a diagnostic study of upper tropospheric cold lows over the western north pacific abstract four summers 1967 1969 1970 1971 of rawinsonde data from four western north pacific island stations guam midway johnston and wake were used to form a three dimensional composite of the subtropical upper tropospheric cold core lows commonly found in the mid pacific trough the basic meteorological parameters of wind height temperature and humidity were utilized to form an initial composite from the 117 lows identified during the period of study satellite mosaics were used to define a composite of horizontal cloud cover the basic composite was harmonically smoothed and dynamically adjusted to generate a consistent set of derived fields that emphasize the important large scale characteristics of the phenomenon north south and east west vertical cross sections through the center of the composite low are used to illustrate the prominent features of the zonal and meridional winds temperature and height anomalies relative vorticity divergence vertical motion and relative humidity field

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

altimeter observations of the peru chile countercurrent data from geosat and topex altimeters are used to infer the structure of the peru chile countercurrent a jet that flows from at least as far north as 10 s historical data suggests 7 s to 35 40 s maintaining its position between approximately 100 300 km offshore although the annual mean current cannot be determined from altimeter observations the nearly antisymmetric patterns in spring and fall combined with historical observations suggest that the countercurrent is poleward at most times and is maximum in spring and minimum in fall previous studies have linked the offshore countercurrent at 7 s to the equatorial undercurrent west of the galapagos islands suggesting that the countercurrent is part of a continuous flow that extends from the western equatorial pacific to the region off chile between 35 40 s

a transbasin mode of interannual variability of the central american gap winds seasonality and large scale forcing abstracta transbasin mode tbm is identified as the leading mode of interannual surface wind variability over the intra americas seas across central america based on empirical orthogonal function analysis the tbm is associated with variability in central american gap winds most closely with the papagayo jet but with considerable signals over the gulfs of tehuantepec and panama although el nino southern oscillation enso is the main large scale forcing the tbm features a distinct seasonality due to sea level pressure slp adjustments across the pacific and atlantic during july september enso causes meridional slp gradient anomalies across central america intensifying anomalous geostrophic winds funneling through papagayo to form the tbm during wintertime enso peaks but imparts little anomalous slp gradient across central america with a weak projection on the tbm because of the competing effects of the pacific north american teleconnection and tropospheric kelvin waves besides enso tropical at

observational analysis of an upper level inverted trough during the 2004 north american monsoon experiment abstract upper level inverted troughs ivs associated with midlatitude breaking rossby waves or tropical upper troposphere troughs tutts have been identified as important contributors to the variability of rainfall in the north american monsoon nam region however little attention has been given to the dynamics of these systems owing to the sparse observational network over the nam region high temporal and spatial observations taken during the 2004 north american monsoon experiment name are utilized to analyze a significant iv that passed over northwestern mexico from 10 to 13 july 2004 the colorado state university gridded dataset which is independent of model analysis over land is the primary data source used in this study results show that the 10 13 july iv disturbance was characterized by a warm anomaly around 100 hpa and a cold anomaly that extended from 200 to 700 hpa the strongest cyclonic circulation was in the upper levels around 200 hpa quasigeostrophic qg diagnostics indicate t

tracking and mean structure of easterly waves over the intra americas sea abstract easterly waves ews are prominent features of the intertropical convergence zone itcz found in both the atlantic and pacific during the northern hemisphere summer and fall where they commonly serve as precursors to hurricanes over both basins a large proportion of atlantic ews are known to form over africa but the origin of ews over the caribbean and east pacific in particular has not been established in detail in this study reanalyses are used to examine the coherence of the large scale wave signatures and to obtain track statistics and energy conversion terms for ews across this region regression analysis demonstrates that some ew kinematic structures readily propagate between the atlantic and east pacific with the highest correlations observed across costa rica and panama track statistics are consistent with this analysis and suggest that some individual waves are maintained as they pass from the atlantic into the east pacific whereas others are generated locally in the caribbean a

integrated silurian conodont and carbonate carbon isotope stratigraphy of the east central appalachian basin abstract the eastern and southeastern margins of the appalachian basin contain extensive exposures of telychian through pridoli upper silurian strata litho and biostratigraphic analyses of these strata over the last century provided a general means for their chronostratigraphic correlation to global series and stage boundaries however a rarity of zonally diagnostic fauna limited precise correlation both within and beyond the appalachian basin recent conodont biostratigraphic studies substantially revised the chronostratigraphic position of these strata by more than a series in some cases much of the interval however remained biostratigraphically unzoned and the precise position of series and stage boundaries remained tentative to improve the chronostratigraphic correlation of these strata to global series and stage boundaries we provide new integrated conodont and high resolution 13ccarb chemostratigraphic analyses from two outcrops located in west virginia and virginia spanning the upper rose hill through tonoloway formations upper telychian through pridoli these new data show that the silurian carbon isotope record for this portion of the appalachian basin is shifted to more negative 13ccarb values than typical global data however the overall isotopic records appear correlative at least within the appalachian basin thereby providing a means for future correlation within the basin for intervals in which biostratigraphy is traditionally lacking these coupled data demonstrate that the ireviken and mulde excursions are contained within our sections the high amplitude lau excursion was however not observed and the present biostratigraphic data suggest that a majority of the ludlow series was either not recorded or was later removed by erosion these coupled analyses therefore indicate that the ludlow pridoli boundary resides within the wills creek formation and we propose that the overlying isotopic record presented here records the late ludlow carbon isotope excursion llcie and silale low previously identified only within the baltic basin

evolution of the monterey bay sea breeze layer as observed by pulsed doppler lidar abstract as part of the land sea breeze experiment lasbex to study the sea breeze at monterey bay the pulsed doppler lidar of the noaa erl wave propagation laboratory performed vertical and nearly horizontal scans of the developing sea breeze on 12 days analyses of doppler velocity data from these scans revealed details on the growth of the sea breeze layer and on the horizontal variability of the sea breeze resulting from inland topography two days were selected for study when the ambient flow was offshore because the onshore flow of the sea breeze was easy to discern from the background flow sequences of vertical cross sections taken perpendicular to the coast showed the beginnings of the sea breeze beneath the land breeze at the coast and the subsequent growth of the sea breeze layer horizontally and vertically on one of the days a transient precursor a minor sea breeze appeared and disappeared before the main sea breeze began in midmorning other issues that the lidar was well suited to stud

ventilation of the subtropical north pacific the shallow salinity minimum abstract the shallow salinity minimum of the subtropical north pacific is shown to be a feature of the ventilated wind driven circulation subduction of low salinity surface water in the northeastern subtropical gyre beneath higher salinity water to the south causes the salinity minimum variation of salinity along surface isopycnals causes variations in density and salinity at the minimum a model of ventilated flow is used to demonstrate how the shallow salinity minimum can arise the model is modified to account for nonzonal realistic winds it is also extended to examine the three dimensional structure of the western shadow zone the boundary between the subtropical and subpolar gyres is given by the zero of the zonal integral of ekman pumping the western shadow zone fills the subtropical gyre at the base of the ventilated layers and decreases in extent with decreasing density for parameters appropriate to the north pacific the eastern shadow zone is of very limited extent observations of salini

a numerical study of the upwelling circulation off central chile effects of remote oceanic forcing 1 a numerical ocean model is used to study the upwelling circulation off central chile in response to local winds and remote forcing in an idealized study of equatorial forced intraseasonal variability period of 50 days a first mode coastal trapped wave ctw paddle is applied to the northern boundary with coastal sea level amplitude of 12 cm without this ctw forcing the steady seasonal winds upwell undercurrent water from depths of 250 320 m to depths of 180 250 m the subsequent formation of mesoscale and headland eddies drive this water into the gulf of arauco and to depths of 50 120 m with the ctw paddle the circulation is strongly modified the mesoscale and headland eddies reform during the ctw upwelling phase during the ctw upwelling phase the upwelling over winds and eddies is enhanced by up to 40 m on the shelf model simulations are undertaken using realistic winds and a ctw paddle modulated by observed sea level without ctw forcing included in the model the agreement with data is poor in the gulf of arauco area the variability of alongshore currents below 130 m is dominated by ctw activity above 130 m wind driven current variability dominates in agreement with the idealized ctw analysis water is found to be upwelled from depths of 320 m to 100 m or less and 10 c undercurrent water is found at the surface and within the gulf

on the wind driven circulation of the south pacific ocean abstract a layered model of the study circulation in the south pacific ocean is constructed along the lines of luyten pedlosky and stommel and driven by the mean annual wind stress distributions computed by hellerman and rosenatein the results of the model agree quite well with published maps of topography of density surfaces and circulation best agreement is found in the deeper layers the deepest modeled layer of density range 26 90 0 27 30 which contains the core layer of the antarctic intermediate water transports northwards some 14 sv 1 sv 106 m3 s 1 between new zealand and south america of this about three quarters comes from the west in an intense zonal jet that rounds the southern tip of new zealand and quickly fans out from the boundary current along those islands into the anticyclonic gyre some 5 sv returns southwards in the australian boundary current much of the anticyclonic gyre in the western south pacific is taken up by a shadow zone formed in the shelter of new zealand

