surface wind response to oceanic fronts 1 the response of surface winds to ocean fronts characterized by sharp gradients in both sea surface temperature sst and ocean currents was analyzed using scatterometer nscat and quikscat wind data and gulf stream path positions in conjunction with simulations made with the pennsylvania state university psu national center for atmospheric research ncar mesoscale model mm5 all match ups between each scatterometer pass and the gulf stream path were visually examined and only those for which the wind field was free of atmospheric fronts or large curvature over a reasonably straight segment of the gulf stream were selected ten match ups met these criteria for the period studied from 16 september 1996 to 29 june 1997 for nscat and from 24 july 1999 to 31 december 2000 for quikscat changes in the modeled surface wind field across the front in each of the ten cases agree well with changes in the observed winds our findings suggest that the perturbation pressure gradient resulting from the thermal forcing by the front accounts for the decrease in wind speed when moving from warm to cold water and the increase observed in the converse in the cases examined the adjustment of the surface wind to the front occurred as a result of the vertical motion induced by horizontal divergence convergence and advection in the marine atmospheric boundary layer mabl the dynamical forcing associated with strong surface currents is also shown to modify scatterometer derived winds finally the numerical simulations suggest that the dynamical and thermal effects are very nearly additive

numerical simulations of the extratropical transition of floyd 1999 structural evolution and responsible mechanisms for the heavy rainfall over the northeast united states abstract this paper examines the extratropical transition et of hurricane floyd along the u s east coast on 16 17 september 1999 using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 1 33 km horizontal grid spacing the 36 h mm5 simulation reproduced the basic features of the et event such as the track of floyd the development of a deep and intense baroclinic zone along the coast and its associated precipitation evolution and the tendency for the heavy 30 cm precipitation to fall in a relatively narrow 30 40 km wide band just inland of the coast however the mm5 overpredicted the moderate 10 20 cm precipitation amounts near the coast by 40 50 as the horizontal grid spacing was reduced to 1 33 km the mm5 was used to diagnose the evolution of the enhanced baroclinic zone and associated heavy precipitation to the north of floyd a deep layer of deformation frontogenesis extended from the surface to 400 mb as a result of confluence between the southeasterl

classification and composite diagnosis of extratropical cyclogenesis events in the southwest pacific abstract characteristic patterns of cyclogenesis in the southwest pacific region are identified from a sample of 40 developing cyclones during 1990 94 cases were chosen objectively to ensure a realistic sampling of typical rather than ideal events a subjective classification based on synoptic scale upper tropospheric flow signatures prior to cyclone intensification suggested four classes into which all but three cases fell three categories each containing about a quarter of the population involved direct coupling with the upper jet they represent cyclone formation beneath i the poleward exit region of a 300 hpa jet upstream from a diffluent trough class u ii the confluent equatorward entrance region of the upper wind maximum e and iii the upper jet exit region where the jet is downstream from the upper trough class d these are analogous to previously identified categories for the western north atlantic region a fourth class involved cyclones forming beneath a preexisting intense up

atmospheric pressure response to mesoscale sea surface temperature variations in the kuroshio extension region in situ evidence several research cruises were conducted across the kuroshio extension front to examine the low level atmospheric responses to mesoscale variations in sea surface temperature sst surface meteorological observations including sea level pressure slp and sst were collected at two moored buoys that were located on either side of the kuroshio extension and from a research vessel as it moved between the two buoys during the various cruises spatial perturbations in slp along the ship transects calculated by subtracting moored buoy slp from that of the moving ship tend to be positive negative where sst is lower higher on spatial scales of about 100 km and the magnitude of these slp perturbations near the sst front can exceed 1 0 hpa radiosonde data also show that the atmospheric boundary layer thins thickens over lower higher sst although the contribution of across track component in the wind cannot be calculated the along track component of divergence suggests low level convergence over higher sst the thermally induced pressure gradient is important in the momentum budget suggesting that sea breeze like local circulations formed over the sst fronts indeed the pressure adjustment mechanism can sometimes dominate even on a scale of 100 km although it is not always observed the time scale in which the boundary layer thickness adjusted to sst is estimated to be 1 day or less

air sea interaction at the southern brazilian continental shelf in situ observations the influence of the cross shelf oceanographic front occurring between the brazil current bc and the brazilian coastal current bcc on the local marine atmospheric boundary layer mabl is investigated here this front is typical of wintertime in the southern brazilian continental shelf sbcs and this is the first time that its effects are investigated over the above mabl here we analyze variability vertical structure and stability of mabl as well as heat fluxes at air sea interface across five oceanographic transects in the sbcs made during a winter 2012 cruise local thermal gradients associated with mixing between distinct water masses play an essential role on mabl modulation and stability although weaker when compared with other frontal regions the cross shelf thermal gradients reproduce exactly what is expected for open ocean regions stronger weaker winds lower higher sea level pressure and a more unstable stable mabl are found over the warm cold side of the oceanographic front between the bc warm and coastal cold waters our findings strongly support the coexistence of both known mabl modulation mechanisms the static and hydrostatic mabl stability this is the first time that these modulation mechanisms are documented for this region turbulent fluxes were found to be markedly dependent on the cross shelf sst gradients resulting in differences of up to 100 w m 2 especially in the southernmost region where the gradients were more intense

sea level pressure minimum along the kuroshio and its extension abstractatmospheric effects of sea surface temperature sst fronts along the kuroshio and kuroshio extension k ke are investigated by examining spatial characteristics of the climatological sea level pressure slp surface winds and surface heat flux q fields based on an in situ observation dataset a hydrostatic effect of the sst front is observed during the northwesterly monsoon characterized by a westward extending low slp wedge trough slightly south of the peak in q along the k ke ageostrophic surface westerlies crossing slp isobars toward a trough center are found north of the low slp wedge apparently because of the eastward acceleration by the vertical mixing effect this feature of the ageostrophic winds is less pronounced south of it a north south asymmetry arising as vertical mixing accelerates decelerates eastward ageostrophic winds north south of it while the slp trough near the sst front is found nearly year round except for summer its meridional location seasonally migrates pr

el nino southern oscillation signal associated with middle holocene climate change in intercorrelated terrestrial and marine sediment cores north island new zealand a synchronous textural variation in intercorrelated high resolution sediment records from floodplain continental shelf and continental slope settings of the eastern north island new zealand provides evidence of increased storminess after ca 4 ka an upcore change in sediment texture reflects the transition to landsliding which supplanted fluvial incision as the dominant mode of sediment production in the middle holocene this signal which appears in all three records indicates a regional response to external forcing and records the impact of an intensified atmospheric circulation marking the establishment of the contemporary climate that is strongly influenced by the el nino southern oscillation the change in climate was a hemispheric event and in the southern hemisphere its timing is confirmed by independent proxy records from elsewhere in new zealand and the circum south pacific region

