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

why do baroclinic waves tilt poleward with height theoretical and modeling studies of nongeostrophic effects in baroclinic waves predict that baroclinic waves should tilt poleward with height with a larger tilt in total meridional wind than in geostrophic quantities regression analysis of ncep ncar reanalysis 6 hourly data demonstrates that observed baroclinic waves do indeed tilt poleward with height although the observed tilt is smaller than predicted by previous studies the meridional ageostrophic wind enhances the poleward tilt of meridional wind perturbations despite being smaller in amplitude than the meridional geostrophic wind by a factor of 5 an improved estimate of the structure of the meridional ageostrophic wind in baroclinic waves is calculated assuming force balance several important terms in this estimate have been left out of previous estimates of the meridional ageostrophic wind three terms in the improved estimate produce nearly all of the poleward tilt of the meridional wind 1 the advection of geostrophic zonal wind perturbations by the mean zonal wind 2 the convergence of the eddy momentum flux and 3 the effect of friction the poleward tilt with height of baroclinic waves explains why upper level storm tracks tend to occur poleward of near surface baroclinic regions and may play a role in the midwinter suppression of the pacific storm track

eddy zonal flow feedback in the southern hemisphere abstract the variability of the zonal mean zonal wind in the southern hemisphere is studied using eof analysis and momentum budget diagnostics of ncep reanalysis data 1978 97 the leading eof of the zonal mean zonal wind is well separated from the remaining eofs and represents the north south movement of the midlatitude jet analysis of the momentum budget shows that a positive feedback between the zonal mean wind anomalies and the eddy momentum fluxes accounts for the unusual persistence of eof1 and plays an important role in the selection of the leading eof of midlatitude variability further analysis also shows a propagating feedback common to both eof1 and eof2 which is responsible for the poleward drift of wind anomalies with time the observations support the following feedback mechanism anomalous baroclinic wave activity is generated at the latitude of anomalous temperature gradient that by thermal wind coincides with the latitude of the anomalous zonal jet the net propagation of baroclinic

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

variations of northern hemisphere storm track and extratropical cyclone activity associated with the madden julian oscillation abstractthis study investigates the intraseasonal variations of the northern hemispheric storm track associated with the madden julian oscillation mjo during the extended boreal winter november april using 36 yr 1979 2014 of reanalysis data from era interim two methods have been used to diagnose storm track variations in the first method the storm track is quantified by the temporal filtered variance of 250 hpa meridional wind vv250 or mean sea level pressure pp the intraseasonal anomalies of vv250 composited for eight mjo phases are characterized by a zonal band of strong positive or negative anomalies meandering from the pacific all the way across north america and the atlantic into northern europe with weaker anomalies of opposite sign at one or both flanks the results based on pp are consistent with those based on vv250 except for larger zonal variations which may be induced by surface topography in the second method an objective cyclone tracking scheme has been used to track the

mesoscale air sea interaction and its role in eddy energy dissipation in the kuroshio extension abstractusing the high resolution community earth system model cesm output this study investigates air sea interaction and its role in eddy energy dissipation in the kuroshio extension ke regi

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

a new perspective on southern hemisphere storm tracks abstract a detailed view of southern hemisphere storm tracks is obtained based on the application of filtered variance and modern feature tracking techniques to a wide range of 45 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data it has been checked that the conclusions drawn in this study are valid even if data from only the satellite era are used the emphasis of the paper is on the winter season but results for the four seasons are also discussed both upper and lower tropospheric fields are used the tracking analysis focuses on systems that last longer than 2 days and are mobile move more than 1000 km many of the results support previous ideas about the storm tracks but some new insights are also obtained in the summer there is a rather circular strong deep high latitude storm track in winter the high latitude storm track is more asymmetric with a spiral from the atlantic and indian oceans in toward antarctica and a subtropical jet related lower latitu

isotopic spikes from tropical cyclones in surface waters opportunities in hydrology and paleoclimatology abstract the stable isotopic ratio of precipitation from tropical cyclones is very low compared to that of normal summer precipitation lawrence and gedzelman 1996 tropical storms allison and chantal made landfall in southeast texas in the summer of 1989 and dumped large amounts of rain isotope ratios of surface waters measured at five different sites decreased markedly after the passage and remained low for a few weeks the return of isotope values to normalcy following these storms varied from site to site reflecting differences among the hydrological environments during other summers from 1985 to 1993 isotope ratios of rains were higher and in the normal range calculations using air temperatures and oxygen isotope measurements of the surface waters show that organically precipitated fresh water carbonate should have recorded the two oxygen isotopic spikes produced by allison and chantal at all five sites this suggests that isotopic analysis of ancient fresh water fossil carbonate shells fossil mammal teeth or tree rings might be used to document past tropical cyclone activity