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

simulation of a north american monsoon gulf surge event and comparison to observations abstractgulf surges are transient disturbances that propagate along the gulf of california goc from south to north transporting cool moist air toward the deserts of northwest mexico and the southwest united states during the north american monsoon they have been shown to modulate precipitation and have been linked to severe weather and flooding in northern mexico and the southwest united states the general features and progression of surge events are well studied but their detailed evolution is still unclear to address this several convection permitting simulations are performed over the core monsoon region for the 12 14 july 2004 gulf surge event this surge event occurred during the north american monsoon experiment which allows for extensive comparison to field observations a 60 h reference simulation is able to reproduce the surge event capturing its main characteristics speed and direction of motion thermodynamic changes during its passage and strong northward moisture flux while the ti

silurian conodont biostratigraphy and carbon δ13ccarb isotope stratigraphy of the victor mine v 03 270 ah core in the moose river basin the moose river basin in ontario canada contains nearly 1 km of silurian marine strata and although it has been studied for more than a century its precise correlation globally has not been constrained herein a core from the victor mine in the moose river basin was examined for conodont biostratigraphy and carbonate carbon 13ccarb isotope chemostratigraphy to provide a detailed chronostratigraphic framework for the silurian strata severn river ekwan river and attawapiskat formations in the moose river basin the recovery of aspelundia expansa aspelundia fluegeli fluegeli distomodus staurognathoides ozarkodina polinclinata estonica pterospathodus eopennatus and aulacognathus bullatus as well as the lower aeronian upper aeronian lower telychian valgu and ascending limb of the sheinwoodian ireviken positive carbonate carbon 13ccarb isotope excursions provide significantly improved chronostratigraphic correlation of llandovery strata in the moose river basin

silurian stratigraphy of the hudson bay lowland in quebec carbonates of late llandoverian to ludlovian age divided into the severn river ekwan river and kenogami river formations crop out in the drainage basin of the harricana river the severn river formation consists of a succession of alternating wackestone and packstone beds 17 5 m thick the packstones are ascribed to storm events and carry a deeper water fauna than the wackestones the ekwan river formation is divided into four units a barren dolostone at the base sandy wackestones and packstones with a coral fauna another barren dolomudstone and at the top a unit of argillaceous nodular limestone rich in leperditid ostracods the units are ascribed to shallow subtidal intertidal and supratidal environments three benthic assemblages characterized by ostracods corals rhynchonellids and the brachiopods brachyprion and dalejina are distinguished in order of increasing depth two transgressive events in llandoverian c4 and c6 times are marked by coral rich units in the severn river and ekwan r

ventilation of the subtropical north pacific abstract the ventilation of the subtropical north pacific is studied using a simple analytical model the model is forced by winter mixed layer density and depth calculated from the levitus climatology and wind stress curl from the hellerman and rosenstein wind stress data the wind driven gyre in the north pacific is shallow no more than 1 4 km the gross feature of the subduction rate is very similar to the results by huang and qiu based on data analysis of the levitus climatology with a total ventilation rate of 31 3 sv sv 106 m3 s 1 including 20 8 sv due to the vertical pumping and 10 5 sv due to lateral induction the age of water within the ventilated thermocline is relatively young it is no more than 10 years old except near the southeast corner of the basin the young age indicates a fast communication between the atmosphere and the upper ocean on a timescale of less than 10 years the vertical mass partition is slightly different from the results based on analysing climatology by huang a

integrated graptolite conodont biostratigraphy and organic carbon chemostratigraphy of the llandovery of kallholn quarry dalarna sweden abstract a revised graptolite and conodont biostratigraphy together with new organic carbon isotope data for the middle aeronian to lower telychian llandovery lower silurian of kallholn quarry central sweden are presented the base of the section is marked by an unconformity between the ordovician boda limestone and aeronian shales with limestone nodules belonging to the pribylograptus leptotheca biozone these are overlain by strata assigned to the lower lituigraptus convolutus biozone the stimulograptus sedgwickii biozone previously recorded from the section is absent and marked by an unconformity which is overlain by radiolarian rich graptolitic shales belonging to the stimulograptus halli biozone the overlying telychian strata are assigned to the spirograptus guerichi spirograptus turriculatus and streptograptus crispus biozones conodonts indicate that the boundary between the distomodus staurognathoides biozone and pterospathodus eopennatus superzone lies within the sp turriculatus biozone as it does also in the ohesaare core estonia the 13corg record shows mostly minor fluctuations but with a distinct twin peaked positive excursion in the upper sp turriculatus biozone close to the boundary with the overlying streptograptus crispus biozone the excursion in the kallholn section may correlate with the earliest positive shift in 13c values at the onset of the excursion associated with the valgu event or it may represent a new excursion provisionally named the kallholn excursion preceding this many more bentonites 36 occur in the section than previously recorded geochemical studies are needed to confirm whether the osmundsberg bentonite which may or may not be equivalent to the o bed in estonia and latvia is present

decadal changes in water mass characteristics at 24 n in the subtropical north atlantic ocean abstract three transatlantic hydrographic sections across 24 n through the center of the subtropical gyre are analyzed for evidence of decadal changes in water mass characteristics in the main thermocline there has been a steady increase in salinity from 1957 to 1981 to 1992 the salinity at a given potential temperature between 12 c and 17 c has increased at a nearly constant rate of 0 010 per decade at constant potential density salinity and temperature both increased at rates of 0 018 per decade and 0 065 c per decade in the intermediate waters between 800 and 1500 dbar salinity has increased as well on average by as much as 0 025 from 1981 to 1992 either on constant potential temperature or constant density surfaces these changes cannot be due to vertical heaving of a constant water mass structure and they cannot be easily explained in terms of horizontal shifts in the subtropical gyre water mass structure throughout the water column down to 2000 dbar and across the zonal extent of the 24 n

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

characteristic atmospheric states during mid summer droughts over central america and mexico annual precipitation over central america and large areas of mexico is typically characterised by its bimodal distribution with a precipitation minimum in july to august that occurs between two separate maxima from may to july and august to october several theories have been proposed to explain this phenomenon which is often termed the mid summer drought msd but most fail to address the different characteristics associated with individual msd events here a regression based approach is used to detect and quantify the annual and climatological msd signature over central america and mexico this approach has been evaluated and shown to be robust for various datasets with different spatial resolutions it was found that in the southeast of the mexico central america region msds start earlier and end later than elsewhere and are thus longer in duration however the coast of the gulf of mexico cuba and large areas of central america exhibit climatologically stronger msds changes in precipitation brought about by the interaction between reversals of the onshore offshore winds and orographic forcing associated with the steep mountainous terrain have also been shown to be significant factors in the timing of msd occurrences offering support for a combined theory of large scale dynamics and regional forcing using self organising maps soms as an analysis tool it was found that msd events over the domain display strong spatial variability the msds over the domain also generate distinct signatures and may be forced by particular mechanisms we found that el nino southern oscillation enso could be a potential classifier for the som identified atmospheric states based on the correspondence of msd occurrences with enso phases

eastern tropical pacific hydrologic changes during the past 27 000 years from d h ratios in alkenones 1 the tropical pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation quantifying the role of the tropics in late pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period here we present records of hydrogen isotope ratios dd of alkenones from the panama basin off the colombian coast that document hydrologic changes in equatorial south america and the eastern tropical pacific over the past 27 000 years a and the past 3 centuries in detail comparison of alkenone dd values with instrumental records of precipitation over the past 100 a suggests that dd can be used as a hydrologic proxy on long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the intertropical convergence zone and an associated reduction of pacific moisture transport into colombia precipitation increases at 17 ka in concert with sea surface temperature sst cooling in the north atlantic and the eastern tropical pacific a regional coupled model forced by negative sst anomalies in the caribbean simulates an intensification of northeasterly trade winds across central america increased evaporative cooling and a band of increased rainfall in the northeastern tropical pacific these results are consistent with the alkenone sst and dd reconstructions that suggest increasing precipitation and sst cooling at the time of heinrich event 1

