cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

tectonic significance of paleobotanically estimated climate and altitude of the late eocene erosion surface colorado erosion beveled the laramide front range uplift in colorado to a surface of low relief by the end of the eocene this study uses j a wolfe s new multivariate climate analysis techniques to determine the paleoelevation of this regional surface by examining the overlying 35 ma florissant flora a multiple regression model explaining 93 3 of the variance in mean annual temperature was developed using wolfe s dataset of 31 leaf physiognomic character states for 86 modern vegetation sites these character states were scored on 29 species collected from one facies of the florissant lake beds the paleotemperature estimate of mean annual temperature 10 7 plus minus 1 5c derived from these data when combined with sea level temperature and terrestrial lapse rate implies a late eocene paleoelevation of 2 4 2 7 km pliocene uplift is thus not required to explain the present elevation of 2 5 km it is unclear when and why the southern rocky mountains achieved this elevation magmatic crustal thickening can explain the late eocene high elevation of the southern rockies but neither this mechanism nor compressive thickening explains why the great plains which are tied to the florissant elevation by the wall mountain tuff were also high this paleoelevation estimate indicates that regional surfacesmore of planation could be formed at high elevation in the eocene probably because of peculiarities of the eocene climate less

the 21ne production rate in quartz revisited abstract i have revised our earlier production rate determination of 21ne in terrestrial quartz s niedermann th graf j s kim c p kohl k marti and k nishiizumi 1994 earth planet sci lett 125 341 355 taking account of improved knowledge about the exposure age of samples used in that work and applying distinct procedures for scaling to sea level and high latitudes the corrected value of 19 0 3 7 atoms g 1 a 1 is in excellent agreement with expectations based on nuclear properties j masarik and r c reedy 1995 earth planet sci lett 136 381 395 and closely corresponds to the present day production rate in the case of substantial variations of the geomagnetic field in the past as proposed by several studies the revised value can consistently be used with suitable correction methods

dating of sirius group tillites in the antarctic dry valleys with cosmogenic3he and21ne we measured in situ produced cosmogenic3he and21ne in boulder and bedrock surface samples in and near sirius group tillites from two localities in southern victoria land antarctica pyroxene quantitatively retains cosmogenic3he for millions of years the deposit at mt fleming has a minimum exposure age of 6 5 ma while 6 ma is a probable minimum age for the table mountain tillite these lower limits not taking into account erosion of the sampled surfaces are based on the samples with the highest concentrations of cosmogenic noble gases and currently accepted production rates since the plagioclase bearing mt fleming samples almost certainly lost part of their cosmogenic ne the minimum exposure age at this location is presumably even 50 higher than the stated value the concentrations of cosmogenic ne in our samples constrain uplift rates of the transantarctic mountains to 170 m ma these data contradict the hypothesis of a collapse of the east antarctic ice sheet in the pliocene coupled with high uplift rates and support the model of a stable ice sheet since the middle miocene

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

storm track response to oceanic eddies in idealized atmospheric simulations abstractlarge scale oceanic fronts such as in western boundary currents have been shown to play an important role in the dynamics of atmospheric storm tracks little is known about the influence

enhanced upward heat transport at deep submesoscale ocean fronts the ocean is the largest solar energy collector on earth the amount of heat it can store is modulated by its complex circulation which spans a broad range of spatial scales from metres to thousands of kilometres in the classical paradigm fine oceanic scales less than 20 km in size are thought to drive a significant downward heat transport from the surface to the ocean interior which increases oceanic heat uptake here we use a combination of satellite and in situ observations in the antarctic circumpolar current to diagnose oceanic vertical heat transport the results explicitly demonstrate how deep reaching submesoscale fronts with a size smaller than 20 km are generated by mesoscale eddies of size 50 300 km in contrast to the classical paradigm these submesoscale fronts are shown to drive an anomalous upward heat transport from the ocean interior back to the surface that is larger than other contributions to vertical heat transport and of comparable magnitude to air sea fluxes this effect can remarkably alter the oceanic heat uptake and will be strongest in eddy rich regions such as the antarctic circumpolar current the kuroshio extension and the gulf stream all of which are key players in the climate system deep reaching small scale oceanic fronts can drive upward heat transport from the ocean interior to the surface in eddy rich regions suggest satellite and in situ observations of the antarctic circumpolar current

