cross season relation of the south china sea precipitation variability between winter and summer the present study reveals cross season connections of rainfall variability in the south china sea scs region between winter and summer rainfall anomalies over northern south china sea in boreal summer tend to be preceded by the same sign rainfall anomalies over southern south china sea in boreal winter denoted as in phase relation and succeeded by opposite sign rainfall anomalies over southern south china sea in the following winter denoted as out of phase relation analysis shows that the in phase relation from winter to summer occurs more often in el nino la nina decaying years and the out of phase relation from summer to winter appears more frequently in el nino la nina developing years in the summer during the el nino la nina decaying years cold warm and warm cold sea surface temperature sst anomalies develop in tropical central north pacific and the north indian ocean respectively forming an east west contrast pattern the in phase relation is associated with the influence of anomalous heating cooling over the equatorial central pacific during the mature phase of el nino la nina events that suppresses enhances precipitation over southern south china sea and the impact of the above east west sst anomaly pattern that reduces increases precipitation over northern south china sea during the following summer the impact of the east west contrast sst anomaly pattern is confirmed by numerical experiments with specified sst anomalies in the el nino la nina developing years regional air sea interactions induce cold warm sst anomalies in the equatorial western north pacific the out of phase relation is associated with a rossby wave type response to anomalous heating cooling over the equatorial central pacific during summer and the combined effect of warm cold sst anomalies in the equatorial central pacific and cold warm sst anomalies in the western north pacific during the mature phase of el nino la nina events

asymmetry of atmospheric circulation anomalies over the western north pacific between el nino and la nina the asymmetry of the western north pacific wnp low level atmospheric circulation anomalies between the el nino and la nina mature winter is examined an anomalous wnp cyclone wnpc center during la nina tends to shift westward relative to an anomalous wnp anticyclone wnpac center during el nino two factors may contribute to this asymmetric response thefirst factor is the longitudinal shifting of el nino and la nina anomalous heating the composite negative precipitation anomaly center during la ninai s located farther to the west of the composite positive precipitation anomaly center during el nino the westward shift of the heating may further push the wnpc westward relative to the position of the wnpac the second factor is the amplitude asymmetry of sea surface temperature anomalies sstas in the wnp namely the amplitude of local cold ssta during el nino is greater than that of warm ssta during la nina the asymmetry of ssta is originated from the asymmetric ssta tendencies during the enso developing summer although both precipitation and surface wind anomalies are approximately symmetric the surface latent heat flux anomalies are highly asymmetric over the key wnp region where the climate mean zonal wind speed is small both the anomalous westerly during el nino and the anomalous easterly during la nina in the region lead to an enhanced surface evaporation strengthening weakening the enhancement of the cold warm ssta in situ during el nino la nina the asymmetry of the ssta in the wnp is further amplified due to anomalous wind differences between el nino and la nina in their mature winter atmo spheric general circulation model experiments demonstrate that both factors contribute to the asymmetry between the wnpac and wnpc the asymmetric circulation in the wnp contributes to the asymmetry of temporal evolutions between el nino and la nina

characteristics of seismic survey pulses and the ambient soundscape in baffin bay and melville bay west greenland in 2012 a seismic survey campaign involving four vessels was conducted in baffin bay west greenland long distance 150 km pre survey acoustic modeling was performed in accordance with regulatory requirements four acoustic recorders three with hydrophones at 100 200 and 400 m depths measured ambient and anthropogenic sound during the survey additional recordings without the surveys were made from september 2013 to september 2014 the results show that 1 the soundscape of baffin bay is typical for open ocean environments and melville bay s soundscape is dominated by glacial ice noise 2 there are distinct multipath arrivals of seismic pulses 40 km from the array 3 seismic sound levels vary little as a function of depth 4 high fidelity pre survey acoustic propagation modeling produced reliable results 5 the daily sel did not exceed regulatory thresholds and were different using southall bowles ellison finneran gentry greene kastak ketten miller nachtigall richardson thomas a

linking observations of the asian monsoon to the indian ocean sst possible roles of indian ocean basin mode and dipole mode abstract the authors investigate the relationship between sea surface temperature sst in the tropical indian ocean tio and the seasonal atmosphere circulation in the asian monsoon region amr using the maximum covariance analyses mcas the results show that the asian monsoon circulation is significantly correlated with two dominant sst anomaly ssta modes the indian ocean basin mode iob and the indian ocean dipole mode iod the peak ssta of the iob appears in spring and has a much stronger relationship with the asian summer monsoon than the peak of the iod does whereas the peak ssta for the iod appears in fall and shows a stronger link to the asian winter monsoon than to the asian summer monsoon in addition the iob in spring has a relatively stronger link with the atmospheric circulation in summer than in other seasons the large scale atmospheric circulation and ssta patterns of the covariability of the first two dominant mca modes are described for the first mca mode a warm iob persis