equatorial pacific 13 c water eddies in the eastern subtropical south pacific ocean abstract argo float profile data are used to analyze warm salty weakly stratified subthermocline eddies of tropical origin in the eastern subtropical south pacific ocean these eddies contain anomalous signatures of the equatorial pacific 13 c water that is carried poleward within the peru chile undercurrent pcu as it flows along the west coast of south america from their source along the chilean coast between 29 and 39 s the eddies spread westward and slightly northward likely at least partly advected by the subtropical gyre the eddy water properties contrast strongly with the colder fresher more strongly stratified waters of subantarctic origin being carried northward then westward by the gyre near the eddy source about 6 of argo profiles sample eddies that are above selected thresholds for both salinity and potential vorticity anomalies relative to maps of the mean distributions of these properties on and around the core isopycnal for the eddies the proportion of such profiles dimini

simulation of the intraseasonal variability over the eastern pacific itcz in climate models during boreal summer convective activity over the eastern pacific epac inter tropical convergence zone itcz exhibits vigorous intraseasonal variability isv previous observational studies identified two dominant isv modes over the epac i e a 40 day mode and a quasi biweekly mode qbm the 40 day isv mode is generally considered a local expression of the madden julian oscillation however in addition to the eastward propagation northward propagation of the 40 day mode is also evident the qbm mode bears a smaller spatial scale than the 40 day mode and is largely characterized by northward propagation while the isv over the epac exerts significant influences on regional climate weather systems investigation of contemporary model capabilities in representing these isv modes over the epac is limited in this study the model fidelity in representing these two dominant isv modes over the epac is assessed by analyzing six atmospheric and three coupled general circulation models gcms including one super parameterized gcm spcam and one recently developed high resolution gcm gfdl hiram with horizontal resolution of about 50 km while it remains challenging for gcms to faithfully represent these two isv modes including their amplitude evolution patterns and periodicities encouraging simulations are also noted in general spcam and hiram exhibit relatively superior skill in representing the two isv modes over the epac while the advantage of spcam is achieved through explicit representation of the cumulus process by the embedded 2 d cloud resolving models the improved representation in hiram could be ascribed to the employment of a strongly entraining plume cumulus scheme which inhibits the deep convection and thus effectively enhances the stratiform rainfall the sensitivity tests based on hiram also suggest that fine horizontal resolution could also be conducive to realistically capture the isv over the epac particularly for the qbm mode further analysis illustrates that the observed 40 day isv mode over the epac is closely linked to the eastward propagating isv signals from the indian ocean western pacific which is in agreement with the general impression that the 40 day isv mode over the epac could be a local expression of the global madden julian oscillation mjo in contrast the convective signals associated with the 40 day mode over the epac in most of the gcm simulations tend to originate between 150 e and 150 w suggesting the 40 day isv mode over the epac might be sustained without the forcing by the eastward propagating mjo further investigation is warranted towards improved understanding of the origin of the isv over the epac

satellite observations of the wind jets off the pacific coast of central america part i case studies and statistical characteristics measurements of near surface winds by the nasa scatterometer nscat from october 1996 through june 1997 are analyzed to investigate the three major wind jets along the pacific coast of central america that blow over the gulfs of tehuantepec papagayo and panama each jet is easily identifiable as locally intense offshore winds in the lee of low elevation gaps through the sierra madre mountain range the jets have relatively narrow cross stream width but often extend several hundred kilometers or more into the pacific the tehuantepec and papagayo jets sometimes merge with the northeast trade winds of the pacific the tehuantepec jet was highly energetic with characteristic timescales of about 2 days events were triggered by high pressures associated with cold surges into the gulf of mexico that originated over the great plains of north america the papagayo and panama jets were much more persistent than the tehuantepec jets the winds at both of these lower latitude locations exhibited a strong seasonal variation with almost exclusively offshore flow from late november 1996 through late may 1997 and periods of onshore flow in october and november during the late stages of the 1996 central american monsoon season superimposed on this low frequency seasonal variation were events with characteristic timescales of a few days based on nscat data the spatial and temporal evolution of major wind events is described in detail for three representative case studies in december 1996 the jets developed sequentially from north to south consistent with the notion that wind events in the two lower latitude jets are associated with cold air outbreaks that trigger the tehuantepec jet a day or so earlier in november 1996 and march 1997 the papagayo and panama jets were strongly influenced by tropical phenomena that had little apparent association with the tehuantepec jet these latter two case studies together with the distinction between the statistical characteristics of the three jets suggest that the papagayo and panama jets are predominantly controlled by a mechanism that is very different from the across gap pressure gradients associated with high pressure systems of midlatitude origin that control the tehuantepec jet

a mechanism for enhanced upwelling off central chile eddy advection 1 a regional numerical model is developed for the mid chile shelf and ocean circulation 30 s to 43 s the model is forced with mean summertime wind stress and transports from a global model over the first 10 days deep 250 300 m peru undercurrent puc water is upwelled to depths of 170 270 m after this time upwelling by the steady winds is largely shut down and a 55 km diameter cyclonic eddy is found to grow in deep water off punta lavapie the mechanism for eddy growth is identified to be baroclinic instability of an initial offshore meander of the equatorward chile coastal current ccc over a period of more than 100 days the onshore arm of the deep water eddy upwells puc water to depths of 150 m toward the shelf a shallow headland eddy then sweeps this puc water to depths of less than 50 m and into the gulf of arauco the net upwelling of 200 m is the largest found for the region observational evidence is cited for the existence of the deep water cyclonic eddy over a period of 4 months a spatially intermittent puc is also found to lie below the ccc in agreement with observational studies the model also predicts the existence of an offshore branch of the ccc that is directed to the northwest

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

dianeutral motion water mass conversion and nonlinear effects on the density ratio in the pacific thermocline abstract the averaged hydrography of levitus has been used to form maps of various quantities that contribute to dianeutral advecion in the pacific thermocline on much of the 26 50 neutral surface cabbeling and thermobaricity contribute between 0 2 10 7 m s 1 and 2 10 7 m s 1 to the total dianeutral velocity assuming a lateral diffusivity of 103 m2 s 1 the dianeutral advection caused by vertical turbulent mixing is also mapped on several surfaces in the pacific ocean assuming a vertical diffusivity of 10 5 m2 s 1 the typical dianeutral velocity caused by vertical mixing is 10 7 m s 1 this upwelling across the 26 20 neutral surface at an average depth of about 200 m is positive and quite strong throughout the whole equatorial region there is a striking pattern of strong dianeutral upwelling in the central pacific on the 26 50 neutral surface while in the eastern pacific on the same surface there is a large region of downwelling subsurface water mass conversion is defined as the rate

heat and moisture budgets of an intense midlatitude squall line abstract rawinsonde data from ok pre storm are used to calculate the heat and moisture budgets during the late mature through dissipating stages of an intense squall line system with a trailing stratiform region budgets have been computed at three separate times using composited data from approximately 30 rawinsondes over three hour intervals data spacing is marginally adequate to resolve features within the broad 200 km stratiform region but not the narrow 40 km leading convective line low level radar data and surface accumulated rainfall are used to partition the system into convective line and stratiform regions and to cheek the accuracy of the heat and moisture budgets the squall line had a pronounced descending rear inflow jet that extended toward the front of the system with time and strong front to rear flow above and beneath this jet the diagnosed vertical motion showed deep ascent in the leading convective line and upper level ascent above lower level descent in the trailing stratif

the relationship between tropical easterly waves and surges over the gulf of california during the north american monsoon abstract coastally trapped disturbances which occur over the gulf of california and are commonly referred to as gulf surges are an important mechanism in the transport of low level moisture into the southwestern united states to determine whether or not gulf surges develop in association with the passage of tropical easterly waves as hypothesized in previous studies standard surface observations and european centre for medium range weather forecasts reanalysis data during the months of july and august over a 14 yr period are examined results indicate that tropical easterly wave troughs often cross western mexico 1 3 days prior to surge onset at yuma arizona indicating a strong correlation between these two events this analysis documents yet another mechanism by which the tropics influences convection in the midlatitudes

climatological features of cutoff low systems in the northern hemisphere this study presents the first multidecadal climatology of cutoff low systems in the northern hemisphere the climatology was constructed by using 41 yr 1958 98 of ncep ncar reanalysis data and identifying cutoff lows by means of an objective method based on imposing the three main physical characteristics of the conceptual model of cutoff low the 200 hpa geopotential minimum cutoff circulation and the specific structure of both equivalent thickness and thermal front parameter fields several results were confirmed and climatologically validated 1 the existence of three preferred areas of cutoff low occurrence the first one extends through southern europe and the eastern atlantic coast the second one is the eastern north pacific and the third one is the northern china siberian region extending to the northwestern pacific coast the european area is the most favored region 2 the known seasonal cycle with cutoff lows forming much more frequently in summer than in winter 3 the short lifetime of cutoff lows most cutoff lows lasted 2 3 days and very few lasted more than 5 days and 4 the mobility of the system with few cutoff lows being stationary furthermore the long study period has made it possible i to find a bimodal distribution in the geographical density of cutoff lows for the european sector in all the seasons with the exception of winter a summer displacement to the ocean in the american region and a summer extension to the continent in the asian region and ii to detect northward and westward motion especially in the transitions from the second to third day of occurrence and from the third to fourth day of occurrence the long term cutoff low database built in this study is appropriate to study the interannual variability of cutoff low occurrence and the links between cutoff lows and jet stream systems blocking or major modes of climate variability as well as the global importance of cutoff low in the stratosphere troposphere exchange mechanism which will be the focus of a subsequent paper

