molybdenum drawdown during cretaceous oceanic anoxic event 2 during the cretaceous greenhouse episodes of widespread ocean deoxygenation were associated with globally occurring events of black shale deposition possibly the most pronounced of these oceanic anoxic events oae s was the cenomanian turonian oae2 94 ma however although certain redox sensitive trace metals tend to be preferentially sequestered in sediments deposited under anoxic conditions with mo drawdown being specifically prone to euxinic settings these elements are generally somewhat depleted in sediments deposited during oae2 to understand the driving factors responsible for this depleted trace metal drawdown we have studied a low latitude section from the proto north atlantic ocean tarfaya s57 where existing biomarker and iron sulphur data point to a dominantly euxinic water column with periodic transitions to ferruginous fe rich water column conditions we utilise a variety of redox proxies fe speciation redox sensitive trace metals and mo isotopes which in combination allows us to evaluate the detailed nature of ocean redox conditions and hence controls on trace metal drawdown the results suggest that seawater 98mo values may have ranged between 0 6 and 1 1 during oae2 likely connected to changes in the local mo reservoir as a consequence of low and probably heterogeneous concentrations of mo in the ocean the very low mo toc ratios at tarfaya and elsewhere in the proto north atlantic may support a model in which deep water circulation was partially restricted within and between the north atlantic and other ocean basins we propose that the combination of a low and possibly heterogeneous 98mo of seawater mo together with low mo toc ratios points to a large decrease in the global oceanic mo reservoir during oae2 reflecting a major global scale increase in mo drawdown under persistent euxinic conditions 2016 elsevier b v

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

propagation mechanisms for the madden julian oscillation the madden julian oscillation mjo is examined using 20 years of outgoing long wave radiation and national centers for environmental prediction national center for atmospheric research re analysis data two mechanisms for the eastward propagation and regeneration of the convective anomalies are suggested the first is a local mechanism operating over the warm pool region at the phase of the mjo with a dipole structure to the convection anomalies there is enhanced tropical convection over the eastern indian ocean and reduced convection over the western pacific over the equatorial western indian ocean the equatorial rossby wave response to the west of the enhanced convection includes a region of anomalous surface divergence associated with the anomalous surface westerlies and pressure ridge this lends to suppress ascent in the boundary layer and shuts off the deep convection eventually leading to a convective anomaly of the opposite sign over the indonesian sector the equatorial kelvin wave response to the east of the enhanced convection includes a region of anomalous surface convergence into the anomalous equatorial surface easterlies and pressure trough which will tend to favour convection in this region the indonesian sector is also influenced by an equatorial rossby wave response of opposite sign to the west of die reduced convection over the western pacific which also has a region of anomalous surface convergence associated with its anomalous equatorial surface easterlies and pressure trough hence convective anomalies of either sign tend to erode themselves from the west and initiate a convective anomaly of opposite sign via their equatorial rossby wave response and expand to the east via their equatorial kelvin wave response the second mechanism is global involving an anomaly completing a circuit of the equator enhanced convection over the tropical western pacific excites a negative mean sea level pressure m s l p anomaly which radiates rapidly eastward as a dry equatorial kelvin wave at approximately 35 m s 1 over the eastern pacific it is blocked by the orographic barrier of the andes and central america for several days before propagating through the gap at panama after rapidly propagating as a dry equatorial kelvin wave over the atlantic the m s l p anomaly is delayed further by the east african highlands before it reaches the indian ocean and coincides with the development of enhanced convection at the start of the next mjo cycle

studies of el nino and interdecadal variability in tropical sea surface temperatures using a nonnormal filter abstract a dynamically based filter is used to separate tropical sea surface temperatures ssts into three components the evolving el nino signal the global tropical trend and the background the components thus isolated are not independent on the contrary this procedure allows us to see the importance of the interdecadal signal to the predictability of el nino the data filtered in this way reveal el nino signals in the equatorial indian ocean and in the north tropical atlantic ocean that are remarkably similar a signature of el nino in the south tropical atlantic leads nino 3 4 sst anomalies by about 9 months the time series of a global tropical trend is found to have a very smooth parabolic structure in unfiltered data this trend conspires with el nino to obscure a meridional tropical atlantic dipole which is significant in the filtered background sst data

