the role of tropical atlantic sst anomalies in modulating western north pacific tropical cyclone genesis the connection between north tropical atlantic nta sea surface temperature sst anomalies and tropical cyclone tc genesis over the western north pacific wnp and associated physical mechanisms are investigated in this study we demonstrate a remarkable negative correlation of wnp tc genesis frequency with the preceding boreal spring nta sst anomalies our analysis suggests that major factors for tc genesis including distributions of large scale vorticity and midtropospheric humidity are rendered unfavorable by remote teleconnections while barotropic energy conversion from the large scale flow is suppressed as shown in recent studies the remote teleconnection from the atlantic is sustained and enhanced throughout the typhoon season through local air sea interactions these results suggest that boreal spring nta sst anomaly could be a new predictor for the seasonal wnp tc activity

statistical occurrence and mechanisms of the 2014 2016 delayed super el nino captured by a simple dynamical model the recent 2014 2016 period was marked by a failed el nino favoring a subsequent extreme el nino with dramatic worldwide impacts here this new type of major event so called the delayed super el nino is realistically captured by a simple dynamical model for the equatorial pacific with emphasis on the role of state dependent stochastic wind bursts we analyze qualitative analogues for this event compared and contrasted with the 1997 1998 super el nino in ensemble experiments based on the simple model in agreement with recent studies the timing and intensity of such an event is strongly controlled by atmospheric wind bursts both easterly and westerly in particular the early stalling by easterly wind bursts and subsequent development by westerly wind bursts as observed during 2014 2016 is consistently retrieved we show in addition that individual wind bursts may control the main characteristics of the event only during its early development while sequences of consecutive wind bursts have more important cumulative effects another important result from the present analysis is the significant statistical occurence of the delayed super el nino around 20 30 compared with the one of directly formed super events as that of 1997 1998 such a high occurence is directly linked to the random evolution of wind bursts and is retrieved here for all phases of the el nino southern oscillation used for the initiation of the ensemble experiments these results suggest that the delayed super el nino is not an unusual type of super event and could reoccur in the future

about the role of westerly wind events in the possible development of an el nino in 2014 similarities between early 1997 and 2014 has prompted climate scientists to wonder if an el nino matching the 1997 el nino of the century could develop in 2014 until april 2014 the equatorial pacific exhibited positive heat content anomalies along with an eastward warm pool displacement similar to those found during the onset of strong el nino events yet in july 2014 the warm pool had retreated back to its climatological positions and equatorial temperature anomalies were much weaker than in mid 1997 dedicated oceanic simulations reveal that these weak interannual anomalies can be attributed to differences in westerly wind event wwe sequences in contrast with 1997 the lack of wwes from april to june significantly limited the growth of eastern pacific anomalies and the eastward warm pool displacement in 2014 with the absence of additional wwe activity prospects for a mature el nino in late 2014 are fading

westerly wind events in the tropical pacific 1986 95 abstract based on examination of 10 yr of 10 m winds and wind anomalies from european centre for medium range weather forecasts ecwmf analysis definitions for westerly wind events wwes of eight different types are proposed the authors construct a composite for each type of event show that a simple propagating gaussian model satisfactorily describes the evolution of zonal wind anomaly for each type of event and determine the scales of each composite event by fitting the model to each composite the authors discuss the wwes that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment toga coare intensive observing period iop and show the extent to which these composite events are able to reproduce the major westerly wind features of the iop the frequency of occurrence of each type of wwe for each year of this record and by calendar month are described the authors find several types of events are negatively correlated with the annual mean troup souther

the south pacific meridional mode as a thermally driven source of enso amplitude modulation and uncertainty abstractthis study seeks to identify thermally driven sources of enso amplitude and uncertainty as they are relatively unexplored compared to wind driven sources pacific meridional modes are argued to be wind triggers for enso events this study offers an alternative role for the south pacific meridional mode spmm in enso dynamics not as an enso trigger but as a coincident source of latent heat flux lhf forcing of enso ssta that if correctly incorrectly predicted could reduce increase enso prediction errors we utilize a coupled model simulation in which enso variability is perfectly periodic and each el nino experiences identical wind stress forcing differences in el nino amplitude are primarily thermally driven via the spmm when el nino occurs coincidentally with positive phase spmm the positive spmm lhf anomaly counteracts a fraction of the lhf damping of el nino allowing for a more intense el nino if the spmm phase is instead negative the spmm lhf amplifies the lhf damping of el nin

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

relationship between the equatorial and meridional modes of climatic variability in the tropical atlantic the tropical atlantic ocean exhibits two primary modes of interannual climate variability an equatorial mode analogous to but weaker than the pacific el nino phenomenon and a meridional mode that does not have a pacific counterpart the equatorial mode is responsible for warm and cold sea surface temperature sst events mainly in the gulf of guinea and is identifiable by abnormal changes in the equatorial thermocline slope resulting from zonal wind anomalies in the western tropical atlantic the meridional mode is characterized by a north south interhemispheric gradient of sst anomalies here it is shown using observed surface and subsurface oceanic temperatures that the meridional mode is linked to the equatorial mode at both decadal and short interannual 1 2 years time scales both modes involve north south displacements of the itcz as in the annual response

variability of the western pacific warm pool structure associated with el nino sea surface temperature sst structure inside the western pacific warm pool wpwp is usually overlooked because of its distinct homogeneity but in fact it possesses a clear meridional high low high pattern here we show that the sst low in the wpwp is significantly intensified in july october of el nino years especially extreme el nino years and splits the 28 5 c isotherm defined wpwp wpwp split for simplification composite analysis and heat budget analysis indicate that the enhanced upwelling due to positive wind stress curl anomaly and western propagating upwelling rossby waves account for the wpwp split zonal advection at the eastern edge of split region plays a secondary role in the formation of the wpwp split composite analysis and results from a matsuno gill model with an asymmetric cooling forcing imply that the wpwp split seems to give rise to significant anomalous westerly winds and intensify the following el nino event lead lag correlation shows that the wpwp split slightly leads the nino 3 4 index

sea surface temperature in the north tropical atlantic as a trigger for el nino southern oscillation events the el nino southern oscillation in the pacific ocean influences temperature in other tropical ocean basins reanalysis data and model simulations suggest that temperature anomalies in the north tropical atlantic may also influence the development of la nina events

the nature of the stochastic wind forcing of enso abstractel nino southern oscillation enso is commonly viewed as a low frequency tropical mode of coupled atmosphere ocean variability energized by stochastic wind forcing despite many studies h

tropical indian ocean influence on northwest pacific tropical cyclones in summer following strong el nino abstract in the summer following a strong el nino tropical cyclone tc number decreases over the northwest nw pacific despite little change in local sea surface temperature the authors analysis suggests el nino induced tropical indian ocean tio warming as the cause the tio warming forces a warm tropospheric kelvin wave that propagates into the western pacific inducing surface divergence off the equator the tropospheric kelvin wave suppresses convection and induces an anomalous anticyclone over the nw pacific both anomalies unfavorable for tcs the westerly vertical shear associated with the warm kelvin wave reduces the magnitude of vertical shear in the south china sea and strengthens it in the nw pacific an east west variation that causes tc activity to increase and decrease in respective regions these results help improve seasonal tc prediction