the influence of sea surface temperature on surface wind in the eastern equatorial pacific weekly to monthly variability abstract temporal correlations between near equatorial surface wind and sea surface temperatures sst at 11 w in the eastern pacific ocean are investigated using data from an array of moored sensors between 5 n and 5 s the signature of tropical instability waves with periods of 20 30 days is apparent in time series of sst and both the meridional and zonal wind components results indicate the existence of a band of pronounced horizontal divergence in the surface wind field associated with the large meridional sst gradient equatorial front normally located just north of the equator perturbations of the equatorial front by the instability waves induce fluctuations in the overlying winds evidence of the air sea coupling is stronger in time series of the meridional gradients of wind and sst than between time series of the variables themselves the meridional differencing serves as a high pass filter in the space domain which removes planetary scale wind fluctuations that are unrelated to the local sst

response of surface nutrient inventories and nitrogen fixation to a tropical cyclone in the southwest pacific to examine the controls of new nitrogen supply in oligotrophic waters nitrogen fixation and nutrients were monitored during a quasi lagrangian study in surface waters of the north tasman sea during march april 2006 the study was initiated coincident with a tropical cyclone with high rainfall and winds that eroded surface layer density structure and increased surface phosphate and silicate concentrations by 50 however there was no corresponding increase in nitrate as the enhanced vertical mixing perturbed the phosphacline but not the deeper nitracline dissolved iron was highest in the upper 20 m and declined to a minimum at 100 150 m indicating wet deposition as the source as also inferred from the salinity decrease nitrogen fixation increased significantly by an order of magnitude over the following 9 d in deckboard perturbation experiments immediately after the cyclone phosphate and iron addition did not elicit a response in nitrogen fixation whereas 8 d later when in situ dissolved iron had declined the addition of iron stimulated nitrogen fixation by 1 5 fold conversely the addition of dust from australia and the gobi desert immediately after the cyclone increased nitrogen fixation by 2 and 4 5 fold respectively the observed 10 fold increase in nitrogen fixation in situ exceeded that reported in other nutrient perturbation experiments despite comparatively low in situ dissolved iron indicating that iron bioavailability may be a critical factor although stimulation by a cyclone was unexpected it promoted favorable conditions for diazotrophy by enhancing phosphate availability in the absence of nitrate and increased dissolved iron supply and availability via wet deposition this suggests that future increases in tropical cyclones combined with other climate driven trends may increase nitrogen fixation in the north tasman sea

direct observations of atmospheric boundary layer response to sst variations associated with tropical instability waves over the eastern equatorial pacific tropical instability waves tiws with a typical wavelength of 1000 km and period of 30 days cause the equatorial front to meander and result in sst variations on the order of 18 28c vertical soundings of temperature humidity and wind velocity were obtained on board a japanese research vessel which sailed through three fully developed sst waves from 1408 to 1108w along 28n during 21 28 september 1999 a strong temperature inversion is observed throughout the cruise along 28n capping the planetary boundary layer pbl that is 1 1 5 km deep temperature response to tiw induced sst changes penetrates the whole depth of the pbl in response to an sst increase air temperature rises in the lowest kilometer and shows a strong cooling at the mean inversion height as a result this temperature dipole is associated with little tiw signal in the observed sea level pressure slp the cruise mean vertical profiles show a speed maximum at 400 500 m for both zonal and meridional velocities sst based composite profiles of zonal wind velocity show weakened intensified vertical shear within the pbl that is consistent with enhanced reduced vertical mixing causing surface wind to accelerate decelerate over warm cold ssts taken together the temperature and wind soundings indicate the dominance of the vertical mixing over the slp driving mechanism based on the authors measurements a physical interpretation of the widely used pbl model proposed by lindzen and nigam is presented

extratropical transition of tropical cyclones over the western north pacific part i evolution of structural characteristics during the transition process abstract the development of extratropical cyclone structural characteristics that resulted from the extratropical transition of typhoon ty david 1997 and ty opal 1997 over the western north pacific is examined david moved poleward ahead of a midlatitude trough that was moving eastward as the dominant midlatitude circulation feature over the western north pacific during the transition david coupled with the midlatitude trough which led to the evolution of an intense cyclone that became the primary circulation over the north pacific although opal also moved poleward ahead of a midlatitude trough the principal midlatitude feature over the western north pacific was a preexisting stationary cyclone over the kamchatka peninsula during transition opal weakened and became a secondary cyclone to the preexisting primary north pacific cyclone the structural characteristics of the evolving extratropical cyclone with respect to each case are examined in the context of the interaction between a vortex an

satellite measurements reveal persistent small scale features in ocean winds four year averages of 25 kilometer resolution measurements of near surface wind speed and direction over the global ocean from the quikscat satellite radar scatterometer reveal the existence of surprisingly persistent small scale features in the dynamically and thermodynamically important curl and divergence of the wind stress air sea interaction over sea surface temperature fronts throughout the world ocean is evident in both the curl and divergence fields as are the influences of islands and coastal mountains ocean currents such as the gulf stream generate distinctive patterns in the curl field these previously unresolved features have important implications for oceanographic and air sea interaction research

determination of a consistent time for the extratropical transition of tropical cyclones part i examination of existing methods for finding et time abstract as a tropical cyclone moves poleward and interacts with the midlatitude circulation the question of whether it will undergo extratropical transition et and if it does whether it will reintensify or dissipate is a complex problem several quantities have been proposed in previous studies to describe extratropical transition including frontogenesis 500 hpa geopotential heights and cyclone phase space parameters in this study these parameters are explored for their utility in defining an et time using the navy s operational global assimilation and prediction system gridded analyses the 500 hpa geopotential heights and frontogenesis currently do not have objective numerical definitions therefore this study attempts to establish and examine threshold values that may be used to objectively define the et time cyclone phase space already has numerical threshold values that can be examined results show that the 500 hpa geopotential height open wave distinguishes 81 of 82 cases but it fails

