gauge data are used

the generation of synthetic sea surface temperature data for the equatorial pacific ocean abstract synthetic monthly sst anomaly data are constructed using frequency domain analyses of significant principle components derived from reconstructed sst data in the equatorial pacific ocean the model provides insight into the dominant physical processes contained in each component and retains the relevant statistical properties of the original data such as the mean variance and autocorrelation thus numerous sets of synthetic sst anomaly data can be produced for the equatorial pacific that are statistically indistinguishable from the original sst anomaly data the spatial and temporal sst signatures of the biennial intradecadal and decadal pseudoperiodicities are reproduced including their frequency and duration of occurrence specifically the enso warm and cold event signatures recur in the synthetic data at peak return periods of 2 4 3 5 5 0 and 6 4 yr moreover the anticipated return period of an extreme enso event with a maximum sst anomaly magnitude of 1 7 c is approximately every

identification and separation of mount pinatubo and el nino southern oscillation land surface temperature anomalies empirical data analyses are performed to detect and separate the signals of the volcanic eruption and el nino events in the observed surface air temperature sat anomalies over land for the 2 years following the pinatubo eruption composite analyses of surface temperatures for the 1950 1997 period excluding the 2 years following each of the three major volcanic eruptions agung el chichon and pinatubo show that the distribution of sat anomalies over most land areas for the el nino composite is opposite to that for the la nina composite the pattern of sat anomalies changes from season to season this feature is more prominent over north america than over the other continents singular value decomposition analyses show that following the pinatubo eruption el nino signals were weak over eurasia but relatively strong over the other continents over north america the 1991 1992 el nino event contributed more than 50 to the observed surface cooling of about 1 0 c in june july and august 1992 globally averaged the maximum cooling over land with the el nino southern oscillation signals removed is 0 5 c in september october and november 1992 and september october and november 1993

sea surface temperature variability in coastal areas of the northeastern pacific related to the el nino southern oscillation and the pacific decadal oscillation we examined monthly time series 1950 to 1999 of sea surface temperature sst anomalies in 47 quadrants 2 2 along the coast of north america and their relation to the el nino southern oscillation enso and the pacific decadal oscillation pdo we used the multivariate enso index mei and the pdo index pdoi and assumed a linear interaction of the mechanisms behind their interannual variations then we examined sst anomalies as functions of mei and pdoi using multiple linear regression mlr on average enso influence decreases poleward but is still dominant at 31 n northward the pdo signal dominates mlr was also applied to selected sea level height slh series enso effects on slh were clear up to 48 n while pdo showed a weak effect only in the gulf of alaska this suggests that poleward of southern california enso effects may be largely restricted to the inshore coastal environment