the southern oscillation part vi anomalies of sea level pressure on the southern hemisphere and of pacific sea surface temperature during the development of a warm event abstract the paper shows the discrete mean three month anomalies of sea level pressure on the southern hemisphere during the year before and the year of a warm event in the southern oscillation together with associated anomalies of sea surface temperature in the south pacific 0cean the two sets anomalies develop in a parallel and physically logical sequence over the south pacific ocean in conjunction with changes in the south pacific convergence zone nearly all of the southern hemisphere responds to the southern oscillation but the response is largest in the australia south pacific sector large anomalies of sea level pressure form well ahead of any on the northern hemisphere and this observation together with the conspicuous anomalies in the region of australia and the south pacific suggest that the origin of the southern oscillation must be sought in this region

improvement of enso prediction using a linear regression model with a southern indian ocean sea surface temperature predictor 1 this study presents a detailed comparison between three enso precursors which can predict across the spring persistence barrier the anomalous equatorial pacific upper ocean heat content the zonal equatorial wind stress anomaly in the far western pacific and sst anomalies in the south east indian ocean seio during the late boreal winter a new correlation analysis confirms that el nino la nina onsets are preceded by significant cold warm sst anomalies in the seio during the late boreal winter after the 1976 77 climate regime shift thus the objective is to examine the respective potential of these three enso precursors to predict enso events across the boreal spring barrier during recent decades surprisingly in this focus cross validated hindcasts of the linear regression models based on the lagged relationship between nino3 4 sst and the predictors suggest that seio sst anomalies during the late boreal winter is the more robust enso predictor

blocking in the southern hemisphere abstract the focus of this paper is on the frequency and spatial distributions of blocking and persistent anomalies of geopotential height over the southern hemisphere the analysis is based upon daily height fields at 1000 and 500 mb for both summer and winter histogram frequency distributions of height anomalies and maps of the skewness and kurtosis have been computed blocking events are objectively defined by requiring a large positive anomaly to exist for 5 days or more composite flow and anomaly fields for several cases are presented and examined in detail the geographical distribution of the frequency of lame amplitude 150 gpm anomalies at 500 mb that persist for only 1 3 days is very similar to that of the high frequency band 2 8 day period variances that identity the storm tracks in the southern hemisphere the primary location for blocking in the southern hemisphere is in the new zealand sector and blocking occurs through a local enhancement of the climatological split in the mean westerli

influence of the antarctic circumpolar wave on el nino and its multidecadal changes from 1950 to 2001 1 the slow eastward phase propagation of covarying sea surface temperature sst and sea level pressure slp anomalies in the antarctic circumpolar wave acw persisted in the midlatitude southern ocean from 1950 to 2001 its northern extent reached into the subtropical south indian and south pacific oceans where it influenced the magnitude and phase of el nino in the eastern equatorial pacific ocean this is corroborated by the observation that multidecadal changes in the acw can also explain multidecadal changes in the way el nino evolved over the last half of the twentieth century before 1977 el nino evolved from the slow eastward phase propagation of a coupled sst slp wave across the subtropical south pacific ocean to south america then equatorward along the eastern boundary to the equator during this epoch the acw expanded equatorward into a warmer subtropical south pacific ocean accounting for the subtropical coupled sst slp wave that initiated el nino after 1977 el nino evolved from the slow eastward phase propagation of a coupled sst slp wave across the tropical pacific ocean during this epoch the acw receded from a colder subtropical south pacific ocean but expanded into a warmer subtropical south indian ocean there it spawned a coupled sst slp wave directed equatorward into the warm pool north of australia thereafter propagating eastward into the eastern equatorial pacific ocean to initiate el nino if this pattern of global warming persists into the 21st century then the acw will continue to influence el nino through the south indian ocean

interactive feedback between enso and the indian ocean abstract a feedback process of the indian ocean sst on enso is investigated by using observed data and atmospheric gcm it is suggested that warming in the indian ocean produces an easterly wind stress anomaly over indonesia and the western edge of the pacific during the mature phase of el nino the anomalous easterly wind in the western pacific during el nino helps a rapid termination of el nino and a fast transition to la nina by generating upwelling kelvin waves thus warming in the indian ocean which is a part of the el nino signal operates as a negative feedback mechanism to enso this indian ocean feedback appears to operate mostly for relatively strong el ninos and results in a la nina one year after the mature phase of the el nino this 1 yr period of phase transition implies a possible role of indian ocean enso coupling in the biennial tendency of the enso atmospheric gcm experiments show that indian ocean sst forcing is mostly responsible for the easterly wind anomalies in the western pacific