atmospheric circulations induced by a midlatitude sst front a gcm study the atmospheric effects of sea surface temperature sst anomalies over and near western boundary currents are a matter of renewed interest the general circulation model gcm of the laboratoire de meteorologie dynamique lmd z has a zooming capability that allows a regionally increased resolution this gcm is used to analyze the impact of a sharp sst front in the north atlantic ocean two simulations are compared one with climatological ssts and the other with an enhanced gulf stream front the results corroborate the theory developed previously by the present team to explain the impact of oceanic fronts in this theory the vertical velocity at the top of the atmospheric boundary layer has two components mechanical and thermal it is the latter that is dominant in the tropics while in midlatitudes both play a role in determining the wind convergence above the boundary layer the strengthened sst front does generate the previously predicted stronger ascent above the warmer water south of the front and stronger descent above the colder waters to the north in the gcm simulations the ascent over the warm anomalies is deeper and more intense than the descent

measurement of ancient cosmogenic 21ne in quartz from the 28 ma fish canyon tuff colorado abstract measurement of 21 ne in quartz from the 28 ma buried fish canyon tuff of colorado yielded a maximum of 2 75 0 57 10 6 21 ne atoms g sio 2 1 above nucleogenic and modern concentrations this quantity represents cosmogenic 21 ne produced on the fish canyon tuff surface prior to the deposition of the overlying carpenter ridge tuff ancient 21 ne was isolated through the analysis and identification of 1 background 21 ne produced from particle interactions or inherited and 2 cosmogenic 21 ne produced from modern radiation multiple samples of fish canyon tuff shielded during both exposure periods 28 ma ago and in modern time yielded the background that was then subtracted from all samples likewise samples of fish canyon exposed today but well below the fish canyon carpenter ridge contact and therefore shielded 28 ma ago yielded a modern component that was also removed from all sample concentrations the presence of an ancient cosmogenic isotope in a buried surface has several potential applications including the quantification of paleoelevation paleolatitude and pre quaternary erosion rates

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

midlatitude wind stress sea surface temperature coupling in the vicinity of oceanic fronts the influences of strong gradients in sea surface temperature on near surface cross front winds are explored in a series of idealized numerical modeling experiments the atmospheric model is the naval research laboratory coupled ocean atmosphere mesoscale prediction system coamps model which is fully coupled to the regional ocean modeling system roms ocean model a series of idealized two dimensional model calculations is carried out in which the wind blows from the warm to cold side or the cold to warm side of an initially prescribed ocean front the evolution of the near surface winds boundary layer and thermal structure is described and the balances in the momentum equation are diagnosed the changes in surface winds across the front are consistent with previous models and observations showing a strong positive correlation with the sea surface temperature and boundary layer thickness the coupling arises mainly as a result of changes in the flux richardson number across the front and the strength of the coupling coefficient grows quadratically with the strength of the cross front geostrophic wind the acceleration of the winds over warm water results primarily from the rapid change in turbulent mixing and the resulting unbalanced coriolis force in the vicinity of the front much of the loss gain of momentum perpendicular to the front in the upper and lower boundary layer results from acceleration deceleration of the flow parallel to the front via the coriolis term this mechanism is different from the previously suggested processes of downward mixing of momentum and adjustment to the horizontal pressure gradient and is active for flows off the equator with sufficiently strong winds although the main focus of this work is on the midlatitude strong wind regime calculations at low latitudes and with weak winds show that the pressure gradient and turbulent mixing terms dominate the cross front momentum budget consistent with previous work

