westward propagation of latitudinal asymmetry in a coupled ocean atmosphere model abstract hemispheric asymmetries of continental geometry have long been speculated to be the cause of the northern hemisphere position of the intertropical convergence zone over the central and eastern pacific it is unknown however how the effects of continental asymmetries are transmitted to and felt by the central pacific thousands of kilometers away this paper proposes a transmitter mechanism by investigating the response of a coupled ocean atmospheric model to a symmetry breaking force by the american continents the model treats land forcing implicitly as an eastern boundary condition in the absence of oceanic feedback the model response to the eastern boundary forcing is tightly trapped and confined to a small longitudinal extent off the coast whereas the climate over the interior ocean is symmetric about the equator ocean atmosphere coupling greatly enhances the transmissibility of the effects of the land forcing establishing large latitudinal asymmetry over a great zonal extent a westwar

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

optimal channel networks a framework for the study of river basin morphology optimal channel networks ocns are dendritic structures obtained by minimizing the local and global rates of energy dissipation in a continuously fed in space and time plane aggregation system reminiscent and based on the properties of the planform of three dimensional natural drainage networks geomorphological and fractal properties of ocns are known from earlier studies by the authors this paper explores further the structures derived by optimization of energy dissipation rates optimality of subnetworks and of basin shapes is investigated as a by product of competition for drainage a new perspective on the possible prediction of the width function of a basin network and hence of its hydrologic response is obtained by exploiting ocn techniques requiring only the definition of the outer boundaries of the basin the interplay between hillslope processes and the development of drainage networks is addressed aiming at the relative role and the mutual interrelations of geology and optimal organization in the structure of mature river basins also addressed is the issue of multiscaling and multifractality in the spatial organization of the network it is concluded that ocn approaches provide a comprehensive framework for the study of the morphology of geophysical structures

modulation of equatorial turbulence by a tropical instability wave 1 strong modulation of turbulent mixing by a westward propagating tropical instability wave tiw was observed in the stratified shear layer between the equatorial undercurrent euc and the surface mixed layer during october and november 2008 at 0 n 140 w the unique deep diurnal cycle mixing in the stratified layer beneath the equatorial cold tongue was observed where nighttime turbulent mixing was a factor of 10 greater than during daytime the turbulent kinetic energy dissipation rate e was 10 6 w kg 1 and the turbulent heat flux was 500 w m 2 at least 5 10 times greater than observed previously in the central equatorial pacific turbulence mixing varied significantly during the four distinct phases of the meridional flow associated with the tiw observations during the northward to southward transition recorded the largest values of reduced shear squared the thickest nighttime surface mixed layer the deepest penetration of the deep cycle turbulence and the largest turbulent heat flux and largest integrated e in the deep cycle layer dcl during steady southward flow the depth of the bases of the nighttime surface mixed layer and of the dcl were the shallowest a 50 m thick layer of strong turbulence was observed immediately above the euc core during the northward to southward and steady southward phases here the average e exceeded 10 6 w kg 1 the eddy diffusivity exceeded 10 3 m2 s 1 and the turbulent heat flux was 500 w m 2 to parameterize mixing in the central equatorial pacific accurately numerical models must simulate the enhancement of mixing associated with tiws and also the variability of mixing in different tiw phases

attribution and impacts of upper ocean biases in ccsm3 the largest and potentially most important ocean near surface biases are examined in the community climate system model coupled simulation of present day conditions they are attributed to problems in the component models of the ocean or atmosphere or both tropical biases in sea surface salinity sss are associated with precipitation errors with the most striking being a band of excess rainfall across the south pacific at about 8 s cooler than observed equatorial pacific sea surface temperature sst is necessary to control a potentially catastrophic positive feedback involving precipitation along the equator the strength of the wind driven gyres and interbasin exchange is in reasonable agreement with observations despite the generally too strong near surface winds however the winds drive far too much transport through drake passage 190 sv 1 sv 10 6 m 3 s 1 but with little effect on sst and sss problems with the width separation and location of western boundary currents and their extensions create large correlated sst and sss biases in midlatitudes ocean model deficiencies are suspected because similar signals are seen in uncoupled ocean solutions but there is no evidence of serious remote impacts the seasonal cycles of sst and winds in the equatorial pacific are not well represented and numerical experiments suggest that these problems are initiated by the coupling of either or both wind components the largest mean sst biases develop along the eastern boundaries of subtropical gyres and the overall coupled model response is found to be linear in the south atlantic surface currents advect these biases across much of the tropical basin significant precipitation responses are found both in the northwest indian ocean and locally where the net result is the loss of an identifiable atlantic intertropical convergence zone which can be regained by controlling the coastal temperatures and salinities biases off south america and baja california are shown to significantly degrade precipitation across the pacific subsurface ocean properties on both sides of the equator and the seasonal cycle of equatorial sst in the eastern pacific these signals extend beyond the reach of surface currents so connections via the atmosphere and subsurface ocean are implicated other experimental results indicate that the local atmospheric forcing is only part of the problem along eastern boundaries with the representation of ocean upwelling another likely contributor

the topography of optimal drainage basins a model for drainage networks and their associated landscapes has been developed this model is based on the minimum energy dissipation principle and an empirical relationship s q between the slope s of each link in a channel network and the mean annual discharge q that flows through it the model was studied using six different values for the exponent the surfaces of these minimum energy dissipation drainage networks appear to be more complex than simple self affine fractals the drainage basins in these optimal drainage networks have power law size area distributions with a universal exponent which is independent of the value of for the minimum energy dissipation drainage networks obtained using a particular value for the basin shapes are similar to each other an empirical relationship has also been found to relate the basins length width ratio to the value of