climate change on the yucatan peninsula during the little ice age we studied a 5 1 m sediment core from aguada x caamal 20 36 6 n 89 42 9 w a small sinkhole lake in northwest yucatan mexico between 1400 and 1500 a d oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2 2 and the benthic foraminifer ammonia beccarii parkinsoniana appeared in the sediment profile indicating a hydrologic change that included increased lake water salinity pollen from a core in nearby cenote san jose chulchaca showed a decrease in mesic forest taxa during the same period oxygen isotopes of shell carbonate in sediment cores from lakes chichancanab 19 53 0 n 88 46 0 w and salpeten 16 58 6 n 89 40 5 w to the south also increased in the mid 15th century but less so than in aguada x caamal climate change in the 15th century is also supported by historical accounts of cold and famine described in maya and aztec chronicles we conclude that climate became drier on the yucatan peninsula in the 15th century a d near the onset of the little ice age lia comparison of results from the yucatan peninsula with other circum caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the lia at that time sea surface temperatures cooled and aridity in the circum caribbean region increased

air sea interaction effects in the lower troposphere across the north wall of the gulf stream abstract significant atmospheric and oceanographic differences have often been observed in the regions lying on either side of the north wall of the gulf stream satellite visible range sensors have revealed changes in reflectivity across the gulf stream believed to be due to changes in sea state that are related to these atmospheric and oceanic differences in addition lines of low level cloud paralleling the edge of the gulf stream have been observed to persist in satellite imagery for several days at a time anomalous radar propagation also has been noted to occur in these same regions in an attempt to document the interrelation of these phenomena the lower atmosphere over the north wall of the gulf stream was studied on two separate occasions sea state photography and measurements of sea surface temperature air temperature dew point temperature and atmospheric pressure were made by an instrumented rp 3a aircraft flying at various altitudes from the gulf stream across the north wall and onto

seasonal variations in the southern hemisphere storm tracks and jet streams as revealed in a reanalysis dataset abstract regional characteristics of the climatological seasonal variations in southern hemisphere sh storm tracks are examined based on a reanalysis dataset when differences in vertical structure between the subpolar and subtropical jet streams spj and stj respectively are considered the regional characteristics can be interpreted reasonably well from a potential vorticity perspective of baroclinic eddy growth and downstream development of a baroclinic wave packet eddy activity in the upper and lower tropospheres is strongest in the core region of the spj over the eastern south atlantic and indian ocean throughout the year even in austral winter when the intense stj forms over the indian ocean and south pacific showing its eddy driven nature the spj accompanies the strong surface westerlies along a well defined baroclinic zone above an intense oceanic frontal zone in this core region of the storm track low level eddy activity is strongly correlated with the local near surface baroclinicity

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

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

low stable isotope ratios of tropical cyclone rains tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems with a mean value slightly above that of water vapor near the sea surface the isotope ratios also decrease radially inward to the eye wall but appear to be anomalously low even near the periphery of the rain shield these findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone s water and energy budgets

passage of tropical storm allison 2001 over southeast texas recorded in δ18o values of ostracoda freshwater ostracoda collected in ephemeral pond waters derived from tropical storm allison 2001 texas recorded the unusually low oxygen isotope values of that storm therefore the potential clearly exists in locations where tropical cyclones make landfall to obtain a long term record of tropical cyclone activity from fossil ostracode calcite

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

the annual cycle of northern hemisphere storm tracks part i seasons abstractin this paper and part ii a comprehensive picture of the annual cycle of the northern hemisphere storm tracks is presented and discussed for the first time it is based on both feature trac

importance of resolving kuroshio front and eddy influence in simulating the north pacific storm track abstractlocal and remote atmospheric responses to mesoscale sst anomalies associated with the oceanic front and eddies in the kuroshio extension region ker are studied using high 27 km and low resolution 162 km regional climate model simulations in the north pacific in the high resolution simulations removal of mesoscale sst anomalies in the ker leads to not only a local reduction in cyclogenesis but also a remote large scale equivalent barotropic response with a southward shift of the downstream storm track and jet stream in the eastern north pacific in the low resolution simulations no such significant remote response is found when mesoscale sst anomalies are removed the difference between the high and low resolution model simulated atmospheric responses is attributed to the effect of mesoscale sst variability on cyclogenesis through moist baroclinic instability it is only when the model has sufficient resolution to resolve small scale diabatic heating that the full effect of mesoscale sst