on the coupling of wind stress and sea surface temperature a simple quasi equilibrium analytical model is used to explore hypotheses related to observed spatial correlations between sea surface temperatures and wind stress on horizontal scales of 50 500 km it is argued that a plausible contributor to the observed correlations is the approximate linear relationship between the surface wind stress and stress boundary layer depth under conditions in which the stress boundary layer has come into approximate equilibrium with steady free atmospheric forcing warmer sea surface temperature is associated with deeper boundary layers and stronger wind stress while colder temperature is associated with shallower boundary layers and weaker wind stress two interpretations of a previous hypothesis involving the downward mixing of horizontal momentum are discussed and it is argued that neither is appropriate for the warm to cold transition or quasi equilibrium conditions while one may be appropriate for the cold to warm transition solutions of a turbulent large eddy simulation numerical model illustrate some of the processes represented in the analytical model a dimensionless ratio a is introduced to measure the relative influence of lateral momentum advection and local surface stress on the boundary layer wind profile it is argued that when a 1 and under conditions in which the thermodynamically induced lateral pressure gradients are small the boundary layer depth effect will dominate lateral advection and control the surface stress

response of the atmospheric boundary layer to a mesoscale oceanic eddy in the northeast atlantic fields of air sea turbulent fluxes and bulk variables were derived from satellite sensor data from february to april 2001 over a region of the northeast atlantic where a field experiment programme oce an multidisciplinaire meso echelle pomme was conducted the satellite products are in good agreement with in situ data in terms of heat fluxes sea surface temperature and wind speed the central part of the experimental domain presented a cyclonic eddy in the ocean which corresponded to a cold sea surface temperature sst anomaly winds were weaker within the eddy than outside of it with lower latent and sensible heat loss in order to analyze the relationship between the sst and wind anomalies three numerical experiments were conducted with a regional atmospheric model three 3 month runs of the model were performed using a realistic sst field a smoothed sst field in which the cold sst was not present reference run and an sst field where the cold anomaly was increased by two degrees successively the fields simulated with the realistic sst were consistent with satellite sensor derived observations in particular the weak wind area over the cold sst anomaly was successfully rendered whereas it was not present in the forcing fields taken individually the three runs did not reveal the presence of secondary circulations however anomalous secondary circulations were clearly identified with respect to the reference run the origin of the latter circulations was investigated with the giordani and planton generalization of the sawyer eliassen equations according to our results differential heating induced by the cold sst anomaly mostly altered the vertical wind through the effect of friction and only marginally through pressure gradient forces in the upper part of the boundary layer the wind speed increased decreased over downstream the cold sst we found that stability was the main factor that induced the simulated patterns of the friction term in the diagnostic equations therefore our results show that mesoscale wind patterns were significantly affected by sst gradients through the effect of stability in a region of low oceanic eddy activity

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

comments on the gulf stream convergence zone in the time mean winds abstractin a recent study o neill et al analyzed the divergence of surface winds above the northwest atlantic in the time mean a band of convergence is found overlying the southern flank of th

low frequency variability in the midlatitude atmosphere induced by an oceanic thermal front abstract this study examines the flow induced in a highly idealized atmospheric model by an east west oriented oceanic thermal front the model has a linear marine boundary layer coupled to a quasigeostrophic equivalent barotropic free atmosphere the vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet parallel to the oceanic front s isotherms a large gyre develops on either side of this jet cyclonic to the north and anticyclonic to the south of it as the jet intensifies during spinup from rest it becomes unstable the most unstable wave has a length of about 500 km it evolves into a meander and eddies detach from the eastern edge of each gyre the dependence of the atmospheric dynamics on the strength t of the oceanic front is studied the gulf stream and kuroshio fronts correspond roughly in the scaling used here to t 7 c for weak fronts t 4 c the circulation is steady and exhibits two large antisymmetric gyres sepa