the hakon mosby mud volcano 330 000 years of focused fluid flow activity at the sw barents sea slope studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity this paper describes the internal structure of the hakon mosby mud volcano hmmv in the southwestern barents sea and presents a conceptual model of its evolution the lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas rich fluids and free gas however the analysis of high resolution single channel seismic scs data reveals for the first time the existence of a pseudo mud chamber at the top of the 3 km deep central conduit it was once created at the seabed and is now a buried expression that acts as mud chamber the pseudo mud chamber is situated approximately 300 m below the seafloor directly above the 330 ka bear island slide bis scar reflection and below glacigenic debris flow deposits that constitute the sediment on top the sediment profiler data indicates a younger mud deposit above the debris flows which points to a reactivation of the mud volcano the reactivation was most likely triggered by the contrast in density between the gas rich mud chamber and the high density debris flow deposits three stages i e initiation sealing and reactivation and a second active period define the evolution of this young mud volcano both the morphology and size of the conduit as well as in situ temperature gradients point towards a focused and rapid fluid flow

controls on gas hydrate system evolution in a region of active fluid flow in the sw barents sea abstract the location and stability of gas hydrates in the sw barents sea is poorly constrained due to complex geological geochemical and geophysical conditions including poor controls on regional heat flow and gas chemistry understanding the stability of gas hydrates in this region is important as recent studies suggest destabilizing hydrates may lead to methane discharge into the ocean and possibly in to the atmosphere here we use high resolution 3d p cable seismic data combined with 3d heat flow and fluid flow models to place new constraints on gas hydrate stability in this region the 3d p cable seismic data acquired in 2009 west of loppa high show cross cutting reverse polarity high amplitude reflectors interpreted as the base of gas hydrate stability to constrain heat flow fluid flow and gas hydrate stability within the 3d seismic volume we use a 3d steady state finite difference diffusive thermal model that incorporates regional bottom water temperature from ctd casts expected geothermal gradients and gas composition derived from well data in general modelled bottom simulating reflectors are deeper than observed bsrs our analysis weighs multiple factors that might explain the discrepancy between observed and modelled bottom simulating reflector depths from this analysis we propose that the most significant discrepancies in bsr depth are likely related to changes in regional fluid heat flow and fluid geochemistry the anomalously shallow bottom simulating reflectors can be explained via vertical fluid flow that might include ensuing potential effects on gas composition pore water salinity and temperature our estimate suggest that a maximum vertical fluid flux of approximately 12 mm y is necessary to explain the most significant anomalies our study provides new insight into regional heat flow geochemistry and end member vertical fluid flux rates in the barents sea moreover it documents that the fluid flow system is active and most likely very dynamic

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

near surface hydrocarbon anomalies in shelf sediments off spitsbergen evidences for past seepages 1 as global warming occurs the dissociation of bound methane on arctic shelves due to ocean current temperature changes may become a major contributor to the global methane budget and thus contribute to strong positive climate feedback mechanisms however little is known about the magnitude and fate of methane emissions from shallow submarine sediments to the atmosphere in the peculiar area in this paper we present one of the first direct evidences for seepage on the northwestern barents sea shelf by studying the molecular and isotopic signatures of low molecular weight hydrocarbons in seawater near surface sediment pore space and the sediment matrix at 26 locations we provide a detailed view on the partitioning of gaseous hydrocarbons in the sediment water interface off spitsbergen in the free gas phase low concentration of methane 28 ng g wet sediment paired with constantly high isotopic values 65 is consistent with high impact of methane oxidation on the isotopic composition in contrast high concentrations of adsorbed ch4 up to 5292 ng g wet 63 m and c2 ethane through pentane up to 1724 ng g wet 63 m in the sediment matrix suggest that the adsorbed gas is reasonably well protected against microbial degradation moreover the isotopic and molecular signatures of adsorbed ch4 38 60 100 5300 ng g wet 63 m and c2h6 20 36 30 1700 ng g wet 63 m indicate an integrated but strongly varying signal of historic thermally derived hydrocarbon plumes plus in situ adsorbed gas of biological origin this suggests a minimal exchange and unlike histories of free and adsorbed gas the majority of gaseous hydrocarbons in the adsorbed pool may be the result of past seepages past upward flow of thermogenic gas and impregnation with mature hydrocarbons was particularly strong along tectonic lineaments active petroleum source rocks along the continental margin and migration of gaseous hydrocarbons at re activated fault systems might explain the anomalies along these conduits

westerly wind bursts and their relationship with intraseasonal variations and enso part ii energetics over the western and central pacific abstract the mechanism of synoptic scale eddy development in the generation of westerly wind bursts wwbs over the western central pacific and their relationship with the el nino southern oscillation enso and the madden julian oscillation mjo were examined in the wwb occurrences barotropic structures of equatorial eddy westerlies with cyclonic disturbances were found from the surface to the upper troposphere the dominant contributions to substantial eddy kinetic energy eke were the barotropic energy conversion kmke in the lower and middle tropospheres and the conversion from eddy available potential energy peke in the upper troposphere low frequency environmental westerlies centered near the equator preceded strong zonal convergence and meridional shear resulting in the substantial kmke the activation of synoptic convection also contributed to an increase in eke through peke these energies were redistributed to the lower equatorial troposphere through energy flux convergence gke the

a comparison of sea surface salinity in the equatorial pacific ocean during the 1997 1998 2012 2013 and 2014 2015 enso events sea surface salinity sss variability during the 1997 1998 el nino event and the failed 2012 2013 and 2014 2015 el nino events is explored using a combination of observations and ocean reanalyses previously studies have mainly focused on the sea surface temperature sst and sea surface height ssh variability this analysis utilizes salinity data from argo and the simple ocean data assimilation soda reanalysis to examine the sss variability advective processes and evaporation minus precipitation e p variability is understood to influence sss variability using surface wind surface current evaporation and precipitation data we analyze the causes for the observed sss variability during each event barrier layer thickness and upper level salt content are also examined in connection to subsurface salinity variability both advective processes and e p variability are important during the generation and onset of a successful el nino while a lack of one or both of these processes leads to a failed enso event

interannual variation in the tropical cyclone formation over the western north pacific abstract the interannual variation in tropical cyclone genesis frequency over the western north pacific was examined for the active tropical cyclone including summer and fall during 1979 94 an emphasis was put on the possible effect of the interannual variation of atmospheric circulation and monsoon trough on tropical cyclone occurrence the major findings of this study are the following a distinct increase decrease of tropical cyclone genesis frequency occurs north of the climatological location of the monsoon trough in the philippine sea during summers june august with anomalous cold warm sea surface temperature sst over the nino3 region the interannual variation of tropical cyclone genesis in this region results from the appearance of an anomalous cyclonic anticyclonic cell situated in a summer teleconnection wave train emanating from the western tropical pacific and progressing along the rim of the north pacific in addition to the north south interannual variation there is also a long