atmosphere ocean thermal coupling in the north atlantic a positive feedback in this article it is examined whether a positive atmosphere ocean feedback is found over the north atlantic through a series of general circulation model gcm experiments a 60 year integration of an atmospheric gcm agcm coupled with a 50 m deep motionless ocean was conducted the coupled run was compared with two uncoupled runs one with prescribed mid latitude climato logical sea surface temperatures ssts and the other with daily ssts derived from the coupled experiment the uncoupled atmosphere forces the slab ocean to obtain sst responses in these runs consistent with previous studies the coupled atmosphere ocean fields show interannual variances larger than those in the uncoupled runs due to reduction in the local thermal damping patterns of maximum atmosphere ocean covariability show the north atlantic oscillation nao and tripole sst anomalies both in the coupled and uncoupled fields indicating a dominant role of the atmosphere in generating the sst anomalies on the other hand analyses of the temporal variability in the three runs suggest an active role of sst anomalies in determining the polarity of the air sea coupled variability longer than the interannual time scale a combined analysis of forcing sst upper air height and the response sst anomalies in the uncoupled run identified that a patch of positive sst anomalies in the mid latitude band around 40 n effectively excite the positive phase of the nao which in turn reinforces the tripole sst anomalies this relationship was further confirmed by a nine member ensemble agcm experiment forced by the relevant sst anomalies since the forcing and response sst anomaly patterns bear some resemblance these results manifest positive feedback at work in the coupled atmosphere ocean patterns the processes responsible for this positive feedback were elaborated by a series of linear model experiments the local thermal adjustment of the atmosphere to the sst anomalies results in increased precipitation over the gulf stream region associated diabatic heating applied to a linear baroclinic model yields a positive height response to the east which highly influences the southern part of the nao this stationary response in turn induces a northward deflection in the storm track activity leading to an eddy vorticity feedback that tends to force the positive phase of the nao

influences of atlantic climate change on the tropical pacific via the central american isthmus recent global coupled model experiments suggest that the atmospheric bridge across central america is a key conduit for atlantic climate change to affect the tropical pacific a high resolution regional ocean atmosphere model roam of the eastern tropical pacific is used to investigate key processes of this conduit by examining the response to a sea surface temperature sst cooling over the north atlantic the atlantic cooling increases sea level pressure driving northeasterly wind anomalies across the isthmus of panama year round while the atmospheric response is most pronounced during boreal summer fall when the tropical north atlantic is warm and conducive to deep convection the pacific sst response is strongest in winter spring when the climatological northeast trade winds prevail across the isthmus during winter the northeasterly cross isthmus winds intensify in response to the atlantic cooling reducing the sst in the gulf of panama by cold and dry advection from the atlantic and by enhancing surface turbulent heat flux and mixing this gulf of panama cooling reaches the equator and is amplified by the bjerknes feedback during boreal spring the equatorial anomalies of sst and zonal winds dissipate quickly in early summer as the seasonal development of the cold tongue increases the stratification of the atmospheric boundary layer and shields the surface from the atlantic influence that propagates into the pacific as tropospheric rossby waves the climatological winds over the far eastern pacific warm pool turn southwesterly in summer fall superimposed on which the anomalous northesterlies induce a weak sst warming there the roam results are compared with global model water hosing runs to shed light on intermodel consistency and differences in response to the shutdown of the atlantic meridional overturning circulation implications for interpreting paleoclimate changes such as heinrich events are discussed the results presented here also aid in understanding phenomena in the present climate such as the central american midsummer drought and atlantic multidecadal oscillation

marine redox variability from baltica during extinction events in the latest ordovician early silurian abstract it is well documented that upper ordovician and silurian successions record multiple marine turnover events including the second largest mass extinction in the phanerozoic widespread glaciation and multiple global carbon cycle perturbations whereas causal mechanisms for the late ordovician major mass extinction event involving climate paleoceanographic variation and 13c records have been published similar records remain poorly constrained for subsequent extinction events in the early silurian here we present new organic matter carbon isotope 13corg chemostratigraphy and corresponding paleoredox proxies fe speciation mn v mo and pyrite sulfur isotopes from two organic rich drill core sections in sweden and latvia that span the upper katian through lower wenlock stages 446 431 ma pyritized fe and bulk sedimentary mn concentrations from upper ordovician strata in southern sweden suggest a local redox shift to more reducing conditions in the late hirnantian possibly including euxinic anoxic and sulfidic water column conditions that coincide with the second mass extinction pulse the new high resolution 13corg and 34spyr datasets from the late aeronian early silurian interval within both drill cores show positive excursions that are broadly coincident with the associated sandvika and sedgwickii extinction events independently fe speciation and bulk sedimentary trace metal data from this late aeronian interval record locally euxinic conditions in both the deep basinal sweden and distal shelf latvia settings before and during the late aeronian positive 13c excursion this multiproxy paleoredox dataset provides the first direct evidence for local to regional expansion of reducing marine conditions coincident with this early silurian late aeronian biotic event and positive 13c excursion additionally new 34spyr values spanning the llandovery wenlock boundary interval in the latvia core show a positive excursion coincident with fe speciation and trace metal enrichments that imply a local redox perturbation with intermittently euxinic bottom waters during the rising limb of the ireviken positive 13c excursion the combination of these geochemical data for local to regional scale more data required for global interpretations changes in marine redox conditions with paleobiological records and evidence for eustatic sea level rise indicate that environmental stresses related to an expansion of anoxic to euxinic conditions were a probable driver for several extinction events during the latest ordovician early silurian

a climatology of central american gyres abstractcentral american gyres cags are large closed cyclonic circulations that occur during the rainy season may november which can yield exceptional rainfall leading to catastrophic flooding and large societal impacts a reanalysis based climatology of cags is developed from an algorithm that distinguishes cag cases from other systems this algorithm identified cag cases based on circulation intensity a broad radius of maximum winds and the existence of closed earth relative cyclonic flow based on these criteria 47 cag cases were identified from 1980 to 2010 featuring a bimodal distribution of cases with maxima in may june and september november cag cases are composited into two categories based on their upper tropospheric pv structure nonbaroclinic cags are more common n 42 and characterized by an upper tropospheric anticyclone while baroclinic cags are less common n 5 and characterized by an upper tropospheric trough whereas a nonbaroclinic cag has anomalous moisture and preci

long term hydrographic changes at 52 and 66 w in the north atlantic subtropical gyre caribbean abstract in july september 1997 two hydrographic lines were done in the western n atlantic along longitudes of 52 and 66 w as part of the woce one time hydrographic survey of the oceans each of these two lines approximately repeated earlier ones done during the international geophysical year s igy and the mid 1980s because of this repeated sampling long term hydrographic changes in the water masses can be examined in this report we focus on temperature and salinity changes within the subtropical gyre mainly between latitudes of 20 and 35 n and compare our results to those presented by bryden et al 1996 who examined changes along a zonal line at 24 n most recently occupied in 1992 since this most recent 24 n section in 1992 substantial changes have occurred in the western part of the subtropical gyre at the depths of the labrador sea water lsw in particular we see clear evidence for colder fresher labrador sea water throughout the gyre on our two recent sections that was not yet present in 1992 at similar longitudes along 24 n at shallower depths inhabited by waters that are an admixture of mediterranean mw and antarctic intermediate waters aaiw our recent survey shows an increase in salinity which can only be attributed to changes in water masses on potential temperature or neutral density surfaces furthermore waters above the mw aaiw layer and into the deeper part of the main pycnocline have continued to become saltier and warmer throughout the 40 year period spanned by our sections these latter changes have been dominantly due to a vertical sinking of density surfaces as t s changes in density surfaces are small but depths of individual t s horizons have increased with time the net change since the igy shows a mean temperature increase between 800 and 2500 m depth at a rate of 0 57 c century with a corresponding steric sea level rise of 1 mm yr and a net downward heave with small values near the top and bottom and a maximum rate of 2 7 m yr at 1800 m depth changes in the deep caribbean indicate a warming since the igy due to temperature increases of the inflowing source waters in the subtropical gyre at 1800m depth but no significant change in the deep salinity