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

cosmogenic noble gas studies in the oldest landscape on earth surface exposure ages of the dry valleys antarctica extraordinarily high surface exposure ages have been determined for sirius group tillites of mt fleming and mt feather as well as at localities in the inner dry valleys using cosmogenic helium and neon ages of 10 ma at mt fleming 5 3 ma at mt feather and 6 5 ma at insel mountain are among the highest nominal exposure ages published so far these values are minimal ages as they are based on the assumption of zero erosion and uplift the mt feather sample independently confirms the pre pliocene age of the sirius group sediments in the dry valleys as previously determined at mt fleming the insel mountain samples provide evidence for a landscape formation of the inner dry valleys not later than late miocene time assuming conservatively low values of 2 5 cm ma 1 for erosion rate and 50 m ma 1 for uplift rate we infer that the sirius group tillites at mt fleming were deposited earlier than 20 ma ago this indicates that the overriding of the dry valleys block of the transantarctic mountains by the east antarctic ice sheet occurred not later than the early miocene maximum long term erosion rates in the inner dry valleys must be 15 cm ma 1 down to altitudes 1000 m since such low erosion rates require permanently cold and hyperarid conditions the response of antarctica to the pliocene warm climatic episode must have been small cosmogenic nuclide data from both the inner dry valleys and the sirius group sediment localities support the hypothesis of a stable east antarctic ice sheet since at least late miocene time implying that the climate of antarctica was decoupled from that of lower southern latitudes we present also new elemental 21ne production rates of p21 mg 196 atoms g 1 yr 1 and p21 al 55 atoms g 1 yr 1 at sea level and high geomagnetic latitude these figures are consistent with a 3he production rate of p3 110 atoms g 1 yr 1 similar to previously published values this consistency provides evidence that pyroxene is retentive for both helium and neon over at least 10 ma cosmogenic ne in quartz and pyroxene has a 22ne 21ne cos ratio of 1 266 0 040 and 1 159 0 040 respectively

cosmic ray exposure dating with in situ produced cosmogenic 3he results from young hawaiian lava flows in an effort to determine the in situ production rate of spallation produced cosmogenic 3 he and evaluate its use as a surface exposure chronometer we have measured cosmogenic helium contents in a suite of hawaiian radiocarbon dated lava flows the lava flows ranging in age from 600 to 13 000 years were collected from hualalai and mauna loa volcanoes on the island of hawaii because cosmic ray surface exposure dating requires the complete absence of erosion or soil cover these lava flows were selected specifically for this purpose the 3 he production rate measured within olivine phenocrysts was found to vary significantly ranging from 47 to 150 atoms g 1 yr 1 normalized to sea level although there is considerable scatter in the data the samples younger than 10 000 years are well preserved and exposed and the production rate variations are therefore not related to erosion or soil cover data averaged over the past 2000 years indicate a sea level 3 he production rate of 125 30atoms g 1 yr 1 which agrees well with previous estimates the longer record suggests a minimum in sea level normalized 3 he production rate between 2000 and 7000 years 55 15atoms g 1 yr 1 as compared to samples younger than 2000 years 125 30 atoms g 1 yr 1 and those between 7000 and 10 000 years 127 19atoms g 1 yr 1 the minimum in production rate is similar in age to that which would be produced by variations in geomagnetic field strength as indicated by archeomagnetic data however the production rate variations a factor of 2 3 0 8 are poorly determined due to the large uncertainties in the youngest samples and questions of surface preservation for the older samples calculations using the atmospheric production model of o brien 1979 35 and the method of lal and peters 1967 11 predict smaller production rate variations for similar variation in dipole moment a factor of 1 15 1 65 because the production rate variations archeomagnetic data and theoretical estimates are not well determined at present the relationship between dipole moment and production rate will require further study precise determination of the production rate is an important uncertainty in the surface exposure technique but the data demonstrate that it is feasible to date samples as young as 600 years of age providing that there has been no erosion or soil cover therefore the technique will have important applications for volcanology glacial geology geomorphology and archaeology

response of surface wind divergence to mesoscale sst anomalies under different wind conditions abstractthe response of the atmospheric boundary layer to mesoscale sea surface temperature sst is often characterized by a link between wind stress divergence and downwind sst gradients in this

the atmospheric response to weak sea surface temperature fronts abstractthe response of the atmospheric boundary layer to fronts of sea surface temperature sst is characterized by correlations between wind stress divergence and the downwind component of the sst gradient and between the wind stress curl and the crosswind component of the sst gradient the associated regression or coupling coefficients for the wind stress divergence are consistently larger than those for the wind stress curl to explore the underlying physics the authors introduce a linearized model of the atmospheric boundary layer response to sst induced modulations of boundary layer hydrostatic pressure and vertical mixing in the presence of advection by a background ekman spiral model solutions are a strong function of the sst scale and background advection and recover observed characteristics the coupling coefficients for wind stress divergence and curl are governed by distinct physics wind stress divergence results from either large scale winds crossing the front or from a thermally direct