storm frequency and magnitude in response to holocene climate variability lake tutira north eastern new zealand abstract a mid to late holocene record of storm events is preserved in the sediments of lake tutira located on the eastern north island of new zealand previous studies of a 6 m sediment core established a storm chronology for the last 2250 years eden d n page m j 1998 palaeoclimatic implications of a storm erosion record from late holocene lake sediments north island new zealand palaeogeogr palaeoclimatol palaeoecol 139 37 58 here we extend the record using a 27 m sediment core to lake formation 7200 cal yr ago outside the last 500 yr of human influence the core records landscape response to natural climate variability and to tectonism volcanism associated with the active collisional plate boundary setting based on sedimentological and biogeochemical analyses 1400 layers of dominantly terrigenous storm derived sediment have been identified a storm event chronology supported by twelve tephra and three 14c ages indicates that storm magnitude and frequency has varied over the last 7200 yr twenty five periods with an increased frequency of large storms occur typically of decadal to centennial duration periods of major storm activity occur at about 500 700 1100 1250 1850 2100 2850 3200 3600 4000 4300 4500 4700 4900 5700 5900 and 6850 6900 cal yr bp several other local and regional climate proxies record conditions that are consistent with the timing and periodicity of major storms in the tutira record a period centred on 2000 yr ago has the highest incidence of storms with a recurrence of 1 storm 2 9 yr this is identified as a time of major environmental change by several other records by comparison average storm frequency throughout the record is 1 storm 5 yr and while this is consistent with modern el nino southern oscillation enso periodicity the record shows no increase in frequency around 4000 years at the time of enso intensification this likely reflects new zealand s location between tropical and polar latitudes where climate shifts are driven by the interplay between enso interdecadal pacific oscillation ipo and the southern annular mode sam the lake tutira record provides support for the growing evidence that climate variability during the holocene has involved periods of rapid change correlation of this detailed storm event and sediment flux record with other geomorphic and sedimentary records in the nearby waipaoa source to sink sedimentary system improves understanding of the timing and rates of climatically induced landscape change and its downstream effects

ocean atmosphere covariability in the western arabian sea abstract the western arabian sea exhibits strong spatial variability in sea surface temperature sst during the southwest monsoon with changes in sst that can exceed 5 c over 200 km exploration of satellite based and in situ data shows a strong connection between mesoscale sst features and changes in the atmospheric boundary layer the fundamental relationship is that of weak strong wind velocities overlying cold warm sst features there are also coherent changes in other near surface meteorological parameters such as the air sea temperature difference and relative humidity indicating changes in the stability of the planetary boundary layer over the mesoscale sst features these relationships are similar to those recently reported over the equatorial pacific tropical instability wave region this observed covariability of atmospheric boundary layer structure and sst results in variations of the surface heat and moisture fluxes latent heat flux is modified by changes in relative humidity principa

tropical cyclones in the southwest pacific spatial patterns and relationships to southern oscillation and sea surface temperature abstract an analysis of a 20 yr dataset of tropical cyclones in the southwest pacific has been made to determine the spatial patterns of cyclone occurrence and how these depend on the southern oscillation so and sea surface temperature a local measure of cyclone incidence is defined as the number of cyclones that enter into a 2 lat long square during some period eg within one season and this quantity is mapped for four southern oscillation index soi categories the maps show that the geographical distribution of cyclone incidence shifts eastward and northward during negative soi phases and vice versa the mean annual incidence for the whole region is 28 higher than average for our strongly negative so category and 16 below average for our near zero category to explore the roles of the so and local sst correlation analysis was applied to mean values of cyclone incidence for four subregions of 20 longitude width between 10 and 22 s markedly different soi sst responses were found on either s

extratropical transition of southwest pacific tropical cyclones part ii midlatitude circulation characteristics abstract this second of two papers on extratropical transition et over the southwest pacific ocean focuses on the variability of et a climatology of et onset based on a previously described objective technique shows that et commences 15 of latitude nearer the equator on average than similar cases from the northern hemisphere characteristic midlatitude circulation patterns accompanying et near 30 s are identified by means of empirical orthogonal function eof analysis of 50 storms the first eigenvector pattern explaining nearly half the circulation variability expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to cradled and captured classifications previously described for the southeast indian ocean the second eof distinguishes redeveloping from weakening storms reintensifying storms were located beneath strong cyclonic vorticity advection cva near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of

the effect of large scale flow on low level frontal structure and evolution in midlatitude cyclones abstract observational and modeling studies documented in the literature indicate that the large scale flow has an important effect on the structure and evolution of low level fronts in midlatitude cyclones the purpose of this paper is to address the role of the large scale flow on low level cyclone frontal structure and evolution through a combined observational and idealized modeling approach analyses of two observed cyclone cases embedded in large scale diffluence and confluence respectively are presented to illustrate two possible cyclone frontal structures and evolutions specifically the cyclone moving into a diffluent high amplitude ridge becomes meridionally elongated and possesses a strong meridionally oriented cold front and a weak warm front the cold front rotates into the warm front forming an occluded front in the manner of the norwegian cyclone model as indicated by the narrowing of the thermal ridge connecting the warm sector to the cyclone center in contrast the cyclone moving i

extratropical transition of tropical cyclones over the western north pacific part ii the impact of midlatitude circulation characteristics abstract two characteristic midlatitude circulation patterns labeled northwest and northeast are found to be associated with extratropical transition et of tropical cyclones over the western north pacific ocean although in both cases the tropical cyclone moves poleward ahead of a midlatitude trough the primary midlatitude circulation is either that trough or is a large quasi stationary cyclone to the northeast of the poleward moving tropical cyclone transition into a northwest pattern typically results in the development within 36 h of an intense extratropical cyclone that moves north northeast a tropical cyclone that moves into a northeast pattern enters into strong zonal flow between the primary midlatitude circulation and the subtropical ridge to the southeast these systems move rapidly eastward and do not intensify significantly during the 36 h following transition in part i of this study the et of typhoon ty david 1997 and the et of ty opal 1997 were investigated in terms of the form

holocene sedimentary record from lake tutira a template for upland watershed erosion proximal to the waipaoa sedimentary system northeastern new zealand abstract a holocene lake record from northeastern new zealand provides a detailed record of environmental controls on upper watershed sedimentation and is proximal to the waipaoa margins source to sink focus site in that context lake tutira in hawke s bay was cored in 2003 to recover a complete sedimentary record since the lake s formation ca 7 2 ka the 27 14 m long core contains alternating lithotypes that are sedimentary responses to lacustrine organic accumulation normal to severe rainfalls earthquakes and volcanism a diatom allochthonous ranking scheme pollen counts and c and n percentages were used to identify intra lake and watershed derived storm deposits and modes of lithotype deposition the lithotypes and depositional modes are tephras volcanic airfall organic rich mud algal rich lake sedimentation massive to weakly graded brown silty clay beds homogenites and redeposited lake sediments grey graded sandy mud beds intense storm delivered sediment and thin yellow clay layers run off from small storms using 12 tephras and 3 radiocarbon ages to provide a chronology the long term sedimentation rate is ca 3 3 mm year which increases to 10 mm year following european colonisation storm beds occur in response to rainfall events with no obvious correlation to el nino southern oscillation polarity or strength moreover no single climate index appears to correlate strongly with the historic rainfall event record having characterised and identified storm beds over the lake s history a hindcast relationship implies that around 53 pre historic storms occurred with a magnitude similar to the severe cyclone bola event of 1988 plus 7 potentially larger storm events despite the prominence of storm beds a summation of the total percent thickness as an indication of the relative modes of emplacement for each lithotype shows that proportionally the balance of intra lake versus storm sources preserved in the lake bed is 69 and 26 respectively as well as storms lake sedimentation is strongly influenced by earthquakes that destabilize the terrigenous sediment laden lake margins to generate homogenites represented by the brown silty clay beds these deposits tend to be thicker after a hiatus in seismic activity and after sustained periods of lake margin loading as inferred from the occurrence of thick graded storm beds comparison with marine records on the adjacent continental margin suggests that more terrestrial events are captured in the lake record due to i close hillslope lake connectivity with little intervening storage of sediment compared with the waipaoa sedimentary system and ii the preservation of event stratigraphy at tutira compared to its reduced preservation in the dynamic marine environment only major storms such as cyclone bola leave an imprint traceable to the ocean whereas identifiable sedimentary responses to individual earthquakes are localized although through landscape preconditioning and sediment production they contribute to the overall high terrigenous input to the ocean in contrast low frequency high magnitude perturbations volcanic eruptions european deforestation are preserved through the source to sink sedimentary system consistent with earlier hypotheses