combined textural and stable isotopic data as proxies for the mid cretaceous paleoclimate a case study of lacustrine stromatolites in the gyeongsang basin se korea abstract microbial interference of the prevailing sedimentary dynamics during stromatolite growth records vital biogeochemical information which reflects the prevailing paleoclimatic conditions this study documents the simultaneous geochemical and textural changes in mid cretaceous lacustrine stromatolites gyeongsang basin se korea deposited in a semi arid setting fibrous calcite micrite couplets in the stromatolites occurring in the sinyangdong hwasan and banyawol formations constitute the basic growth cycles and can be divided into first second and third order cycles second order cycles show couplets with gradual textural changes from fibrous calcite to micrite laminae and three different types of micrite are present sometimes one type of micrite evolves into another within the second order cycle in the sinyangdong stromatolites consistent enrichments in 18o and depletion in 13c towards micrites within the sinyangdong and hwasan stromatolite couplets and a concomitant depletion of both isotopes from fibrous calcite to micrite in the banyawol sample can be observed these shifts reflect paleohydrological changes in the lake water related to paleoproductivity and paleosalinity fluctuations relatively higher paleosalinity values within the sinyangdong lake water system is registered by higher 18o values of fibrous calcite and micrite in the sy 3 than in the sy 1 and sy 2 stromatolites the consistent shifts in 18o and 13c isotopes in different textural growth fabrics indicate that paleohydrological factors could play a significant role in the formation of these primary lacustrine carbonates textural changes shown by the frequency of the growth cycles also corresponds with oxygen and carbon isotopic values these results appear to have been influenced by climate related paleohydrological changes

reconstructing 7000 years of north atlantic hurricane variability using deep sea sediment cores from the western great bahama bank q1 enso show abrupt changes around 6000 yrs b p but most coastal sedimentary records do not span this time period establishing longer records is essential for understanding mid holocene patterns of storminess and their climatic drivers which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep sea and bank edge sediments may offer an unexplored archive of long term hurricane activity here we develop this new approach reconstructing more than 7000 years of north atlantic hurricane variability using coarse grained deposits in sediment cores from the leeward margin of the great bahama bank high energy event layers within the resulting archive are 1 broadly correlated throughout an offbank transect of multi cores 2 closely matched with historic hurricane events and 3 synchronous with previous intervals of heightened north atlantic hurricane activity in overwash reconstructions from puerto rico and elsewhere in the bahamas lower storm frequency prior to 4400 yrs b p in our records suggests that precession and increased nh summer insolation may have greatly limited hurricane potential intensity outweighing weakened enso and a stronger west african monsoon factors thought to be favorable for hurricane development

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

dominant anomaly patterns in the near surface baroclinicity and accompanying anomalies in the atmosphere and oceans part i north atlantic basin abstract variability in the monthly mean flow and storm track in the north atlantic basin is examined with a focus on the near surface baroclinicity b bxi byj dominant patterns of anomalous b found from empirical orthogonal function eof analyses generally show patterns of shift and changes in the strength of b composited anomalies in the monthly mean wind at various pressure levels based on the signals in the eofs display robust accompanying anomalies in the mean flow up to 50 hpa in the winter and up to 100 hpa in other seasons anomalous eddy fields accompanying the anomalous bx patterns exhibit broadly speaking structures anticipated from linear theories of baroclinic instabilities and suggest a tendency for anomalous wave fluxes to accelerate decelerate the surface westerly accordingly atmospheric anomalies accompanying by anomalies have patterns different from those that accompany bx anomalies but are as large as those found for bx anomalies in the sea surface temperature sst found for