identification of a large upper cretaceous polygonal fault network in the hammerfest basin implications on the reactivation of regional faulting and gas leakage dynamics sw barents sea abstract we use a high resolution 3d seismic dataset covering 970 km2 over the snohvit and albatross gas fields of the hammerfest basin in the barents sea in order to investigate the basin fault architecture and identify potential fluid pathways of deeper thermogenic gas and fluids a polygonal fault pf interval not previously published is described in the three non connected blocks within campanian sequences which could imply a permeable complex network of pathways that facilitate the vertical migration of hydrocarbons along the fault planes the dominant orientation of the pfs is similar to the main regional tectonic fault trend ew suggesting a tectonic influence upon the development of polygonal faults although some individual pfs locally seem to develop orthogonally to regional 1st order tectonic faults a lithologic control on the occurrence of pf patterns is evident as none are observed within calcareous low clay sediments the pf networks present three main orientations dominant ene wsw secondary nne ssw and a minor ne sw paleocene early eocene faults peefs prevail above the pf networks with coinciding ene wsw fault strikes interpreted as preferential reactivation of the pf systems numerous amplitude anomalies linked to the escape of thermogenic fluids from the jurassic reservoir were identified we present a conceptual model where the 1st order reactivated faults and peefs acted as pathways for fluids from the deeper hydrocarbon reservoirs the peefs are partially sealing with a lateral migration component interplay between the pfs peefs and the 1st order reactivated faults focuses the fluids vertically along the polygonal fault traces creating a wider diffuse zone which form large gas cloud anomalies in the seismic data

an extension of ldeo5 model for enso ensemble predictions this study provided an extension to the latest version of lamont doherty earth observation ldeo5 prediction system first an ensemble coupled data assimilation cda system based on the ensemble kalman filter was established both the kaplan sea surface temperature sst data from january 1856 to december 2018 and the ecmwf twentieth century reanalysis era 20c wind data from january 1900 to february 2010 were assimilated for prediction initialization second an ensemble prediction ep system was established using stochastic optimal perturbation that represented the uncertainty in the physical process the assimilation experiments showed that assimilating multi source data yielded better results than assimilating single source data the analyses of nino3 4 sst anomalies and zonal wind stress zws anomalies were in good agreement with the observed counterparts respectively the root mean square errors of both nino3 4 sst anomalies and zws anomalies were found to be significantly reduced compared to the values obtained before assimilation the modeled upper layer depth anomalies along the equator and subsurface temperature anomalies in the nino3 4 region were also found to be similar to the observed counterparts a long term ensemble hindcast was conducted using the ep system for the past 163 years from january 1856 to december 2018 results showed that the predictions initialized by assimilating multi source data yielded best deterministic skill reaching the international advanced level a comparative analysis revealed that the ep system predicted the warm events well followed by cold and neutral events

impacts of tropical north atlantic sst on western north pacific landfalling tropical cyclones abstractthis study examines the impacts of tropical north atlantic tna sea surface temperature anomaly ssta on western north pacific wnp landfalling tropical cyclones tcs the authors find that tna ssta has significant negative correlations with the frequency of tcs making landfall in china vietnam the korean peninsula and japan and the entirety of east asia tna ssta influences the frequency of tc landfalls in these regions by regulating tc genesis location and frequency associated with modulated environmental conditions during cold tna sst years larger low level relative vorticity and weaker vertical wind shear lead to more tc formations over the south china sea scs and western philippine sea wps and larger low level relative vorticity higher midlevel relative humidity and weaker vertical wind shear result in more tc formations over the eastern part of wnp ewnp more tcs forming over different regions are important for more tc landfalls in vietnam mainly forming over the scs and w

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

strong influence of westerly wind bursts on el nino diversity el nino diversity and its genesis are debated an overview of existing work along with a fuzzy clustering analysis and simulations suggest that the asymmetry irregularity and extremes of el nino result from westerly wind bursts

charging el nino with off equatorial westerly wind events the buildup of the warm water in the equatorial pacific prior to an el nino event is considered a necessary precondition for event development while the event initiation is thought to be triggered by bursts of westerly wind however in contrast to the view that warm water slowly builds up years before an el nino event the volume of warm water in the equatorial pacific doubled in the first few months of 2014 reaching values that were consistent with the warm water buildup prior to the extreme 1997 1998 el nino it is notable that this dramatic warm water buildup coincided with a series of westerly wind bursts in the western tropical pacific this study uses linear wave theory to determine the effect of equatorial and off equatorial westerly wind events on the warm water volume wwv of the pacific it is found that westerly wind events have a significant impact on equatorial wwv with all events initially acting to increase wwv which highlights why wwes are so effective at exciting enso in fact our results suggest that the single westerly wind burst which peaked in the first few days of march in 2014 was largely responsible for the coincident dramatic observed increase in wwv how long the equatorial region remains charged however depends on the latitude of the westerly wind event for instance a single equatorially symmetric westerly wind event ultimately acts to discharge wwv via the reflection of upwelling rossby waves which makes it difficult to more gradually build wwv given multiple wwes in contrast when the wind events occur off the equator the subsequent discharge is significantly damped and in some cases the equatorial region can hold the heat charge for the duration of the simulations 6 months as such off equatorial wwes can not only charge equatorial region wwv in the short term but are also a mechanism to more gradually build equatorial region wwv in the longer term given that these off equatorial wwes have a relatively small projection onto the equatorial kelvin wave we argue these events can be considered as a mechanism to modulate the background state in which enso operates

mooring observations of equatorial currents in the upper 1000 m of the western pacific ocean during 2014 time depth variations of the equatorial currents over the upper 1000 m depth in the western pacific ocean were directly measured by acoustic doppler current profiler moorings at 2 degrees n 140 degrees e and 4 7 degrees n 140 degrees e during january august 2014 intraseasonal variations of the equatorial currents with periods of 37 73 days were observed encompassing the north equatorial countercurrent necc northern branch of the south equatorial current sec equatorial undercurrent euc equatorial intermediate current eic north intermediate countercurrent nicc and north equatorial subsurface current nesc compared with previous studies based mainly on shipboard synoptic surveys the 8 month time series of velocity profiles provided direct evidence for the existence of nesc captured reversals of the eic in may and the nesc in june from westward to eastward direction and revealed larger vertical extensions of the sec and nesc and greater depths of the eic and nicc than previously thought according to a global analysis product of ocean surface current during january april 2014 the necc was located around its southernmost position and with its the weakest intensity over the past 20 years some of the anomalous characteristics of these flows may be related to the fickle el nino of 2014

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

tropical pacific sea surface temperature anomalies el nino and equatorial westerly wind events abstract the authors examine global statistical relationships between westerly wind events wwes and sea surface temperature anomaly ssta variability using a compositing technique for the period 1986 98 the authors describe the extent to which equatorial wwes are associated with central and eastern equatorial pacific waveguide warming and with local ssta changes under the wwe their goal is to quantify the extent to which equatorial wwes are fundamental to the onset and maintenance of warm el nino southern oscillation conditions in order to understand the effect of wwes on ssta evolution they begin by examining how ssta changes in the absence of equatorial wwes they find that ssta tends toward mean climate values in the absence of equatorial wwes whether the eastern equatorial pacific has close to normal ssta or warmer than normal ssta the two equatorial wwe types whose main surface wind anomalies are west of the date line are associated with weak local surface cooling the equatorial wwe type t

role of high and low frequency winds and wave reflection in the onset growth and termination of the 1997 1998 el nino the present study aims at studying the role played by high frequency wind variability wave reflection and easterly wind anomalies in the western pacific in the onset growth and termination phases of the 1997 1998 el nino using the trident intermediate coupled model and observations while the anomalous strength of the trade winds in 1996 favored the initiation of a warm event in 1997 via western pacific boundary rossby wave reflection the actual timing of the onset and the amplitude of the event resulted from the large march 1997 wind event once initiated high frequency westerly winds strongly contributed to the rapid growth of the warm event and to the displacement of the eastern edge of the warm pool moreover both easterly and westerly high frequency wind variability in 1997 1998 contributed to the amplitude of the event set the evolution of the warm event and potentially influenced the equatorial pacific conditions at least one year after the el nino event in addition eastern boundary reflection also significantly contributed to the amplitude and duration of the warm event whereas its termination was a combination of various factors reflection of upwelling rossby waves at the western boundary and large easterly wind anomalies observed in the western pacific from november 1997 to early 1998 these factors were sufficient to terminate the event and to switch temperature anomalies from warm to cold to conclude understanding the coupling between the high and low frequency wind variability i e studying enso as a multi scale phenomenon will certainly lead to a better comprehension of the diversity of its behavior and potentially to an improvement of its predictability