simulations of the extratropical transition of tropical cyclones contributions by the midlatitude upper level trough to reintensification abstract the extratropical cyclone development processes during the reintensification stage of an extratropical transition from a tropical cyclone tc are described using numerical simulations three control simulations without a tropical cyclone present examine the extratropical cyclogenesis associated with upper level troughs that are characterized as weak moderate and strong when no tropical cyclone is included in the simulation the minimum surface pressures attained with the weak moderate and strong troughs are 1003 991 and 977 mb respectively in all three cases the low tilts northwestward with height during intensification and the rainfall pattern and eventual occlusion are representative of classic extratropical cyclone development the interactions of a tropical cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the extratropical transition of the tropical cyclone in the three trough with tc case

tropical cyclone climatology of the south pacific ocean and its relationship to el nino southern oscillation abstractclimatological features of tropical cyclones in the south pacific ocean have been analyzed based on a new archive for the southern hemisphere a vortex tracking and statistics package is used to examine features such as climatological maps of system intensity and the change in intensity with time average tropical cyclone system movement and system density an examination is presented of the spatial variability of these features as well as changes in relation to phase changes of the el nino southern oscillation phenomenon a critical line is defined in this study based on maps of cyclone intensity to describe the statistical geographic boundary for cyclone intensification during el nino events the critical line shifts equatorward while during la nina events the critical line is generally displaced poleward regional variability in tropical cyclone activity associated with el nino southern oscillation phases is examined in relation to the variability of large scale atmospheric or oceanic varia

extratropical transition of southwest pacific tropical cyclones part i climatology and mean structure changes a database of tropical cyclone best track and intensity information for the southwest pacific ocean basin is used to construct a 28 year climatology for tropical cyclones that move into middle latitudes of the nine or so tropical cyclones that form each year an average of about three can be expected to migrate south of 358s with the greatest fraction in march storms entering the tasman sea west of new zealand nz move almost due south on average and retain greater intensity than those to the east of nz where storms decay quickly while moving rapidly away to the southeast storms east of nz are embedded in a stronger more zonal flow than those to the west which move poleward ahead of a larger amplitude trough during el nino years tropical cyclones that move into middle latitudes exhibit stronger zonal motion and occur over a wider range of longitudes than during la nina years storm intensity is only weakly correlated with concurrent sst anomalies suggesting that atmospheric circulation is the dominant influence on storm properties average structure changes during extratropical transition et are identified using the ncep ncar reanalysis dataset for a subset of 33 transitioning storms during 1980 97 composites are used to construct a three dimensional conceptual model of the transformation from a mature hurricane to an asymmetric baroclinic midlatitude cyclone southwest pacific tropical cyclones encounter the baroclinic westerlies early in their lives accounting for their average eastward and poleward motion at maximum average intensity near 208s baroclinic effects are already important with warm frontogenesis appearing in the southeast quadrant and outflow aloft into a downstream subtropical wind maximum that moves poleward with the storm by 258s the average tc has lost the characteristic symmetric anticyclonic outflow aloft and acquired the characteristics of a baroclinic midlatitude storm including regions of warm and cold frontogenesis a vertical motion dipole and a westward tilt with height from about 308s poleward a second upper tropospheric wind maximum appears west of the storm with strengthening cyclonic vorticity advection aloft below about 400 hpa the storm retains the vertical warm cyclonic core as it migrates poleward

fundamental and higher mode rayleigh wave characteristics of ambient seismic noise in new zealand 1 in order to use ambient seismic noise for mapping earth s structure it is important to understand the spatiotemporal characteristics of the noise field this study uses data collected during four austral winter months of 2002 to investigate new zealand s ambient seismic noise field in the double ocean wave frequency range 0 1 0 3 hz it is shown via beamforming analysis that there are two distinct dispersive waves in the data these waves can be separated their estimated phase velocities 2 5 2 and 4 3 km s in the frequency range 0 14 0 25 hz match well with fundamental and higher mode rayleigh dispersion curves studies of double wave frequency microseisms elsewhere generally show the rayleigh noise fields to be dominated by fundamental mode waves the reason why higher mode signals are observed here may reflect a combination of long ocean wave periods large waveheights the direct deep water approach to narrow continental margins and the proximity of the seismograph array to the source regions citation brooks l a j townend p gerstoft s bannister and l carter 2009 fundamental and higher mode rayleigh wave characteristics of ambient seismic noise in new zealand geophys res lett 36 l23303 doi 10 1029 2009gl040434

barometric pressure variations associated with eastern pacific tropical instability waves abstract barometric pressure surface temperature and wind time series in the eastern equatorial pacific are analyzed to determine if oceanic tropical instability wave tiw sea surface temperature variations cause barometric pressure gradients large enough to influence the atmospheric boundary layer during the study period from april 2001 to september 2002 11 tiws propagated westward past 110 w causing a spectral peak at 20 30 days in the sea surface temperature sst meridional difference between 2 n 110 w and 0 110 w likewise the meridional pressure difference also had a spectral peak in the 20 30 day tiw band cross spectral analysis shows that within the tiw band sst induced pressure variations were roughly 0 1 hpa c 1 in magnitude the resulting pressure gradient force is comparable in magnitude to other terms in the meridional momentum balance implications about the role of the boundary layer capping in the adjustment to sst forcing are discussed