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

persistent nature of secondary diurnal modes of precipitation over oceanic and continental regimes abstract this investigation seeks a better understanding of the assorted mechanisms controlling the global distribution of diurnal precipitation variability based on the use of the tropical rainfall measuring mission trmm microwave radiometer and radar data the horizontal distributions of precipitation s diurnal cycle are derived from 8 yr of trmm microwave imager tmi and precipitation radar pr measurements involving three trmm standard rain retrieval algorithms the resultant distributions are analyzed at various spatiotemporal scales the results reveal both the prominent and expected late evening le to early morning em precipitation maxima over oceans and the counterpart prominent and expected mid to late afternoon mla maxima over continents moreover and not generally recognized the results reveal a widespread distribution of secondary maxima which generally mirror their counterpart regime s behavior occurring over both oceans and continents that is many ocean regions exhibit clear

the tropical precipitation response to andes topography and ocean heat fluxes in an aquaplanet model this aquaplanet modeling study using the geophysical fluid dynamics laboratory atmospheric model version 2 1 gfdl am2 1 examines how ocean energy transport and topography influence the location of tropical precipitation addingrealistic andes topographyregionally displaces tropical rainfallfromthe equator into the northern hemisphere even when the wind evaporation feedback is disabled the relative importance of the andes compared to the asymmetric hemispheric heating of the atmosphere by ocean transport is examined by including idealized and realistic zonally averaged surface heat fluxes also known as q fluxes in the slab ocean a hemispherically asymmetric q flux displaces the tropical rainfall toward the hemisphere receiving the greatest heating by the ocean the zonal mean displacement of rainfall is greater in simulations with a realistic q flux than with a realistic andes topography simulations that add both a q flux and topography displace rainfallfarthertothenorthintheregion1208tothewestoftheandesthaninsimulationsthatonlyhaveaqflux cloud and clear sky radiative feedbacks in the tropics and subtropics of this model both act to amplify the energy flux and the precipitation response to a given hemispheric asymmetry in oceanic forcing

processes in the pacific la nina onset triggered by the atlantic nino previous observational and model studies have shown that a warm cold event in the equatorial atlantic during the boreal summer are related to the development of a pacific la nina el nino event that is fully developed in the following winter although the connection takes place via atmospheric bridge the processes at work have not been clarified for such a remote and lagged relationship the present paper uses a partially coupled atmosphere ocean model to infer a mechanism by which a pacific el nino event can be developed in this way enhanced equatorial convection in the equatorial atlantic during a warm event results in enhanced subsidence and surface wind divergence over the equatorial pacific around the dateline this wind anomaly contributes to pile up water in the western equatorial pacific triggering a perturbation in the depth of the oceanic thermocline which propagates eastward as an equatorial kelvin wave from autumn to winter the thermocline shallowing as the wave propagates allows for cooling of the oceanic mixed layer through anomalous temperature advection by anomalous zonal currents and by mean vertical entrainment velocity zonal advective and thermocline feedbacks reinforce the surface winds anomalies over the central eastern equatorial pacific setting up the conditions for the development of a cold event in this ocean the sequence during an atlantic cold event is similar with the appropriate change in signs these findings are relevant to enso predictability at seasonal timescales

a new method for determining magnetization direction from gravity and magnetic anomalies application to the deep structure of the worcester graben the aeromagnetic field over the worcester graben a major n s oriented fault bounded sedimentary basin shows a large positive anomaly of 100 nt amplitude near the town of tetbury a new method for the determination of the magnetization direction of the causative body was employed that searches for the maximum correlation between the observed gravity anomaly and the pseudo gravity anomaly computed for a range of orientations of the magnetization vector the method suggests a vertical magnetization for the causative body of the tetbury anomaly a three dimensional magnetic model of the body has the form of a cone elongated n s whose base is at 6 0 km and upper surface at 3 1 km as indicated by power spectrum analysis of the anomaly a two dimensional model derived from the gravity field and constrained by the surface geology borehole data and existing density measurements cannot simulate the observed anomaly over the centre of the graben however when the magnetic body is included in the gravity model the fit is much improved the western side of the body is probably imaged on a seismic reflection profile to the north the body magnetic model of the body has the form of a cone elongated n s whose base is at 6 0 km and upper surface at 3 1 km as indicated by power spectrum analysis of the anomaly a two dimensional

manifestation of remote response over the equatorial pacific in a climate model 1 in this paper we examine the simulations over the tropical pacific ocean from long term simulations of two different versions of the center for ocean land atmosphere studies cola coupled climate model that have a different global distribution of the inversion clouds we find that subtle changes made to the numerics of an empirical parameterization of the inversion clouds can result in a significant change in the coupled climate of the equatorial pacific ocean in one coupled simulation of this study we enforce a simple linear spatial filtering of the diagnostic inversion clouds to ameliorate its spatial incoherency as a result of the gibbs effect while in the other we conduct no such filtering it is found from the comparison of these two simulations that changing the distribution of the shallow inversion clouds prevalent in the subsidence region of the subtropical high over the eastern oceans in this manner has a direct bearing on the surface wind stress through surface pressure modifications the sst in the warm pool region responds to this modulation of the wind stress thus affecting the convective activity over the warm pool region and also the large scale walker and hadley circulation the interannual variability of sst in the eastern equatorial pacific ocean is also modulated by this change to the inversion clouds consequently this sensitivity has a bearing on the midlatitude height response the same set of two experiments were conducted with the respective versions of the atmosphere general circulation model uncoupled to the ocean general circulation model but forced with observed sst to demonstrate that this sensitivity of the mean climate of the equatorial pacific ocean is unique to the coupled climate model where atmosphere ocean and land interact therefore a strong case is made for adopting coupled ocean land atmosphere framework to develop climate models as against the usual practice of developing component models independent of each other

interpretation of the gravity and magnetic anomalies of the cappadocia region central turkey the cappadocia region located in central turkey is characterized by widespread lava flows and volcanoclastic deposits dating from miocene to quaternary gravity and aeromagnetic anomalies of the region appear to present similar high and low amplitude regions although the aeromagnetic anomalies exhibit a rather complex pattern which is thought to be caused by remanent magnetization the low pass filtered aeromagnetic map shows a deep seated magnetic anomaly which may be linked to the widespread volcanic activity at the surface the pseudogravity transformation of the upward continued anomaly has been constructed the pseudogravity anomaly demonstrates some form of clockwise rotation this anomaly was modelled by means of a three dimensional method the top and bottom of the body are at 6 3km and 11km including the flight height from the ground surface respectively this deep body is ellipsoidal and extends along an e w direction which is in line with the regional stress direction deduced from gps measurements a new mobilistic dynamo tectonic system appears to explain the body s e w elongation the modelled body may be the source for the inferred geothermal energy of the region magnetic measurements were carried out on oriented rock samples collected from outcrops of ignimbrites and basalts providing directions and intensities of remanent magnetization susceptibilities and koeningsberger q ratios standard deviations of remanent directions of the natural remanent magnetization nrm display a wide scatter implying unreliability of the surface data reduction to pole rtp transformation of magnetic anomalies was successful with the induced magnetization angle despite the complex pattern of magnetic anomalies