masking of interannual climate proxy signals by residual tropical cyclone rainwater evidence and challenges for low latitude speleothem paleoclimatology 1 the anomalously low oxygen isotope ratio 18o values of tropical cyclone rainfall can transfer proxy information about past tropical cyclone activity to stalagmite oxygen isotope records isotopically distinct stormwater reaches the growing crystal surface as a coherent slug or after attenuation by mixing with isotopically normal vadose groundwaters a high resolution micromilled stalagmite stable isotope record from belize shows that residual tropical cyclone water from hurricane mitch masked the oxygen isotope record of a major el nino event on decadal time scales measured 18o values are affected by changes in local tropical cyclone frequency despite the tropical cyclone masking effect the structure of the missing el nino event is preserved in the atm 7 carbon isotope ratios 13c values in tropical cyclone prone regions the fidelity of stalagmite oxygen isotope proxy data to recording background climate signals is modulated by temporal variations in local tropical cyclone rainfall and the sensitivity of individual stalagmites to tropical cyclone masking varies with hydrology speleothem 13c values unaffected by tropical cyclones can preserve the underlying structure of climatic variability for low latitude speleothems with c o isotope covariance intervals in which the 18o values are significantly lower than 13c values predict may indicate periods when local tropical cyclone masking of isotope derived precipitation records is enhanced by greater infiltration of tropical cyclone rain the temporal structure in stalagmite c o isotope covariance has paleoenvironmental meaning that may be revealed by exploring factors associated with independent behavior in each isotope ratio respectively tropical cyclone masking presents new challenges to paleoclimatology and a source of hypotheses for paleotempestology

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

late holocene climate change for the eastern interior united states evidence from high resolution δ 18 o values of sagittal otoliths abstract stable oxygen isotope values were determined for freshwater drum aplodinotus grunniens sagittal otoliths recovered from the eastman rockshelter archaeological site in northeast tennessee to evaluate climate change for the eastern interior united states from 5500 calendar years ago to the present micromilled samples representing less than six days of otolith growth were extracted to acquire high resolution intra otolith variation in 18 o values freshwater drum sagittal otoliths form annual bands due to thermally induced growth cessation below 10 c 18 o h 2 o values can be calculated once a high resolution carbonate sample representing the beginning of the growing season is isolated maximum summer temperature can be calculated using the seasonal minimum 18 o caco 3 value and the 18 o h 2 o value maximum summer temperatures calculated from the freshwater drum sagittae suggest that summer temperatures generally decrease from 29 c at 5 5 ka to 22 c at 0 3 ka however warmer climates at 2 9 1 7 1 6 and 1 2 1 0 ka punctuate this trend a more complete picture of the climate is reconstructed because 18 o h 2 o values which are a function of the ratio of summer to winter precipitation are also calculated a relatively low average 18 o h 2 o value of 8 1 vsmow was calculated at 1 0 ka suggesting cold winters dry summers and or wet winters may have prevailed during part of the medieval warm period in tennessee contrary to studies suggesting that the holocene was extremely stable and the hypsithermal was invariably warm and dry additional evidence suggesting both significant climate variability and evidence for a wetter mid holocene is presented

testing coral based tropical cyclone reconstructions an example from puerto rico abstract complimenting modern records of tropical cyclone activity with longer historical and paleoclimatological records would increase our understanding of natural tropical cyclone variability on decadal to centennial time scales tropical cyclones produce large amounts of precipitation with significantly lower 18 o values than normal precipitation and hence may be geochemically identifiable as negative 18 o anomalies in marine carbonate 18 o records this study investigates the usefulness of coral skeletal 18 o as a means of reconstructing past tropical cyclone events isotopic modeling of rainfall mixing with seawater shows that detecting an isotopic signal from a tropical cyclone in a coral requires a salinity of 33 psu at the time of coral growth but this threshold is dependent on the isotopic composition of both fresh and saline end members a comparison between coral 18 o and historical records of tropical cyclone activity river discharge and precipitation from multiple sites in puerto rico shows that tropical cyclones are not distinguishable in the coral record from normal rainfall using this approach at these sites

impacts of sst anomalies in the agulhas current system on the regional climate variability abstractthe potential impact of the variability in the agulhas current system on the large scale atmospheric state in the southern hemisphere is examined using the monthly near surface baroclinicity as the key parameter for the period between september 1980 and august 2002 dominant patterns of anomalous near surface baroclinicity found from empirical orthogonal function eof analyses in the region that includes most of the agulhas current system show a wide variety of anomaly patterns some of which indicate spatial shifts in the position of the agulhas retroflection and or agulhas return current composited anomalies in various atmospheric fields sea surface temperature and the net surface heat flux at the air sea boundary based on the signals in the eofs suggest that sea surface temperature anomalies in the agulhas current system thermally force the atmosphere on the synoptic scale via modification of the near surface baroclinicity in march and april and possibly in january and february as well

