the tails of the satellite auroral footprints at jupiter the electromagnetic interaction between io europa and ganymede and the rotating plasma that surrounds jupiter has a signature in the aurora of the planet this signature called the satellite footprint takes the form of a series of spots located slightly downstream of the feet of the field lines passing through the moon under consideration in the case of io these spots are also followed by an extended tail in the downstream direction relative to the plasma flow encountering the moon a few examples of a tail for the europa footprint have also been reported in the northern hemisphere here we present a simplified alfvenic model for footprint tails and simulations of vertical brightness profiles for various electron distributions which favor such a model over quasi static models we also report here additional cases of europa footprint tails in both hemispheres even though such detections are rare and difficult furthermore we show that the ganymede footprint can also be followed by a similar tail finally we present a case of a 320 degrees long io footprint tail while other cases in similar configurations do not display such a length

two regimes of the equatorial warm pool part i a simple tropical climate model abstract atmosphere ocean coupled processes responsible for generating and maintaining the equatorial warm pool were investigated using models of different complexities the primary focus was to answer the following question why is the observed warm pool concentrated around the maritime continent in this first of a two part series the solutions of a simple conceptual model that represents the tropical pacific and indian oceans interacting via the walker circulation are examined when the interbasin coupling is sufficiently strong surface wind convergence over the maritime continent associated with easterly trades over the pacific acts to generate the equatorial westerly over the indian ocean leading to a warm pool spontaneously emerging between the two ocean basins the conceptual model shows that tropical climate has two equilibria depending upon the ocean basin widths a single warm pool regime corresponding to the current climate and a split warm pool regime that accompanies warm pools created in

contribution to the circulation climatology of the eastern equatorial pacific lower atmospheric jets novel data sets have been evaluated to reappraise the annual cycle of atmospheric circulation over the pacific in the eastern pacific cross equatorial surface winds from the southern hemisphere generate an oceanic cold tongue immediately to the south of the equator the associated lower tropospheric thickness pattern entails a minimum of absolute topography in the midtroposphere near the equator and together with the small coriolis parameter this causes a jet stream of up to 10 ms 1 at 700 600 mbar centered at 0 2 n the jet is most intense in late boreal winter because then the near equatorial surface low pressure trough is flat the jet is fed by lower tropospheric convergence over equatorial south america and by upper tropospheric convergence and subsidence over a narrow equatorial zone of the eastern pacific over the central pacific a jet of up to 10 ms 1 is found at 10 12 n and 925 850 mbar while friction brakes the flow in the layer of steepest meridional pressure gradient near the surface this lower tropospheric jet as the surface pressure gradient is also strongest in late boreal winter overall the ncep analyses resolve the near surface circulation less well than the long term ship observations however the midtropospheric equatorial jet over the eastern pacific is also borne out by the 1967 1971 radiosoundings over galapagos and the lower tropospheric trade wind jet over the central pacific was also identified from the intense radiosonde program of the march april 1967 line islands experiment

ocean atmosphere interaction in the making of the walker circulation and equatorial cold tongue abstract the climate over the equatorial pacific displays a pronounced asymmetry in the zonal direction that is characterized by the walker circulation in the atmosphere and the cold tongue in the ocean an intermediate coupled ocean atmosphere model is used to investigate the driving force and the ocean atmosphere interaction mechanism for the generation of the zonal asymmetry in the far eastern pacific the upwelling at the equator is weak because zonal winds are blocked by the andes the off equatorial upwelling induced by southerly cross equatorial winds is thus crucial for cooling the eastern pacific a realistic cold tongue appears in the coupled model only when this southerly wind forcing is included the southerly winds cause the sea surface temperature to fall in the east enhancing the zonal heat contrast and hence intensifying easterly winds across the basin these anomalous easterlies induce more equatorial upwelling and raise the thermocline in the east amplifying the initial cooling by th

processes controlling the mean tropical pacific precipitation pattern part ii the spcz and the southeast pacific dry zone the nature of the south pacific convergence zone spcz is addressed by focusing on the dry and cool zone bounded by it and the coast of south america through numerical experiments as shown in a companion paper this dry zone is due to a large extent to orographically forced subsidence here it is shown that the northwestward expansion of this dry zone can be explained by advection of low moist static energy by the trade winds these results provide an explanation of the geometry of the western edge of the dry zone and therefore of the eastern edge of the adjacent spcz sea surface temperature underneath the spcz is enhanced by relatively high near surface humidity through evaporative processes which feeds back into its organization however in this model this feedback is not critical for the existence of the spcz the subsidence associated with the itcz in the north hemisphere negatively affects the precipitation rate in the spcz it was also found that the sensitivity of the forced response is largest for peak orographic heights below 3000 m which indicates that the exact representation of the andes in numerical models might not be as critical as that of lower orography such as that in southern africa