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

modulation of equatorial pacific westerly easterly wind events by the madden julian oscillation and convectively coupled rossby waves synoptic wind events in the equatorial pacific strongly influence the el nino southern oscillation enso evolution this paper characterizes the spatio temporal distribution of easterly ewes and westerly wind events wwes and quantifies their relationship with intraseasonal and interannual large scale climate variability we unambiguously demonstrate that the madden julian oscillation mjo and convectively coupled rossby waves crw modulate both wwes and ewes occurrence probability 86 of wwes occur within convective mjo and or crw phases and 83 of ewes occur within the suppressed phase of mjo and or crw 41 of wwes and 26 of ewes are in particular associated with the combined occurrence of a crw mjo far more than what would be expected from a random distribution 3 wind events embedded within mjo phases also have a stronger impact on the ocean due to a tendency to have a larger amplitude zonal extent and longer duration these findings are robust irrespective of the wind events and mjo crw detection methods while wwes and ewes behave rather symmetrically with respect to mjo crw activity the impact of enso on wind events is asymmetrical the wwes occurrence probability indeed increases when the warm pool is displaced eastward during el nino events an increase that can partly be related to interannual modulation of the mjo crw activity in the western pacific on the other hand the ewes modulation by enso is less robust and strongly depends on the wind event detection method the consequences of these results for enso predictability are discussed

influence of oceanic intraseasonal kelvin waves on eastern pacific hurricane activity abstractrecent studies have highlighted the role of subsurface ocean dynamics in modulating eastern pacific epac hurricane activity on interannual time scales in particular the well known el nino southern oscillation enso recharge discharge mechanism has been suggested to provide a good understanding of the year to year variability of hurricane activity in this region this paper investigates the influence of equatorial subsurface subannual and intraseasonal oceanic variability on tropical cyclone tc activity in the epac that is to say it examines previously unexplored time scales shorter than interannual in an attempt to explain the variability not related to enso using ocean reanalysis products and tc best track archive the role of subannual and intraseasonal equatorial kelvin waves ekw in modulating hurricane intensity in the epac is examined it is shown first that these planetary waves have a clear control on the subannual and intraseasonal variability of thermocline depth in the epac

on the variety of coastal el nino events we examine the connection between interannual anomalies of sea surface temperature sst in the central and far eastern equatorial pacific associated with basin scale and coastal el ninos variations of the sst anomalies in these two regions are largely coherent meaning coastal el ninos mostly occur together with the commonly studied basin scale el ninos of particular interest for this study though is the understanding of the coastal el ninos that are not accompanied by basin scale el ninos or that follow basin scale el ninos such coastal el ninos can have catastrophic societal consequences in western south america we identify seven coastal el ninos during 1979 2017 namely 1983 1987 1998 2008 2014 2015 and 2017 these coastal el ninos are driven by different mechanisms the coastal el ninos in 1983 1987 and 1998 occurred after basin scale el ninos a unique feature of such extreme basin scale el ninos like in 1982 1983 1986 1987 and 1997 1998 is an equatorially centered intertropical convergence zone during its decaying phase as a result positive sst anomalies persist and sometimes even strengthen in the eastern pacific in the subsequent boreal spring early summer leading to coastal el ninos the coastal el ninos in 2014 and 2015 on the other hand resulted from westerly wind bursts in the western pacific that forced downwelling kelvin waves and a thermocline depression in the far eastern pacific the formation of coastal el ninos in 2008 and 2017 were associated with westerly surface wind anomalies in the eastern equatorial pacific and largely driven by ocean surface heat flux anomalies these two coastal el ninos occur during the warm phase of the seasonal cycle so that warm ssts are amplified and or the warm season is extended along the west coast of south america thus there is a wide variety of the coastal el ninos in terms of evolution mechanism and timing

prolonged el nino conditions in 2014 2015 and the rapid intensification of hurricane patricia in the eastern pacific hurricane patricia was the most intense tropical cyclone on record in the eastern north pacific or atlantic reaching a peak intensity of 95 m s 1 only 30 h after attaining hurricane status 33 m s 1 here it is shown that exceptionally warm sea surface temperatures ssts a deeper than normal thermocline and strong near surface salinity stratification all aided patricia s rapid intensification combining to increase its potential intensity by 1 14 m s 1 anomalous surface warming and thermocline deepening along patricia s track were driven by prolonged el nino conditions during 2014 2015 and punctuated by the buildup to the extreme el nino of 2015 2016 in the region where patricia intensified sst was 1 5 c higher and sea surface height was 10 cm higher compared to conditions during the last extreme el nino in 1997 emphasizing the extraordinary nature of the 2015 anomalies

joint impact of north and south pacific extratropical atmospheric variability on the onset of enso events previous studies have indicated that boreal winter subtropical and extratropical sea surface pressure slp anomalies over both the north and south pacific are significantly related to the el nino southern oscillation enso state in the following boreal winter here we use observational data and model simulations to show that the ability of the boreal winter north pacific slp anomalies to initiate enso events a year later may strongly depend on the state of the simultaneous south pacific slp anomalies and vice versa when the boreal winter north pacific slp anomalies are of the opposite sign to the simultaneous south pacific anomalies the correlation of the north or south pacific anomalies with the following enso state becomes much weaker and the strength of the enso events also tends to be weaker one possible reason for this is that when the boreal winter north and south pacific slp anomalies have the opposite sign the westerly anomalies over the western central equatorial pacific during the following boreal summer are greatly reduced by the interference between the antecedent north and south pacific slp anomalies thereby not favoring the development of enso events further analysis indicates that a combination of north and south pacific precursor signals may serve to enhance the enso prediction skill

a simple approach to quantifying the noise enso interaction part ii the role of coupling between the warm pool and equatorial zonal wind anomalies stochastic forcing has been used conceptually to explain enso irregularity more recently the concept of state dependent multiplicative stochastic forcing has been explored as an explanation of a number of enso properties by calculating the state dependence factor of enso zonal wind stress noise forcing on sst we are able to separate the additive and multiplicative components of the wind stress noise forcing of enso spatially the months with large additive or multiplicative components all resemble previous studies on westerly wind bursts they differ from each other in that the wind stresses are significantly stronger during months with a large multiplicative noise component it is further shown that when the multiplicative noise component is large there have been large values of the wind stress noise in the preceding months this is not true of the months when the additive component is large the multi month growth of the wind stress from the multiplicative noise process is shown to be related to an eastward migration of the western pacific warm pool which is coupled to the wind stress through convection this process is shown to be significantly weakened in a climate model when the ocean and atmosphere are uncoupled