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

ranging bowhead whale calls in a shallow water dispersive waveguide this paper presents the performance of three methods for estimating the range of broadband 50 500 hz bowhead whale calls in a nominally 55 m deep waveguide conventional mode filtering cmf synthetic time reversal str and triangulation the first two methods use a linear vertical array to exploit dispersive propagation effects in the underwater sound channel the triangulation technique used here while requiring no knowledge about the propagation environment relies on a distributed array of directional autonomous seafloor acoustics recorders dasars arranged in triangular grid with 7 km spacing this study uses simulations and acoustic data collected in 2010 from coastal waters near kaktovik alaska at that time a 12 element vertical array spanning the bottom 63 of the water column was deployed alongside a distributed array of seven dasars the estimated call location to array ranges determined from cmf and str are compared with dasar triangulation results for 19 whale calls the vertical array ranging results are generally within 10 of the dasar results with the str results providing slightly better agreement the results also indicate that the vertical array can range calls over larger ranges and with greater precision than the particular distributed array discussed here whenever the call locations are beyond the distributed array boundaries

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

airgun inter pulse noise field during a seismic survey in an arctic ultra shallow marine environment offshore oil and gas exploration using seismic airguns generates intense underwater pulses that could cause marine mammal hearing impairment and or behavioral disturbances however few studies have investigated the resulting multipath propagation and reverberation from airgun pulses this research uses continuous acoustic recordings collected in the arctic during a low level open water shallow marine seismic survey to measure noise levels between airgun pulses two methods were used to quantify noise levels during these inter pulse intervals the first based on calculating the root mean square sound pressure level in various sub intervals is referred to as the increment computation method and the second which employs the hilbert transform to calculate instantaneous acoustic amplitudes is referred to as the hilbert transform method analyses using both methods yield similar results showing that the inter pulse sound field exceeds ambient noise levels by as much as 9 db during relatively quiet conditions inter pulse noise levels are also related to the source distance probably due to the higher reverberant conditions of the very shallow water environment these methods can be used to quantify acoustic environment impacts from anthropogenic transient noises e g seismic pulses impact pile driving and sonar pings and to address potential acoustic masking affecting marine mammals

diverse influences of enso on the east asian western pacific winter climate tied to different enso properties in cmip5 models the influence of el nino southern oscillation enso on the east asian western pacific eawp climate in boreal winter is investigated in the phase 5 of the coupled model intercomparison project cmip5 model results and then compared to that in the phase 3 cmip3 results in particular the role played by the differences among models in enso properties including the amplitude and longitudinal extension of enso s sea surface temperature sst pattern is analyzed results show that an eastward shrinking of enso s sst pattern leads to quite weak circulation and climatic responses over the eawp regions in the models on the contrary a westward expansion of the sst pattern shifts the anomalous walker circulation too far west the resultant precipitation anomalies and lower tropospheric atmospheric rossby wave responses both extend unrealistically into the indian ocean and the hemispheric asymmetry of the rossby wave response is missing all these features lead to unrealistic climatic impacts of ensoover the eawp regions in contrasttothe abovetwocases areasonablelongitudinalextensionof enso s sst pattern corresponds to better enso teleconnections over the eawp regions nevertheless the atmospheric responses over the western pacific are still located farther west than observed implying a common bias of cmip5 models in this case a larger amplitude of enso variability to some extent helps to reduce model biases and facilitate better climatic responses to enso in the eawp regions compared with cmip3 models cmip5 models perform better in representing enso s impacts on the east asian winter climate

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

the two interannual variability modes of the western north pacific subtropical high simulated by 28 cmip5 amip models using the output of the atmospheric model intercomparison project amip experiments of 28 models from the fifth phase of the coupled model intercomparison project cmip5 the models performances in the simulation of the two dominant interannual variability modes of the western north pacific subtropical high wnpsh are investigated in the observation the positive phases of these two modes feature an anomalous anticyclone over the western north pacific wnp but the first mode m1 is closely connected with the sea surface temperature sst anomalies over the tropical indian ocean tio the maritime continent mc and the equatorial central pacific cp while the second mode m2 is closely connected with the sst anomalies over the wnp the m1 is well captured by the cmip5 amip models forced by the historical sst suggesting the m1 is an sst forced mode the cmip5 amip models capture the close relationship of the m1 with the sst anomalies over the tio the mc and the cp the forcing mechanisms of m1 in the cmip5 amip models are consistent with the observation including a kelvin wave emanating from the tio and a local hadley circulation originating from the mc different from the high reproducibility of the m1 the m2 is only moderately reproduced by the multi model ensemble mme mean of the cmip5 amip models the simulated anomalous wnpsh of the m2 is weaker and shifts southwestward in the mme and many individual models compared to the observation among the five anomalous wnpsh years associated with the m2 the mme captures the anomalous wnpsh only in 1993 and 1994 but not in 1980 1981 and 1987 the partial reproducibility of the m2 by the cmip5 amip models suggests the m2 is neither a pure atmospheric internal mode nor a pure sst forced mode the observed close relationship between the anomalous wnpsh and the wnp sst anomalies is underestimated by the cmip5 amip models suggesting the local sst wnpsh relationship may depend on the air sea interaction over the wnp