jupiter s main auroral oval observed with hst stis 1 an extended series of fuv images obtained on 7 days during winter 2000 2001 with fixed pointing yielded highly accurate tracking of emisson features as jupiter rotated they provided newly detailed measurements of the degree of corotation of auroral emissions and their variations with changing central meridian longitude this 2 month data set provides a statistical average location of the auroral emission and leads to the definition of new reference ovals the overall auroral morphology pattern is shown to be fixed in system iii longitude and unchanged over a 5 year period when arranged in central meridian longitude ranges the images show a significant contraction of the northern main oval as the central meridian longitude increases from 115 to 255 the main auroral oval brightness is globally very stable in comparison with its terrestrial counterpart it is shown to vary with magnetic local time increasing from noon to dusk and then decreasing again in the magnetic evening hectometric emissions observed simultaneously with galileo and cassini reveal interplanetary shocks propagating outward from the sun which may be related to the contraction of the main auroral oval observed in the hst images taken on 14 december 2000 in addition we find that a brightening and a significant contraction of the main oval observed on 13 january 2001 corresponded to a time of increased solar wind dynamic pressure

the pacific cold tongue and the enso mode a unified theory within the zebiak cane model abstract the equatorial tropical pacific climate system is a delicate coupled system in which winds driven by gradients of sea surface temperature sst within the basin interact with the ocean circulation to maintain sst gradients this results in a time mean state having a strong zonal temperature contrast along the equator with an eastern cold tongue and a western warm pool by the same coupled processes interannual variability known as the el nino southern oscillation enso is present in the pacific this variability can be attributed to an oscillatory coupled mode the enso mode in the equatorial ocean atmosphere system using a zebiak cane type intermediate coupled model the coexistence of an eastern cold tongue in the annual mean state and enso in the pacific climate system is investigated the enso mode arises as a robust oscillatory mode on a coupled mean state and becomes unstable if the cold tongue of the mean state is sufficiently strong the origin of this mode its propagation mechanis

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

io volcanism seen by new horizons a major eruption of the tvashtar volcano jupiter s moon io is known to host active volcanoes in february and march 2007 the new horizons spacecraft obtained a global snapshot of io s volcanism a 350 kilometer high volcanic plume was seen to emanate from the tvashtar volcano 62 n 122 w and its motion was observed the plume s morphology and dynamics support nonballistic models of large io plumes and also suggest that most visible plume particles condensed within the plume rather than being ejected from the source in images taken in jupiter eclipse nonthermal visible wavelength emission was seen from individual volcanoes near io s sub jupiter and anti jupiter points near infrared emission from the brightest volcanoes indicates minimum magma temperatures in the 1150 to 1335 kelvin range consistent with basaltic composition

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

the multiple spots of the ganymede auroral footprint 1 the interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere called the satellite footprints so far footprints have been detected for io europa ganymede and enceladus these footprints are usually seen as single spots however the io footprint the brightest one displays a much more complex morphology made of at least three different spots and an extended tail here we present hubble space telescope fuv images showing evidence for a second spot in the ganymede footprint the spots separation distance changes as ganymede moves latitudinally in the plasma sheet as is seen for the io footprint this indicates that the processes identified at io are universal moreover for similar ganymede system iii longitudes the distance may also vary significantly with time indicating changes in the plasma sheet density we identified a rapid evolution of this distance 8 days after the detection of a volcanic outburst at io suggesting that such auroral observations could be used to estimate the plasma density variations at ganymede

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

the climate response of the indo pacific warm pool to glacial sea level growing climate proxy evidence suggests that changes in sea level are important drivers of tropical climate change on glacial interglacial time scales these paleodata suggest that rainfall patterns over the indo pacific warm pool ipwp are highly sensitive to the landmass configuration of the maritime continent and that lowered sea level contributed to large scale drying during the last glacial maximum lgm ca 21 000 years before present using the community earth system model version 1 2 cesm1 we investigate in detail the mechanisms by which lowered sea level influenced the climate of the ipwp during the lgm the cesm1 simulations show that in agreement with previous hypotheses changes in atmospheric circulation are initiated by the exposure of the sunda and sahul shelves ocean dynamical processes amplify the changes in atmospheric circulation by increasing the east west sea surface temperature sst gradient along the equatorial indian ocean the coupled mechanism driving this response is akin to the bjerknes feedback and results in a large scale climatic reorganization over the indian ocean with impacts extending from east africa to the western tropical pacific exposure of sahul shelf and the associated changes in surface albedo play a key role because it is more effective at exciting the positive feedback than exposure of the sunda shelf this mechanism could explain the pattern of dry wet eastern western indian ocean identified in climate proxies and lgm simulations however this response also requires a strengthened sst gradient along the equatorial indian ocean and it is currently unclear whether this is detectable in marine paleoreconstructions strategies to resolve this issue are discussed