influence of westerly wind events stochasticity on el nino amplitude the case of 2014 vs 2015 the weak el nino of 2014 was preceded by anomalously high equatorial pacific warm water volume wwv and strong westerly wind events wwes which typically lead to record breaking el nino like in 1997 and 2015 here we use the cnrm cm5 coupled model to investigate the causes for the stalled el nino in 2014 and the necessary conditions for extreme el ninos this model is ideally suited to study this problem because it simulates all the processes thought to be critical for the onset and development of el nino it captures el nino preconditioning by wwv the wwes characteristics and their deterministic behaviour in response to warm pool displacements our main finding is that despite their deterministic control wwes display a sufficiently strong stochastic component to explain the distinct evolutions of el nino in 2014 and 2015 a 100 member ensemble simulation initialized with early spring equatorial conditions analogous to those observed in 2014 and 2015 demonstrates that early year elevated wwv and strong wwes preclude the occurrence of a la nina but lead to el ninos that span the weak with few wwes to extreme with many wwes range sensitivity experiments confirm that numerous strong wwes shift the el nino distribution toward larger amplitudes with a particular emphasis on summer fall wwes occurrence which result in a five fold increase of the odds for an extreme el nino a long simulation further demonstrates that sustained wwes throughout the year and anomalously high wwv are necessary conditions for extreme el nino to develop in contrast we find no systematic influence of easterly wind events ewes on the el nino amplitude in our model our results demonstrate that the weak amplitude of el nino in 2014 can be explained by wwes stochastic variations without invoking ewes or remote influences from outside the tropical pacific and therefore its peak amplitude was inherently unpredictable at long lead time

gas seepage as an indicator of deeper prospective reservoirs a study based on exploration 3d seismic data three periods of sustained gas seepage in geological time have been revealed in danish block 5604 26 in the north sea by the use of exploration 3d seismic data the most recent period is indicated by a cluster of seismic chimneys which ties in to buried craters near the seabed and possible present gas escape through the seabed along with amplitude anomalies indicating a shallow gas sand charged by gas migrating from a deeper level the cluster of seismic chimneys indicative of vertical gas migration is visible down to 1 5 s twt 1500 ms and therefore the gas is interpreted as migrating from a deeper stratigraphic horizon below this level it becomes difficult to see the chimneys due to complex faulting the faults may work as gas migration pathways the geometry of the cluster of seismic chimneys indicates that the gas has been migrating from one point the nearest possible source of the gas is an underlying prospect where an oil and gas discovery has been made two earlier periods of gas seepage are indicated by mounds possibly carbonate buildups over gas seepages in pliocene time and similarly buried craters formed by gas seepages in an earlier period in pliocene time the results of this study are that gas seepage is a periodical process in geological time and that its presence and associated features can be used as an indicator of deeper prospective reservoirs

recent changes in enso teleconnection over the western pacific impacts the eastern china precipitation dipole abstractthe eastern china precipitation dipole ecpd features an out of phase relationship between boreal summer precipitation over the middle and lower reaches of the yangtze river and the hetao region to its northwest the precipitation dipole is strongly influenced by enso teleconnections over the western tropical pacific here it is shown that a pronounced weakening of both the rainfall variability over eastern china as well as the precipitation dipole structure occurred around the mid 1990s the changes have been analyzed by considering two epochs one during 1979 95 and the other during 1996 2009 the characteristic feature of the circulation anomaly during the first epoch is the well known east asia pacific pacific japan eap pj pattern a quasi meridional teleconnection pattern emanating from the western tropical pacific on the other hand during the latter epoch eastern china precipitation variability occurs as an integral part of the circulation anomalies over the western pacific in contrast

contributions of sst anomalies in the indo pacific ocean to the interannual variability of tropical cyclone genesis frequency over the western north pacific abstractthis study attempts to evaluate quantitatively the contributions of sea surface temperature sst anomalies in the indo pacific ocean to the interannual variability of tropical cyclone tc

three dimensional structure of fluid conduits sustaining an active deep marine cold seep 1 cold seeps in deep marine settings emit fluids to the overlying ocean and are often associated with such seafloor flux indicators as chemosynthetic biota pockmarks and authigenic carbonate rocks despite evidence for spatiotemporal variability in the rate locus and composition of cold seep fluid emissions the shallow subseafloor plumbing systems have never been clearly imaged in three dimensions using a novel high resolution approach we produce the first three dimensional image of possible fluid conduits beneath a cold seep at a study site within the blake ridge gas hydrate province complex dendritic features diverge upward toward the seafloor from feeder conduits at depth and could potentially draw flow laterally by up to 103 m from the known seafloor seep a pattern similar to that suggested for some hydrothermal vents the biodiversity community structure and succession dynamics of chemosynthetic communities at cold seeps may largely reflect these complexities of subseafloor fluid flow

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

modulation of westerly wind bursts by sea surface temperature a semistochastic feedback for enso abstract westerly wind bursts wwbs in the equatorial pacific are known to play a significant role in the development of el nino events they have typically been treated as a purely stochastic external forcing of enso recent observations however show that wwb characteristics depend upon the large scale sst field the consequences of such a wwb modulation by sst are examined using an ocean general circulation model coupled to a statistical atmosphere model i e a hybrid coupled model an explicit wwb component is added to the model with guidance from a 23 yr observational record the wwb parameterization scheme is constructed such that the likelihood of wwb occurrence increases as the western pacific warm pool extends a semistochastic formulation which has both deterministic and stochastic elements the location of the wwbs is parameterized to migrate with the edge of the warm pool it is found that modulation of wwbs by sst strongly affects the characteristics of enso in particular coupled fe

atlantic warm pool acting as a link between atlantic multidecadal oscillation and atlantic tropical cyclone activity 1 multidecadal variability of atlantic tropical cyclone activity is observed to relate to the atlantic multidecadal oscillation amo a mode manifesting primarily in sea surface temperature sst in the high latitudes of the north atlantic in the low latitudes of the north atlantic a large body of warm water called the atlantic warm pool awp comprises the gulf of mexico the caribbean sea and the western tropical north atlantic awp variability occurs on both interannual and multidecadal timescales as well as with a secular variation the awp multidecadal variability coincides with the signal of the amo that is the warm cool phases of the amo are characterized by repeated large small awps since the climate response to the north atlantic sst anomalies is primarily forced at the low latitudes and the awp is in the path of or a birthplace for atlantic tropical cyclones the influence of the amo on atlantic tropical cyclone activity may operate through the mechanism of the awp induced atmospheric changes the awp induced changes related to tropical cyclones that we emphasize here include a dynamical parameter of tropospheric vertical wind shear and a thermodynamical parameter of convective instability more specifically an anomalously large small awp reduces enhances the vertical wind shear in the hurricane main development region and increases decreases the moist static instability of the troposphere both of which favor disfavor atlantic tropical cyclone activity this is the most plausible way in which the amo relationship with atlantic tropical cyclones can be understood

