cenozoic magmatism of the valencia trough western mediterranean relationship between structural evolution and volcanism abstract the cenozoic magmatism of the valencia trough is characterized by the existence of two volcanic cycles the first cycle early miocene middle miocene comprises calc alkaline rocks which have been recognized in the central to eastern offshore areas and in mallorca the second cycle middle miocene to recent is represented mainly by poorly differentiated alkaline rocks which are predominantly distributed along the iberian margin of the valencia trough in accordance with the inferred structural evolution of the valencia trough petrological and geochemical data as well as volcanological evidence we suggest that two different geodynamic environments existed during these magmatic cycles the early to middle miocene calc alkaline volcanism developed under compressive tectonic conditions and seems to be associated with the northwestern dipping subduction of the african plate in contrast the middle miocene to recent alkaline volcanism is associated with extensional tectonics and can be explained within the framework of a low volcanicity rift model three zones catalan valencian and columbretes each located at different parts of the rift structure can be distinguished in the middle miocene to recent volcanism this intraplate volcanism results from partial melting due to extension driven decompression with the largest degrees of melting in the centre of the valencia trough columbretes volcanic zone in the catalan volcanic zone a progressive increase in the extension rate from the first to the last volcanic episode has occurred favouring the interaction of two mantle sources

age and sr isotopic signature of the catoctin volcanic province implications for subcrustal mantle evolution variations in chemical and sr isotopic signatures of a series of basaltic flows have been correlated with newly mapped stratigraphic sections in the upper precambrian catoctin flood basalts in the central appalachians element mobility through fluid interaction is commonly observed in flows with a well developed fabric but some samples with more massive textures commonly in the cores of thicker flows still retain relict clinopyroxene and igneous textures and show only minor element redistribution five whole rock samples with relict igneous textures and a clinopyroxene mineral separate yield an isochron with an age of 570 36 ma 2sigma and a strontium initial ratio of 0 7035 1 this age is consistent with recent paleontological evidence for a latest precambrian time for catoctin volcanism and along with isotopic age determinations of 680 710 ma for other rift related magmatism suggests either a two stage or a very long protracted episode of continental rifting paleogeographic reconstruction indicates that the original site of eruption for the lavas must have been at least 56 km to the east in the same geographic location from which the mesozoic appalachian tholeiite terrane evolved variations in sr isotopic signatures and differences in major element abundances between these two sequences suggest mantle heterogeneitiesmore that must have developed beneath the eastern north american craton during the interim 400 m y less

intensification of ocean fronts by down front winds abstract many ocean fronts experience strong local atmospheric forcing by down front winds that is winds blowing in the direction of the frontal jet an analytic theory and nonhydrostatic numerical simulations are used to demonstrate the mechanism by which down front winds lead to frontogenesis when a wind blows down a front cross front advection of density by ekman flow results in a destabilizing wind driven buoyancy flux wdbf equal to the product of the ekman transport with the surface lateral buoyancy gradient destabilization of the water column results in convection that is localized to the front and that has a buoyancy flux that is scaled by the wdbf mixing of buoyancy by convection and ekman pumping suction resulting from the cross front contrast in vertical vorticity of the frontal jet drive frontogenetic ageostrophic secondary circulations ascs for mixed layers with negative potential vorticity the most frontogenetic ascs select a preferred cross front width and do not translate with