what controls the mean east west sea surface temperature gradient in the equatorial pacific the role of cloud albedo abstractthe mean east west sea surface temperature gradient along the equator is a key feature of tropical climate tightly coupled to the atmospheric walker circulation and the oceanic east west thermocline tilt it effectively defines tropical climate conditions in the pacific its presence permits the el nino southern oscillation phenomenon what determines this temperature gradient within the fully coupled ocean atmosphere system is therefore a central question in climate dynamics critical for understanding past and future climates using a comprehensive coupled model community earth system model cesm the authors demonstrate how the meridional gradient in cloud albedo between the tropics and midlatitudes sets the mean east west sea surface temperature gradient in the equatorial pacific to change in the numerical experiments the authors change the optical properties of clouds by modifying the atmospheric water path but only in the shortwave radiation scheme of the model when is va

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

the influence of ocean surface temperature gradient and continentality on the walker circulation part i prescribed tropical changes abstract a coarse mesh global climate model developed at the goddard institute for space studies giss has been used to assess the influence of ocean surface temperature ost gradient and continentality on the walker circulation the basic model climate was established by a five year integration in which the prescribed seasonal cycle in ost distribution was identical for each year in the model climate the walker circulation is characterized in the zonal plane by three pairs of clockwise and counterclockwise cells to the troposphere three separate winter experiments were performed in which the normal west to east ost gradients in the tropical pacific were replaced by a uniform distribution in the band from 8 n to 16 s each experiment was characterized by osts set at the warmest coldest or mean temperatures in the band the model response features statistically significant changes in the intensity of the various cells and branches with small shifts in the east west extent the overall structure in

a coupled theory of tropical climatology warm pool cold tongue and walker circulation abstract based on results from analytic and general circulation models the authors propose a theory for the coupled warm pool cold tongue and walker circulation system the intensity of the coupled system is determined by the coupling strength the local equilibrium time and latitudinal differential heating most importantly this intensity is strongly regulated in the coupled system with a saturation level that can be reached at a modest coupling strength the saturation west east sea surface temperature difference and the associated walker circulation corresponds to about one quarter of the latitudinal differential equilibrium temperature this regulation is caused primarily by the decoupling of the sst gradient from a strong ocean current the author s estimate suggests that the present pacific is near the saturation state furthermore the much weaker walker circulation system in the atlantic ocean is interpreted as being the result of the influence of the adjacent land which is able to extend

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

role of tropics in changing the response to milankovich forcing some three million years ago appeared in regions that today have intense oceanic upwelling the eastern equatorial pacific and the coastal zones of southwestern africa and california there was furthermore a significant change in the earth s response to milankovich forcing obliquity signals became large but those associated with precession and eccentricity remained the same the latter change in the earth s response can be explained by hypothesizing that the global cooling during the cenozoic affected the thermal structure of the ocean it caused a gradual shoaling of the thermocline around 3 ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions this brought into play feedbacks involving

estimating central equatorial pacific sst variability over the past millennium part i methodology and validation abstractconstraining the low frequency lf behavior of general circulation models gcms requires reliable observational estimates of lf variability this two part paper presents multiproxy reconstructions of nino 3 4 sea surface temperature over the last millennium applying two techniques composite plus scale cps and hybrid regularized expectation maximization regem truncated total least squares ttls to a network of tropical high resolution proxy records this first part presents the data and methodology before evaluating their predictive skill using frozen network analysis fna and pseudoproxy experiments the fna results suggest that about half of the nino 3 4 variance can be reconstructed back to a d 1000 but they show little lf skill during certain intervals more variance can be reconstructed in the interannual band where climate signals are strongest but this band is affected by dating uncertainties which are not formally addressed here the cps reliably estimates interannual varia