an interdecadal change in the influence of the central pacific enso on the subsequent north tropical atlantic spring sst variability around the mid 1980s north tropical atlantic nta spring sea surface temperature sst tends to be warmer cooler than normal in central pacific cp el nino decaying years during 1960s to mid 1980s however the relationship between the nta spring sst and cp el nino southern oscillation enso is weakened after mid 1980s this study presents this interdecadal change and investigates possible causes before the mid 1980s above normal nta sst peaks in post el nino spring the cp el nino can affect nta spring sst by inducing a negative phase of north atlantic oscillation nao anomaly over north atlantic from winter to spring this negative nao circulation weakens the azores high and causes weaker than normal trade wind as a result less heat loses from the nta ocean and above normal sst anomalies generated in contrast after the middle 1980s the connection between cp enso and nao like anomaly has been disrupted this leads to a weakening of cp enso influences on the nta spring sst the observed change in the relationship between nta spring sst and cp enso is likely related to the state of the polar vortex before the middle 1980s the polar vortex is weak this favors the propagation of enso related wave flux the rossby wave trains spread to the stratosphere during el nino conditions and cause weaker than normal polar vortex resulting in a negative nao in the low levels and the subtropical jet is enhanced and elongated which provides a potential waveguide for wave activity propagating to the atlantic through a tropospheric way however the polar vortex is strong after mid 1980s preventing the propagation of the enso related wave trains through the stratosphere or the troposphere

the march 1997 westerly wind event and the onset of the 1997 98 el nino understanding the role of the atmospheric response in a previous study the effect of the march 1997 westerly wind event wwe on the evolution of the tropical pacific ocean was studied using an ocean general circulation model gcm the response was characterized by i a cooling of the far western pacific 0 88c ii a rapid eastward displacement of the warm pool 2000 km in a month and iii a weak warming of the central eastern pacific along the path of the oceanic kelvin wave excited by the wwe 0 58c in this study the atmospheric response to these aspects of the sea surface temperature sst response are investigated using an atmospheric gcm forced with the sst anomalies from the ocean only experiments the results have demonstrated that the three aspects of the sst anomaly field generated by the wwe

tropical cyclone activity in the northwest pacific in relation to the el nino southern oscillation phenomenon abstract the interannual variations in tropical cyclone activity in the northwest pacific nwpac and their relationships with the el nino southern oscillation enso phenomenon were studied using the method of spectral analyses time series of a southern oscillation index soi defined as the sea level pressure difference between easter island and darwin and tropical cyclone activity in the entire nwpac ocean basin as well as in different regions of the nwpac were analyzed two spectral peaks are apparent in all these time series one corresponds to the generally accepted southern oscillation with a period of 3 to 3 5 years and another at the quasi biennial oscillation qbo frequency cross spectral analyses between the soi and tropical cyclone activity show significant coherence in these two spectral peaks the dominant peak is at the southern oscillation frequency with the soi leading typhoon activity by almost a year at the qbo frequency the two series are almost in phase cyclone activity in t

modulation of tropical cyclogenesis location and frequency over the indo western north pacific by the intraseasonal indo western pacific convection oscillation during the boreal extended summer abstractthe influence of the intraseasonal indo western pacific convection oscillation ipco on tropical cyclone tc genesis location and frequency over the indo western north pacific wnp during the boreal extended summer may october is explored observational analysis shows that the impacts of the intraseasonal ipco on tcs over the indo wnp include an evident phase lock of tc genesis location and distinct differences in tc frequency in the wnp in the positive intraseasonal ipco phase the atmosphere gains heat through the release of latent heat in cumulus convective condensation and the anomalous cyclonic circulation weakens the western pacific subtropical high wpsh and enhances tc genesis thereby tending to produce many more tcs moreover the diminished wpsh and the westward shift of the centers of anomalous cyclonic circulations lock tc genesis locations to the west wnp and lower latitudes around 5 20 n especially in the south china sea the almost opposite situation occurs in a nega

assessing the relationship between mjo and equatorial pacific wwbs in observations and cmip5 models abstractthis study evaluates the relationship between the madden julian oscillation mjo and the occurrence of equatorial pacific westerly wind bursts wwbs during the convective mjo phase anom

effects of westerly wind bursts on el nino a new perspective daily observations from 1971 to 2010 reveal that every el nino during this period was accompanied by congregated westerly wind bursts suggesting a close relationship of these bursts with both cold tongue and warm pool el nino events with the addition of burst like multiplicative noise to an intermediate ocean atmosphere coupled model it is shown that westerly wind bursts by generating eastward equatorial surface currents and downwelling kelvin waves could be responsible for the existence of the warm pool el nino and for the irregularity and extremes of the cold tongue el nino whether these bursts give rise to one type of el nino or the other depends on the timing of their occurrence relative to the phase of the recharge discharge cycle of the equatorial upper ocean heat content

gas hydrate stability zone modelling in areas of salt tectonics and pockmarks of the barents sea suggests an active hydrocarbon venting system the barents sea seabed exhibits an area of major glacial erosion exposing parts of the old hydrocarbon basins in this region we modelled the gas hydrate stability field in a 3d perspective including the effects of higher order hydrocarbon gases we used 3d seismic data to analyse the linkage between fluid flow expressions and hydrate occurrences above old sedimentary basin systems and vertical faults pockmarks showed a relation to fault systems where some of them are directly connected to hydrocarbon bearing sedimentary formations the influence of bottom water temperature pore water salinity and geothermal gradient variation on gas hydrate stability zone ghsz thickness is critically analysed in relation to both geological formations and salt tectonics our analysis suggests a highly variable ghsz in the barents sea region controlled by local variations in the parameters of stability conditions recovery of gas hydrate sample from the region and presence of gas enhanced reflections below estimated bsr depths may indicate a prevalent gas hydrate stable condition

enhanced influences of tropical atlantic sst on wnp nio atmosphere ocean coupling since the early 1980s abstractthis paper reports a new finding and related mechanism the forcing effect of the tropical atlantic ta sea surface temperature sst on the atmosphere ocean coupling in the western north pacific wnp and northern indian ocean nio since the early 1980s the ta sst has increased and notably exhibited an enhanced interannual statistical relationship with the wnp subtropical high and nio sst in boreal summer empirical diagnostics reveal the following spatial pattern linking the ta sst and the atmosphere ocean coupling in the pacific and indian ocean 1 a cyclonic anticyclonic circulation pair straddling the equator over the eastern pacific 2 an anticyclonic cyclonic circulation pair straddling the equator in the wnp and indian ocean 3 overturning circulation with ascending descending and descending ascending anomalies over the ta and tropical western pacific respectively and 4 positive negative sst anomaly in the ta and nio the characteristics of this pattern are consistent