investigation of the deep structure of the sivas basin innereast anatolia turkey with geophysical methods abstract sivas basin is the easternmost and third largest basin of the central anatolian basins in this study gravity aeromagnetic and seismic data are used to investigate the deep structure of the sivas basin together with the well seismic velocity data geological observations from the surface and the borehole data of the celalli 1 well basement depth is modeled three dimensionally 3d using the gravity anomalies and 2d gravity and magnetic models were constructed along with a n s trending profile densities of the rock samples were obtained from the distinct parts of the basin surface and in situ susceptibilities were also measured and evaluated in comparison with the other geophysical and geological data additionally seismic sections in spite of their low resolution were used to define the velocity variation in the basin in order to compare depth values and geological cross section obtained from the modeling studies deepest parts of the basin 12 13 km determined from the 3d model are located below the settlement of hafik and to the south of zara towns geometry extension and wideness of the basin together with the thickness and lithologies of the sedimentary units are reasonably appropriate for further hydrocarbon exploration in the sivas basin that is still an unexplored area with the limited number of seismic lines and only one borehole

influences of continental monsoons and air sea coupling on the climate of the equatorial pacific abstract an air sea land coupled model of intermediate complexity was used to reveal the important roles of air sea coupling and adjacent continental monsoons i e american monsoons and asian australian monsoons on the annual cycle and mean state of the equatorial pacific excluding the effects of adjacent continental monsoons the simulated mean sst in the western pacific displays a warm bias the sst seasonal cycle exhibits an erroneous dominant annual component in the western pacific and insufficient strength and a 2 month phase delay in the equatorial eastern pacific the air sea coupling alone cannot sustain the full strength of the annual marches of the itcz cold tongue complex this is because the diabatic heating associated with the itcz rainfall generates both a southerly and a westerly component to its equatorward side while the southerly cools the cold tongue establishing a positive feedback to enhance the itcz and the equatorial westerly favors cold tongue warming inducing a negative fe

observations of annual and el nino thermal and flow variations at 0 110 w and 0 95 w during 1980 1985 moored measurements of the surface wind and of the current and temperature fields within the uppermost 250 m were recorded from march 1980 to september 1985 at 0 110 w and from july 1981 to november 1983 at 0 95 w at these sites the annual mean thicknesses of the equatorial undercurrent euc and of the surface portion of the south equatorial current sec were about 200 m and 20 m respectively the annual mean euc core speed was 0 9 m s 1 annual cycles of temperature and zonal current at 110 w were most distinctive near the surface at nominal depths of 15 m and 47 5 m the average annual amplitudes were 1 5 c and 0 5 m s 1 at about 100 m the annual amplitudes were about 0 5 c and 0 10 m s 1 at 15 m the annual mean zonal current was 0 05 m s 1 which was not representative of the monthly mean zonal current in april the monthly mean direction was eastward and in october it was westward with speeds of about 0 5 m s 1 in both months warmer water occurred in april and colder water in october the direction of the zonal wind component was westward throughout the year and the annual amplitude of the zonal wind was only about 2 5 times larger than that of the zonal current the average amplitude of the annual cycle of the meridional current component was less than 0 05 m s 1 and not distinguishable from year to year monthly mean variations monthly mean anomalous or el nino currents at 110 w were defined as the difference between the observations and the annual cycle during the august december 1982 onset phase of el nino the strength of the normally westward flowing near surface sec was greatly reduced to near zero speed by an el nino eastward flowing zonal current of about 0 3 m s 1 the largest vertically averaged 15 250 m zonal current anomaly 0 5 m s 1 occurred in january and february 1983 and represented a substantial decrease in the eastward transport of the euc causing a disappearance of the undercurrent the duration of the euc disappearance was longer at 95 w than at 110 w a surface intensified eastward jet with a maximum daily speed of 1 75 m s 1 at 15 m occurred in may 1983 at 110 w but not at 95 w a massive redistribution of heat throughout the mixed layer and thermocline was associated with the 1982 1983 el nino beginning in august 1982 the thermocline at 110 w and 95 w sank 100 m reaching its maximum depth in december 1982 temperatures at 100 m and 150 m which normally were about 15 c and 14 c reached 27 5 c and 22 5 c the time rate of change of the 15 to 200 m heat content was 500 w m 2 during the august december 1982 warming phase and 460 w m 2 during the january february 1983 subsurface cooling phase the euc disappeared during the subsurface cooling phase a second less intensive mixed layer deepening occurred in may 1983 at 95 w but not at 110 w

meridional structure of the seasonally varying mixed layer temperature balance in the eastern tropical pacific abstract the eastern tropical pacific ocean is important climatically because of its influence on the el nino southern oscillation enso cycle and the american monsoon accurate prediction of these phenomena requires a better understanding of the background climatological conditions on which seasonal to interannual time scale anomalies develop in the region this study addresses the processes responsible for the seasonal cycle of sea surface temperature sst in the eastern tropical pacific using 3 yr april 2000 march 2003 of moored buoy and satellite data between 8 s and 12 n along 95 w results indicate that at all latitudes surface heat fluxes are important in the mixed layer temperature balance at 8 s in a region of relatively deep mean thermocline and mixed layer local storage of heat crossing the air sea interface accounts for much of the seasonal cycle in sst in the equatorial cold tongue and the intertropical convergence zone where mean upwelling leads to relatively thin mixed layers ver

daily states of the march april east pacific itcz in three decades of high resolution satellite data abstractzonally elongated areas of cloudiness that make up the east pacific intertropical convergence zone itcz can take on several configurations in instantaneous observations a novel statistical model is used to automatically assess the daily state of the east pacific itcz using infrared satellite images from 1980 to 2012 four itcz states are defined based on itcz location relative to the equator north nitcz and south sitcz of the equator simultaneously north and south of the equator ditcz for double itcz and over the equator eitcz a fifth itcz state is used to classify days when no zonally elongated area of cloudiness is present aitcz for absent itcz the itcz states can occur throughout the year except for the eitcz which is not present during june october with the nitcz state dominating in terms of frequency of occurrence interannual variability of the state distribution is large the most striking variability in itcz states is observed in spring during march april the ditcz