air sea heat exchanges characteristic of a prominent midlatitude oceanic front in the south indian ocean as simulated in a high resolution coupled gcm abstract an integration of a high resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature sst is analyzed to investigate air sea heat exchanges characteristic of the midlatitude oceanic frontal zone the focus of this paper is placed on a prominent sst front in the south indian ocean which is collocated with the core of the southern hemisphere storm track time mean distribution of sensible heat flux is characterized by a distinct cross frontal contrast it is upward and downward on the warmer and cooler flanks respectively of the sst front acting to maintain the sharp gradient of surface air temperature sat that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track induced by cross frontal advection of cold warm air associated with migratory atmospheric disturbances the surface flux is highly variable with intermittent en

ocean frontal effects on the vertical development of clouds over the western north pacific in situ and satellite observations abstract a suite of shipboard and satellite observations are analyzed and synthesized to investigate the three dimensional structure of clouds and influences from sea surface temperature fronts over the western north pacific sharp transitions are observed across the kuroshio extension ke front in the marine atmospheric boundary layer mabl and its clouds the ocean s influence appears to extend beyond the mabl with higher cloud tops in altitude along the ke front than the surroundings in winter intense turbulent heat release from the ocean takes place on the southern flank of the ke front where the cloud top penetrates above the mabl and reaches the midtroposphere in this band of high cloud tops frequent lightning activity is observed the results of this study suggest a sea level pressure mechanism for which the temperature gradient in the mabl induces strong surface wind convergence on the southern flank of the ke front deepening the clouds there in early summer sea fog frequently occurs on

observations of sst induced perturbations of the wind stress field over the southern ocean on seasonal timescales the surface wind stress response to sea surface temperature sst over the latitude range 308 608 si n the southern ocean is described from the national aeronautics and space administration s quikscat scatterometer observations of wind stress and reynolds analyses of sst during the 2 yr period august 1999 to july 2001 while ocean atmosphere coupling at midlatitudes has previously been documented from several case studies this is the first study to quantify this relation over the entire southern ocean the spatial structures of the surface wind perturbations with wavelengths shorter than 108 latitude by 308 longitude are closely related to persistent spatial variations of the sst field on the same scales the wind stress curl and divergence are shown to be linearly related respectively to the crosswind and downwind components of the sst gradient the curl response has a magnitude only about half that of the divergence response this observed coupling is consistent with the hypothesis that sst modification of marine atmospheric boundary layer mabl stability affects vertical turbulent mixing of momentum inducing perturbations in the surface winds the nonequivalence between the responses of the curl and divergence to the crosswind and downwind sst gradients suggests that secondary circulations in the mabl may also play an important role by producing significant perturbations in the surface wind field near sst fronts that are distinct from the vertical turbulent transfer of momentum the importance of the wind stress curl in driving ekman vertical velocity in the open ocean implies that the coupling between winds and sst may have important feedback effects on upper ocean processes near sst fronts

polar airstream cyclogenesis in the australasian region a composite study using ecmwf analyses abstract cold air disturbances that form upstream of the main polar frontal cloud band and evolve into comma shapes are observed in almost any satellite image of the midlatitudes of the southern hemisphere this study describes general features of the three dimensional structure and dynamics of these polar airstream developments using composites from 30 typical cases from the australasian area constructed from analyses prepared by the european centre for medium range weather forecasts ecmwf the major finding from this study is that an upstream upper level southwesterly jet streak present in each of the 30 cases at genesis is necessary for development composites of initial stages showed the surface vorticity center coupled with the poleward exit region of this upper jet and directly beneath the cyclonic vorticity advection maximum by the 300 hpa flow relative to the translating disturbance this net import of cyclonic vorticity acts initially to amplify the upper trough near the surface the environ

sst induced surface wind variations over the brazil malvinas confluence satellite and in situ observations abstract the confluence of the brazil malvinas currents maintains strong sea surface temperature sst fronts in the midlatitude southwestern atlantic year round sst effects on near surface stability and surface wind variations are examined in this region using satellite and in situ datasets satellite observations show strong weak surface wind speeds over the warm brazil cold malvinas current a novel feature of this study is the construction of a high resolution surface meteorological dataset that is based on historical ship observations analysis of this new in situ dataset reveals an increased reduced sea air temperature difference over the brazil malvinas current indicating destabilization stabilization in the atmospheric boundary layer these results are consistent with the sst induced vertical mixing mechanism for wind adjustment the sst effect on the near surface atmosphere is observed both in the climatology and on interannual time scales in the brazil malvinas confluence along a zo

the influence of the madden julian oscillation on tropical cyclone activity in the fiji region abstract this study examines the modulation of tropical cyclone tc activity by the madden julian oscillation mjo in the fiji samoa and tonga regions fst region using joint typhoon warning center best track cyclone data and the mjo index developed by wheeler and hendon results suggest strong mjo tc relationships in the fst region the tc genesis patterns are significantly altered over the fst region with approximately 5 times more cyclones forming in the active phase than in the inactive phase of the mjo this modulation is further strengthened during el nino periods the large scale environmental conditions i e low level relative vorticity upper level divergence and vertical wind shear associated with tc genesis show a distinct patterns of variability for the active and inactive mjo phases the mjo also has a significant effect on hurricane category and combined gale and storm category cyclones in the fst region the occurrences of both these cyclone categories are increased in the active

the extratropical transition of tropical cyclones part i cyclone evolution and direct impacts abstractextratropical transition et is the process by which a tropical cyclone upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes transforms into an extratropical cyclone this process is influenced by and influences phenomena from the tropics to the midlatitudes and from the meso to the planetary scales to extents that vary between individual events motivated in part by recent high impact and or extensively observed events such as north atlantic hurricane sandy in 2012 and western north pacific typhoon sinlaku in 2008 this review details advances in understanding and predicting et since the publication of an earlier review in 2003 methods for diagnosing et in reanalysis observational and model forecast datasets are discussed new climatologies for the eastern north pacific and southwest indian oceans are presented alongside updates to western north pacific and north atlantic ocean climatologies advances in understanding and in some cases mode

the impact of tropical remnants on extratropical cyclogenesis case study of hurricanes danielle and earl 1998 abstract the importance of remnant tropical cyclone tc circulation and moisture structures is investigated for a simultaneous extratropical transition et event involving ex hurricanes danielle and earl september 1998 although both storms undergo prolonged periods of reintensification following et the forcings involved in each of their redevelopment processes differ fundamentally a review of the tropical and baroclinic et modes in the north atlantic stresses the importance of jet front structures to the nature of the reintensification process ex hurricane danielle begins to redevelop in the eastern half of the basin in the downstream poleward sector of an intensifying polar jet the system undergoes a tropical mode of reintensification resulting in a troposphere deep warm environment surrounding the storm devoid of near surface fronts and maintained by strong tropopause folds at its periphery ex hurricane earl reintensifies near the eastern seaboard according to a baroclinic mode under the i

upper ocean thermal variations in the north pacific during 1970 1991 abstract a newly available extensive compilation of upper ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400 m depth in the north pacific during 1970 1991 a prominent decade long perturbation in climate occurred during this time period surface waters cooled by 1 c in the central and western north pacific and warmed by about the same amount along the west coast of north america from late 1976 to 1988 comparison with data from coads suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly the vertical structure of seasonal thermal anomalies in the central north pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400 m depth individual cold events descend rapidly 100 m yr 1 superimposed upon a slower cooling 15 m yr 1 the inter