testing the limits of paleozoic chronostratigraphic correlation via high resolution 500 k y integrated conodont graptolite and carbon isotope δ13ccarb biochemostratigraphy across the llandovery wenlock silurian boundary is a unified phanerozoic time scale achievable the resolution and fidelity of global chronostratigraphic correlation are direct functions of the time period under consideration by virtue of deep ocean cores and astrochronology the cenozoic and mesozoic time scales carry error bars of a few thousand years k y to a few hundred k y in contrast most of the paleozoic time scale carries error bars of plus or minus a few million years m y and chronostratigraphic control better than 1 m y is considered high resolution the general lack of paleozoic abyssal sediments and paucity of orbitally tuned paleozoic data series combined with the relative incompleteness of the paleozoic stratigraphic record have proven historically to be such an obstacle to intercontinental chronostratigraphic correlation that resolving the paleozoic time scale to the level achieved during the mesozoic and cenozoic was viewed as impractical impossible or both here we utilize integrated graptolite conodont and carbonate carbon isotope delta c 13 carb data from three paleocontinents baltica avalonia and laurentia to demonstrate chronostratigraphic control for upper llandovery through middle wenlock telychiansheinwoodian similar to 436 426 ma strata with a resolution of a few hundred k y the interval surrounding the base of the wenlock series can now be correlated globally with precision approaching 100 k y but some intervals e g uppermost telychian and upper shein woodian are either yet to be studied in sufficient detail or do not show sufficient biologic speciation and or extinction or carbon isotopic features to delineate such small time slices although producing such resolution during the paleozoic presents an array of challenges unique to the era we have begun to demonstrate that erecting a paleozoic time scale comparable to that of younger eras is achievable less

the south pacific current the southern hemisphere subtropical front stf is a narrow zone of transition between upper level subtropical waters to the north and subantarctic waters to the south it is found near 40 degrees s across the south atlantic and south indian oceans and is associated with an eastward geostrophic current band the current band in each basin is found at or just north of the surface front except near the eastern boundaries where most of the subtropical waters turn north into the eastern limbs of the subtropical gyres the bands associated with the stf are thus distinct features separated from the strong zonal flows of the antarctic circumpolar current farther south the authors have referred to the current bands in the two respective oceans as the south atlantic current and the south indian ocean current in this paper the authors use the historical database from the south pacific ocean to investigate the geostrophic flow associated with the stf there the stf extends across the southern tasman sea from south of tasmania to southern new zealand and a weak eastward flow appears to be associated with it the transport amounts to only about 3 sv 1sv 10 6 m 3 s 1 little of which passes south of new zealand mixing within the eddy rich tasman sea may account for this weakness while also setting up another more significant front in the northern tasman sea the tasman front it branches off from the east australian current toward the north of new zealand along which moves a flow of about 14 sv after passing north of new zealand a portion of this current flows east to contribute to a current band near 30 degrees s while another portion turns south as the east auckland current and meets with subantarctic waters near chatham rise 44 degrees s thus reestablishing the stf an enhanced eastward current band is associated with the front there one that extends across the remainder of the south pacific and is referred to as the south pacific current in comparison with its counterparts in the other basins which typically begin by carrying 30 sv atlantic to 60 sv indian in the upper 1000 m in their western portions before weakening to 10 15 sv in the east the south pacific current is weak near chatham rise it starts with a transport of approximately 5 sv and it remains near this strength as it shifts gradually north across the basin toward south america the current appears to split into two smaller bands in the region of 115 degrees 85 degrees w while near 28 degrees 5 83 degrees w it begins to turn more strongly north and becomes shallower and weaker potential vorticity distributions indicate that this current acts as an impediment toward the northward spreading of antarctic intermediate water but why the south pacific current east of new zealand should be so much weaker than its counterparts in the other basins is not particularly clear it may be due to the presence of new zealand and other topographic barriers to deep now east of australia to the axis of the subtropical gyre in the south pacific shifting more rapidly southward with depth than those elsewhere thus causing greater reductions in the underlying zonal velocities and to strong poleward eddy heat and salt fluxes in the other two basins leading to smaller cross stf gradients in the pacific

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

observations of a convectively coupled kelvin wave in the eastern pacific itcz abstract a case study of a convectively coupled kelvin wave in the eastern pacific intertropical convergence zone itcz is presented as observed during the 1997 pan american climate studies pacs tropical eastern pacific process study tepps the large scale convective envelope associated with this disturbance with a zonal scale of approximately 1000 2000 km propagates eastward at 15 m s 1 along the mean convective axis of the itcz this envelope consists of many smaller scale westward moving convective elements with zonal scales on the order of 100 500 km as the convectively coupled kelvin wave disturbance propagates eastward it exerts a strong control on local convection radar and vertical profiler data collected aboard the noaa r v ronald h brown during the wave passage show that convection deepens rapidly as the kelvin wave approaches from the west progressing from isolated shallow cumuli to organized deep convective features within just 12 h initially rainfall in the vicinity of the s

hydrography of the eastern south pacific ocean results from the sonne 102 cruise may june 1995 abstract full depth conductivity temperature depth hydrographic measurements were taken in may june 1995 along 28 15 35 15 and 43 15 s from the chilean coast to 86 88 w from the r v sonne sections of potential temperature salinity neutral density and oxygen are presented to illustrate the water column structure in this sparsely sampled region a more comprehensive database on all available hydrographic data from the region was compiled these data and available meteorological data are used to help in the interpretation of the sonne results a number of important features found in the sections are discussed including a shallow salinity minimum apparently ventilated from south of 37 s salt fingering as a possible mechanism to transport high salinity subtropical water into the shallow salinity minimum equatorial subsurface water subantarctic mode water and antarctic intermediate water geostrophic calculations of alongshore flow show the poleward peru chile undercurrent at each of the three sections with a poleward descending core and peak velocities of 10 cm s 1 as in earlier works a deep pacific outflow is found near the chilean coast part of a clockwise deep circulation in the chile basin

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

diurnal cycle of convection during the 2004 north american monsoon experiment abstract the diurnal cycle of summer monsoon convection in the coastal mountainous region of northwestern mexico is investigated using data from the 2004 north american monsoon experiment name data from a special sounding network consisting of research and operational sites have been quality controlled and combined with surface wind profiler and pibal observations to create a gridded dataset over the name domain this study concentrates on results from the interior portion of the name sounding network where gridded analysis fields are independent of model data special attention is given to surface and pibal observations along the western slope of the sierra madre occidental smo in order to obtain an optimal analysis of the diurnally varying slope flows results show a prominent sea breeze land breeze cycle along the western slopes of the smo there is a deep return flow above the afternoon sea breeze as a consequence of the elevated smo immediately to the east the upslope flow along the western

the low level circulation of the north american monsoon as revealed by quikscat five years 1999 2003 of near surface quikscat ocean winds over the gulf of california and northeast pacific ocean are used to characterize the changes in the low level circulation associated with the north american monsoon our analysis shows that the onset of the summer season is accompanied by a seasonal reversal of the flow along the gulf of california with the establishment of a time mean southerly wind throughout the gulf this reversal not evident in the global reanalysis products occurs in late spring and precedes the onset of the monsoonal rains in the core of the monsoon the time mean flow is found to be modulated by transient events namely gulf surges detected in the near surface wind field as periods of enhanced southerly flow which typically originate at the southern end of the gulf and propagate northward the histogram of the summertime along shore winds identifies these surges as a distinct population of events readily distinguishable from the background flow

surges over the gulf of california during the mexican monsoon abstract northward surges of relatively cool moist maritime air from the tropical pacific into the southwestern united states occur via the gulf of california every summer during the mexican monsoon season these surges advect large amounts of moisture northward and promote increased convective activity in arizona mesoscale model output from 32 successive 24 h simulations are used to examine both the large scale and mesoscale features associated with surge events model data are compared to high resolution aircraft measurements on two days showing clearly that the model is capable of reproducing many of the detailed structures found in the observations results from a large scale analysis indicate that strong surges are produced in the model when a midlatitude trough is in the proper phase relationship with a tropical easterly wave weak surges occur when this relationship is missing