equatorial atlantic variability and its relation to mean state biases in cmip5 coupled general circulation model gcm simulations participating in the coupled model intercomparison project phase 5 cmip5 are analyzed with respect to their performance in the equatorial atlantic in terms of the mean state 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial sst gradient whose sign is opposite to observations westerly surface wind biases in boreal spring play an important role in the reversed sst gradient by deepening the thermocline in the eastern equatorial atlantic and thus reducing upwelling efficiency and sst cooling in the following months both magnitude and seasonal evolution of the biases are very similar to what was found previously for cmip3 models indicating that improvements have only been modest the weaker than observed equatorial easterlies are also simulated by atmospheric gcms forced with observed sst they are related to both continental convection and the latitudinal position of the intertropical convergence zone itcz particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability the dependence of equatorial easterlies on itcz latitude shows a marked asymmetry from the equator to 15 n the equatorial easterlies intensify approximately linearly with itcz latitude when the itcz is south of the equator on the other hand the equatorial easterlies are uniformly weak despite serious mean state biases several models are able to capture some aspects of the equatorial mode of interannual sst variability including amplitude pattern phase locking to boreal summer and duration of events the latitudinal position of the boreal spring itcz through its influence on equatorial surface winds appears to play an important role in initiating warm events

estimating the magnetization direction of crustal structures by means of an equivalent source algorithm abstract the estimation of the direction of the total magnetization vector of a magnetic source is the first step of a reliable modelling of a magnetic anomaly when remanent magnetization is not negligible we present a new method to obtain the magnetization direction of a crustal body based on an iterative equivalent layer inversion of a magnetic anomaly the main advantage of the proposed approach is that no a priori information about the source is needed the method is suitable for the interpretation of isolated magnetic sources for which magnetization is expected to be uniform in direction but not necessarily in intensity we have verified the success of the technique with synthetic data and with the magnetic anomaly of el hierro volcanic island

formation and variability of a northerly itcz in a hybrid coupled agcm continental forcing and oceanic atmospheric feedback abstract despite the equatorial symmetry of the annual mean insolation the intertropical convergence zone itcz and the collocated band of high sea surface temperature sst assume perennial northern latitudes over the eastern pacific and atlantic an atmospheric general circulation model is coupled with an intermediate ocean model to study continental forcing and oceanic atmospheric interaction that act to break the equatorial symmetry the model reaches a statistically symmetric mean state under perfectly symmetric conditions with the continental coasts running along meridians when a bulge of landmass is added to the eastern continent north of the equator it initiates a coupled ocean atmosphere wave front that propagates westward across the ocean basin cooling the ocean surface and suppressing deep convection on and south of the equator as a result the itcz shifts into the northern hemisphere in contrast to this basinwide response little latitudinal asymmetry develops in the coupled model when

interhemispheric influence of the atlantic warm pool on the southeastern pacific abstract the atlantic warm pool awp is a large body of warm water comprising the gulf of mexico caribbean sea and western tropical north atlantic the awp can vary on seasonal interannual and multidecadal time scales the maximum awp size is in the boreal late summer and early fall with the largest extent in the year being about 3 times the smallest one the awp alternates with the amazon basin in south america as the seasonal heating source for circulations of the hadley and walker type in the western hemisphere during the boreal summer fall a strong hadley type circulation is established with ascending motion over the awp and subsidence over the southeastern tropical pacific this is accompanied by equatorward flow in the lower troposphere over the southeastern tropical pacific as dynamically required by the sverdrup vorticity balance it is shown by analyses of observational data and ncar community atmospheric model simulations that an anomalously large small awp during the boreal summer f

the south atlantic anticyclone as a key player for the representation of the tropical atlantic climate in coupled climate models the key role of the south atlantic anticyclone saa on the seasonal cycle of the tropical atlantic is investigated with a regionally coupled atmosphere ocean model for two different coupled domains both domains include the equatorial atlantic and a large portion of the northern tropical atlantic but one extends southward and the other northwestward the saa is simulated as internal model variability in the former and is prescribed as external forcing in the latter in the first case the model shows significant warm biases in sea surface temperature sst in the angola benguela front zone if the saa is externally prescribed these biases are substantially reduced the biases are both of oceanic and atmospheric origin and are influenced by ocean atmosphere interactions in coupled runs the strong sst austral summer biases are associated with a weaker saa which weakens the winds over the southeastern tropical atlantic deepens the thermocline and prevents the local coastal upwelling of colder water the biases in the basins interior in this season could be related to the advection and eddy transport of the coastal warm anomalies in winter the deeper thermocline and atmospheric fluxes are probably the main biases sources biases in incoming solar radiation and thus cloudiness seem to be a secondary effect only observed in austral winter we conclude that the external prescription of the saa south of 20 s improves the simulation of the seasonal cycle over the tropical atlantic revealing the fundamental role of this anticyclone in shaping the climate over this region

reduction of the thermocline feedback associated with mean sst bias in enso simulation associated with the double inter tropical convergence zone problem a dipole sst bias pattern cold in the equatorial central pacific and warm in the southeast tropical pacific remains a common problem inherent in many contemporary coupled models based on a newly developed coupled model we performed a control run and two sensitivity runs one is a coupled run with annual mean sst correction and the other is an ocean forced run by comparison of these three runs we demonstrated that a serious consequence of this sst bias is to severely suppress the thermocline feedback in a realistic simulation of the el nino southern oscillation firstly the excessive cold tongue extension pushes the anomalous convection far westward from the equatorial central pacific prominently diminishing the convection low level wind feedback and thus the air sea coupling strength secondly the equatorial surface wind anomaly exhibits a relatively uniform meridional structure with weak gradient contributing to a weakened wind thermocline feedback thirdly the equatorial cold sst bias induces a weakened upper ocean stratification and thus yields the underestimation of the thermocline subsurface temperature feedback finally the dipole sst bias underestimates the mean upwelling through a undermining equatorial mean easterly wind stress and b enhancing convective mixing and thus reducing the upper ocean stratification which weakens vertical shear of meridional currents and near surface ekman divergence

processes leading to double intertropical convergence zone bias in cesm1 cam5 abstractthe double intertropical convergence zone itcz bias in the eastern pacific in the community earth system model version 1 with community atmosphere model version 5 cesm1 cam5 is diagnosed in cam5 standalone the northern itcz is associated with inertial instability and the southern itcz is thermally forced after air sea coupling the processes on both hemispheres are switched because the spatial pattern of sea surface temperature sst is changed biases occur during boreal spring in both cam5 and the ocean model in cam5 alone weaker than observed equatorial easterly in the tropical eastern south pacific leads to weaker evaporation and an increase in local sst the shallow meridional circulation overly converges in the same region in the cam5 standalone simulation the planetary boundary layer and middle troposphere are too humid and the large scale subsidence is too weak at the middle levels these biases may result from excessive shallow convection behavior in cam5 the extra moisture wou