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

downstream development associated with the extratropical transition of tropical cyclones over the western north pacific abstract the movement of a tropical cyclone into the midlatitudes involves interactions among many complex physical processes over a variety of space and time scales furthermore the extratropical transition et of a tropical cyclone may also result in a high amplitude rossby wave response that can extend to near hemispheric scales after an et event occurs over the western portion of a northern hemisphere ocean basin the high amplitude downstream response often forces anomalous midlatitude circulations for periods of days to a week these circulations may then be related to high impact weather events far downstream of the forcing by the et event in this study downstream development following et events over the western north pacific ocean is examined local eddy kinetic energy analyses are conducted on four cases of north pacific tropical cyclones of varying characteristics during et into varying midlatitude flow characteristics during 15 july 30 september 2005 the goal is to examine the impact of e

the transformation of tropical storm agnes into an extratropical cyclone part i the observed fields and vertical motion computations abstract this is the first of two papers dealing with the transformation of tropical storm agnes june 1972 into an extratropical cyclone synoptic analyses and vertical motion patterns are used to describe the behavior of agnes over a five day period subsequent to initial landfall during which time agnes regained tropical storm strength prior to transforming into an extratropical cyclone and dissipating input data for all calculations are obtained from optimum interpolation objective analyses with a resolution of 1 latitude longitude in the horizontal and 100 mb in the vertical a modified 9 level version of krishnamurti s 1968a diagnostic balance model is discussed and applied to the data set to determine the fields of vertical motion redevelopment of agnes subsequent to initial landfall is the result of the spread of an area of appreciable cyclonic vorticity advection aloft over the periphery of the low level circulation devoid of significant baroclinicity unlike a corresponding midlatitude sto

shear velocity structure of the northland peninsula new zealand inferred from ambient noise correlations 1 ambient noise correlation has been successfully applied in several cases to regions with dense seismic networks whose geometries are well suited to tomographic imaging the utility of ambient noise correlation based methods of seismic imaging where either network or noise field characteristics are less ideal has yet to be fully demonstrated in this study we focus on the northland peninsula of new zealand using data from five seismographs deployed in a linear pattern parallel to the direction from which most of the ambient noise arrives shear wave velocity profiles computed from rayleigh and love wave dispersion curves using the neighborhood algorithm are in good agreement with the results of a previous active source refraction experiment and a teleseismic receiver function and surface wave analysis in particular we compute a path averaged moho depth of 28 km along a 250 km profile the use of both rayleigh and love wave measurements enables us to estimate the degree of radial anisotropy in the crust yielding values of 2 15 these results demonstrate that ambient noise correlation methods provide useful geophysical constraints on lithospheric structure even for nonoptimal network geometries and noise field characteristics

the extratropical transitions of hurricanes felix and iris in 1995 abstract the extratropical transitions of hurricanes felix and iris in 1995 are examined and compared both systems affected northwest europe but only iris developed significantly as an extratropical system in both cases the hurricane interacts with a preexisting extratropical system over the western atlantic the remnants of the exhurricanes can be identified and tracked across the atlantic as separate low level potential vorticity pv anomalies the nature of the baroclinic wave involved in the extratropical transition is described from a pv perspective and shown to differ significantly between the two cases the role of vertical shear in modifying the hurricane structure during the early phase of the transition is investigated iris moved into a region of strong shear the high pv tower of iris developed a marked downshear tilt felix moved into a vertically sheared environment also but the shear was weaker than for iris and the pv tower of felix did not tilt much iris maintained its warm core struc

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

large scale influences on the evolution of winter subtropical maritime cyclones affecting australia s east coast abstractsubtropical maritime low pressure systems frequently impact australia s eastern seaboard closed circulation lows in the tasman sea region are termed east coast cyclones ecc they can evolve in a range of climatic environments and have proven most destructive during the late autumn winter period using criteria based on pressure gradients inferred wind field and duration an objectively determined database of ecc occurrences is established to explore large scale influences on ecc evolution subclassification based on evolutionary trajectory reveals two dominant storm types during late autumn winter easterly trough lows etl and southern secondary lows ssl synoptic composites are used to investigate the climatological evolution of each storm type etl cyclogenesis occurs along the eastern seaboard at the confluence of warm moist subtropical easterlies and cool air over the continent that is advected from higher latitudes ssl develop when a cold extratropical cyclone moves equatorward and

synoptic and frontal scale influences on tropical transition events in the atlantic basin part i a six case survey abstract the process by which a baroclinic vertically sheared extratropical cyclone is transformed into a warm core vertically stacked tropical cyclone is known as tropical transition six recent tropical transitions of strong extratropical precursors in the subtropical north atlantic are compared to better understand the manner by which some of the canonical structures and dynamical processes of extratropical cyclones serve to precondition the cyclone for transition all six transitions resulted from the interaction between a surface baroclinic zone and an upper level trough during the extratropical cyclogenesis of each storm a period of intense near surface frontogenesis along a bent back warm front occurred to the northwest of each sea level pressure minimum within the resultant circulation diabatic redistribution of potential vorticity pv promoted the growth of a low level pv maximum near the western end of the warm front concurrently the upper level pv anomaly associated with each trough w