a comparison of late quaternary forest changes in new caledonia and northeastern australia a pollen record from lake xere wapo southeast new caledonia is the longest continuous terrestrial record to be recovered from the tropical southwest pacific and reveals a series of millennial scale changes in vegetation over the last 130 000 yr a comparison of the lake xere wapo record with the key northeast australian record of lynch s crater reveals regional patterns of change from 120 000 to 50 000 yr ago the vegetation around lake xere wapo alternated between rainforest and maquis with fire an important disturbance factor in the last 50 000 yr fire is almost absent from the record and the vegetation assumes a character unprecedented in the preceding 100 000 yr dominated by dacrydium and podocarpus pollen the most compelling aspect of the comparison with lynch s crater is that the much discussed araucaria decline at around 45 000 yr ago in northern queensland is matched by a similar decline in the lake xere wapo record d 2005 university of washington all rights reserved

bowhead whale localization using asynchronous hydrophones in the chukchi sea this paper estimates bowhead whale locations and uncertainties from bayesian inversion of modally dispersed calls recorded on asynchronous recorders in the chukchi sea alaska bowhead calls were recorded on a cluster of seven asynchronous ocean bottom hydrophones that were separated by 0 5 7 5 km a warping time frequency analysis is used to extract relative mode arrival times as a function of frequency for nine frequency modulated whale calls that dispersed in the shallow water environment each call was recorded on multiple hydrophones and the mode arrival times are inverted for the whale location in the horizontal plane source instantaneous frequency if water sound speed profile subbottom layering and geoacoustic parameters relative recorder clock drifts and residual error standard deviation all with estimated uncertainties a simulation study shows that accurate prior environmental knowledge is not required for accurate localization joint inversion of multiple recorded calls is shown to substantially reduce localization source if and relative clock drift uncertainties whale location uncertainties are estimated between 30 and 160 m and clock drift uncertainty is estimated between 3 and 26 ms the clock synchronization provided by the inversion is sufficient for localizing other types of marine mammal calls using simpler time difference of arrival methods

interannual and interdecadal variations of the east asian summer monsoon and tropical pacific ssts part i roles of the subtropical ridge the interannual relationship between the east asian summer monsoon and the tropical pacific ssts is studied using rainfall data in the yangtze river valley and the ncep reanalysis for 1951 96 the datasets are also partitioned into two periods 1951 77 and 1978 96 to study the interdecadal variations of this relationship a wet summer monsoon is preceded by a warm equatorial eastern pacific in the previous winter and followed by a cold equatorial eastern pacific in the following fall this relationship involves primarily the rainfall during the pre mei yu mei yu season may june but not the post mei yu season july august in a wet monsoon year the western north pacific subtropical ridge is stronger as a result of positive feedback that involves the anomalous hadley and walker circulations an atmospheric rossby wave response to the western pacific complementary cooling and the evaporation wind feedback this ridge extends farther to the west from the previous winter to the following fall resulting in an 850 hpa anomalous anticyclone near the southeast coast of china this anticyclone 1 blocks the pre mei yu and mei yu fronts from moving southward thereby extending the time that the fronts produce stationary rainfall 2 enhances the pressure gradient to its northwest resulting in a more intense front and 3 induces anomalous warming of the south china sea surface through increased downwelling which leads to a higher moisture supply to the rain area a positive feedback from the strong monsoon rainfall also appears to occur leading to an intensified anomalous anticyclone near the monsoon region this sst subtropical ridge monsoon rainfall relationship is observed in both the interannual timescale within each interdecadal period and in the interdecadal scale the sst anomalies sstas change sign in northern spring and resemble a tropospheric biennial oscillation tbo pattern during the first interdecadal period 1951 77 in the second interdecadal period 1978 96 the sign change occurs in northern fall and the tbo pattern in the equatorial eastern pacific sst is replaced by longer timescales this interdecadal variation of the monsoon sst relationship results from the interdecadal change of the background state of the coupled ocean atmosphere system this difference gives rise to the different degrees of importance of the feedback from the anomalous circulations near the monsoon region to the equatorial eastern pacific in a wet monsoon year the anomalous easterly winds south of the monsoon enhanced anomalous anticyclone start to propagate slowly eastward toward the eastern pacific in may and june apparently as a result of an atmosphere ocean coupled wave motion these anomalous easterlies carry with them a cooling effect on the ocean surface in 1951 77 this effect is insignificant as the equatorial eastern pacific sstas already change from warm to cold in northern spring probably as a result of negative feedback processes discussed in enso mechanisms in 1978 96 the equatorial eastern pacific has a warmer mean sst a stronger positive feedback between ssta and the walker circulation during a warm phase tends to keep the ssta warm until northern fall when the eastward propagating anomalous easterly winds reach the eastern pacific and reverse the ssta