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

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

displacement history of a limestone normal fault scarp northern israel from cosmogenic 36cl the abundance of cosmogenic 36 cl measured in 41 limestone samples from a 9 m high bedrock fault scarp allows us to construct the 14 kyr fault displacement history of the nahef east normal fault northern israel 300 m above sea level n33 latitude the nahef east fault is one of a series of fault scarps located along the 700 m high zurim escarpment a major geomorphic feature samples at the top of the scarp have the highest nuclide concentrations 79 x 10 4 atoms g rock 1 samples at the base have the lowest 11 x 10 4 atoms g rock 1 using chemical data from the samples nahef east fault scarp geometry and surface and subsurface production rates for the 36 cl producing reactions we have constructed a numerical model that calculates 36 cl accumulation on a scarp through time given a series of unique displacement scenarios the resulting model 36 cl concentrations are compared to those measured in the scarp samples faulting histories that result in a good match between measured and modeled 36 cl abundances show three distinct periods of fault activity during the past 14 kyr with over 6 vertical meters of motion occurring during a 3 kyr time period in the middle holocene smaller amounts of displacement occurred before and after the period of most rapid motion the episodic behavior of the nahef east fault indicates that the average displacement rate of this fault system has varied through time

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

cosmogenic 3he and 21ne age of the big lost river flood snake river plain idaho the big lost river flood in southeastern idaho occurred 20 500 calibrated yr b p on the basis of dates derived from cosmogenic 3 he and 21 ne measurements of samples from flood deposited boulders and from scour features this date corresponds to a date of 16 900 14 c yr b p and is close in age to several other cataclysmic flood events in western north america it may mark evidence for widespread warming at the end of the pleistocene in western north america the big lost river flood was smaller than some other late pleistocene floods such as the bonnevi1le flood and the missoula floods thus some samples exposed after the flood had significant amounts of cosmogenic 3 he and 21 ne that was acquired before the flood occurred

the role of back pressure in the atmospheric response to surface stress induced by the kuroshio abstractthe effect of ocean current drag on the atmosphere is of interest as a test case for the role of back pressure because the response is independent of the thermally induced modulation of the boundary layer stability and hydrostatic pressure the authors use a regional atmospheric model to investigate the impact of drag induced by the kuroshio in the east china sea on the overlying winter atmosphere ocean currents dominate the wind stress curl compared to the impacts of sea surface temperature sst fronts wind stress convergences and divergences are weakly enhanced even though the ocean current is almost geostrophic these modifications change the linear relationships coupling coefficients between the wind stress curl divergence and the sst laplacian crosswind and downwind gradients clear signatures of the ocean current impacts are found beyond the sea surface sea surface pressure back pressure decreases near the current axis and precipitation increases over the downwind region however

estimation of seasonal morpho sedimentary changes at headland bound and exposed beaches along south maharashtra west coast of india knowledge on seasonal variation of morpho sedimentary processes of tropical beaches is essential to evaluate inter annual variations to devising best protection strategy for the coastal zone a study was taken up to understand the seasonal changes of physical processes at the headland bound and compared with exposed beaches the spatio temporal morpho sedimentary dynamics were carried out through beach profiles sediment samples and simulated wave climates across two complete annual cycle the beach profile survey was carried out using rtk gps wherein the gradistat was used for analysing sediment samples the seasonal wave climates were studied with the swan model coupled with wavewatch iii observation shows the sediment environment at headland bound beach is strongly dominated by fine sand throughout the year whereas the exposed beach is illustrated from fine to medium sand across seasonal scale the seasonal change in beach morphology occurs considerably in the exposed beach than that compared to headland bound successively the occurrence of shoreline retreat is shown maximum up to 20 m in at the exposed beach during the monsoon both the locations showed strong seasonal variation in the wave energy as well as direction whereas the nearshore wave energy at exposed beach is comparatively high with an average of 8342 j m2 than the headland bound due to less deviation in the wave propagation the analysis of seasonal wave pattern together with beach morpho sedimentary processes exhibit the influence of wave conditions at the exposed beach when compared with headland bound beach and so the study implies for offset morphological changes and tailored management to protect the beaches from natural coastal hazards