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

a 40 year climatology of extratropical transition in the eastern north pacific abstracta 42 yr study of eastern north pacific tropical cyclones tcs undergoing extratropical transition et is presented using the japanese 55 yr reanalysis dataset by using cyclone phase space cps to differentiate those tcs that undergo et from those that do not it is found that only 9 of eastern north pacific tcs that developed from 1971 to 2012 complete et compared with 40 in the north atlantic using a combination of cps empirical orthogonal function eof analysis and composite analysis it is found that the evolution of et in this basin differs from that observed in the north atlantic and western north pacific possibly as a result of the rapidly decreasing sea surface temperatures north of the main genesis region the presence of a strong deep subtropical ridge extending westward from north america into the eastern north pacific is a major factor inhibiting et in this basin similar to other basins eastern north pacific et generally occurs in conjunction with an approaching midlatitud

synoptic scale environments of predecessor rain events occurring east of the rocky mountains in association with atlantic basin tropical cyclones abstractthe synoptic scale environments of predecessor rain events pres occurring to the east of the rocky mountains in association with atlantic basin tropical cyclones tcs are examined pres that occurred during 1988 2010 are subjectively classified based upon the synoptic scale upper level flow configuration within which the pre develops with a focus on the following 1 the position of the jet streak relative to the tc 2 the position of the jet streak relative to trough and ridge axes and 3 the positions of trough and ridge axes relative to the pre and to the tc three categories were identified from this classification procedure jet in ridge southwesterly jet and downstream confluence pre relative composite analysis for each category reveals that consistent with previous studies pres typically occur near a low level baroclinic zone beneath the equatorward entrance region of an upper level jet streak and in the presence of a stream of water vapor from a tc despite these common

synoptic scale diagnosis of the extratropical transition of a southwest pacific tropical cyclone abstract this is the first of two case studies on the transformation of tropical storms in the southwest pacific this study uses ecmwf analyses and observations to examine the behavior of tropical cyclone patsy in december 1986 prior to and during its transit to midlatitudes these analyses adequately depicted synoptic scale features during the extratropical phase but underestimated the inner core of strong wind during the hurricane phase interactions with troughs in the subtropical westerlies provided the impetus for the major motion and structure changes during patsy s life during the hurricane phase patsy was steered by the flow above 400 hpa the passage of a first trough to poleward led to disintegration of the characteristic tropical cyclone structure decay was due to shearing effects loss of upper level outflow and the transient incorporation of cooler air into the low level circulation a few days later patsy commenced moving rapidly south as a single center as ascent redeveloped in the p

the effects of sst induced surface wind speed and direction gradients on midlatitude surface vorticity and divergence abstract the effects of surface wind speed and direction gradients on midlatitude surface vorticity and divergence fields associated with mesoscale sea surface temperature sst variability having spatial scales of 100 1000 km are investigated using vector wind observations from the seawinds scatterometer on the quick scatterometer quikscat satellite and sst from the advanced microwave scanning radiometer for earth observing system amsr e aqua satellite the wind sst coupling is analyzed over the period june 2002 august 2008 corresponding to the first 6 years of the amsr e mission previous studies have shown that strong wind speed gradients develop in response to persistent mesoscale sst features associated with the kuroshio extension gulf stream south atlantic and agulhas return current regions midlatitude sst fronts also significantly modify surface wind direction the surface wind speed and direction responses to typical sst differences of about 2 4 c are on average about 1 2 m s 1 and 4

observations of marine atmospheric boundary layer transitions across the summer kuroshio extension abstract the baiu and kuroshio extension ke fronts both zonally oriented and nearly collocated east of japan are the dominant summertime features of the atmosphere and ocean respectively over the midlatitude northwest pacific an atmospheric sounding campaign was conducted on board the r v roger revelle during the 2005 summer transects of soundings across the ke front are analyzed to study its effects on the atmosphere along with continuous surface meteorological and ceilometer cloud base observations while the ke front remained nearly stationary during the cruise the baiu front displayed large meridional displacements that changed wind direction across the ke front the presence of sharp sea surface temperature sst gradients anchored by the ke enhanced the thermal and moisture advection causing substantial changes in the marine atmospheric boundary layer mabl structure when the baiu front was displaced north of the ke front southwesterly winds advected warm humid air from the subtropics

variability of southern hemisphere cyclone and anticyclone behavior further analysis abstract this paper presents some additional results on the use of an automatic scheme for tracking surface cyclones and anticyclones the southern hemisphere sh total amount of synoptic tracks every 12 h was analyzed for the 1973 96 period using sea level pressure from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis composites for seven el nino en and la nina ln years were constructed in order to analyze the association between the hemispheric cyclone and anticyclone propagation and the phase of the el nino southern oscillation enso phenomenon a climatological view of cyclone and anticyclone tracks and orphan centers superposed on the same map is presented and analyzed a large area with overlapped cyclone and anticyclone tracks is seen between 30 and 60 s which is approximately the climatological position of the sh transient activity to the north of 30 s the subtropical south atlantic high is embedded in a region with just

enso sam interactions during the middle and late holocene a new chronology of large magnitude rainfall events derived from the continuous high resolution lake tutira storm sediment record covers the last 6800 years and provides the first insight into changes in el nino southern oscillation enso teleconnections to the higher southern latitudes to be obtained from new zealand synthesis with independent paleoclimate records from the tropical pacific and antarctica also reveals a millennial scale waxing and waning of the teleconnections that were not visible in the narrow historical window previously used to view interactions between enso and the southern annular mode sam consistent with modern enso behaviour we find teleconnections to the southwest pacific varied throughout the middle and late holocene depending on the strength and phase of enso and the phase of the sam we suggest that precession driven changes in the seasonal cycle of solar radiation exert a first order control on the interaction between the two climate modes consequently their present

cluster analysis of tropical cyclone tracks in the southern hemisphere a probabilistic clustering method is used to describe various aspects of tropical cyclone tc tracks in the southern hemisphere for the period 1969 2008 a total of 7 clusters are examined three in the south indian ocean three in the australian region and one in the south pacific ocean large scale environmental variables related to tc genesis in each cluster are explored including sea surface temperature low level relative vorticity deep layer vertical wind shear outgoing longwave radiation el nino southern oscillation enso and the madden julian oscillation mjo composite maps constructed 2 days prior to genesis show some of these to be significant precursors to tc formation most prominently westerly wind anomalies equatorward of the main development regions clusters are also evaluated with respect to their genesis location seasonality mean peak intensity track duration landfall location and intensity at landfall enso is found to play a significant role in modulating annual frequency and mean genesis location in three of the seven clusters two in the south indian ocean and one in the pacific the enso modulating effect on genesis frequency is caused primarily by changes in low level zonal flow between the equator and 10 s and associated relative vorticity changes in the main development regions enso also has a significant effect on mean genesis location in three clusters with tcs forming further equatorward poleward during el nino la nina in addition to large shifts in mean longitude the mjo has a strong influence on tc genesis in all clusters though the amount modulation is found to be sensitive to the definition of the mjo