east pacific ocean eddies and their relationship to subseasonal variability in central american wind jets subseasonal variability in sea surface height ssh over the east pacific warm pool off central america is investigated using satellite observations and an eddy resolving ocean general circulation model ssh variability is organized into two southwest tilted bands on the northwest flank of the tehuantepec and papagayo wind jets and collocated with the thermocline troughs eddy like features of wavelength similar to 600 km propagate southwestward along the high variance bands at a speed of 9 13 cm s wind fluctuations are important for eddy formation in the gulf of tehuantepec with a recurring interval of 40 90 days when forced by satellite wind observations the model reproduces the two high variance bands and the phase propagation of the tehuantepec eddies our observational analysis and model simulation suggest the following evolution of the tehuantepec eddies on the subseasonal timescale in response to the gap wind intensification a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks an energetics analysis based on the model simulation indicates that besides wind work barotropic and baroclinic instabilities of the mean flow are important for the eddy growth both observational and model results suggest a re intensification of the anticyclonic eddy in response to the subsequent wind jet event off papagayo ocean eddy formation is not well correlated with local wind jet variability in both the gulfs of tehuantepec and papagayo subseasonal ssh variability is preferentially excited on the northwest flank of the wind jet factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed

mean three dimensional circulation in the northeast tropical pacific abstract historical xbt data are used to construct a mean climatology of the three dimensional geostrophic circulation in the northeast tropical pacific southwest of mexico and central america and are diagnosed based on linear dynamics forced with satellite scatterometer winds unlike the familiar central tropical pacific where the zonal scales are very large and the wind forcing nearly a function of latitude alone the north pacific east of about 120 w is strongly influenced by wind jets blowing through gaps in the central american cordillera the curl imposed by these wind jets imprints on the ocean producing a distinctive pattern of thermocline topography and geostrophic currents that are consistent with the sverdrup balance notably the weakening of the north equatorial countercurrent near 110 w is due to the wind forcing given the observed stratification and wind stress curl planetary vorticity conservation also determines the distribution of vertical velocity in the region with about 3 5 sv

diurnal cycle of surface flows during 2004 name and comparison to model reanalysis abstract during the north american monsoon experiment name an unprecedented surface dataset was collected over the core monsoon region observations from 157 surface sites in this region along with twice daily quick scatterometer quikscat oceanic winds were quality controlled and processed into a gridded dataset covering the domain 15 40 n 90 120 w at 1 h 0 25 resolution for the period from 1 july to 15 august using this dataset the mean temporal variability and diurnal characteristics of the monsoon surface flow are documented with detail not previously possible being independent of model data over land these objectively analyzed surface products are compared to similar analyses from a special north american regional reanlysis for name narr name that was produced for the same period observed surface fields indicate that a robust land sea breeze circulation is present over most of the gulf of california goc region in response to the strong diurnal heating of landmasses on both sides

modulation of eastern north pacific hurricanes by the madden julian oscillation abstract hurricane and tropical storm statistics verify the modulation of eastern pacific tropical systems by the madden julian oscillation mjo as hypothesized by maloney and hartmann over twice as many named tropical systems hurricanes and tropical storms accompany equatorial 850 mb westerly anomalies than accompany equatorial easterly anomalies and the systems that do exist are stronger hurricanes are over four times more numerous during westerly phases of the mjo than during easterly phases the current study constructs a composite life cycle of the mjo during may november 1979 95 using an index based on the 850 mb equatorial zonal wind equatorial kelvin waves propagating eastward from convective regions of the western pacific ocean alter dynamical conditions over the eastern pacific ocean westerly easterly equatorial 850 mb wind anomalies are accompanied by enhanced suppressed convection over the eastern pacific hurricane region convection locally amplifies the wind anomalies over the ea

changes in the advection of antarctic intermediate water to the northern chilean coast during the last 970 kyr 1 the antarctic intermediate water aaiw is a key player in global scale oceanic overturning processes and an important conduit for heat fresh water and carbon transport the aaiw past variability is poorly understood mainly due to the lack of sedimentary archives at intermediate water depths we present records of benthic stable isotopes from sediments retrieved with the seafloor drill rig marum mebo at 956 m water depth off northern chile geob15016 27 29 48 s 71 07 58 w that extend back to 970 ka the sediments at this site are presently deposited at the boundary between aaiw and pacific deep water pdw for previous peak interglacials our results reveal similar benthic 13c values at site geob15016 and of a newly generated stack of benthic 13c from various deep pacific cores representing the average pdw this suggests unlike today the absence of aaiw at the site and the presence of nearly pure pdw in contrast more positive 13c values at site geob15016 compared to the stack imply a considerable aaiw contribution during cold phases of interglacials and especially during glacials besides we used three short sediment cores to reconstruct benthic 13c values from the aaiw core during the last glacial and found a 13c signature similar to today s assuming that this was the case also for the past 970 kyr we demonstrate that sea level changes and latitudinal migrations of the aaiw formation site can only account for about 50 of the full range of past 13c increases at site geob15016 during cold periods other processes that could explain the remaining of the positive 13c anomalies are increases in glacial aaiw production and or deeper convection of the aaiw with respect to preceding interglacials

zonal mean wind the indian monsoon and july drying in the western atlantic subtropics 1 a fully closed zonal momentum budget is decomposed to explain the occurrence of zonal mean easterlies at subtropical latitudes in july eddy momentum fluxes from stationary eddies most prominently the western sector of the indian monsoon tibetan high are the primary mechanism governing the negative tendency of zonal mean momentum near 20 n 30 n this strengthening of the zonal mean easterlies in july is significantly correlated with the concurrent strengthening of the north atlantic subtropical high nash and the rainfall deficit in the western north atlantic watl interannual variations of the indian monsoon reflect changes in the strength of these zonal mean easterlies with downstream teleconnections on the westward displacement of the nash and precipitation in the watl an increase in rainfall in india from june to july corresponds to a decrease in rainfall in the watl

mean surface circulation and mesoscale turbulent flow characteristics in the eastern south pacific from satellite tracked drifters 1 circulation of the eastern south pacific region 10 34 s 70 100 w was studied using drifting buoy trajectories from 1979 to 2003 three different current regimes were highlighted the south equatorial current flowing westward north of 26 s with surface velocities of 7 8 cm s 1 the south pacific current an eastward current of 2 cm s 1 south of 25 30 s and the chile peru current a northwestward flow of 6 cm s 1 found to the east of 82 w and south of 22 s the velocity variance distribution showed the regional flow to be anisotropic in nature maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns with higher energy levels near the south american coast the lagrangian time and length scales of the turbulent flow revealed typical values of 5 9 0 6 days and 40 7 5 4 km in the zonal direction and of 3 5 0 4 days and 29 3 4 km in the meridional direction the estimated diffusivities were 4 9 0 5 107 cm2 s 1 and 2 6 0 3 107 cm2 s 1 in the eastward and northward directions respectively finally we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large scale circulation mean horizontal heat and salt diffusive fluxes were around 25 w m 2 and 50 g m 2 d 1

seasonal climatology of hydrographic conditions in the upwelling region off northern chile over 30 years of hydrographic data from the northern chile 18os 24os upwelling region are used to calculate the surface and subsurface seasonal climatology extending 400 km offshore the data are interpolated to a grid with sufficient spatial resolution to preserve cross shelf gradients and then presented as means within four seasons austral winter july september spring october december summer january march and fall april june climatological monthly wind forcing surface temperature and sea level from three coastal stations indicate equatorward upwelling favorable winds throughout the year weakest in the north seasonal maximum alongshore wind stress is in late spring and summer december march major water masses of the region are identified in climatological t s plots and their sources and implied circulation discussed surface fields and vertical transects of temperature and salinity confirm that upwelling occurs year round strongest in summer and weakest in winter bringing relatively fresh water to the surface nearshore surface geostrophic flow nearshore is equatorward throughout the year during summer an anticyclonic circulation feature in the north which extends to at least 200 rn depth is evident in geopotential anomaly and in both temperature and geopotential variance fields subsurface fields indicate generally poleward flow throughout the year strongest in an undercurrent near the coast this undercurrent is strongest in summer and most persistent and organized in the south south of 21os a subsurface oxygen minimum centered at 250 m is strongest at lower latitudes low salinity subsurface water intrudes into the study area near 100 m predominantly in offshore regions strongest during summer and fall and in the southernmost portion of the region the climatological fields are compared to features off baja within the somewhat analogous california current and to measurements from higher latitudes within the chile peru current system

importance of water mass formation regions for the air sea co2 flux estimate in the southern ocean 1 carioca drifters and ship data from several cruises in the subantarctic zone saz of the pacific ocean approximately 40 s 55 s have been used in order to investigate surface co2 partial pressure pco2 and dissolved inorganic carbon dic patterns the highest dic values were determined in regions of deep water formation characterized by deep mixed layer depths mld as estimated from argo float profiles as a result these areas act as sources of co2 to the atmosphere using an empirical linear relationship between dic sea surface temperature sst and mld we then combine dic with at based on salinity and compute pco2 finally we derive monthly fields of air sea co2 flux in the saz our fit predicts the existence of a realistic seasonal cycle close to equilibrium with the atmosphere in winter and a sink when biological activity takes place it also reproduces the impact that deep water formation regions close to the subantarctic front saf and in the eastern part of the saz have on the uptake capacity of the area these areas undersampled in previous studies have high pco2 and as a result our estimates 0 05 0 03 pgc yr 1 indicate that the pacific saz acts as a weaker sink of co2 than suggested by previous studies which neglect these source regions