too low δ18o of paleo meteoric low latitude water do paleo tropical cyclones explain it abstract isotopic analysis of rock samples showed anomalously 18 o depleted reconstructed isotopic composition of paleo meteoric water over southern israel between the late cretaceous and the early miocene with 18 o w as low as 14 smow this range is significantly lighter than the expected values for rain at the relevant paleo latitudes 8 n to 25 n it is similar or lighter than areas with meteoric water at the present climate in which rainfall contribution from tropical cyclone tc is significant rainfall from tcs is 18 o depleted because of the recirculation of the vapor into repeated precipitation or distillation cycles a paleo geographic reconstruction of the region shows that throughout the period there was a warm ocean to the east and southeast of the relevant area thus tcs formed over the ocean and made landfall on the coastline at a distance of 300 to 400 km to the east the reconstructed composition of the rainwater implies dominance of tcs at these times furthermore the combination of warmer seas and lighter rainwater than at present suggests that the tcs were more dominant than in the most tc prone coastal areas at the present climate the results of the present study suggest that climate during the relevant time periods was very different from the present with tc activity similar or exceeding the most tc prone locations in the world at the present climate this might also hint that warmer sea waters in the geological past were conducive to greater tc activity than in the present climate answering this question requires additional research

cold season synoptic scale waves over subtropical south america the most active winter synoptic scale wave patterns over south america are identified using an extended empirical orthogonal function eeof technique and are physically diagnosed using composite methods results show that the leading modes of short timescale variability propagate along two main paths over the subtropical jet latitudes 308s and over the subpolar jet latitudes 608s this research focuses on the subtropical mode and its evolution over south america the observed structure of the systems associated with the subtropical mode resembles that of midlatitude baroclinic waves both cyclonic and anticyclonic perturbations display significant modifications in their threedimensional structure as they evolve over extratropical and subtropical south america while the upper level perturbations are mostly unaffected when moving eastward the lower level perturbations advance following the shape of the andes mountains and exhibit an abrupt equatorward migration at the lee side of the mountains as a result of such detachment smaller eddy heat fluxes are observed in the vicinity of the orography and consequently a weaker eddy baroclinic growth is observed once the upper level system is on the lee side the perturbations acquire a more typical baroclinic wave structure and low level intensification of the system occurs the latter is largest around 1000 km east of the orography where enhanced moisture transports from tropical latitudes along the eastern portion of the low level cyclone favor precipitation occurrence over southeastern south america those precipitation processes seem to provide a diabatic source of energy that further contributes to the strengthening of the low level cyclone in addition an intensification of the cyclone once over the ocean was found in 60 of the situations considered which is consistent with previous research suggesting an additional source of moisture and heat flux due to the warm waters of the brazil current

a stepwise screening system to select storm sensitive stalagmites taking a targeted approach to speleothem sampling methodology a stepwise stalagmite sample screening process was applied in order to select a stalagmite as a sensitive recorder of recent tropical cyclone rainfall events near belize field and laboratory criteria were combined in series to screen out candidate stalagmites whose characteristics indicated lower sensitivity to stormwater infiltration the approach described here was designed to increase the likelihood that selected stalagmites would increase the signal noise ratio of the target phenomenon in the resulting proxy records this four stage method for sample selection may be an important methodological consideration for researchers attempting to use speleothems for stable isotope paleotempestology hallmarks of this approach include 1 establishing a priori scientific targets 2 applying sample criteria in the form of contra indicators and 3 organizing the sample screening protocol into a series of practical stages the overall approach to stalagmite selection presented here supports cave conservation and can be adapted readily by others in support of different scientific goals it is hoped that other investigators will also publish field and laboratory sample selection schemes as increased transparency will provide new information invaluable to replication efforts and to advancing the field of speleothem paleo environmental studies

the importance of quaternary records in reducing risk from tropical cyclones numerous late holocene records of tropical cyclones have been collected from north east queensland australia they are in the form of multiple sedimentary ridges paralleling the shore the ridges are composed of coral fragments or shell and sand or pure sand a method to determine the intensity of the tropical cyclone responsible for deposition of the ridges at each site has been applied and the results suggest that in the majority of cases these features were deposited by very high magnitude events the results suggest that extrapolations of long term cyclone magnitude and frequencies from the 30 to 40 year long instrumental record which is the method commonly used to assess risk from this hazard substantially underestimate the risk from this hazard this is confirmed for the cairns region by an 800 year long high resolution isotope record of tropical cyclones preserved in a limestone stalagmite together the sedimentary and isotope records suggest that tropical cyclone activity in north east queensland has been in a phase of quiescence since before european settlement of the region in approximately ad 1870 it is suggested that the incorporation of the palaeo record into risk assessments will provide a more realistic guide to the magnitude frequency relationship of tropical cyclones and help reduce risk from this hazard as a consequence