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

high resolution satellite measurements of the atmospheric boundary layer response to sst variations along the agulhas return current abstract the marine atmospheric boundary layer mabl response to sea surface temperature sst perturbations with wavelengths shorter than 30 longitude by 10 latitude along the agulhas return current arc is described from the first year of sst and cloud liquid water clw measurements from the advanced microwave scanning radiometer amsr on the earth observing system eos aqua satellite and surface wind stress measurements from the quikscat scatterometer amsr measurements of sst at a resolution of 58 km considerably improves upon a previous analysis that used the reynolds sst analyses which underestimate the short scale sst gradient magnitude over the arc region by more than a factor of 5 the amsr sst data thus provide the first quantitatively accurate depiction of the sst induced mabl response along the arc warm cold sst perturbations produce positive negative wind stress magnitude perturbations leading to short scale perturbations in the wind stress curl and divergence fields that are li

modification of surface winds near ocean fronts effects of gulf stream rings on scatterometer quikscat nscat wind observations 1 modifications to surface winds by currents and sea surface temperature sst gradients near frontal boundaries of gulf stream rings are analyzed using satellite sst and scatterometer nasa s quick scatterometer quikscat nasa scatterometer nscat wind observations a component of scatterometer wind approximately equal and opposite to the surface current vector is observed and attributed to the fact that scatterometers detect relative motion of water and air warm core ring wcr ssts act to destabilize the marine atmospheric boundary layer mabl increasing surface wind magnitude by 10 15 and decreasing veering angle by 5 15 relative to large scale mean winds cold core ring ccr ssts cause impacts of similar magnitude and opposite sense magnitudes and directions of modifications are accounted for by mabl dynamics of a nonlinear planetary boundary layer model forced by air sea temperature differences wind modifications occur within tens of kilometers of sst fronts implying a wind response timescale of order 1 hour by contrast uniformity of modified winds across the larger area within rings suggests the response time for the mabl to return to equilibrium downstream from a front exceeds 10 hours over wcrs strong divergence convergence occurs on the upwind downwind side curl is strongly negative positive to the right left side facing downwind opposite patterns are generally seen over ccrs divergence curl peaks where winds blow perpendicular parallel to sst fronts sst image analysis indicates enhanced cloudiness occurs with downwind convergence over wcrs wind stress curl due to ring modifications causes dipolar ekman pumping sufficient to influence ring translation and decay processes

present day stress field in subduction zones insights from 3d viscoelastic models and data abstract 3d viscoelastic fe models were performed to investigate the impact of geometry and kinematics on the lithospheric stress in convergent margins generic geometries were designed in order to resemble natural subduction our model predictions mirror the results of previous 2d models concerning the effects of lithosphere mantle relative flow on stress regimes and allow a better understanding of the lateral variability of the stress field in particular in both upper and lower plates stress axes orientations depend on the adopted geometry and axes rotations occur following the trench shape generally stress axes are oriented perpendicular or parallel to the trench with the exception of the slab lateral tips where rotations occur overall compression results in the upper plate when convergence rate is faster than mantle flow rate suggesting a major role for convergence in the slab along strike tension occurs at intermediate and deeper depths 100 km in case of mantle flow sustaining the sinking lithosphere and slab convex geometry facing mantle flow or in case of opposing mantle flow and slab concave geometry facing mantle flow along strike compression is predicted in case of sustaining mantle flow and concave slabs or in case of opposing mantle flow and convex slabs the slab stress field is thus controlled by the direction of impact of mantle flow onto the slab and by slab longitudinal curvature slab pull produces not only tension in the bending region of subducted plate but also compression where upper and lower plates are coupled a qualitative comparison between results and data in selected subductions indicates good match for south america mariana and tonga kermadec subductions discrepancies as for sumatra java emerge due to missing geometric e g occurrence of fault systems and local changes in the orientation of plate boundaries and rheological e g plasticity associated with slab bending anisotropy complexities in the models

on the importance of midlatitude oceanic frontal zones for the mean state and dominant variability in the tropospheric circulation 1 observations indicate that midlatitude weather systems are organized into storm tracks near oceanic frontal zones with pronounced sea surface temperature sst gradients a pair of atmospheric general circulation model experiments with zonally uniform sst profiles prescribed show that their observed collocation is not fortuitous in one experiment a storm track is anchored around a midlatitude sst front that maintains near surface thermal gradients and energizes eddies westerly momentum transport by eddies produces a well defined polar front jet along the front even in winter when a subtropical jet stream intensifies in the other experiment removal of the sst front leads to a substantial weakening in eddy activity and the pfj especially in winter it also leads to a weakening of the annular mode the dominant mode of westerly jet variability and its notable structural distortion in winter though idealized our experiments suggest the importance of midlatitude oceanic fronts for the tropospheric circulation and its variability

evolution of interdecadal variability in sea level pressure sea surface temperature and upper ocean temperature over the pacific ocean abstract interdecadal variability in sea level pressure slp and sea surface temperature sst anomalies in the pacific ocean was quasiperiodic from 1900 91 the coherent variability of this phenomenon is investigated using gridded observational data from the turn of the century sst and slp and of upper ocean heat content hs from the recent two and a half decades the nominal cycle in atmosphere ocean variables is roughly two decades long but growth and decay can happen on a shorter timescale e g half a cycle or so the authors divide the full cycle into four phases an onset phase during which a weak slp anomaly pattern off japan takes approximately 2 4 yr to expand eastward leads to large slp anomalies in the region of the aleutian low a quasi stationary growth phase with the midlatitude slp anomaly pattern in the eastern ocean intensifies over a 2 4 yr period the persistent slp anomalies evolve in concert with large sst and hs anomalies of the same polarity located to the south sout

the subtropical mode water circulation in the north pacific abstract historical hydrographic data are analyzed to investigate the seasonal variation of the subsurace pycnostad in the northwestern part of the north pacific and to relate it to the circulation of subtropical mode water stmw a gyre scale scheme of stmw circulation is deduced based on its observed climatological formation area and climatological geostrophic flow fields the deduced circulation is supported by climatological features of the subsurface hydrography presented separately for the non large meander period and the large meander period of the kuroshio zonal and meridional sections and isopycnal maps of potential vorticity and apparent oxygen utilization the kuroshio countercurrent composing the kuroshio recirculation system advects stmw formed in the wintertime thick mixed layer immediately off the kuroshio and the kuroshio extension during the non large meander period the recirculation system has a single anticyclonic gyre centered near 30 n 137 e and advects stmw formed off the kurosh

the extratropical transition of tropical cyclone edisoana 1990 abstractdocumentation of southwest indian ocean swio tropical cyclones tcs and extratropical transition et events is sparse in the refereed literature the authors present a climatology of swio tc and et events for 1989 2013 the swio averages 9 tropical cyclones tcs per year in this modern era of these tcs 44 undergo extratropical transition et or four per year a case study of tc edisoana 1990 the most rapidly intensifying swio post et tc between 1989 and 2013 shows that extratropical interactions began when an approaching trough embedded in the subtropical jet stream stj induced et on 7 march as edisoana underwent et a subtropical ridge downstream amplified in response to poleward directed positive potential vorticity pv advection associated with diabatically convectively driven upper level outflow from tc edisoana this amplifying lower latitude ridge phased with a lower amplitude higher latitude ridge embedded in the polar front jet pfj resulting in the merger of the t