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

fast sst error growth in the southeast pacific ocean comparison between high and low resolution ccsm4 retrospective forecasts sea surface temperature errors that develop after 1 week are investigated as a function of resolution using retrospective forecasts from the community climate system model one version resolves the ocean and atmosphere to approximately 1 while the second version resolves the ocean to 0 1 and the atmosphere to 0 5 the forecasts are initialized on january 1 from 1982 to 2003 the spatial pattern of the pacific basin sea surface temperatures errors after 1 week is mostly similar at both resolutions with the exception of the coast of south america the coastal ocean surface cools within the higher resolution simulations but warms within the lower resolution simulations the difference in the ocean surface temperature is instead attributed to differing changes in the upwelling coastal upwelling increases within the higher resolution simulation increasing the lower tropospheric stability and encouraging the cloud cover in contrast the upwelling decreases within the lower resolution simulations at 27 s allowing the ocean surface to warm in spite of cooling from the atmosphere in both simulations the northward winds and surface currents weaken because the south pacific sea level pressure high moves westward the increased oceanic upwelling in the high resolution simulation is instead attributed to an increase in the westward zonal currents the high resolution model resolves the narrow humboldt current while the low resolution model does not this study demonstrates that the processes responsible for sst errors in eastern upwelling boundary current regions change when the oceanic grid spacing becomes fine enough to allow resolution of the oceanic boundary currents

impact of mountains on tropical circulation in two earth system models abstracttwo state of the art earth system models esms were used in an idealized experiment to explore the role of mountains in shaping earth s climate system similar to previous studies removing mountains from both esms results in the winds becoming more zonal and weaker indian and asian monsoon circulations however there are also broad changes to the walker circulation and el nino southern oscillation enso without orography convection moves across the entire equatorial indo pacific basin on interannual time scales enso has a stronger amplitude lower frequency and increased regularity a wider equatorial wind zone and changes to equatorial wind stress curl result in a colder cold tongue and a steeper equatorial thermocline across the pacific basin during la nina years anomalies associated with enso warm events are larger without mountains and have greater impact on the mean tropical climate than when mountains are present without mountains the centennial mean pacific walker circulation wea

seismic reflection investigations into the stratigraphy and structural evolution of the worcester basin two seismic reflection lines recently shot in the western part of the worcester basin suggest that its western boundary is defined by major syn depositional normal faults downthrowing to the east and active throughout permo triassic times farther east other faults can be seen within the basin these moved at various times during the permian and triassic and profoundly affected patterns of sedimentation the subsidence history of the basin can be explained by two phases of lithospheric stretching one in the permian and the second in early triassic times giving a cumulative stretching factor of about 1 2 this is consistent with the regional pattern of normal faulting provided that stretching was either one dimensional oblique to the n s and e w directions or two dimensional

a possible basaltic deep source of the south central england magnetic anomaly the group of large positive magnetic anomalies in south central england is shown to originate from two sources at different depths the shallow source originates from silesian basic igneous rocks the anomaly of the deeper source has been isolated by upward continuation and inverted via pseudofield transformation the magnetic model is interpreted as a large body of basaltic rocks intruding the middle crust it is proposed that the body was emplaced by buoyant ascent and may be the cause of the stability of the london platform during mesozoic times it is speculated that the basalt was intruded in a back arc environment during the period preceding the variscan orogeny

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

variations of zonal currents in the central tropical pacific during 1970 to 1987 sea level and dynamic height measurements the annual and interannual variations of the major zonal currents of the central tropical pacific for the period 1970 1987 are described by analyzing two data sets sea level data from a few selected island stations and ship of opportunity expendable bathythermograph xbt observations the annual cycles of geostrophic surface current indices dynamic height or sea level difference between the ridge and the trough defining the current in the north equatorial current nec and north equatorial countercurrent necc are found to be in phase maxima in november to be strong and to explain about 50 of the total variance the annual cycle of volume transport relative to 400 dbar in the necc is also strong but nec volume transport has a weak annual cycle the discrepancy between the nec surface current and the transport is due to the variation of the surface current being larger than that of the deep currents the annual cycle of the transport of the south equatorial current sec is 6 months out of phase with that of the nec and necc phases of the annual cycles of the sea level and dynamic height indices of flow agree well in general but there are significant differences between the annual amplitudes of the two types of measurements these differences arise from a variety of sources dynamic height reference level assumptions longitudinal spacing of sea level gauges meridional resolution of sea level array and different signal to noise ratios for the two sets of indices the necc shows marked flow maxima during the peaks of the strong ninos of 1972 and 1982 which were followed by near disappearance of the current the following year these fluctuations are clearly present in both the surface current indices and the volume transport in 1976 and 1986 1987 moderate ninos the same pattern is not marked the el nino signal in nec transport is weak there was a strong rise of equatorial sea level during the early phases of the 1972 and 1982 ninos followed by a fall the next year this resulted in a decrease of the transport of the sec in the first year followed by an increase to a maximum during the second year the maximum coincides with a minimum in necc transport

mixed layer modeling in the east pacific warm pool during 2002 two vertical mixing models the modified dynamic instability model of price et al pwp and k profile parameterizaton kpp are used to analyze intraseasonal sea surface temperature sst variability in the northeast tropical pacific near the costa rica dome during boreal summer of 2002 anomalies in surface latent heat flux and shortwave radiation are the root cause of the three intraseasonal sst oscillations of order 1 c amplitude that occur during this time although surface stress variations have a significant impact on the third event a slab ocean model that uses observed monthly varying mixed layer depths and accounts for penetrating shortwave radiation appears to well simulate the first two sst oscillations but not the third the third oscillation is associated with small mixed layer depths 5 m forced by and acting with weak surface stresses and a stabilizing heat flux that cause a transient spike in sst of 2 c intraseasonal variations in freshwater flux due to precipitation and diurnal flux variability do not significantly impact these intraseasonal oscillations these results suggest that a slab ocean coupled to an atmospheric general circulation model as used in previous studies of east pacific intraseasonal variability may not be entirely adequate to realistically simulate sst variations further while most of the results from the pwp and kpp models are similar some important differences that emerge are discussed