analysis of the 13 14 july gulf surge event during the 2004 north american monsoon experiment abstract gulf surges are disturbances that move northward along the gulf of california goc frequently advecting cool moist air from the goc or eastern tropical pacific ocean into the deserts of the southwest united states and northwest mexico during the north american monsoon nam little attention has been given to the dynamics of these disturbances because of the lack of reliable high resolution data across the nam region high temporal and spatial observations collected during the 2004 north american monsoon experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13 14 july 2004 integrated sounding systems deployed along the east coast of the goc and an enhanced network of rawinsonde sites across the nam region are used in this study observations show that the 13 14 july gulf surge occurred in two primary stages the first stage was preceded by anomalous low level warming along the northern goc on 13 july sharp cooling moistening and increased

the relationship of transient upper level troughs to variability of the north american monsoon system abstract relationships between transient upper tropospheric troughs and warm season convective activity over the southwest united states and northern mexico are explored analysis of geopotential height and vorticity fields from the north american regional reanalysis and cloud to ground lightning data indicates that the passage of mobile inverted troughs ivs significantly enhances convection when it coincides with the peak diurnal cycle 1800 0900 utc over the north american monsoon nam region the preferred tracks of ivs during early summer are related to the dominant modes of pacific sea surface temperature sst variability when la nina like el nino like conditions prevail in the tropical pacific and the eastern north pacific has a horseshoe shaped negative positive sst anomaly ivs preferentially track farther north south and are slightly typically one iv more less numerous these results point to the important role that synoptic scale disturbances play in modulating the diurnal cycle

warming and circulation change in the eastern south pacific ocean deep ocean temperature salinity and dissolved oxygen observations in the eastern south pacific ocean collected during the late austral fall in 1995 are compared with observations made there 28 years earlier during the same season and similar el nino southern oscillation phase warming observed above 800 m at 43 s reflects the production of warmer subantarctic mode water in recent decades warming observed above 1600 m at 28 s is due to downward isotherm displacement and southward movement of water masses by 100 200 km as revealed by joint analysis of temperature and oxygen data such changes would be expected for a weaker subtropical gyre in the south pacific an observed oxygen decrease between about 1800 m and 2900 m at 28 s may indicate enhanced southward boundary current flow at mid depths off chile

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

influence of spatial resolution on diurnal variability during the north american monsoon abstract diurnal variability is an important yet poorly understood aspect of the warm season precipitation regime over southwestern north america in an effort to improve its understanding diurnal variability is investigated numerically using the fifth generation pennsylvania state university psu ncar mesoscale model mm5 the goal herein is to determine the possible influence of spatial resolution on the diurnal cycle the model is initialized every 48 h using the operational ncep eta model 212 grid 40 km model analysis model simulations are carried out at horizontal resolutions of both 9 and 3 km overall the model reproduces the basic features of the diurnal cycle of rainfall over the core monsoon region of northwestern mexico and the southwestern united states in particular the model captures the diurnal amplitude and phase with heavier rainfall at high elevations along the sierra madre occidental in the early afternoon that shifts to lower elevations along the west slopes in the evening a

the lower atmosphere over the gulf of california automated meteorological observations at coastal and island stations instrumented aircraft flights and coastal soundings were made between july 1983 and june 1985 to define the variations of the lower atmosphere over the northern half of the gulf of california during the two important climatic seasons the mid latitude winter and the subtropical summer a marine layer is well defined over water during both seasons but dissipates within a few kilometers inland the winter large scale pressure field is dominated by the great basin high over the southwestern united states modulated by upper level synoptic activity it causes 3 to 6 days events of northwesterly winds 8 12 m s 1 directed along the gulf s axis which are coherent over basin scales and bring cool dry desert air over the gulf the vertical scale of these winds is 700 1000 m over land on the western side of the gulf close to the height of the baja california mountains but only 100 400 m over water defined by the wintertime inversion cross gulf winds related to topographic effects during upper level trough passages over baja california are particularly intense in the northwestern portion of the gulf the winter marine layer is defined by a 1 to 4 5 c temperature inversion and a dew point temperature of 6 11 c a moisture content of 6 8 g kg 1 weak subsidence reduces dew point values to 4 c above the inversion winter winds above the marine layer are coherent 0 8 across the width of the gulf the summer large scale pressure field is dominated by a thermal low over the southwestern united states and drives weak 2 5 m s 1 southeasterly winds also directed primarily along the gulf which are less spatially uniform than winter winds air temperature and moisture content are rather constant and topographic effects are absent the summer marine layer is on the order of 200 300 m thick with dew point temperatures of 26 28 c 21 24 g kg 1 and capped by a weak temperature inversion 1 2 c over water aloft the dew point temperature is 17 21 c and winds are weak and uncorrelated across the width of the gulf during june and early july 1984 four week long pulses of southeasterly winds 10 m s 1 support the existence reported previously of moisture surges from the gulf into the sonoran desert a dynamical analysis of subdiurnal motions shows that the cross gulf momentum balance is geostrophic the along gulf balance is ageostrophic with the along gulf pressure gradient opposed by friction at the surface these results are consistent with a scale analysis of the equations of motion in the marine layer over the gulf of california

mesoscale variability and nutrient phytoplankton distributions off central southern chile during the upwelling season the influence of mesoscale eddies abstract mesoscale features are recurrently found in the coastal transition zone ctz off central southern chile 35 40 s a region characterized by seasonal wind driven coastal upwelling in this study oceanographic data from two consecutive cruises carried out during the upwelling season january 2009 were combined with satellite time series data in order to characterize the structure and evolution of mesoscale eddies and to explore their influence on phytoplankton structure and nutrient distribution in the context of organic carbon exchanges between the coastal upwelling zone and the ctz two coastally generated contiguous mesoscale eddies 2 months old were characterized a surface cyclonic eddy cc1 and a subsurface anticyclonic eddy aa1 the distributions of salinity and dissolved oxygen together with nutrients suggested that both eddies were sites of vertical injection of high nutrient concentrations from the equatorial subsurface water mass essw into the upper layer in the ctz in addition eddy aa1 in combination with an upwelling plume was involved in the offshore advection of nutrients from the core of the essw located in the coastal zone at shallow depths

the central american midsummer drought regional aspects and large scale forcing abstract the midsummer drought msd is a diminution in rainfall experienced during the middle of the rainy season in southern mexico and central america as well as in the adjacent caribbean gulf of mexico and eastern pacific seas the aim of this paper is to describe the regional characteristics of the msd and to propose some possible forcing mechanisms satellite and in situ data are used to form a composite of the evolution of a typical msd which highlights its coincidence with a low level anticyclone centered over the gulf of mexico and associated easterly flow across central america the diurnal cycle of precipitation over the region is reduced in amplitude during midsummer the msd is also coincident with heavy precipitation over the sierra madre occidental part of the north american monsoon reanalysis data are used to show that the divergence of the anomalous low level flow during the msd is the main factor governing the variations in precipitation a linear baroclinic model is used to show

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

multiscale variability of the flow during the north american monsoon experiment abstract the 2004 north american monsoon experiment name provided an unprecedented observing network for studying the structure and evolution of the north american monsoon this paper focuses on multiscale characteristics of the flow during name from the large scale to the mesoscale using atmospheric sounding data from the enhanced observing network the onset of the 2004 summer monsoon over the name region accompanied the typical northward shift of the upper level anticyclone or monsoon high over northern mexico into the southwestern united states but in 2004 this shift occurred slightly later than normal and the monsoon high did not extend as far north as usual consequently precipitation over the southwestern united states was slightly below normal although increased troughiness over the great plains contributed to increased rainfall over eastern new mexico and western texas the first major pulse of moisture into the southwest occurred around 13 july in association with a strong gulf of californi

optimal estimation of hydrographic station data and derived fields abstract optimal estimation is applied to contouring and analysis of hydrographic sections measured fields such as temperature and salinity and derived fields such as geostrophic velocity are decomposed into large scale and small scale components first a heavily sampled basin scale field is estimated and subtracted from the data a small scale field barely resolved by the hydrography is then found from the residuals the power and utility of the technique are illustrated by means of examples using a short section from the straits of florida and a transatlantic section along 24 n