atmospheric response to a midlatitude sst front alongfront winds abstractsatellite observations and modeling studies show that midlatitude sst fronts influence the marine atmospheric boundary layer mabl and atmospheric circulation here the weather research and forecasting wrf mesoscale model is used to explore the atmospheric response to a midlatitude sst front in an idealized dry two dimensional configuration with a background wind oriented in the alongfront direction the sst front excites an alongfront wind anomaly in the free atmosphere with peak intensity just above the mabl this response is nearly quasigeostrophic in contrast to the inertia gravity wave response seen for cross front background winds the free atmosphere response increases with the background wind in contrast to previously proposed sst frontal mabl models the mabl winds are nearly in ekman balance however a cross front wind develops in the mabl as a result of friction and rotation such that the mabl cross front rossby number e 0 2 the mabl vorticity balance and scaling arguments

diagnostics for near surface wind response to the gulf stream in a regional atmospheric model abstractthe mechanisms acting on near surface winds over the gulf stream are diagnosed using 5 yr outputs of a regional atmospheric model the diagnostics for the surface layer momentum vector its curl and its convergence are developed with a clear separation of pressure adjustment from downward momentum inputs from aloft in the surface layer system the results suggest that the downward momentum mixing mechanism plays a dominant role in contributing to the annual mean climatological momentum curl whereas the pressure adjustment mechanism plays a minor role in contrast the wind convergence is mainly due to the pressure adjustment mechanism this can be explained by the orientation of background wind to the sea surface temperature front the diagnostics also explain the relatively strong seasonal variation in surface layer momentum convergence and the small seasonal variation in curl finally the surface layer response to other western boundary currents is examined using a reanalysis dataset

impacts of the mesoscale ocean atmosphere coupling on the peru chile ocean dynamics the current induced wind stress modulation the ocean dynamical responses to the surface current wind stress interaction at mesoscale are investigated in the south east pacific using a high resolution regional ocean atmosphere coupled model two simulations are compared one includes the surface current in the wind stress computation while the other does not in the coastal region absolute wind velocities are different between the two simulations but the wind stress remains very similar as a consequence the mean regional oceanic circulation is almost unchanged on the contrary the mesoscale activity is strongly reduced when taking into account the effect of the surface current on the wind stress this is caused by a weakening of the eddy kinetic energy generation near the coast by the wind work and to intensified offshore eddy damping we show that above coherent eddies the current stress interaction generates eddy damping through ekman pumping and eddy kinetic energy dissipation through wind work this alters significantly the coherent eddy vertical structures weakening the temperature and vorticity anomalies and increasing strongly the vertical velocity anomalies associated to eddies

atmospheric response to mesoscale sea surface temperature anomalies assessment of mechanisms and coupling strength in a high resolution coupled model over the south atlantic many aspects of the coupling between the ocean and atmosphere at the mesoscale on the order of 20 100 km remain unknown while recent observations from the southern ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind cloud coverage and rain the mechanisms responsible for explaining these atmospheric changes are not well established here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere ocean regional model consortium for small scale modeling regional ocean modelling system cosmo roms configured at a horizontal resolution of 10 km for the south atlantic and run for a 3 month period during austral winter of 2004 the model simulated changes in surface wind cloud fraction and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time from diagnosing the model s momentum balance it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer rather than secondary flows driven by horizontal pressure gradients this is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features this results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux

atmospheric response to sea surface temperature mesoscale structures recent studies have revealed that strong sea surface temperature sst fronts on the scale of a western boundary current significantly affect not just the marine boundary layer but the entire troposphere this has aroused renewed interest in air sea interactions the present study investigates the atmospheric response to fixed sst anomalies associated with mesoscale oceanic eddies and submesoscale filaments using idealized simulations our main result is that in weak wind conditions the vertical velocity in the planetary boundary layer pbl is linearly proportional to the sst laplacian this is established by a quantitative analysis in the spatial space as well as in the spectral space comparing the responses to two different sst fields shows that vertical velocities are much more intense when the submesoscales are more energetic these results hold for different configurations of the atmospheric large scale state and for different pbl parameterizations surface winds play the role of low pass filter and reduce the response at the smaller scales to our knowledge this study is the first to clearly reveal the high impact of oceanic submesoscales on the atmospheric boundary layer at midlatitudes as well as the direct link between the vertical velocity and the sst laplacian