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

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

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

ocean atmosphere interaction and the tropical climatology part i the dangers of flux correction abstract this sequence of papers examines the role of dynamical feedbacks between the ocean and the atmosphere in determining features of the tropical climatology a stripped down intermediate coupled ocean atmosphere model is used to provide a prototype problem for the pacific basin here the authors contrast the fully coupled case with the case where flux correction is used to construct the climatology in the fully coupled case the climatology is determined largely by feedback mechanisms within the ocean basin winds driven by gradients of sea surface temperature sst within the basin interact with the ocean circulation to maintain sst gradients for all realistic cases these lead to a unique steady solution for the tropical climatology in the flux corrected case the artificially constructed climatology becomes unstable at sufficiently large coupling leading to multiple steady states as found in a number of coupled models using continuation methods we show that there is a topological change i

the dynamics of idealized convection schemes and their effect on the zonally averaged tropical circulation in this paper the effect of a simple convection scheme on the zonally averaged tropical general circulation is examined within an idealized moist gcm to obtain broad classifications of the influence of convection on the tropics this is accomplished with a simplified convection scheme in the style of betts and miller the scheme is utilized in a moist gcm with simplified physical parameterizations gray radiation with zonally symmetric slab mixed layer ocean boundary conditions comparisons are made with simulations without a convection scheme i e with large scale condensation lsc only with the moist convective adjustment mca parameterization and with various formulations and parameter sets with a simplified betts miller sbm scheme with the control run using the sbm scheme the tropics become quieter and less dependent on horizontal resolution as compared with the lsc or mca simulations the hadley circulation mass transport is significantly reduced with the sbm scheme as is the itcz precipitation an important factor determining this behavior is the parameterization of shallow convection without shallow convection the convection scheme is largely ineffective at preventing convection from occurring at the grid scale the sensitivities to convection scheme parameters are also examined the simulations are remarkably insensitive to the convective relaxation time and only mildly sensitive to the relative humidity of the reference profile provided significant large scale condensation is not allowed to occur the changes in the zonally averaged tropical circulation that occur in all the simulations are understood based on the convective criteria of the schemes and the gross moist stability of the atmosphere

the effect of the galapagos islands on the equatorial pacific cold tongue abstract a reduced gravity ocean general circulation model of the tropical pacific ocean is used to determine potential improvements to the simulated equatorial pacific cold tongue region through choices in horizontal resolution and coastline geometry in particular for the galapagos islands four simulations are performed with identical climatological forcing results are compared between model grids with and without the galapagos islands with coarse and fine resolutions it is found that properly including the galapagos islands results in the obstruction of the equatorial undercurrent euc which leads to improvements in the simulated spatial structure of the cold tongue including a basinwide warming of up to 2 c in the east central pacific the obstruction of the euc is directly related to the improvements east of the galapagos islands and for the basinwide reduction of the tropical cold bias through an equatorial dynamical adjustment the pattern of sst warming resulting from the inclusion of the

estimating the magnetization direction of sources from southeast bulgaria through correlation between reduced to the pole and total magnitude anomalies we present a new method to estimate the direction of the magnetization vector of geological bodies based upon the correlation between the reduced to the pole field for tentative values of the magnetization direction and the total magnitude anomaly obtained by a transform of the measured magnetic field the reduced to the pole and the total magnitude anomaly are centred over the sources in the case of 2d anomalies or well centred in the case of compact 3d sources and have similar patterns for the same source the method has several important advantages over similar transform correlation methods for estimation of the magnetization direction it calculates only one transform for many tentative values of the magnetization direction the method does not use derivatives of any order and relies on confident isolation of the target anomalies based on one of the compared transforms the total magnitude anomaly we studied the performance of the method on five 2 5d and compact 3d sources we analysed possible inherent to the method errors as well as errors due to interference from neighbouring sources finally we estimated the magnetization vector direction of the main sources causing the magnetic field in the burgas region and the adjoining southeast bulgarian black sea shelf the sources in the black sea shelf show prevalently reverse magnetization while the sources on land have normal or reverse magnetization

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

crustal growth and late precambrian early palaeozoic plate tectonic evolution of england and wales comparison of the basement rocks of britain reveals major contrasts to the n and s of the iapetus suture solway shannon line north of the suture polymetamorphic high grade basement schists and gneisses and igneous rocks date from about 2900 ma to c 400 ma the latter age corresponding to closure of the iapetus ocean by contrast s of the suture in england and wales the basement is dominantly low grade metamorphic rock together with intrusive and extrusive igneous and sedimentary rocks there is little geological or geochemical evidence for the presence of basement older than c 900 ma below this area and the predominant expression of crustal growth in england and wales is indicated by radiometric ages between c 700 ma and 450 ma reflecting late precambrian palaeozoic magmatism and metamorphism palaeomagnetic data from scotland demonstrate that the crust in northern britain developed as an integral part of the laurentian shield during mid proterozoic times 1600 1000 ma the palaeomagnetic record from the pre ordovician rocks of england and wales shows that this area was unrelated to the laurentian shield prior to closure of the iapetus ocean the apparent polar wander a p w path is that of a distinct microplate involved in rapid growth of iapetus during early cambrian times and emplaced in its present configuration adjacent to northern britain as a result of subduction of the ocean basin between cambrian and silurian times we conclude that whereas the basement to the north of the iapetus suture formed an essentially continental unit from 2900 to 400 ma the basement of england and wales is a result of crustal growth from about 900 ma to 400 ma and formed by accretion of island arcs associated accretionary prisms and fore arc basin sediments within the iapetus ocean