mid infrared observations of io s volcanism from the ground in 2011 and 2012 abstract we report the latest volcanic activity on io based on our ground based observations made in 2011 and 2012 using just a 1 m telescope at 8 9 m where io s thermal radiation dominates solar reflected light seen at shorter wavelengths a particular result from these observations is that the power we detected from a bright hotspot at the longitude of 282 18 perhaps daedalus patera was 10 13 w which is comparable to that of loki patera the most powerful volcanic hotspot on io we conclude this hotspot is one of the most powerful volcanic hotspots on io but its activation is not as frequent as loki patera

reconnection and dipolarization driven auroral dawn storms and injections jupiter displays many distinct auroral structures among which auroral dawn storms and auroral injections are often observed contemporaneously however it is unclear if the contemporaneous nature

io s volcanism controls jupiter s radio emissions 1 jupiter s sodium nebula showed an enhancement in late may through the beginning of june 2007 this means io s volcanic activity and the magnetosphere s plasma content increased during this period on the other hand jupiter s radio emission called hom became quiet after the sodium nebula enhancement the hom emission is considered to be related to the activity of aurorae on jupiter these observation results therefore suggest that the increase in plasma supply from io into jupiter s magnetosphere weakens its field aligned current which generates the radio emissions and aurorae on jupiter by comparing our observation results to recent model and observation results we add supporting evidence to the possibility that io s volcanism controls jupiter s magnetospheric activity

tightly linked zonal and meridional sea surface temperature gradients over the past five million years the climate of the tropics and surrounding regions is defined by pronounced zonal east west and meridional equator to mid latitudes gradients in sea surface temperature these gradients control zonal and meridional atmospheric circulations and thus the earth s climate global cooling over the past five million years since the early pliocene epoch was accompanied by the gradual strengthening of these temperature gradients here we use records from the atlantic and pacific oceans including a new alkenone palaeotemperature record from the south pacific to reconstruct changes in zonal and meridional sea surface temperature gradients since the pliocene and assess their connection using a comprehensive climate model we find that the reconstructed zonal and meridional temperature gradients vary coherently over this time frame showing a one to one relationship between their changes in our model simulations we systematically reduce the meridional sea surface temperature gradient by modifying the latitudinal distribution of cloud albedo or atmospheric co2 concentration the simulated zonal temperature gradient in the equatorial pacific adjusts proportionally these experiments and idealized modelling indicate that the meridional temperature gradient controls upper ocean stratification in the tropics which in turn controls the zonal gradient along the equator as well as heat export from the tropical oceans we conclude that this tight linkage between the two sea surface temperature gradients posits a fundamental constraint on both past and future climates global mean temperatures during the pliocene epoch were warmer than at present with a shallow meridional temperature gradient numerical simulations suggest that since the pliocene the meridional and zonal temperature gradients have varied in tandem

eocene el nino evidence for robust tropical dynamics in the hothouse much uncertainty surrounds the interactions between the el nino southern oscillation enso and long term global change past periods of extreme global warmth exemplified by the eocene 55 to 35 million years ago provide a good testing ground for theories for this interaction here we compare eocene coupled climate model simulations with annually resolved variability records preserved in lake sediments the simulations show pacific deep ocean and high latitude surface warming of approximately 10 degrees c but little change in the tropical thermocline structure atmosphere ocean dynamics and enso in agreement with proxies this result contrasts with theories linking past and future hothouse climates with a shift toward a permanent el nino like state

geochemical processes in kandi basin benin west africa a combined hydrochemistry and stable isotopes approach abstract detailed hydrochemical and stable isotopic data of surface and groundwater were used to understand the geochemical processes occurring in the kandi basin in benin hydrochemical investigations show that waters in this basin are of low mineralization with values of total dissolved solids tds generally less than 1200 mg l water types in the basin are hco3 mg hco3 na cl na hco3 ca cl ca and most fall in mixture water type i e hco3 mixe and cl no3 mixe the mineralization is governed essentially by the dissolution of dolomite calcite aragonite and magnesite but not cation exchange reactions the stable isotope approach underlined the interchange phenomenon between aquifers in the basin direct recharge of aquifers by surface waters in some areas and recharge of aquifers by modern precipitation which influence the groundwater geochemistry in the basin anthropic origin of nitrates is underlined by stable isotopes