the gulf stream convergence zone in the time mean winds abstractthe distribution of surface divergence in the northwest atlantic is investigated using 10 years of satellite wind observations from quikscat and a 1 yr simulation from the coamps atmospheric model a band of time mean surface convergence overlies the gulf stream called here the gulf stream convergence zone gscz and has been attributed previously to a local boundary layer response to gulf stream sst gradients however this analysis shows that the gscz results mainly from the aggregate impacts of strong convergence anomalies associated with storms propagating along the storm track which approximately overlies the gulf stream storm surface convergence anomalies are one to two orders of magnitude greater than the time mean convergence and produce a highly asymmetric divergence distribution skewed toward convergent winds the sensitivity of the sign and magnitude of the time mean divergence to extreme weather events is demonstrated through analysis using an extreme value filter conditional samp

greater frequency variability of landfalling tropical cyclones at centennial compared to seasonal and decadal scales assessing risk from tropical cyclones and predicting the impact of this hazard under a human altered climate is based exclusively upon the behaviour of these events over the past 50 100 yr and often less critical to these determinations is an understanding of the full extent of the natural variability of this hazard the coarse resolution of millennial scale sedimentary records brevity of the instrumental register imprecision of longer historical accounts and lack of any long term high resolution records has led to the assumption that the total variability of tropical cyclone behaviour is encompassed within the seasonal to multi decadal oscillations observed to date we present a near 800 yr long annual resolution isotope record of tropical cyclones in northeast australia which displays marked centennial scale regimes our record demonstrates that the frequency variability of intense landfalling cyclones is greatest at centennial scale compared to seasonal and decadal oscillations switching between centennial scale regimes in this record occurred rapidly 10 20 yr highlighting the importance of accounting for this phenomenon in coastal planning and risk assessment our study highlights the importance of obtaining high resolution multi century records of tropical cyclone activity in order to more accurately assess future impacts of this hazard to human society

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

stalagmite stable isotope record of recent tropical cyclone events we present a 23 yr stalagmite record 1977 2000 of oxygen isotope variation associated with 11 tropical cyclones tcs from actun tunichil muknal cave in central belize high resolution microsampling yielded a record of monthly to weekly temporal resolution that contains abrupt decreases negative excursions in calcite 18 o values that correspond with recent tc rain events nearby a logistic discriminant model reliably identifi ed tc proxy signals using the measurable parameters 18 o and 13 c values and single point changes in 18 o value the logistic model cor rectly identifi ed 80 of excursions as tc events and incorrectly classifi ed only 1 of nearly 1200 nonstorm sampling points in addition to enabling high resolution tc frequency reconstruction this geologic proxy also provides information about the intensity of individual tcs a multiple regression predicted tc intensity r 2 0 465 p 0 034 using sampling frequency and excursion amplitude consistent with previous low resolution studies we found that the decadal average 18 o value was lower during the 1990s when several tcs produced rainfall in the area but higher during the 1980s when only one tc struck longer accurately dated high resolution speleo them stable isotope records may be a useful new tool for paleotempestology to clarify associa tions between highly variable tc activity and the dynamic range of quaternary climate

use of contrasting d h ratios of snows and groundwaters of eastern new york state in watershed evaluation the d h ratios of snow on the ground and groundwaters in eastern new york state in early spring differ by 50 notation this is large in comparison to the analytical precision of 1 and permits estimation of the input of snowmelt directly to runoff versus groundwater input to runoff resulting from increased hydraulic head as the snow melts and percolates into the ground in 1978 the high overflow resulting from snowmelt contained only 25 meltwater the rest was provided by an increased groundwater exfiltration