the role of topographically induced vortices in tropical cyclone formation over the indian ocean abstractthe role of sumatra and adjacent topographic features in tropical cyclone tc formation over the indian ocean io is investigated sumatra as well as the malay peninsula and java have mountainous terrain that partially blocks low level flow under typical environmental stratification for easterly low level flow these terrain features often produce lee vortices some of which subsequently shed and move westward from the northern and southern tips of sumatra and thence downstream over the io since sumatra straddles the equator extending in a northwest southeast direction from approximately 6 n to 6 s the lee vortices while counter rotating are both cyclonic hence they can serve as initial disturbances that eventually contribute to tc formation over the io in addition low level equatorial westerly flow impinging on sumatra is also typically blocked and diverges at times contributing to cyclonic circulations over the io primarily near the southern end of the island data from two recen

impact of southeast indian ocean sea surface temperature anomalies on monsoon enso dipole variability in a coupled ocean atmosphere model recent studies show that southeast indian ocean seio ssts are a highly significant precursor of transitions of the whole monsoon el nino southern oscillation enso system during recent decades however the reasons for this specific interannual variability have not yet been identified unequivocally from the observations among these the possibility of seio sst driven variability in the monsoon enso system is investigated here by inserting positive negative seio temperature anomalies in the february s restart files of a state of the art coupled general circulation model gcm for 49 years of a control simulation for each year of the control simulation the model was then integrated for a 1 year period in fully coupled mode these experiments show that indian summer monsoon ism and tropical indian ocean dipole mode iodm events are significantly influenced by the seio temperature perturbations inserted in the mixed layer of the coupled gcm several months before a warm seio perturbation inserted in late boreal winter slowly propagates northward during the following seasons implies enhanced ism rainfall and finally triggers a negative iodm pattern during boreal fall in agreement with observations a reversed evolution is simulated for a cold seio perturbation it is shown that the life cycle of the simulated seio signal is driven by the positive wind evaporation sst coastal upwelling and wind thermocline sst feedbacks further diagnosis of the sensitivity experiments suggests that stronger ism and iodm variabilities are generated by excluding the el nino years of the control simulation or when the initial background state in the seio is warmer this finding confirms that iodm events may be triggered by multiple factors other than enso including subtropical seio sst anomalies however the enso mode does not react significantly to the seio temperature perturbation in the perturbed runs even though the simulated pacific pattern agrees with the observations during boreal fall these discrepancies with the observations may be linked to model biases in the pacific and to the too strong enso simulated by this coupled gcm these modeling evidences confirm that subtropical indian ocean sst anomalies generated by mascarene high pulses during austral summer are a significant precursor of both ism and iodm events occuring several months later

seasonality in the madden julian oscillation abstract this study using observational data and global reanalysis products synthesizes existing knowledge on the seasonality in the madden julian oscillation mjo and discusses its possible dependence on the mean background state the seasonality in the mjo is documented in terms of its components in low level zonal wind and precipitation a single peak season boreal winter exists near the equator in the indian and western pacific oceans for the broad tropical region however the seasonality in the mjo is featured by a latitudinal migration across the equator between two peak seasons the primary peak season is in boreal winter december march during which mjo signals are mainly confined to the indian and western pacific ocean and reach their maxima in the south pacific convergence zone the secondary peak season is boreal summer june september during which the strongest mjo occurs north of the equator from the bay of bengal to the south china sea and another separated region of strong mjo

a diagnostic study of the evolution of the mjo from indian ocean to maritime continent wave dynamics versus advective moistening processes abstractthe evolution processes for propagating madden julian oscillations with strong magnitude over the indian ocean io and maritime continent mc are investigated through a diagnosis of ecmwf reanalysis data for november april 1982 2011 a scale separated lower tropospheric 1000 700 hpa moisture budget is analyzed for four stages of composite life cycle suppressed cloud developing convective and decaying overall the budgets in the io and mc are dominated by wave induced boundary layer convergence in the anomalous easterlies wc and advection starting from the suppressed stage in the central io moistening by wc and advection by easterly anomalies contributes to an initiation of the mjo convection in the western io while surface evaporation and or shallow convection moistens the central io in the following cloud developing and convective stage in the central io moistening by wc and advection by the downstream kelvin rossby wave east of central io lead to eastward propagation of deep conve