consequences of shoaling of the central american seaway determined from modeling nd isotopes the central american seaway played a pivotal role in shaping global climate throughout the late cenozoic recent geological surveys have provided new constraints on timing of the seaway shoaling while neodymium isotopic e nd data measured on fossil teeth debris and ferromanganese crusts have helped define the history of water masses in the region here we provide the first 3 d simulations of e nd responses to the shoaling seaway our model suggests that a narrow and shallow seaway is sufficient to affect interoceanic circulation that inflow outflow balance between the caribbean and the antilles responds nonlinearly to sill depth and that a seaway narrower than 400 km is consistent with an active atlantic meridional overturning circulation during the late miocene simulated e nd values in the caribbean confirm that inputs from radiogenic pacific waters in the caribbean decrease as the seaway shoals despite model limitations a comparison between our results and e nd values recorded in the caribbean helps constrain the depth of the central american seaway through time and we infer that a depth between 50 and 200 m could have been reached 10 ma ago

auroral evidence of io s control over the magnetosphere of jupiter 1 contrary to the case of the earth the main auroral oval on jupiter is related to the breakdown of plasma corotation in the middle magnetosphere even if the root causes for the main auroral emissions are io s volcanism and jupiter s fast rotation changes in the aurora could be attributed either to these internal factors or to fluctuations of the solar wind here we show multiple lines of evidence from the aurora for a major internally controlled magnetospheric reconfiguration that took place in spring 2007 hubble space telescope far uv images show that the main oval continuously expanded over a few months engulfing the ganymede footprint on its way simultaneously there was an increased occurrence rate of large equatorward isolated auroral features attributed to injection of depleted flux tubes furthermore the unique disappearance of the io footprint on 6 june appears to be related to the exceptional equatorward migration of such a feature the contemporary observation of the spectacular tvashtar volcanic plume by the new horizons probe as well as direct measurement of increased io plasma torus emissions suggest that these dramatic changes were triggered by io s volcanic activity

processes controlling the mean tropical pacific precipitation pattern part i the andes and the eastern pacific itcz abstract the question of why the intertropical convergence zone itcz is generally north of the equator in the tropical pacific is addressed experiments with an atmospheric general circulation model coupled to idealized representations of the ocean show that the presence of the andes is enough to lower sea surface temperature sst off the west coast of south america through evaporation thus promoting a north south asymmetry with the itcz north of the equator which is amplified by interactions between the ocean and the atmosphere the evaporative cooling results mainly from the subsidence of low specific humidity air which is due in turn to the mechanical effect of the andes on the zonal mean flow the positive feedback from low level clouds on sst is an important factor for the efficiency of the mechanism described west of 120 w the presence of the rockies and himalayas produces a comparable forcing to that of the andes but this is not enough to reverse or neutralize the north south asymmetry se

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

a simple model for the pacific cold tongue and enso abstract a conceptual model is constructed based upon the bjerknes hypothesis of tropical atmosphere ocean interaction it is shown that strong feedbacks among the trade winds equatorial zonal sea surface temperature contrast and upper ocean heat content occur in the tropical pacific basin coupled atmosphere ocean dynamics produce both the strong pacific cold tongue climate state and the el nino southern oscillation enso phenomenon the cold tongue climate state is unstable and gives rise to the self sustained enso which can be understood as an equatorial ocean recharge oscillator the small basin size and the influence of a wind system resulting from heating sources of its adjacent landmasses are responsible for a weak and stable atlantic cold tongue state that cannot support enso like interannual variability the presence of westerly wind associated with the walker circulation ascending at the western pacific warm pool disables the dynamical coupling processes in the equatorial indian ocean as a

a stability analysis of tropical ocean atmosphere interactions bridging measurements and theory for el nino abstract interactions between the tropical oceans and atmosphere permit a spectrum of natural modes of oscillation whose properties period intensity spatial structure and direction of propagation depend on the background climatic state i e the mean state this mean state can be described by parameters that include the following the time averaged intensity of the pacific trade winds the mean depth h of the thermocline and the temperature difference across the thermocline t a stability analysis by means of a simple coupled ocean atmosphere model indicates two distinct families of unstable modes one has long periods of several years involves sea surface temperature variations determined by vertical movements of the thermocline that are part of the adjustment of the ocean basin to the fluctuating winds requires a relatively deep thermocline and corresponds to the delayed oscillator the other family requires a shallow thermocline has short periods of a year or two has sea surface tempe