storm track response to ocean fronts in a global high resolution climate model synoptic atmospheric eddies are affected by lower tropospheric air temperature gradients and by turbulent heat fluxes from the surface in this study we examine how ocean fronts affect these quantities and hence the storm tracks we focus on two midlatitude regions where ocean fronts lie close to the storm tracks the north west atlantic and the southern ocean an atmospheric climate model of reasonably high resolution 50 km is applied in a climate length 60 year simulation in order to obtain stable statistics simulations with frontal structure in the sea surface temperature sst in one of the regions are compared against simulations with globally smoothed sst we show that in both regions the ocean fronts have a strong influence on the transient eddy heat and moisture fluxes not just in the boundary layer but also in the free troposphere local differences in these quantities between the simulations reach 20 40 of the maximum values in the simulation with smoothed sst averaged over the entire region of the storm track over the ocean the corresponding differences are 10 20 the effect on the transient eddy meridional wind variance is strong in the boundary layer but relatively weak above that the potential mechanisms by which the ocean fronts influence the storm tracks are discussed and our results are compared against previous studies with regional models aquaplanet models and coarse resolution coupled models

numerical experiments of the storm track sensitivity to oceanic frontal strength within the kuroshio oyashio extensions the sensitivity of the north pacific storm track to midlatitude oceanic frontal strength within the kuroshio oyashio extensions is investigated by applying artificially changed meridional sea surface temperature sst gradients in the weather research forecasting model version 3 4 the result of sensitivity experiments further confirms the close relationship between the storm track activity and meridional sst gradient i e the storm track activity can be intensified as a response to increases in the oceanic frontal strength in order to better understand the mechanism for the storm track intensification due to increased sst gradient velocity temperature correlation and local energetics are analyzed the result indicates that the enhancement of the meridional sst gradient leads to amplitude magnification of eddy meridional velocity and temperature and their phase consistency suggesting that synoptic scale eddies tend to approach the optimum structure for the baroclinic energy conversion which is mainly responsible for the sst front induced enhancement of storm track activity in order to estimate the impact of the oceanic front on the maintenance of the near surface baroclinicity further investigation is made by the composite analysis with the increase in oceanic frontal strength the near surface baroclinicity experiences a slow but strong restoration the increase in the meridional sst gradient results in the intensification in the cross frontal differential sensible heat flux which can more effectively offset the relaxing effect of the transient eddy poleward heat transport

spatial patterns and intensity of the surface storm tracks in cmip5 models abstractto improve the understanding of storm tracks and western boundary current wbc interactions surface storm tracks in 12 cmip5 models are examined against era interim all models capture an equatorward displacement toward the wbcs in the locations of the surface storm tracks maxima relative to those at 850 hpa an estimated storm track metric is developed to analyze the location of the surface storm track it shows that the equatorward shift is influenced by both the lower tropospheric instability and the baroclinicity basin scale spatial correlations between models and era interim for the storm tracks near surface stability sst gradient and baroclinicity are calculated to test the ability of the gcms match reanalysis an intermodel comparison of the spatial correlations suggests that differences relative to era interim in the position of the storm track aloft have the strongest influence on differences in the surface storm track position however in the north atlantic biases in the surf

the signature of the midlatitude tropospheric storm tracks in the surface winds abstract storm track analysis is applied to the meridional winds at 10 m and 850 hpa for the winters of 1999 2006 the analysis is focused on the north atlantic and north pacific ocean basins and the southern ocean spanning the region south of the indian ocean the spatial patterns that emerge from the analysis of the 850 hpa winds are the typical free tropospheric storm tracks the spatial patterns that emerge from the analysis of the surface winds differ from the free tropospheric storm tracks the spatial differences between the surface and free tropospheric storm tracks can be explained by the influence of the spatial variability in the instability of the atmospheric boundary layer strongly unstable boundary layers allow greater downward mixing of free tropospheric momentum momentum mixing and this may be the cause of the stronger surface storm tracks in regions with greater instability in the time mean principal component analysis suggests that the basin scale variability that is reflected in th

micro scale analysis of tree ring δ18o and δ13c on α cellulose spline reveals high resolution intra annual climate variability and tropical cyclone activity high resolution analysis of stable carbon and oxygen isotopic composition 13c and 18o of tree ring cellulose has been increasingly in demand for the study of climate seasonality droughts and tropical cyclone hurricane activity the peeling grinding method commonly used for tree ring cellulose preparation is both time consuming and labor intensive and often results in cross tracheid sampling that masks high frequency intra annual climate signals and short term climate events here we present a new method by extracting tree ring cellulose directly from wholewood spline that omits the peeling grinding step and allows for micro scale 13c and 18o analysis that facilitates high resolution seasonal climate study this ultrasound assisted non destructive extraction method has significantly increased the output of tree ring cellulose preparation while retaining the wood cell fabric wood cell wall fibers collected from the cellulose spline were directly loaded into pre weighed silver or tin capsules and packed after oven drying for stable oxygen or carbon isotope analysis a 3 045 mm annual ring subdivided over 26 sections for 13c and 18o analysis revealed remarkable intra annual isotopic variations 1 62 for 13c and 5 85 for 18o the intra annual 13c values inversely covary with the seasonal precipitation pattern suggesting moisture regulation on tree ring 13c variations the high resolution 18o analysis unravels tropical cyclone activities hurricanes frances and ivan in 2004 that are characterized by an abrupt decline in 18o values by 2 6 with a v shape pattern in tree ring latewood an algorithm is developed for establishing regional patterns of tree ring seasonal 13c and 18o for the study of the mean state of climate seasonality and its anomalies