global association of the madden julian oscillation with monsoon lows and depressions previous research has revealed that monsoon lows and depressions are modulated on intraseasonal time scales in a few regions including india australia and the east pacific this study examines whether such modulation occurs on a global scale and in particular how the madden julian oscillation mjo is associated with changes in synoptic scale vortices across all monsoon regions the spatial climatology of monsoon disturbances is largely insensitive to mjo amplitude however monsoon disturbance frequency mdf varies substantially with mjo phase with regional perturbations of 25 to 90 percent of the seasonal mean value across the tropics in off equatorial locations mdf maxima occur in locations where the mjo enhances low level cyclonic vorticity typically near the western edge of mid level moisture perturbations in contrast equatorial mdf perturbations are in phase with mjo moisture and rainfall anomalies with maxima in regions with strong low level zonal wind convergence

southern hemisphere extra tropical forcing a new paradigm for el nino southern oscillation the main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid latitude southern hemisphere climate and the el nino southern oscillation enso signal while our analysis confirms that enso is a dominant source of interannual variability in the southern hemisphere it is also suggested here that subtropical dipole variability in both the southern indian and atlantic oceans triggered by southern hemisphere mid latitude variability may also provide a controlling influence on enso in the equatorial pacific this subtropical forcing operates through various coupled air sea feedbacks involving the propagation of subtropical sea surface temperature sst anomalies into the deep tropics of the atlantic and indian oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these sst anomalies linking the three tropical basins at the beginning of the boreal spring this atmospheric response is characterized by a significant weakening of the equatorial atlantic and indian inter tropical convergence zone itcz this weakened itcz forces an equatorial cold kelvin wave response in the middle to upper troposphere that extends eastward from the heat sink regions into the western pacific by modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western pacific ocean this kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial pacific which may trigger el nino onset at the end of the boreal winter these different processes explain why south atlantic and indian subtropical dipole time series indices are highly significant precursors of the nino34 sst index several months in advance before the el nino onset in the equatorial pacific this study illustrates that the atmospheric internal variability in the mid latitudes of the southern hemisphere may significantly influence enso variability however this surprising relationship is observed only during recent decades after the so called 1976 1977 climate regime shift suggesting a possible linkage with global warming or decadal fluctuations of the climate system

diurnal patterns of rainfall in northwestern south america part i observations and context one of the rainiest areas on earth the panama bight and pacific western littoral of colombia is the focal point for a regional modeling study utilizing the fifth generation pennsylvania state university ncar mesoscale model mm5 with nested grids in this first of three parts the observed climatology of the region is presented the seasonal march of rainfall has a northwest southeast axis with western colombia near the center receiving rain throughout the year this study focuses on the august september season the diurnal cycle of rainfall over land exhibits an afternoon maximum over most of south and central america typically composed of relatively small convective cloud systems over some large valleys in the andes and over lake maracaibo a nocturnal maximum of rainfall is observed a strong night morning maximum of rainfall prevails over the coastal ocean propagating offshore and westward with time this offshore convection often takes the form of mesoscale convective systems with sizes comparable to the region s coastal concavities and other geographical features the 10 day period of these model studies 28 august 7 september 1998 is shown to be a period of unusually active weather but with a time mean rainfall pattern similar to longer term climatology it is concluded that the rain producing processes during this time period are likely to be typical of those that shape the seasonal climatology

propagation of the madden julian oscillation through the maritime continent and scale interaction with the diurnal cycle of precipitation the convectively active part of the madden julian oscillation mjo propagates eastward through the warm pool from the indian ocean through the maritime continent the indonesian archipelago to the western pacific the maritime continent s complex topography means the exact nature of the mjo propagation through this region is unclear model simulations of the mjo are often poor over the region leading to local errors in latent heat release and global errors in medium range weather prediction and climate simulation using 14 northern winters of trmm satellite data it is shown that where the mean diurnal cycle of precipitation is strong 80 of the mjo precipitation signal in the maritime continent is accounted for by changes in the amplitude of the diurnal cycle additionally the relationship between outgoing long wave radiation olr and precipitation is weakened here such that olr is no longer a reliable proxy for precipitation the canonical view of the mjo as the smooth eastward propagation of a large scale precipitation envelope also breaks down over the islands of the maritime continent instead a vanguard of precipitation anomalies of 2 5 mm day 1 over 10 6 km 2 jumps ahead of the main body by approximately 6 days or 2000 km hence there can be enhanced precipitation over sumatra borneo or new guinea when the large scale mjo envelope over the surrounding ocean is one of suppressed precipitation this behaviour can be accommodated into existing mjo theories frictional and topographic moisture convergence and relatively clear skies ahead of the main convective envelope combine with the low thermal inertia of the islands to allow a rapid response in the diurnal cycle which rectifies onto the lower frequency mjo hence accurate representations of the diurnal cycle and its scale interaction appear to be necessary for models to simulate the mjo successfully