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

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

formation of the cold tongue and enso in the equatorial pacific basin abstract this paper proposes a mechanism that explains how coupled dynamics alone can spontaneously give rise to a realistic west east asymmetric mean state and an enso like interannual variability without requiring the existence of an external preexisting west east asymmetry in circulation the essence of the newly proposed mechanism is that the basinwide ocean atmosphere coupling acts to reduce the effective restoring force as a result the coupled oceanic waves travel more and more slowly within the equatorial ocean basin as the coupling strength increases when the coupling strength reaches a critical value the zonally leveled thermocline becomes unstable as a result of the weakening of the effective restoring force at which the theoretical limit of the traveling timescale would be infinite without nonlinearity due to nonlinearity in the coupled system this primary air sea interaction instability leads to a west east asymmetric mean state in which the atmosphere has a prevailing easterly and the

the first close up images of jupiter s polar regions results from the juno mission junocam instrument during juno s first perijove encounter the junocam instrument acquired the first images of jupiter s polar regions at 50 70 km spatial scale at low emission angles poleward of 64 68 planetocentric latitude where jupiter s east west banded structure breaks down several types of discrete features appear on a darker background cyclonic oval features are clustered near both poles other oval shaped features are also present ranging in size from 2000 km down to junocam s resolution limits the largest and brightest features often have chaotic shapes two narrow linear features in the north associated with an overlying haze feature traverse tens of degrees of longitude junocam also detected an optically thin cloud or haze layer past the northern nightside terminator estimated to be 58 21 km approximately three scale heights above the main cloud deck junocam will acquire polar images on every perijove allowing us to track the state and evolution of longer lived features

geochemistry and water dynamics application to short time scale flood phenomena in a small mediterranean catchment we report major trace elements and sr isotope data for water samples taken regularly during a four day long september flood of a mediterranean river the vene herault s france the objective is to combine all these data into a dynamic model that describes the origin s and movements of waters and their loads this river drains the runoff from a small mainly carbonate partly karstified watershed with miocene and jurassic lithologies the watershed is also impacted by both agricultural and urban activities both the dissolved and the particulate loads were analyzed concentrations of the dissolved components show major remobilization of almost all elements during the first few hours of the flood water treatment plants and aerosol scavenging followed by a sharp concentration decrease some major species return to their previous summer values ca hco3 while others reach low background levels na k cl s04 some trace elements rb sr cs show similar behaviour but ba appears somewhat unaffected trace element concentrations and ratios define two main periods three in the suspended particulate matter ratios do not allow distinguishing between the three main sources for the dissolved load in the first period miocene jurassic water treatment plants but clearly show the jurassic karst influence later on the 87sr 86sr of the suspended particulate matter is more variable and more radiogenic than in the dissolved phase variations in concentration ratios and sr isotope composition in particulates indicate the large and variable contribution of miocene silicates with some carbonate however there is a need for another component with rb sr higher than bedrocks internal or external to the watershed possibly due to differential erosion dissolved ca and mg fluxes during the flood were calculated at 0 26 ton and 0 029 ton km2 respectively even though the carbonate nature of the watershed restricts variability in sr isotope composition in the dissolved load we distinguish several endmembers seawater marine rain miocene marls jurassic limestones water treatment plants and possibly another attributable to fertilizers combined with major and trace element variations sr isotope fluctuations indicate time varying proportions of different water endmembers at the outflow and suggest a general dynamic model based on pca principal component analysis a 3d representation allows to visualize the geochemical evolution of the vene waters in particular sr isotopes clearly indicate that the inflow of karstic waters during the flood was not continuous but occurred as a series of marked oscillations between flowing waters with chemical signature of miocene lithologies and increasing flushes of deeper waters that interacted with jurassic lithologies

ocean atmosphere interaction and the tropical climatology part ii why the pacific cold tongue is in the east abstract the influence of coupled process on the climatology of the tropical pacific is studied in a model for the interaction of equatorial sst the associated component of the walker circulation and upper ocean dynamics in this part the authors show how different physical mechanisms affect the spatial pattern of the pacific warm pool and cold tongue in this coupled climatology when model parameters give a suitable balance between effects of upwelling and thermocline depth on sea surface temperature and for suitable atmospheric parameters a good prototype for the observed cold tongue configuration is produced this is largely determined by coupled ocean atmosphere processes within the basin presence of an easterly wind s component produced by factors external to the pacific basin can be important in setting up a cooling tendency but this is magnified and modified by a chain of nonlinear feedbacks between trade winds and ocean dynamics affecting the sst gradient within the basin these feedbacks d

a hydrogeological and hydrochemical explanation of the groundwater composition under irrigated land in a mediterranean environment algarve portugal in the campina de faro in the south of portugal agricultural practices have a large impact on groundwater composition these practices involve pumping of water for irrigation from combinations of large diameter shallow wells noras and small diameter deep boreholes furos excess irrigation water returns to the aquifer and mixes with water from the regional groundwater flow system this irrigation return flow is concentrated by strong evapotranspiration and by flushing of fertilisers the concentration increase induces cation exchange whereby ca on the soil exchanger is replaced by na the mixing in the aquifer allows application of a mixing cell model which may then be used to calculate transmissivities from the cl mass balance the calculations are complicated by the time variant behaviour of cl and the method is adjusted to calculate the change of chloride in time results from the calculations appear to be in good agreement with hydrochemical observations