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

silurian llandovery wenlock conodonts from the base of the heceta limestone southeastern alaska the base of the heceta limestone exposed on cap island in southeastern alaska appears to lie close to the top of the celloni zone the succeeding 8 m of strata lies within the amorphognathoides zone and part of the ranuliformis zone this cap island faunal sequence consists of 12 previously described and largely cosmopolitan taxa and nine new possibly more provincial taxa it is particularly characterized by the distinctive new taxa tuxekania barbarajeanae neospathognathodus chapini tokeenia furcata and aspelundia capensis the section is of late llandovery to early wenlock silurian age

convection and easterly wave structures observed in the eastern pacific warm pool during epic 2001 abstract during september october 2001 the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 intertropical convergence zone itcz field campaign focused on studies of deep convection in the warm pool region of the eastern pacific this study combines c band doppler radar sounding and surface heat flux data collected aboard the r v ronald h brown during epic to describe the kinematic and thermodynamic states of the itcz environment together with tendencies in convective structure lightning rainfall and surface heat fluxes as a function of 3 5 day easterly wave phase three easterly waves were observed at the location of the r v brown during epic 2001 wind and thermodynamic data reveal that the wave trough axes exhibited positively correlated u and winds a slight westward phase tilt with height and relatively strong weak northeasterly tropospheric shear following the trough ridge axis temperature and humidity perturbations exhibited mid to

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

south pacific eastern subtropical mode water abstract the structure formation and destruction of south pacific eastern subtropical mode water spestmw are analyzed geographic extent and water properties are discussed by using high quality ctd sections collected between 1991 and 1996 defined as having a planetary potential vorticity magnitude of less than 3 10 10 m 1 s 1 spesmtw has a volume of about 1 1 1015 m3 estimated from ctd data the ventilation of this mode water is described by using data from a high resolution xbt section in concert with 30 month time series from profiling ctd floats some of the first argo deployments published subduction rates allow a mode water formation rate estimate of 8 7 106 m3 s 1 combining this estimate with the volume yields a residence time of about 4 years the density compensating covarying patterns of late winter surface temperature and salinity in the ventilation region of spestmw are shown to contribute to the strength of the mode water however while the destabilizing salinity gradient in sp

air sea interaction over the eastern pacific warm pool gap winds thermocline dome and atmospheric convection high resolution satellite observations are used to investigate air sea interaction over the eastern pacific warm pool in winter strong wind jets develop over the gulfs of tehuantepec papagayo and panama accelerated by the pressure gradients between the atlantic and pacific across narrow passes of central american cordillera patches of cold sea surface temperatures ssts and high chlorophyll develop under these wind jets as a result of increased turbulent heat flux from the ocean and enhanced mixing across the base of the ocean mixed layer despite a large decrease in sst exceeding 38c in seasonal means the cold patches associated with the tehuantepec and papagayo jets do not have an obvious effect on local atmospheric convection in winter since the intertropical convergence zone itcz is located farther south the cold patch of the panama jet to the south on the other hand cuts through the winter itcz and breaks it into two parts a pronounced thermocline dome develops west of the gulf of papagayo with the 208c isotherm only 30 m deep throughout the year in summer when the panama jet disappears and the other two wind jets weaken sst is 0 58c lower over this costa rica dome than the background this cold spot reduces local precipitation by half punching a hole of 500 km in diameter in the summer itcz the dome underlies a patch of open ocean high chlorophyll this thermocline dome is an ocean dynamic response to the positive wind curls south of the papagayo jet which is optimally oriented to excite ocean rossby waves that remotely affect the ocean to the west the meridionally oriented tehuantepec and panama jets by contrast only influence the local thermocline depth with few remote effects on sst and the atmosphere the orographical triggered air sea interaction described here is a good benchmark for testing high resolution climate models now under development

origins and mechanisms of eastern pacific tropical cyclogenesis a case study the genesis of hurricane hernan 1996 in the eastern pacific was investigated using gridded analyses from the european centre for medium range weather forecasts and gridded outgoing longwave radiation hernan developed in association with a wave in the easterlies that could be tracked back to africa in longitude time plots of the filtered y component of the wind 2 6 day period at 700 mb the wave crossed central america near lake nicaragua with little change in its southwest northeast tilt but the most intense convection shifted from near the wave axis in the caribbean to west of the wave axis in the pacific the wave intensified as it moved through a barotropically unstable background state defined by a low pass filter with a 20 day cutoff in the western caribbean and eastern pacific a surge in the southwesterly monsoons and enhanced convection along 108n occurred to the west of the 700 mb wave in the pacific and traveled with the wave this had the effect of enhancing low level vorticity over a wide region ahead of the 700 mb wave available evidence suggests that additional low level vorticity was produced by enhanced flow from the north through the isthmus of tehuantepec as the 700 mb wave approached depression formation did not occur until 6 12 h after the 700mb wave reached this region of large low level vorticity in the gulf of tehuantepec eastern pacific sst and vertical wind shear magnitude are typically favorable for tropical cyclone development in northern hemisphere summer and early fall because the favorable mountain interaction and the surge in the low level monsoons appear to relate directly to the wave in the easterlies it is argued that the strength of such waves reaching central america from the east is the single most important factor in whether subsequent eastern pacific cyclogenesis occurs possible parallels with western pacific cyclogenesis are discussed

integrated δ13ccarb conodont and graptolite biochemostratigraphy of the silurian from the illinois basin and stratigraphic revision of the bainbridge group

controls on sedimentary nitrogen isotopes along the chile margin chilean margin sedimentary n isotope records have been the focus of paleoceanographic studies examining the extent of water column denitrification in the eastern south pacific in the past here we use 15n 14n of nitrate and surface sedimentary n along the chilean coast to investigate the relative contributions of water column denitrification and surface nitrate assimilation by phytoplankton to the sedimentary n isotope record off northern and central chile subsurface enrichment of 15no3 is associated with the lowest oxygen concentrations and maximum nitrate deficits the product of water column denitrification locally at 21 s and through the transport of denitrified waters to the south while elevated the 15n of pycnocline nitrate shows no distinct trend with distance from the omz and is nearly homogenous within the shallow subsurface layer presumably due to lateral circulation along the margin moreover an isotopically depleted and relatively uniform layer exists within the shallow subsurface possibly as a result of the remineralization of newly fixed nitrogen that may work to further homogenize the 15n of the upwelling nitrate whereas the high 15n of sedimentary n in the region is clearly a product of denitrification and its isotopic imprint on nitrate along the margin the northward increase in sedimentary 15n from higher southern latitudes also reflects the degree of surface layer nitrate consumption by phytoplankton the northward increase in sedimentary 15n corresponds to a regional decrease in the surface nitrate concentration and isotopic fractionation during nitrate assimilation is apparent in shallow nitrate 15n a comparison of the 15n in shallow subsurface nitrate and sedimentary n suggests that north of 30 s nearly complete nitrate consumption causes the 15n of sediments to converge on that of the nitrate supply such that denitrification should be the dominant signal in downcore 15n records from these latitudes moreover the lateral homogeneity of the denitrification signal in the subsurface within this region suggests that such records will provide robust reconstructions of denitrification intensity

the midsummer drought over mexico and central america abstract the annual cycle of precipitation over the southern part of mexico and central america exhibits a bimodal distribution with maxima during june and september october and a relative minimum during july and august known as the midsummer drought msd the msd is not associated with the meridional migration of the intertropical convergence zone itcz and its double crossing over central america but rather with fluctuations in the intensity and location of the eastern pacific itcz during the transition from intense to weak weak to intense convective activity the trade winds over the caribbean strengthen weaken such acceleration in the trade winds is part of the dynamic response of the low level atmosphere to the magnitude of the convective forcing in the itcz the intensification of the trade winds during july and august and the orographic forcing of the mountains over most of central america result in maximum precipitation along the caribbean coast and minimum precipitation along the pacific

shallow salinity minima in the north pacific abstract ctd std data from 24 cruises in the north pacific are studied for their vertical salinity structure and compared to bottle observations a triple salinity minimum is found in two separated regions in the eastern north pacific in the first region bounded by the northern edge of the subarctic frontal zone and the 34 n front between 160 and 150 w a middle salinity minimum is found below the permanent pycnocline in the density range of 26 0 and 26 5 this middle minimum underlies reid s shallow salinity minimum and overlies the north pacific intermediate water npiw in the second region southeast of the first a seasonal salinity minimum appears above the shallow salinity minimum at densities lower than 25 1 the shallow salinity minimum and the npiw can be found throughout year while the seasonal minimum only appears in summer and fall the middle and shallow salinity minima as well as the seasonal minimum originate at the sea surface in the northeast pacific the properties at the m