the intermodel diversity of east asia s summer rainfall among cmip5 models abstractbased on the results of 46 phase 5 of the coupled model intercomparison project cmip5 models and empirical orthogonal function analysis it was found that the leading diversity mode of east asian summer rainfall across the models features a dipole structure this structure is characterized by intensified rainfall over southern china and the area south of japan and by weakened rainfall over northern china and explains more than 1 3 of the total intermodel variance the uncertainty in meridional position of intertropical convergence zone itcz over the tropical north pacific caused by rainfall parameterization and air sea interactions is responsible for the mode in models with a southward shifted itcz the heating associated with inadequate rainfall 7 18 n over the tropical northwest pacific excites wave activities that propagate northward and converge south of japan in the midtroposphere in the midtroposphere a positive negative vorticity departure resides north south of the center o

toward mitigating the double itcz problem in ncar ccsm3 1 the appearance of a spurious inter tropical convergence zone south of the equator in the eastern and central equatorial pacific in addition to the observed one north of the equator is a common problem in coupled global climate models the present study investigates this double itcz problem in the ncar ccsm3 it shows that use of a modified zhang mcfarlane convection scheme significantly mitigates the double itcz problem in boreal summer this has a profound impact on the simulated sea surface temperature through cloud radiative forcing feedback both the warm bias in the southern itcz region and the cold bias in the cold tongue over the equator are reduced examination of the time series of precipitation sst and surface energy fluxes shows that depending on the convection parameterization used double or single itcz emerges quickly within the first few months after the model start

the vertical structure and development of the enso anomaly mode during 1979 1989 abstract the latest two pacific basinwide warm episodes 1982 83 and 1986 87 exhibit some common features in their development and vertical structure these features are examined by multivariate empirical orthogonal function analysis of the interannual variability of the ocean atmosphere system along equatorial indian and pacific oceans the updraft and downdraft branches of the anomalous walker circulation originate over the western pacific and the eastern indian ocean respectively the early development of basinwide warming is characterized by the strengthening of a cross equatorial low level southerly component over the eastern pacific and the enhancement of convection and boundary layer westerlies over the western pacific the structure of the enso anomaly mode changes from the cold to the warm phase of the southern oscillation this is attributed to its eastward migration and the intrinsic longitudinal dependence of the vertical structure the latter results from the east west contrast of the air s

asymmetry in zonal phase propagation of enso sea surface temperature anomalies 1 it is often emphasized in the literature that the phase propagation of el nino sea surface temperature sst anomalies along the equator changed from westward to eastward after a mid to late 1970s climate regime shift in the pacific theories have been developed to explain this change of phase propagation in terms of changes in background state on which el nino events develop those theories also suggest that the direction of la nina anomaly phase propagation should have changed from westward to eastward as well however the direction of la nina sst anomaly phase propagation did not change after the mid to late 1970s instead la nina ssts continued to exhibit westward phase propagation along the equator a feature overlooked in both observational analyses and theories this paper highlights the asymmetry in zonal phase propagation between el nino and la nina sea surface temperature anomalies since 1980 and discusses the implications of that asymmetry for understanding el nino southern oscillation enso dynamics

the seasonal cycle over the tropical pacific in coupled ocean atmosphere general circulation models abstract the seasonal cycle over the tropical pacific simulated by 11 coupled ocean atmosphere general circulation models gcms is examined each model consists of a high resolution ocean gcm of either the tropical pacific or near global means coupled to a moderate or high resolution atmospheric gcm without the use of flux correction the seasonal behavior of sea surface temperature sst and eastern pacific rainfall is presented for each model the results show that current state of the art coupled gcms share important successes and troublesome systematic errors all 11 models are able to simulate the mean zonal gradient in sst at the equator over the central pacific the simulated equatorial cold tongue generally tends to be too strong too narrow and extend too far west ssts are generally too warm in a broad region west of peru and in a band near 10 s this is accompanied in some models by a double intertropical convergence zone itcz straddling the equator over the eastern pacific and in others