why the southern hemisphere enso responses lead enso 1 analysis of observational estimates indicates that the el nino southern oscillation enso forced pattern in the extratropical southern hemisphere sh somewhat surprisingly leads the peak phase of enso by one season a rossby wave source rws analysis indicates that the tropical and extratropical rws in the sh develops before the enso peak season and abruptly weakens thereafter further analysis shows that anomalous divergence convergence and corresponding irrotational wind anomalies are sensitive to local seasonality numerical experiments in which the tropical pacific is prescribed with perfectly periodic enso while all other oceans are simulated as a slab mixed layer model coupled to agcm also show similar features additional numerical experiments in which enso forcing is shifted by 6 months i e the enso peak in the southern winter season indicate that the northern hemisphere atmosphere rather than the sh atmosphere precedes enso this result supports the hypothesis that the enso forced pattern in the extratropics is strongly limited by local seasonality rather than by the temporal phase of tropical remote forcing

why precipitation is mostly concentrated over islands in the maritime continent abstract high resolution observations and regional climate model simulations reveal that precipitation over the maritime continent is mostly concentrated over islands analysis of the diurnal cycles of precipitation and winds indicates that this is predominantly caused by sea breeze convergence over islands reinforced by mountain valley winds and further amplified by the cumulus merger processes comparison of a regional climate model control simulation to a flat island run and an all ocean run demonstrates that the underrepresentation of islands and terrain in the maritime continent weakens the atmospheric disturbance associated with the diurnal cycle and hence underestimates precipitation the implication of these regional modeling results is that systematic errors in coarse resolution global circulation models probably result from insufficient representation of land sea breezes associated with the complex topography in the maritime continent it is found that precipitation in the maritime continent

factors controlling rain on small tropical islands diurnal cycle large scale wind speed and topography abstracta set of idealized cloud permitting simulations is performed to explore the influence of small islands on precipitating convection as a function of large scale wind speed the islands are situated in a long narrow ocean domain that is in radiative convective equilibrium rce as a whole constraining the domain average precipitation the island occupies a small part of the domain so that significant precipitation variations over the island can occur compensated by smaller variations over the larger surrounding oceanic area while the prevailing wind speeds vary over flat islands three distinct flow regimes occur rainfall is greatly enhanced and a local symmetric circulation is formed in the time mean around the island when the prevailing large scale wind speed is small the rainfall enhancement over the island is much reduced when the wind speed is increased to a moderate value this difference is characterized by a change in the mechanisms by which convection is forced a thermally forced se

slow oceanic teleconnections linking the antarctic circumpolar wave with the tropical el nino southern oscillation a case study for the period 1982 1994 shows that a major source for the antarctic circumpolar wave is in the western subtropical south pacific where interannual anomalies in sea surface temperature sst and precipitable water prwat form once established these interannual anomalies in tandem with anomalies in sea level pressure slp move south toward the southern ocean the system then migrates east around the globe through a combination of oceanic advection with the antarctic circumpolar current and ocean atmosphere coupling the coincidence of interannual anomalies in sst slp and prwat indicates the extratropical ocean and atmosphere are tightly linked on these timescales large portions of the interannual sst anomalies branch advectively northward into the south atlantic and indian oceans ultimately reaching the tropics in each basin some 6 8 years after appearing in the low latitude pacific this constitutes a slow oceanic teleconnection that is unique in climate dynamics made possible by the continuity of earth s oceans via the southern ocean in the tropical indian ocean these interannual anomalies move east and arrive at the indo pacific transition in advance of the trans pacific propagation of the respective el nino southern oscillation enso phases the interannual sst and prwat anomalies that appear in the subtropical south pacific are directly linked with the enso cycle on the equator through anomalous vertical convection and a regional overturning cell in the troposphere the same cell that initiates fast planetary waves in the atmosphere that carry enso signals around the southern hemisphere on much shorter timescales

barrier effect of the indo pacific maritime continent on the mjo perspectives from tracking mjo precipitation abstractexplanations for the barrier effect of the indo pacific maritime continent mc on the mjo should satisfy two criteria first they should include specific features of the mc namely its intricate land sea distributions and elevated terrains second they should include mechanisms for both the barrier effect and its overcoming by some mjo events guided by these two criteria a precipitation tracking method is applied to identify mjo events that propagate across the mc mjo c and those that are blocked by the mc mjo b about a half of mjo events that form over the indian ocean propagate through the mc most of them 75 become weakened over the mc the barrier effect cannot be explained in terms of the strength horizontal scale or spatial distribution of mjo convection when it approaches the mc from the west a distinction between mjo b and mjo c is their precipitation over the sea versus land in the mc region mjo c events rain much more over the sea than over land whereas rainfall over