wind stress variations and interannual sea surface temperature anomalies in the eastern equatorial pacific abstract vertical advection of temperature is the primary mechanism by which el nino southern oscillation enso time scale sea surface temperature sst anomalies are generated in the eastern equatorial pacific variations in vertical advection are mediated primarily by remote wind forced thermocline displacements which control the temperature of water upwelled to the surface however during some enso events large wind stress variations occur in the eastern pacific that in principle should affect local upwelling rates the depth of the thermocline and sst in this study the impact of these wind stress variations on the eastern equatorial pacific is addressed using multiple linear regression analysis and a linear equatorial wave model the regression analysis indicates that a zonal wind stress anomaly of 0 01 n m 2 leads to approximately a 1 c sst anomaly over the nino 3 region 5 n 5 s 90 150 w due to changes in local upwelling rates wind stress variations of this magnitude occurred in the easte

the influence of sea surface temperature on surface wind in the eastern equatorial pacific seasonal and interannual variability abstract the climate of the eastern pacific exhibits a pronounced equatorial asymmetry boundary layer air originating in the southern hemisphere trades crosses the equator and flows into the intertropical convergence zone itcz whose southern limit is nearly always located at least 4 to the north of the equator the sea surface temperature sst distribution is characterized by a prominent cold tongue centered 1 s a strong frontal zone centered 2 n and a warm eastward current centered near 5 n the surface wind field exhibits a pronounced horizontal divergence as the air flows northward across the oceanic frontal zone these features vary in strength in response to the annual cycle and the el nino southern oscillation phenomenon the northward cross equatorial surface winds the cold tongue and the frontal zone all tend to be strongest during the cold season july through november during the cold season of the coldest years when the cold tongue is most prominent the cross equatorial flow t

seasonal variability in the equatorial pacific abstract five to nine years of observations from the tropical atmosphere ocean array in the tropical pacific are used to document the seasonal cycle of surface winds zonal currents sst thermocline depth and dynamic height along the equator the normally westward surface zonal current reverses direction in late boreal spring and early summer this seasonal variation in the zonal surface current propagates westward as do seasonal variations in the equatorial undercurrent and zonal surface winds at the equator at 5 n and 5 s the seasonal variations in the 20 c isotherm and dynamic height also propagate westward conversely at the equator in the eastern and central pacific the variations in 20 c isotherm depth and dynamic height propagate eastward these seasonal variations are interpreted by means of a simple dynamical model based on linear equatorial wave theory model results indicate that seasonal variability between 5 n and 5 s is dominated by wind forced equatorial kelvin waves and first meridi

simulation of enso with a global atmospheric gcm coupled to a high resolution tropical pacific ocean gcm abstract a global atmospheric general circulation model gcm coupled to an oceanic gcm that is dynamically active only in the tropical pacific simulates variability over a broad spectrum of frequencies even though the forcing the annual mean incoming solar radiation is steady of special interest is the simulation of a realistically irregular southern oscillation between warm el nino and cold la nina states its time scale is on the order of 5 years the spatial structure is strikingly different in the eastern and western halves of the ocean basin sea surface temperature changes have their largest amplitude in the central and eastern tropical pacific but the low frequency zonal wind fluctuations are displaced westward and are large over the western half of the basin these zonal wind anomalies are essentially confined to the band of latitudes 10 to 10 s so that they form a jet and have considerable latitudinal shear during el nino the associated curl contributes to a pair of pronounced minima in th

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

on the annual cycle of the eastern equatorial pacific abstract although the sun crosses the equator twice a year the eastern equatorial pacific has a pronounced annual cycle in sea surface temperature and in both components of the surface winds for example this is in contrast to the indian ocean and western pacific where a semiannual oscillation of the zonal wind is the dominant signal on the equator calculations with a relatively simple coupled ocean atmosphere model indicate that the principal reason for this phenomenon is the marked asymmetry relative to the equator of the time averaged climatic conditions in the eastern tropical pacific the important asymmetries are in surface winds oceanic currents and sea surface temperature the time averaged winds and currents have northward components at the equator and the warmest waters are north of the equator because of those asymmetries seasonally varying solar radiation that is strictly antisymmetric relative to the equator can force a response that has a symmetric component the amplitude of th

the maintenance of an equatorially asymmetric state in a hybrid coupled gcm abstract an ocean general circulation model is coupled with a simple atmosphere model to investigate the formation mechanism of the intertropical convergence zone in the eastern pacific which is observed in the northern hemisphere the coupled model develops an asymmetric state under conditions symmetric about the equator the zonal variation in equatorial upwelling leads to pronounced differences between the western and other parts of the ocean in the western warm water pool region where the cooling effect of the equatorial upwelling is suppressed both atmospheric and oceanic surface conditions are symmetric about the equator on the other hand in the central region where the upwelling cools the equatorial ocean a single itcz forms off the equator in the northern or southern hemisphere depending on the initial condition a strong contrast exists in the sea surface temperature sst between the hemispheres sst is much higher at the latitude of the itcz than that on the other side of the equator thi

on the genesis of the equatorial annual cycle abstract a linear theory is proposed that can explain both the period and the westward propagation of the equatorial annual cycles in the sst and zonal wind a coupled model linearized about a mean state of the air sea system is used this model allows the surface winds to directly change the sst through surface evaporation and vertical mixing in contrast to the formulation of the conventional air sea coupling models that emphasize the effects of winds on ocean dynamics it is demonstrated that the characteristics of the equatorial seasonal cycle including its period phase and amplitude are determined to a large extent by the mean state of the air sea coupling system the meridional wind which is specified here is the most important forcing for the annual cycle in sst suggesting that the equatorial annual cycle is the response to an annual solar forcing in the off equatorial regions

epic 95 w observations of the eastern pacific atmospheric boundary layer from the cold tongue to the itcz abstract the atmospheric boundary layer abl along 95 w in the eastern equatorial pacific during boreal autumn is described using data from the east pacific investigation of climate epic 2001 with an emphasis on the evolution of the thermodynamic abl properties from the cold tongue to the cold advection region north of the sea surface temperature sst front surface sensible and latent heat fluxes and wind stresses between 1 s and 12 n are calculated from data from eight ncar c 130 research aircraft flights and from tropical atmosphere ocean tao buoys reduced surface wind speed and a 10 m s 1 jet at a height of 500 m are found over the equatorial cold tongue demonstrating the dependence of the surface wind speed on surface stability the abl exhibits a maximum in cloud cover on the north downwind side of the warm sst front at 1 3 n turbulent mixing driven by both surface buoyancy flux and radiative cooling at the cloud tops plays a significant role in maintaining the depth and structure of t