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

the interaction between the western indian ocean and enso in cesm several previous studies have suggested that a cool western indian ocean may induce convection over indonesia leading to surface convergence and easterlies over the western equatorial pacific ocean these easterlies then increase the pacific warm water volume favouring el nino in the next year we investigate this mechanism of indian pacific interaction using output from two simulations at 0 1 circ and 1 circ ocean model resolution with the community earth system model cesm no conclusive evidence for the suggested interaction mechanism is found in cesm like many other coupled models cesm has an overly strong sea surface temperature variability in the eastern indian ocean due to an exaggerated sensitivity of the sea surface temperature to thermocline variations due to this bias the effect of the western indian ocean signals on the pacific as found from observational analysis is hidden our analysis shows that this bias can be traced to errors in the time mean vertical temperature profile in the indian ocean this bias needs to be reduced to allow a better investigation of the subtle interactions between the indian and pacific oceans

remote forcing of the northern tropical atlantic sst anomalies on the western north pacific anomalous anticyclone this study uses both observations and numerical modeling experiments to investigate the lead lag relationship and the associated physical mechanism of the western north pacific anomalous anticyclone wnpac with sea surface temperature sst anomalies over the northern tropical atlantic nta the results show that the wnpac from late spring to the middle of autumn has a significant in phase relationship with the nta sst anomalies up to two seasons ahead this relationship reaches a peak when the nta sst leads by approximately 1 2 months and is nearly independent of the el nino southern oscillation variability diagnosis based on observations and numerical experiments using the community atmospheric model version 5 3 reveals that the nta warming favors intensified local convection activity during the spring autumn seasons causing enhanced low level convergence and upper level divergence i e ascending motion over the nta and opposite flow anomalies over the central tropical pacific the enhanced subsidence over the central tropical pacific in turn triggers an anomalous low level anticyclone over the western north pacific moreover the intensity of the anomalous local convection activity that is associated with the nta sst is closely related to the seasonal migration of the atlantic intertropical convergence zone itcz as the atlantic itcz migrates northward the nta sst induced local convection activity extends northward from a narrow band near the equator during early spring to nearly the entire nta region during the middle of summer leading to the strongest remote effect of the nta sst anomalies on the wnpac during late summer and early autumn

modulation of western north pacific tropical cyclone activity by the atlantic meridional mode this study examines the year to year modulation of the western north pacific wnp tropical cyclones tc activity by the atlantic meridional mode amm using both observations and the geophysical fluid dynamics laboratory forecast oriented low ocean resolution version of cm2 5 flor global coupled model 1 the positive negative amm phase suppresses enhances wnp tc activity in observations the anomalous occurrence of wnp tcs results mainly from changes in tc genesis in the southeastern part of the wnp 2 the observed responses of wnp tc activity to the amm are connected to the anomalous zonal vertical wind shear zvws caused by amm induced changes to the walker circulation during the positive amm phase the warming in the north atlantic induces strong descending flow in the tropical eastern and central pacific which intensifies the walker cell in the wnp the intensified walker cell is responsible for the suppressed enhanced tc genesis in the eastern western part of the wnp by strengthening weakening zvws 3 the observed wnptc amm linkage is examined by the long term control and idealized perturbations experiment with flor fa a suite of sensitivity experiments strongly corroborate the observed wnptc amm linkage and underlying physical mechanisms

triggering of el nino by westerly wind events in a coupled general circulation model two ten members ensemble experiments using a coupled ocean atmosphere general circulation model are performed to study the dynamical response to a strong westerly wind event wwe when the tropical pacific has initial conditions favourable to the development of a warm event in the reference ensemble cref no wind perturbation is introduced whereas a strong westerly wind event anomaly is introduced in boreal winter over the western pacific in the perturbed ensemble cwwe our results demonstrate that an intense wwe is capable of establishing the conditions under which a strong el nino event can occur first it generates a strong downwelling kelvin wave that generates a positive sea surface temperature sst anomaly in the central eastern pacific amplified through a coupled ocean atmosphere interaction this anomaly can be as large as 2 5 c 60 days after the wwe secondly this wwe also initiates an eastward displacement of the warm pool that promotes the occurrence of subsequent wwes in the following months these events reinforce the initial warming through the generation of additional kelvin waves and generate intense surface jets at the eastern edge of the warm pool that act to further shift warm waters eastward the use of a ten members ensemble however reveals substantial differences in the coupled response to a wwe whereas four members of cwwe ensemble develop into intense el nino warming as described above four others display a moderate warming and two remains in neutral conditions this diversity between the members appears to be due to the internal atmospheric variability during and following the inserted wwe in the four moderate warm cases the warm pool is initially shifted eastward following the inserted wwe but the subsequent weak wwe activity when compared to the strong warming cases prevents to further shift the warm pool eastwards the seasonal strengthening of trade winds in june july can therefore act to shift warm waters back into the western pacific reducing the central eastern pacific warming this strong sensitivity of the coupled response to wwes may therefore limit the predictability of el nino events as the high frequency wind variability over the warm pool region remains largely unpredictable even at short time lead

the extreme el nino of 2015 2016 the role of westerly and easterly wind bursts and preconditioning by the failed 2014 event at the beginning of 2015 as one year earlier in 2014 the scientific community anticipated that el nino conditions could develop in the tropical pacific by year end such projections were related to the occurrence of westerly wind bursts during winter spring of each year that generated strong downwelling kelvin waves indicative of an emerging el nino however the event s progression quickly stalled in 2014 but actively continued in 2015 leading to an extreme warm event comparable to 1997 or 1982 here we compare climate evolution during these two years using satellite observations and numerical simulations we show that during 2014 el nino development was interrupted mid year by an exceptionally strong easterly wind burst whereas during the second year it continued through the summer further we show that the failed 2014 event created favorable conditions for el nino development during the next year as it kept ocean heat content recharged and the western pacific warm pool extended eastward subsequently the winter spring westerly wind bursts in 2015 were followed by a series of state dependent westerly bursts as part of a strong positive bjerknes feedback analogue simulations with a coupled gcm wherein we superimpose the observed sequences of westerly and easterly wind bursts support these conclusions stressing the role of the failed 2014 event in preconditioning the ocean atmosphere system for the development of an extreme el nino in our simulations the probability of an extreme event following early year westerly wind bursts increases from 14 to nearly 60 due to this preconditioning thus the interplay between westerly and easterly wind bursts shapes el nino development and diversity

cooperative effects of tropical pacific and atlantic sst forcing in southern china winter precipitation variability this study investigates the variability of winter precipitation over southern china sc and the impacts of sea surface temperature sst forcing in the tropical pacific and atlantic oceans the sc winter precipitation displays two major spatial modes a same sign mode with the maximum center located in southeastern china and a north south dipole mode with opposite variations between the lower reach of the yangtze river and the southeastern coast of china both modes are associated with the variation of the western north pacific wnp anticyclone the same sign mode is associated with canonical el nino through the pacific east asian teleconnection in the lower troposphere the north south dipole mode is subject to the impact of the western pacific warm pool associated with the central pacific el nino and equatorial atlantic forcing the influence of equatorial atlantic warming is through an upper tropospheric zonal wave pattern from the tropical atlantic to the mid latitudes of east asia both the tropical pacific and atlantic oceanic forcing induce a north south dipole pattern of winter precipitation anomalies over sc by affecting the northward extension of the wnp anticyclone moreover the observed statistical relationship between the dipole mode and the equatorial atlantic sst anomalies is present in hindcasts forecasts of the ncep climate forecast system version 2 cfsv2 confirming a potential source of the predictability of the north south dipole like variation of the winter precipitation in sc