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

global analysis of the pressure adjustment mechanism over sea surface temperature fronts using airs aqua data 1 we investigate the signatures of atmospheric pressure adjustment mechanism for surface wind convergence divergence over major sea surface temperature sst frontal regions using global observations of satellite sounding and scatterometer lower tropospheric air thickness which includes a sea level pressure component modified by air temperature in the marine atmospheric boundary layer is analyzed and the relation between the laplacian of the thickness and wind convergence are examined among four sst frontal regions in mid latitudes correlation between the thickness laplacian and wind convergence is the largest over the gulf stream followed by those for the agulhas return current and for the brazil malvinas current and relatively small but still significant over the kuroshio oyashio extension these correlations strongly suggest that the pressure adjustment mechanism ubiquitously plays an important role in air sea interaction over the global sst frontal regions furthermore air temperatures in the first two regions exhibit sst relating signatures even in the mid troposphere

lapse rates and other variables applied to estimating paleoaltitudes from fossil floras abstract a previous method for determining paleoaltitude from fossil floras has used the difference between sea level and upland paleotemperatures which is then multiplied by the reciprocal of a normal lapse rate the present study examines other variables that can significantly influence such results terrestrial lapse rates have been calculated for 39 areas of the world based upon mean annual temperature mat mean warm month temperature mat and mean cold month ttemperature cmt these show regional and seasonal variability that is explained by factors including continentality elevation of large massifs or high base levels cold air drainage fog mountain barrier effects and the location of the subtropical high pressure zone lapse rates and projected sea level temperatures based on data from the western united states show distinct regional patterns these indicate that within this region the highest lapse rate and temperature values are correlated with 1 continental climates in the subtropical high pressure zone and 2 areas having relief where the lowest elevation land surfaces base levels occur at high altitude the data are applied to evaluate and revise the methodology for estimating paleoaltitudes variables of climatic change sea level fluctuation and paleogeography are also considered limitations in application of the method are emphasized the method is exemplified by application to the latest eocene florissant flora of colorado u s a although the results are conjectural they strongly suggest that the late eocene erosion surface in the southern rocky mountains occurred at a much higher paleoaltitude than previously thought this high elevation may have resulted from earlier laramide crustal thickening

two types of surface wind response to the east china sea kuroshio front abstracteffects of the sea surface temperature sst front along the east china sea kuroshio on sea surface winds at different time scales are investigated in winter and spring the climatological vector wind is strongest on the sst front while the scalar wind speed reaches a maximum on the warm flank of the front and is collocated with the maximum difference between sea surface temperature and surface air temperature sst sat the distinction is due to the change in relative importance of two physical processes of sst wind interaction at different time scales the sst front induced sea surface level pressure slp adjustment sf slp contributes to a strong vector wind above the front on long time scales consistent with the collocation of baroclinicity in the marine boundary layer and corroborated by the similarity between the thermal wind and observed wind shear between 1000 and 850 hpa in contrast the sst modulation of synoptic winds is more evident on the warm flank of the sst front large ther

mass spectrometric identification of cosmic ray produced neon in terrestrial rocks with multiple neon components studies of cosmic ray produced nuclides in terrestrial rocks are expected to provide important geomorphological and glaciological information such as surface exposure ages erosion rates and extent of glacial cover in the case of the stable nuclide21ne the cosmic ray produced component may represent but one of several components and a component resolution based on three isotope correlations is essential we developed analytical techniques which permit accurate corrections for all interfering ions we show for our modified nier source that corrections for doubly charged species based on constant charge state ratios are not satisfactory the improved techniques permit isotopic studies of 106 atoms of21ne the spallation ratio 22ne 21ne c from si was calibrated using a quartz separate from an allan hills sandstone and yields a value of1 243 0 022 this ratio is expected to be essentially constant for terrestrial quartz samples and should be useful in component resolutions the stepwise release of ne at increasing temperatures shows that cosmic ray produced ne is released from quartz at rather low temperatures this permits an estimate of the activation energy for ne diffusion in quartz 90 10 kj mol

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