tropical pacific sea surface temperatures and preceding sea level pressure anomalies in the subtropical north pacific 1 the correspondence of sea surface temperature sst anomalies to changes in antecedent large scale sea level pressure anomalies is investigated using reanalysis data by statistically examining linearly coupled precursor sea level pressure fields and subsequent sst fields for different lag periods it is possible to isolate a precursor mode of sea level pressure slp variability in the central subtropical north pacific that precedes variations in the january march el nino southern oscillation enso by approximately 12 15 months a sea level pressure index which captures the important characteristics of this precursor mode of variability is developed and evaluated it is shown that both analyzed and observed versions of the index are significantly correlated with the january march enso one year later the slp index is then used to examine the evolution of the surface circulation and temperature structures leading up to mature enso events initially the january march subtropical north pacific slp anomalies are associated with changes in the intensity of the subtropical trade wind regime over the north pacific as well as with sst anomalies over the eastern equatorial pacific and subtropical central pacific in agreement with the correlation statistics associated with the slp and lagged nino3 4 indices both the sea level pressure field and the sst field subsequently develop enso like structures over the course of the following year significant discussion of these results and pertinent areas of future research are provided within the broader context of the enso system

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

mechanisms for the dipolar patterns of rainfall variability over large islands in the maritime continent associated with the madden julian oscillation abstractbefore the eastward propagating rainy envelope of a madden julian oscillation mjo arrives at the maritime continent mc some islands in the mc experience dipolar patterns of rainfall va

preconditions for el nino and la nina onsets and their relation to the indian ocean 1 el nino la nina onset is a challenging problem of enso prediction in this study we introduce two precursors of el nino and la nina onsets one is the equatorial heat content and the other is the western pacific wp wind when the two precursors are considered together both the el nino and la nina onsets can be highly predictable in particular the persistence of the wp wind is more important for the onset than sporadic wind events the persistent wp westerly easterly wind tends to be concurrent with the indian ocean sst cooling warming the indian ocean sst anomaly is partly correlated to an enso event during the previous winter we demonstrate that an asymmetric relation between the indian ocean sst and enso can result in asymmetric progress of onset in the opposite enso phases

pacific meridional mode and el nino southern oscillation 1 we present intriguing evidence that the majority of el nino events over the past four decades are preceded by a distinctive sea surface warming and southwesterly wind anomaly in the vicinity of the intertropical convergence zone itcz during the boreal spring this phenomenon known as the meridional mode mm is shown to be intrinsic to the thermodynamic coupling between the atmosphere and ocean the mm effectively acts as a conduit through which the extratropical atmosphere influences enso modeling results further suggest that the mm plays a vital role in the seasonal phase locking behavior of enso the findings provide a new perspective for understanding the important role of thermodynamic ocean atmosphere feedback in enso and may have profound implications for enso prediction particularly the unresolved issue of the spring predictability barrier citation chang p l zhang r saravanan d j vimont j c h chiang l ji h seidel and m k tippett 2007 pacific meridional mode and el nino southern oscillation geophys res lett 34 l16608 doi 10 1029 2007gl030302

mesoscale variation in diabatic heating around sumatra and its modulation with the madden julian oscillation abstractdiabatic heating in the maritime continent region is controlled by a unique blend of mesoscale variability associated with steep topography and complex coastlines and intraseasonal variabil

persistent positive anomalies in the southern hemisphere circulation abstract long time series of reanalyses from ncep ncar and from ecmwf are used to investigate the occurrence of persistent positive anomalies ppas in the 500 hpa geopotential height field over the southern hemisphere extratropics during 1958 2001 defining persistent anomalies as those of at least 100 m in magnitude lasting for at least 5 days it is found that the region of most frequent occurrence is over the south pacific a cluster analysis of monthly ppa counts shows two distinct patterns one a zonal wavenumber 1 zw1 pattern centered over the southeast pacific near 60 s and the other a zonal wavenumber 3 zw3 pattern with centers near new zealand and over the southern atlantic and indian oceans results were insensitive to the choice of dataset and to the removal of a linear trend from the daily height fields the southeast pacific ppa region is strongly modulated by enso while the zw3 pattern appears only weakly related to enso variability a strong upward trend is apparent in occurrence o