roles of enso and pdo in the link of the east asian winter monsoon to the following summer monsoon abstractthe present study investigates the roles of el nino southern oscillation enso and the pacific decadal oscillation pdo in the relationship between the east asian winter monsoon eawm and the following east asian summer monsoon easm the variability of the eawm is divided into an enso related part named eawmen and an enso unrelated part named eawmres corresponding to a weak eawmen an anomalous low level anticyclone forms over the western north pacific wnp and persists from winter to the following summer this anticyclone enhances southerlies over the coast of east asia in summer hence a weak eawmen tends to be followed by a strong easm and vice versa as such a link is established between the eawmen and the easm the persistence of this wnp anticyclone may be mainly attributed to the sea surface temperature anomalies associated with the enso related eawm part in the tropical indian ocean and the extratropical north pacific in contrast corresponding to a weak eawmres the anomalous wn

combination mode dynamics of the anomalous northwest pacific anticyclone abstractnonlinear interactions between enso and the western pacific warm pool annual cycle generate an atmospheric combination mode c mode of wind variability the authors demonstrate that c mode dynamics are responsible for the development of an anomalous low level northwest pacific anticyclone nwp ac during el nino events the nwp ac is embedded in a large scale meridionally antisymmetric indo pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in asia in contrast to previous studies the authors find the role of air sea coupling in the indian ocean and northwestern pacific only of secondary importance for the nwp ac genesis moreover the nwp ac is clearly marked in the frequency domain with near annual combination tones which have been overlooked in previous indo pacific climate studies furthermore the authors hypothesize a positive feedback loop involving the anomalous low level nwp ac through el nino and c mode interactions the development o

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

relative contribution of enso and east asian winter monsoon to the south china sea sst anomalies during enso decaying years present study investigates respective contributions of el nino southern oscillation enso and east asian winter monsoon eawm to two periods of sea surface temperature sst anomalies in the south china sea scs one subsequent to the enso mature phase and the other in the following summer during 1982 2010 it is found that the sst anomalies in the first period are related to the eawm and the enso impact independent of eawm is weak which differs from previous studies the sst anomalies in the second period are mainly due to the enso effect a heat budget analysis shows that changes in shortwave radiation and wind related surface latent heat flux as well as horizontal advections are the processes leading to the eawm related sst anomalies in the first period the enso related sst anomalies in the second period are contributed by shortwave radiation and latent heat flux anomalies as well as meridional advection and vertical upwelling processes near the southeast coast of indochina peninsula the enso contribution to the scs sst anomalies in the first period is larger before than after the late 1970s this is attributed to an earlier development of enso events that is followed by larger equatorial central and eastern pacific sst anomalies in boreal summer and subsequently larger north indian ocean sst anomalies around october consequently anomalous surface anticyclone over the scs is stronger leading to larger surface heat flux anomalies and thus a larger sst increase around october before than after the late 1970s

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

orographically anchored el nino effect on summer rainfall in central china abstractyear to year variations in summer precipitation have great socioeconomic impacts on china historical rainfall variability over china is investigated using a newly released high resolution dataset the results reveal summer mean rainfall anomalies associated with enso that are anchored by mountains in central china east of the tibetan plateau these orographically anchored hot spots of enso influence are poorly represented in coarse resolution datasets so far in use in post el nino summers an anomalous anticyclone forms over the tropical northwest pacific and the anomalous southwesterlies on the northwest flank cause rainfall to increase in mountainous central china through orographic lift at upper levels the winds induce additional adiabatic updraft by increasing the eastward advection of warm air from tibet in post el nino summers large scale moisture convergence induces rainfall anomalies elsewhere over flat eastern china which move northward from june to august and amount to little in

an intensity index for the east asian winter monsoon the thermal contrast betweenthe asian continentand the adjacent oceans is the primary aspect of the east asian winter monsoon eawm that can be well represented in the sea level pressure slp field based on this consideration a new slp based index measuring the intensity of the eawm is proposed by explicitly taking into account both the east west and the north south pressure gradients around east asia the new index can delineate the eawm related circulation anomalies well including the deepened shallow midtropospheric east asian trough sharpened and accelerated widened and decelerated upper tropospheric east asian jet stream and enhanced weakened lower tropospheric northerly winds in strong weak eawm winters compared with previous indices the new index has a very good performance describing the winter mean surface air temperature variations over east asia especially for the extreme warm or cold winters the index is strongly correlated with several atmospheric teleconnections including the arctic oscillation theeurasianpattern andthenorthpacificoscillation westernpacificpattern implyingthepossible internal dynamics of the eawm variability meanwhile the indexis significantly linked to el ni oscillation enso and the sea surface temperature sst over the tropical indian ocean moreover the sst anomalies over the tropical indian ocean are more closely related to the index than enso as an independent predictor this adds further knowledge to the prediction potentials of the eawm apart from enso the predictability of the index is high in the hindcasts of the centre national de recherches m cnrm model from development of a european multimodel ensemble system for seasonal to interannual prediction demeter hence it would be a good choice to use this index for the monitoring prediction and research of the eawm