equatorial mid tropospheric easterly jet over the eastern pacific comparison from the ecmwf and ncep ncar reanalyses 1 the upper air data set of the european centre for medium range weather forecasts ecm 1979 93 reanalysis is evaluated in comparison to the national centers for environmental prediction national center for atmospheric research ncp reanalysis for the same period attention is focused on the equatorial mid tropospheric easterly jet emtej over the eastern pacific first noted from a short series of rawin soundings at galapagos and then corroborated in its broad spatial context from the ncp 40 year reanalysis the present follow up study contributes a comparison of evidence from the two sources with different model assimilations the major characteristics of the emtej are confirmed although the winds from ecm are overall slower and those from ncp faster than the measurements over galapagos in both ecm and ncp the easterly speed maximum along the equator is over the eastern pacific located around 600 700 mb and further westward at progressively lower elevations divergence prevails in the realm of the speed maximum and is primarily fed by subsidence from aloft the ecm evidence differs from ncp by a more westward location of the easterly speed maximum and overall weaker flow

the asian australian monsoon and el nino southern oscillation in the ncar climate system model features associated with the asian australian monsoon system and el nino southern oscillation enso are described in the national center for atmospheric research ncar global coupled climate system model csm simulation characteristics are compared with a version of the atmospheric component of the csm the ncar ccm3 run with time evolving ssts from 1950 to 1994 and with observations the csm is shown to represent most major features of the monsoon system in terms of mean climatology interannual variability and connections to the tropical pacific this includes a representation of the southern oscillation links between strong asian australian monsoons and associated negative sst anomalies in the eastern equatorial pacific the equatorial sst gradient across the pacific in the csm is shown to be similar to the observed with somewhat cooler mean ssts across the entire pacific by about 18 28c the seasonal cycle of ssts in the eastern equatorial pacific has the characteristic signature seen in the observations of relatively warmer ssts propagating westward in the first half of the year followed by the reestablishment of the cold tongue with relatively colder ssts propagating westward in the second half of the year like other global coupled models the propagation is similar to the observed but with the establishment of the relatively warmer water in the first half of the year occurring about 1 2 months later than observed the seasonal cycle of precipitation in the tropical eastern pacific is also similar to other global coupled models in that there is a tendency for a stronger than observed double itcz year round particularly in northern spring but with a well reproduced annual maximum of itcz strength north of the equator in the second half of the year time series of area averaged ssts for the nino3 region in the eastern equatorial pacific show that the csm is producing about 60 of the amplitude of the observed variability in that region consistent with most other global coupled models global correlations between nino3 time series global surface temperatures and sea level pressure slp show that the csm qualitatively reproduces the major spatial patterns associated with the southern oscillation lower slp in the central and eastern tropical pacific when nino3 ssts are relatively warmer and higher slp over the far western pacific and indian oceans with colder water in the northwest and southwest pacific indices of asian australian monsoon strength are negatively correlated with nino3 ssts as in the observations spectra of time series of indian monsoon australian monsoon and nino3 sst indices from the csm show amplitude peaks in the southern oscillation and tropospheric biennial oscillation frequencies 3 6 yr and about 2 3 yr respectively as observed lag correlations between the nino3 sst index and upper ocean heat content along the equator show eastward propagation of heat content anomalies with a phase speed of about 0 3 m s21 compared to observed values of roughly 0 2 m s21 composites of el nino la nina events in the csm show similar seasonal evolution to composites of observed events with warming cooling of greater than several tenths of a degree beginning early in northern spring of year 0 and diminishing around northern spring of year 11 but with a secondary resurgence in the csm events later in northern spring of year 11 the csm also shows the largest amplitude enso sst and low level wind anomalies in the western tropical pacific with enhanced interannual variability of ssts extending northeastward and southeastward toward the subtropics compared to largest interannual sst variability in the central and eastern tropical pacific in the observations