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

observations of 20 day period meridional current oscillations in the upper ocean along the pacific equator abstract prominent oscillations of the meridional current with a mean period of approximately 20 days have been observed in the upper ocean over several years from may 1979 to october 1985 using moored current measurements along the pacific equator at 95 110 124 140 w and 152 w as well as off but near the equator at 110 and 140 w the fluctuations are relatively narrowband 0 005 cpd in frequency a 95 statistically significant peak in power spectra of meridional current occurred at 110 124 and 140 w but not at 95 and 152 w where the spectral peaks were smaller the dominant wave period decreased by about 4 from 110 to 140 w maximum amplitude was measured at 124 w the amplitude above 80 m was maximum at the equator and decreased poleward from the equator at 15 m the annual averaged root mean square amplitude was about 20 5 cm s 1 and individual peak to trough values reached 150 cm s 1 the wave amplitude decreased with depth and the wave was essentially confined to the upper 80 m

the enso asian monsoon interaction in a coupled ocean atmosphere gcm abstract in this study the authors evaluate the el nino southern oscillation enso asian monsoon interaction in a version of the hadley centre coupled ocean atmosphere general circulation model cgcm known as hadcm3 the main focus is on two evolving anomalous anticyclones one located over the south indian ocean sio and the other over the western north pacific wnp these two anomalous anticyclones are closely related to the developing and decaying phases of the enso and play a crucial role in linking the asian monsoon to enso it is found that the hadcm3 can well simulate the main features of the evolution of both anomalous anticyclones and the related sst dipoles in association with the different phases of the enso cycle by using the simulated results the authors examine the relationship between the wnp sio anomalous anticyclones and the enso cycle in particular the biennial component of the relationship it is found that a strong el nino event tends to be followed by a more rapid decay and i

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

monthly period oscillations in the pacific north equatorial countercurrent monthly period oscillations in temperature and velocity in the vicinity of the north equatorial countercurrent along 140 w are examined using moored time series data collected during 1988 1989 these oscillations which presumably derive their energy from instability of the large scale shear of the zonal equatorial current system are found to be energetic across a broad band of periods of about 15 50 days along 7 n wavelike motions at these periods propagate westward with a phase speed of about 30 40 cm s 1 and a zonal wavelength of 750 1150 km the oscillations are approximately in geostrophic balance with the thermal field with the velocity vector rotating anticyclonically around westward propagating high sea level centers zonal volume transport variations associated with these waves between 5 and 9 n at 20 180 m depth have a standard deviation of about 4 1 sv with peak to peak changes in some instances approaching 20 sv maximum temperature variance along 140 w occurs between 5 and 7 n at 100 150 m depth in a region of strong mean vertical and meridional temperature gradient associated with a thermocline sloping upward to the north at the surface maximum temperature variability occurs from 2 to 5 n in the vicinity of the strong sea surface temperature front north of the equator analysis of the upper ocean temperature balance at 7 n 140 w reveals that meridional advection is important both in the surface layer and in the thermocline vertical advection estimated using vertical velocity calculated from a simplified linear vorticity balance is also important in the thermocline where it contributes a variance comparable to that of meridional advection zonal advection is likely to be significant in the upper 80 m below which it is probably of secondary importance compared to meridional and vertical advection one consequence of advection in the temperature balance is that variance is shifted toward lower frequencies in temperature vis a vis velocity spectra this red shift may account for the apparent difference between periods for instability waves inferred from near equatorial meridional velocity spectra and slightly longer periods reported for oscillations of the sea surface temperature front north of the equator based on satellite imagery

coupled atmosphere ocean model simulations of el nino southern oscillation with and without an active indian ocean an atmospheric general circulation model gcm was coupled with an ocean gcm covering the pacific this coupled model pac was integrated over a 30 year period the pac model stimulates well the mean seasonally varying atmospheric and ocean fields and reproduces interannual variations corresponding to enso el nino southern oscillation the same atmospheric gcm was coupled with an ocean gcm covering the indian ocean and the tropical pacific this coupled model ipc was integrated over a 35 year period the model climate in ipc is fairly reasonable and its pacific part is very similar to the pacific climate of the pac model enso is the major interannual variability in the ipc model the dynamics of enso in ipc are essentially the same as that in pac in the pacific the subsurface ocean heat content anomalies are formed by wind anomalies and show westward propagation centered off the equator after they reach the western pacific they show eastward propagation along the equator they produce changes in the thermocline structure in the eastern equatorial pacific resulting in anomalies in ssts the sst anomalies provide wind anomalies the sign of which is opposite to that of the wind anomalies in the first stage so that thismore chain will continue enso in the pac and ipc models can be regarded as the open quotes delayed oscillator close quotes operating in the pacific although the major interannual variability in the indian ocean is linked to enso in the pacific the indian ocean does not play any active role in the enso cycle in the ipc model interannual variability of monsoon activity in the ipc model is more reasonable than that in the pac model however any definite mechanism for the relationship between monsoon activity and enso does not emerge in the present study 31 refs 14 figs less

observations of coupling between surface wind stress and sea surface temperature in the eastern tropical pacific satellite measurements of surface wind stress from the quikscat scatterometer and sea surface temperature sst from the tropical rainfall measuring mission microwave imager are analyzed for the three month period 21 july 20 october 1999 to investigate ocean atmosphere coupling in the eastern tropical pacific oceanic tropical instability waves tiws with periods of 20 40 days and wavelengths of 1000 2000 km perturb the sst fronts that bracket both sides of the equatorial cold tongue which is centered near 1 8s to the east of 1308w these perturbations are characterized by cusp shaped features that propagate systematically westward on both sides of the equator the space time structures of these sst perturbations are reproduced with remarkable detail in the surface wind stress field the wind stress divergence is shown to be linearly related to the downwind component of the sst gradient with a response on the south side of the cold tongue that is about twice that on the north side the wind stress curl is linearly related to the crosswind component of the sst gradient with a response that is approximately half that of the wind stress divergence response to the downwind sst gradient the perturbed sst and wind stress fields propagate synchronously westward with the tiws this close coupling between sst and wind stress supports the wallace et al hypothesis that surface winds vary in response to sst modification of atmospheric boundary layer stability