in phase transition from the winter monsoon to the summer monsoon over east asia role of the indian ocean 1 analysis of observations shows that the weak east asian winter monsoon eawm to weak east asian summer monsoon easm transitions mainly occur in el nino decaying years whereas strong eawm denoting stronger northerly winds along east asian coast to strong easm denoting less precipitation along the meiyu baiu rainband transitions all occur in non el nino southern oscillation enso years during the period 1979 2009 this new finding implies that enso is not indispensable to the in phase eawm to the easm transitions the present study reveals an important role of the indian ocean in the strong eawm to strong easm transitions and proposes a possible mechanism for these transitions a strong eawm induces more precipitation over the maritime continent and the associated anomalous heating excites a gill matsuno type pattern in the tropics the resultant wind and cloud changes enhance latent heat flux and reduce downward shortwave radiation over the northwestern indian ocean in winter which leads to sst cooling the cold sst anomalies persist to summer and excite an anomalous cyclone over the subtropical western north pacific leading to a strong easm the above processes also operate in the weak eawm to weak easm transitions during which el nino impacts dominate but with additional contributions from the eawm the results of observational analysis are confirmed by numerical experiments with a coupled model

links between annual variations of peruvian stratocumulus clouds and of sst in the eastern equatorial pacific abstract the hypothesis that peruvian stratocumulus play an important role on both the annual mean and annual variations of sea surface temperature sst in the eastern equatorial pacific is examined the problem is addressed by performing sensitivity experiments using the university of california los angeles coupled atmosphere ocean gcm with different idealized temporal variations of stratocumulus in a region along the coast of peru the results obtained are consistent with the notion that peruvian stratocumulus are a key component of the interhemispherically asymmetric features that characterize the annual mean climate of the eastern equatorial pacific including the cold ssts off peru and the absence of a southern itcz the principal new finding of this study is that the annual variations i e deviations from the annual mean of peruvian stratocumulus are linked to the differences between the amplitude duration and westward propagation of the warm and cold phases of the equatorial cold tongue in

a new upper level circulation index for the east asian summer monsoon variability the east asian summer monsoon easm andits variability involvecirculationsystems in both the tropicsand midlatitudes as well as in both the lower and upper troposphere considering this fact a new easm index newi is proposed based on 200 hpa zonal wind which takes into account wind anomalies in the southern about 58n middle about 208n and northern areas about 358n of east asia the newi can capture the interannual easm related climate anomalies and the interdecadal variability well compared to previous indices thenewishowsabetterperformanceindescribingprecipitationandairtemperaturevariationsovereastasia it can also show distinct climate anomalous features in early and late summer the newi is tightly associated with the east asian pacific or the pacific japan teleconnection suggesting a possible role of internal dynamics in the easm variability meanwhile the newi is significantly linked to el nino southern oscillation and tropical indian ocean sea surface temperature anomalies furthermore the newi is highly predictable in the ensembles models indicating its advantage for operational prediction of the easm the physical mechanism of the easm variability as represented by the newi is also explicit both warm advection anomalies of temperaturebyanomalouswesterlywindsandtheadvectionofanomalouspositiverelativevorticitybynortherly basic winds cause anomalous ascending motion over the mei yu changma baiu rainfall area and vice versa over the south china sea area hence this newi would be a good choice to study monitor and predict the easm

enso asymmetry in cmip5 models abstractthe el nino la nina asymmetry is evaluated in 14 coupled models from phase 5 of the coupled model intercomparison project cmip5 the results show that an underestimate of enso asymmetry a common problem noted in cmip3 models remains a common problem in cmip5 coupled models the weaker enso asymmetry in the models primarily results from a weaker sst warm anomaly over the eastern pacific and a westward shift of the center of the anomaly in contrast sst anomalies for the la nina phase are close to observations corresponding atmospheric model intercomparison project amip runs are analyzed to understand the causes of the underestimate of enso asymmetry in coupled models the analysis reveals that during the warm phase precipitation anomalies are weaker over the eastern pacific and westerly wind anomalies are confined more to the west in most models the time mean zonal winds are stronger over the equatorial central and eastern pacific for most models wind forced ocean gcm experiments suggest