westerly wind bursts enso s tail rather than the dog westerly wind bursts wwbs in the equatorial pacific occur during the development of most el nino events and are believed to be a major factor in enso s dynamics because of their short time scale wwbs are normally considered part of a stochastic forcing of enso completely external to the interannual enso variability recent observational studies however suggest that the occurrence and characteristics of wwbs may depend to some extent on the state of enso components implying that wwbs which force enso are modulated by enso itself satellite and in situ observations are used here to show that wwbs are significantly more likely to occur when the warm pool is extended eastward based on these observations wwbs are added to an intermediate complexity coupled ocean atmosphere enso model the representation of wwbs is idealized such that their occurrence is modulated by the warm pool extent the resulting model run is compared with a run in which the wwbs are stochastically applied the modulation of wwbs by enso results in an enhancement of the slow frequency component of the wwbs this causes the amplitude of enso events forced by modulated wwbs to be twice as large as the amplitude of enso events forced by stochastic wwbs with the same amplitude and average frequency based on this result it is suggested that the modulation of wwbs by the equatorial pacific sst is a critical element of enso s dynamics and that wwbs should not be regarded as purely stochastic forcing in the paradigm proposed here wwbs are still an important aspect of enso s dynamics but they are treated as being partially stochastic and partially affected by the large scale enso dynamics rather than being completely external to enso it is further shown that wwb modulation by the large scale equatorial sst field is roughly equivalent to an increase in the ocean atmosphere coupling strength making the coupled equatorial pacific effectively self sustained

what drove the pacific and north america climate anomalies in winter 2014 15 in late 2014 and early 2015 the canonical atmospheric response to the el nino and southern oscillation enso event was not observed in the central and eastern equatorial pacific although nino3 4 index exceeded the threshold for a weak el nino in an effort to understand why it was so this study deconvoluted the observed 2014 15 december january february djf mean sea surface temperature sst precipitation and 200 hpa stream function anomalies into the leading patterns related to the principal components of djf sst variability it is noted that the anomalies of these variables were primarily determined by the patterns related to two sst modes one is the north pacific mode npm and the other the enso mode the npm was responsible for the apparent lack of coupled air sea relationship in the central equatorial pacific and the east west structure of the circulation anomalies over north america while the enso mode linked to ssts in the central and eastern equatorial pacific as well as the circulation in the central equatorial pacific further the enso signal in djf 2014 15 likely evolved from the npm pattern in winter 2013 14 its full development however was impeded by the easterly anomalies in the central equatorial pacific that was associated with negative sst anomalies in the southeastern subtropical pacific in addition the analyses also indicates that the sst anomalies in the nino3 4 region alone were not adequate for capturing the coupling of oceanic and atmospheric anomalies in the tropical pacific due to the fact that this index cannot distinguish whether the sst anomaly in the nino3 4 region is associated with the enso mode or npm or both

role of scale interactions in the abrupt change of tropical cyclone in autumn over the western north pacific tropical cyclone tc activity in autumn september november over the western north pacific experienced an abrupt change in 1998 which can be detected by the bayesian change point analysis during the decade before the regime shift 1988 1997 the occurrence frequency of tc genesis increased significantly over the tropical western pacific where the seasonal cyclonic flow intraseasonal oscillation iso and synoptic scale eddy sse were all strengthened compared to those observed in the decade after 1998 1998 2007 the tc trajectories also exhibited spatial differences during the active decade the tcs had a higher probability to move westward into the philippine sea and the south china sea and recurved northeastward toward the east of japan meanwhile the northwestward propagating tcs approaching taiwan and southeastern coast of china were reduced to understand the role of mean flow iso sse interaction in the decadal changes of sse and associated tc activity we diagnosed a newly proposed sse kinetic energy ke equation that separates the contributions of seasonal mean circulation and iso to the sse the results show that during the active tc decade the sse obtained higher ke from both mean flow and iso through eddy barotropic energy conversion when the enhanced sse momentum flux interacted with the strengthened monsoon trough and vigorous iso cyclonic anomaly over the western tropical pacific the increased sse ke contributed positively to the increased tc genesis over the main genesis region 7 5 20 n 130 170 e it also benefited the growth of tcs over the philippine sea and the south china sea during the active decade the decadal change in tc frequency over the extratropics was related to the eddy baroclinic energy conversion instead of the barotropic conversion associated with scale interaction during the active tc decade sse gained more less ke from the sse available potential energy over the east of japan the east china sea favoring disfavoring the succeeding development of tcs in this region

importance of background seasonality over the eastern equatorial pacific in a coupled atmosphere ocean response to westerly wind events coupled atmosphere ocean response to westerly wind events wwes which sometimes trigger el ninos was investigated using a coupled general circulation model to clarify its dependence on the timing and location of wwes twelve sets of 20 member ensembles were made with an idealized single wwe imposed in different months from january to july and at different longitudes from 160 circ e to 160 circ w the initial ocean states are set to be near neutral to el nino la nina so that the lagged response to wwes can be isolated the results show that sea surface temperature sst in the nino3 4 region increases largely and persistently favorable for el nino growth when a wwe is imposed in may whereas a wwe in march increases sst only in the easternmost pacific in both cases an oceanic kelvin wave propagates eastward to warm the eastern pacific when forced by the wwe in may a positive nino3 4 sst anomaly appears in boreal summer according to the seasonal outcrop of the equatorial thermocline and it can strongly interact with seasonally active tropical rain belt to amplify the sst response further a favorable combination of timing and location that maximize the impact of wwes on el ninos in the subsequent winter is suggested albeit its relevance to nature should severely be tested another experiment with initial ocean states in el nino la nina years showed that the wwes in may are efficient to amplify el nino similar to the neutral case but are not efficient to suppress la nina

lack of westerly wind bursts in unmaterialized el nino years abstractthe lack of westerly wind bursts wwbs when atmospheric intraseasonal variability isv events occur from boreal spring to autumn is investigated by comparing two types of el nino years with unmaterialized el nino uen years although high ocean heat content buildup and several isv events propagating eastward are observed in all three types of years few wwbs accompany these in the uen years the eddy kinetic energy budget analysis based on isv shows that mean westerly winds in the lower troposphere facilitate the development of eddy disturbances including wwbs through convergence and meridional shear of zonal winds in the uen years these westerly winds are retracted westward and do not reach the equatorial central pacific mainly due to interannual components in addition positive sea surface temperature anomalies in the western pacific which are conducive to active convection spread widely in a meridional direction centered on 15 n both westward retracted mean westerlies and off equator

impact of the indian ocean sst basin mode on the asian summer monsoon 1 following an el nino event a basin wide warming takes place over the tropical indian ocean peaks in late boreal winter and early spring and persists through boreal summer our observational analysis suggests that this indian ocean warming induces robust climatic anomalies in the summer indo west pacific region prolonging the el nino s influence after tropical east pacific sea surface temperature has returned to normal in response to the indian ocean warming precipitation increases over most of the basin forcing a matsuno gill pattern in the upper troposphere with a strengthened south asian high near the ground the southwest monsoon intensifies over the arabian sea and weakens over the south china and philippine seas an anomalous anticyclonic circulation forms over the subtropical northwest pacific collocated with negative precipitation anomalies all these anomaly patterns are reproduced in a coupled model simulation initialized with a warming in the tropical indian ocean mixed layer indicating that the indian ocean warming is not just a passive response to el nino but important for summer climate variability in the indo west pacific region the implications for seasonal prediction are discussed