satellite based midlatitude cyclone statistics over the southern ocean 1 scatterometer derived pressure fields and storm tracking 1 a wavelet based method is described for incorporating swaths of surface pressure derived from scatterometer measurements into surface pressure analyses obtained from the european centre for medium range weather forecasts ecmwf the resulting modified pressure fields are used to identify low pressure centers over the southern ocean and to build statistics of midlatitude cyclones during 7 years of the seawinds on quikscat operational period july 1999 to june 2006 the impact of the scatterometer derived pressure swaths is assessed with a statistical analysis of cyclone characteristics central pressure radius depth performed in parallel on the ecmwf and on the modified pressure fields more low pressure centers 5 10 depending on the season are identified with the modified pressure fields in particular incipient lows captured earlier than ecmwf and more short lived mesoscale cyclones with a life span less than 4 days the cyclones identified with the modified pressure fields are characterized by lower central pressure and tighter isobars on average a parallel spectral analysis reveals 1 additional energy at scales less than 2000 km in the modified pressure fields

air humidity and lake δ18o during the latest paleocene earliest eocene in france from recent and fossil fresh water and marine gastropod δ18o δ13c and 87sr 86sr detailed isotopic 18 o 13 c 87 sr 86 sr analyses have been performed on aragonitic fresh water brackish water and marine gastropod shells of latest paleocene earliest eocene age from northwestern europe fresh water shells e g viviparus lymnaea from sparnacian deposits in the paris basin show relatively high 18 o values in the range 4 to 0 1 large intrashell 18 o variability typically 3 is consistent with significant seasonal variation in precipitation and or temperature we also present intrashell isotopic profiles for 22 recent fresh water shells mainly viviparidae representing the major middle to low latitude climate zones e g sweden france portugal lake chad ceylon gambia congo lake victoria new guinea distinct isotopic patterns reflecting humidity and temperature characterize each of the climate zones comparing the results for recent and fossil shells suggests that the climate in northern france during sparnacian time was warm subtropical with a pronounced seasonal drought the 18 o composition of sparnacian lake water has been estimated from the fossil fresh water shell 18 o and by using seasonal temperatures derived from 18 o profiles of fully marine shells the best estimate of the 18 o composition of sparnacian lake water compared with eocene mean ocean water is 1 this is consistent with paleorain 18 o values of 3 to 5 similar to present mean rain 18 o standard mean ocean water values close to 4 in portugal at 40 n the paleolatitude of the paris basin during earliest eocene time the evaporated nature of sparnacian lake water contradicts hypotheses of globally equable humid conditions in the warm early eocene and instead suggests that dry subtropical highs occurred over the eastern parts of the oceans similar to today the results of this study demonstrate the potential of fossil fresh water carbonates to reconstruct the development of subtropical highs and hadley cell circulation in the past

covariations of sea surface temperature and wind over the kuroshio and its extension evidence for ocean to atmosphere feedback abstract satellite microwave measurements are analyzed revealing robust covariability in sea surface temperature sst and wind speed over the kuroshio extension ke east of japan ocean hydrodynamic instabilities cause the ke to meander and result in large sst variations increased reduced wind speeds are found to be associated with warm cold sst anomalies this positive sst wind correlation in ke is confirmed by in situ buoy measurements and is consistent with a vertical shear adjustment mechanism namely an increase in sst reduces the static stability of the near surface atmosphere intensifying the vertical turbulence mixing and bringing fast moving air from aloft to the sea surface south of japan the kuroshio is known to vary between nearshore and offshore paths these paths are very persistent and can last for months to years as the kuroshio shifts its path coherent wind changes are detected from satellite data in particular winds are high south of tokyo when the kuroshio takes the near

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

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