why were some la ninas followed by another la nina this paper investigates why some la nina events are followed by another la nina and some others are not we propose two preconditions that result in continuation of a la nina the first one is that la nina must be a strong event a major la nina this ensures that the reflected rossby wave signal at the eastern boundary of the pacific has a strong westward propagating cold ocean temperature anomaly over the off equatorial region the off equator cold anomaly may not be conducive to the equatorial recharge process and as a result may favor the persistence of cold ocean subsurface temperature anomaly and prevent the transition from la nina to el nino the second precondition is whether there are eastward propagating downwelling kelvin waves during the decay phase of a major la nina eastward propagating downwelling kelvin waves could lead to demise for a tendency for a follow up la nina the equatorial kelvin wave activities are associated with fluctuations of surface wind in the equatorial far western pacific the analysis suggests that both the surface wind in the equatorial far western pacific and the recharge discharge of the equatorial pacific are indicators for occurrence or no occurrence of a follow up la nina event

how to measure the strength of the east asian summer monsoon defining the intensity of the east asian summer monsoon easm has been extremely controversial this paper elaborates on the meanings of 25 existing easm indices in terms of two observed major modes of interannual variation in the precipitation and circulation anomalies for the 1979 2006 period the existing indices can be classified into five categories the east west thermal contrast north south thermal contrast shear vorticity of zonal winds southwesterly monsoon and south china sea monsoon the last four types of indices reflect various aspects of the leading mode of interannual variability of the easm rainfall and circulations which correspond to the decaying el nino while the first category reflects the second mode that corresponds to the developing el nino the authors recommend that the easm strength can be represented by the principal component of the leading mode of the interannual variability which provides a unified index for the majority of the existing indices this new index is extremely robust captures a large portion 50 of the total variance of the precipitation and three dimensional circulation and has unique advantages over all the existing indices the authors also recommend a simple index the reversed wang and fan index which is nearly identical to the leading principal component of the easm and greatly facilitates real time monitoring the proposed index highlights the significance of the mei yu baiu changma rainfall in gauging the strength of the easm the mei yu which is produced in the primary rain bearing system the east asian ea subtropical front better represents the variability of the easm circulation system this new index reverses the traditional chinese meaning of a strong easm which corresponds to a deficient mei yu that is associated with an abnormal northward extension of southerly over northern china the new definition is consistent with the meaning used in other monsoon regions worldwide where abundant rainfall within the major local rain bearing monsoon system is considered to be a strong monsoon

reactions of bowhead whales balaena mysticetus to seismic exploration in the canadian beaufort sea the behavioral reactions of bowhead whales to distant seismic vessels not under our control a controlled approach by a seismic vessel and controlled tests with a single airgun were observed on 21 occasions in the summers of 1980 84 general activities of bowheads exposed to pulses of underwater noise 107 158 db re 1 mu pa from seismic vessels 6 99 km away were observed activities were indistinguishable from those without seismic noise there was no detectable avoidance hints of subtle changes in surfacing respiration and diving behavior were unconfirmed but were consistent with reactions to stronger noise pulses from closer seismic boats in a test with a full scale seismic boat 30 airguns totaling 471 source level 248 db re 1 mu pa closest point of approach 1 1 2 km bowheads began to orient away when the airgun array began to fire 7 1 2 km away however some whales continued apparent near bottom feeding until the vessel was 3 km away whales were displaced by about 2 km reactions were not much stronger than those to any conventional vessel tests with one 0 66 1 airgun showed that some bowheads move away from sources of strong seismic impulses even in the absence of boat noise and that bowheads can detect the direction from which seismic impulses arrive in general bowheads exhibit avoidance reactions when they receive seismic pulses stronger than about 160 db re 1 mu pa evidence of reactions to lower received levels remains inconclusive

spring persistence transition and resurgence of el nino we present a systematic exploration of differences in the spatiotemporal sea surface temperature sst evolution along the equatorial pacific among observed el nino events this inter el nino variability is captured by two leading orthogonal modes which explain more than 60 of the interevent variance the first mode illustrates the extent to which warm sst anomalies sstas in the eastern tropical pacific ep persist into the boreal spring after the peak of el nino our analysis suggests that a strong el nino event tends to persist into the boreal spring in the ep whereas a weak el nino favors a rapid development of cold sstas in the ep shortly after its peak the second mode captures the transition and resurgence of el nino in the following year an early onset el nino tends to favor a transition to la nina whereas a late onset el nino tends to persist long enough to produce another el nino event the spatiotemporal evolution of several el nino events during 1949 2013 can be efficiently summarized in terms of these two modes which are not mutually exclusive but exhibit distinctive coupled atmosphere ocean dynamics