the eastern subtropical pacific origin of the equatorial cold bias in climate models a lagrangian perspective abstractglobal climate models frequently exhibit cold biases in tropical sea surface temperature sst in the central and eastern equatorial pacific here lagrangian particle back trajectories are used to investigate the source regions of the water that upwells along the equator in the ipsl climate model to test and confirm the hypothesis that the sst biases are caused by remote biases advected in from the extratropics and to identify the dominant source regions water in the model is found to be sourced primarily from localized regions along the western and eastern flanks of the subtropical gyres however while the model sst bias is especially large in the northwestern subtropical pacific about 5 c it is found that the eastern subtropics contribute to the equatorial bias the most this is due to two distinct subsurface pathways connecting these regions to the equator the first pathway originating in the northwestern subtropical pacific has relatively long advection time scales close to or exceed

morphology of the uv aurorae jupiter during juno s first perijove observations on 27 august 2016 the nasa juno spacecraft performed its first close up observations of jupiter during its perijove here we present the uv images and color ratio maps from the juno uvs uv imaging spectrograph acquired at that time data were acquired during four sequences three in the north one in the south from 5 00 ut to 13 00 ut from these observations we produced complete maps of the jovian aurorae including the nightside the sequence shows the development of intense outer emission outside the main oval first in a localized region 255 295 system iii longitude and then all around the pole followed by a large nightside protrusion of auroral emissions from the main emission into the polar region some localized features show signs of differential drift with energy typical of plasma injections in the middle magnetosphere finally the color ratio map in the north shows a well defined area in the polar region possibly linked to the polar cap

groundwater geochemistry of a small reservoir catchment in central tunisia abstractdue to the scarcity of water resources in semiarid sedimentary basins hill reservoirs are often constructed torechargegroundwaterandlimitruno inducedwaterloss theimpactofsuchreservoirsongroundwaterchemistryisinvestigatedintheaquifersoftheelgouazinewatershed centraltunisia threegroundwatertypesarerecognised ca hco 3 na clandca so 4 thestrongsimilaritybetweenhostrockandgroundwaterchemistriesindicatessig ni cantrock waterinteraction a owpath alongwhichthechemicalcompositionofthegroundwaterevolves canbeidenti ed using the contrast in stable isotope signature between upstream and downstream groundwater shallowupstreamgroundwaterisrechargedbythein ltrationofrainwaterwiththerateofrechargestronglylinkedtothepermeability of the host lithology calcium and hco 3 are supplied to an alluvial aquifer from a more rapidlyrechargedlimestoneaquiferwiththeconcentrationofcaandhco 3 ionsdecreasingbydilution thealluvialaquiferisalsoenrichedincaandso 4 duringthedownstream owofgroundwaterthroughgypsiferousmaterials thereisevi dence of mixing between meteoric groundwater and evaporated reservoir water below the reservoir and partlyresponsibleforreservoirleakageisasandyaquifer formedbyweatheringanderosionofasandstonehostwhichalsosupplieswatertothealluvialaquifer 2002elsevierscienceltd allrightsreserved 1 introductiona perennial problem for farmers and herdsman insemiaridareaswithoutpermanentriversisthescarcityofwaterowingtothelowanderraticrainfall inthelastcentury globalpopulationexpansionhastremendouslyincreased the pressure on water resources to securewater supply and intensify agricultural production water harvesting is traditionally used to combat theproblemsofvaryingrainfallratesandpopulationden sities one technique of water harvesting oodwater har vesting fwh alsocalledlargecatchmentwaterhar vesting or spate irrigation is widely developed when oodwaterisharvestedinthestreambed thewater owisdammedandstoredintemporaryorpermanentsur face reservoirs water is forced to in ltrate and asaresult torechargetheaquifer withrechargeconcentratedmainly in the valley downstream from the reservoir prinz 1999 fwhisarelativelyinexpensivetechniqueprovidingwaterforthedevelopmentofagricultureandagroforestry and reducing the use of other valuablewater resources such as groundwater water supply isnotalwaysevenandsecureduringtheyeardependingontheclimaticvariability largeevaporationlossesandlossofstoragebysiltationandpollutionarethemainlimitations of fwh social problems like con ictbetweenwaterusersareafurtherdrawbacktothisstyleofwaterharvesting inthemediterraneanbasin waterharvestingplayedan important role in ancient civilisations such as theromanandegyptianempires prinz 1999 duringthe20thcentury moderntechniques groundwaterdrilling largereservoirconstructionetc whicharefavouredbygovernmentpolicy slowlyreplacedtraditionalharvest ing techniques high demands for water during theagricultural growing season which coincides with thedryperiodofthemediterraneanclimate hasresultedinthe depletion of the groundwater table in some areas thelowrenewalrateofgroundwaterresourcesandthe