el nino impacts on precipitation in the western north pacific east asian sector abstract in this study the western north pacific east asian wnp ea rainfall anomaly induced by the strong el nino in 1982 83 1991 92 and 1997 98 and its association with the mean state are examined over the northern part of the wnp ea region north of 20 n which is dominated by southwest northeast tilting frontal systems positive rainfall anomalies from the fall before the el nino peak phase year 0 to the first wet period after the peak phase year 1 are affected by low and midlevel horizontal moisture convergence anomalies induced by low level anticyclonic circulation anomalies over the wnp region that are associated with el nino over the southern part of the wnp ea region south of 20 n which is dominated by tropical convection positive precipitation anomalies in the first and second wet periods of year 0 and negative precipitation anomalies from the fall of year 0 to the second wet period of year 1 are associated with the variation of the net energy into the atmosphere which is main

asymmetry in summertime atmospheric circulation anomalies over the northwest pacific during decaying phase of el nino and la nina the present study has revealed the asymmetric characteristics of summertime atmospheric circulation anomalies over the indo pacific for el nino and la nina as well as the possible mechanism during the summer when el nino has dissipated there are basin wide warming over the tropical indian ocean tio and cooling over the equatorial central and eastern pacific cep the northwest pacific nwp anticyclone is maintained by a combined effect of the tio warming and equatorial cep cooling the impact of tio warming is via the kelvin wave induced divergence mechanism and the effect of cep cooling is by stimulating a rossby wave response to its northwest correspondingly there are lower upper level convergence divergence over the tio and divergence convergence over the nwp the tropical atmospheric waves and large scale circulation anomalies could couple together and maintain the anticyclone however for la nina there are easterly wind anomalies over the equatorial western pacific and the anomalous nwp cyclone nwpc is weak and shifts northwestward which are largely different from el nino the equatorial cep cooling plays a dominant role in the maintenance of nwpc the negative rainfall anomalies induced by cep cooling force the anticyclonic wind anomalies over the wp as a rossby wave response which further cause the lower upper level convergence divergence over the mc and nwp the resultant convergence leads to the enhanced convection there inducing the nwpc as a rossby wave response besides the equatorial easterly wind anomalies trigger the upwelling oceanic kelvin wave and maintain the cep cooling as the bjerknes feedback

origins of biases in cmip5 models simulating northwest pacific summertime atmospheric circulation anomalies during the decaying phase of enso abstractpresent study documents the biases of summertime northwest pacific nwp atmospheric circulation anomalies during the decaying phase of enso and investigates their plausible reasons in 32 coupled model intercomparison project phase 5 models based on an inter model empirical orthogonal function eof analysis of el nino southern oscillation enso related 850hpa wind anomalies the dominant modes of biases are extracted the first eof mode explaining 21 3 of total inter model variance is characterized by a cyclone over the nwp indicating a weaker nwp anticyclone the cyclone appears to be a rossby wave response to unrealistic equatorial western pacific wp sea surface temperature sst anomalies related to excessive equatorial pacific cold tongue in the models on one hand the cold sst biases increase the mean zonal sst gradient which further intensifies warm zonal advection favoring the development and persistence of equatorial wp sst anomalies on the other hand they reduce the anomalou

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

the multidecadal variations of the interannual relationship between the east asian summer monsoon and enso in a coupled model this study investigates the multidecadal variations of the interannual relationship between the east asian summer monsoon easm and el nino southern oscillation enso in 1000 year simulation of a coupled climate model the interannual relationship between enso and easm has experienced pronounced changes throughout the 1000 year simulation during the periods with significant enso easm relationship the enso related circulation anomalies show a pacific japan pj like pattern with significant wave activity flux propagating from the tropics to the north in lower troposphere and from the mid latitudes to the south in upper troposphere the resultant enso related precipitation anomalies are more less than normal over the east asia western north pacific in the decaying summers of el nino events in contrast the circulation and precipitation anomalies are weak over east asia western north pacific during the periods with weak enso easm relationship based on the energy conversion analysis the related anomalies achieve barotropic and baroclinic energy from the mean flow during the periods with strong enso easm relationship on the contrary during the low correlation periods the energy conversion is too weak to form the link between the tropics and mid latitudes the main reason for the multidecadal variations of enso easm relationship is the amplitude discrepancy of sst anomalies over the indo western pacific ocean which in turn leads to the intensity difference of the western north pacific anomalous anticyclone wpac and related climate anomalies

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