ten million year history of a thrust sheet the final deformed state of a fold and thrust belt may be reached by an infinite number of kinematic paths two end member kinematic paths are due to continuous or discontinuous rates of deformation we have used a new magnetostratigraphic section from the spanish pyrenees to calibrate the emplacement history over 10 m y of a major thrust sheet the sierras marginales thrust sheet and the deformation of both its hanging wall and footwall six time windows from before 36 5 ma until after 24 7 ma were recognized on the basis of structural and stratigraphic relationships between syntectonic strata and major structures footwall deformation of the sierras marginales thrust sheet occurred continuously on a detachment within the foreland basin sequence 4 5 km net shortening shortening rates steadily increased from 0 14 to 1 5 mm yr with time although the detachments at the base of the foreland and the detachment at the base of the sierras marginales thrust sheet were active coevally the rate of displacement on the sierras marginales detachment decayed with time and shows considerable variability emplacement of the thrust sheet may be divided into three distinct periods a rapid 13 8 km translation from 37 0 to 36 5 ma 27 6 mm yr a gradual climb of the toe of the thrust sheet up a 4 3 km long ramp across the foreland basin succession from 36 5 to 32 0 ma 0 95 mm yr and a final 8 9 km translation from 32 0 to 29 5 ma 3 56 mm yr internal deformation of the thrust sheet occurred only after it reached its present position at some time before 29 5 ma shortening rates steadily decreased from 0 6 mm yr between 29 5 and 27 8 ma to 0 26 mm yr from 27 8 until after 24 7 ma only 1 km of shortening accumulated during each of the two periods the last shortening localized on the most northerly thrust in the study area folding and subsequent faulting above the detachment beneath the foreland suggest that slip was transmitted to its tip point continuously throughout the deformation in contrast translation followed by internal deformation on the hinterland side of the toe of the sierras marginales thrust sheet indicates a successive deactivation of the southern parts of the detachment with time rate of deformation on both detachments was discontinuous and shows substantial variability about the mean in general the spatial and temporal pattern of deformation was distributed and continuous in detail however shortening was spatially and temporally discontinuous above each detachment and structures related to each one display distinctly different deformational patterns rates and styles

explicit numerical diffusion in the wrf model abstract diffusion that is implicit in the odd ordered advection schemes in early versions of the advanced research core of the weather research and forecasting wrf model is sometimes insufficient to remove noise from kinematical fields the problem is worst when grid relative wind speeds are low and when stratification is nearly neutral or unstable such as in weakly forced daytime boundary layers where noise can grow until it competes with the physical phenomena being simulated one solution to this problem is an explicit sixth order numerical diffusion scheme that preserves the wrf model s high effective resolution and uses a flux limiter to ensure monotonicity the scheme and how it was added to the wrf model are explained the scheme is then demonstrated in an idealized framework and in simulations of salt breezes and lake breezes in northwestern utah

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

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

modeling and analysis of ageostrophic circulation over the azores oceanic front during the semaphore experiment abstract in the conventional quasigeostrophic qg form of the equation developed by hoskins et al the unique forcing of vertical velocity is the geostrophic deformation as the qg or even the semigeostrophic sg hypotheses are not adapted to study the frontal dynamics in the atmospheric boundary layer this paper proposes a generalized expression of the hoskins et al form of the vertical velocity two thermal and three dynamical sources of the vertical velocity are identified these forcings allow for identification of each of the physical processes acting simultaneously on the ageostrophic circulation in the boundary layer this new form of the equation is used to explain wind increase in the atmospheric boundary layer over the warm waters of the sea surface temperature sst front observed during a fair anticyclonic day of the semaphore experiment 1993 and simulated with a nonhydrostatic mesoscale atmospheric model since the sst gradients are weak of the order of 1 5 c 100 km 1 the surfac

mesoscale sst wind stress coupling in the peru chile current system which mechanisms drive its seasonal variability satellite observations and a high resolution regional ocean atmosphere coupled model are used to study the air sea interactions at the oceanic mesoscale in the peru chile upwelling current system coupling between mesoscale sea surface temperature sst and wind stress ws intensity is evidenced and characterized by correlations and regression coefficients both the model and the observations display similar spatial and seasonal variability of the coupling characteristics that are stronger off peru than off northern chile in relation with stronger wind mean speed and steadiness the coupling is also more intense during winter than during summer in both regions it is shown that ws intensity anomalies due to sst anomalies are mainly forced by mixing coefficient anomalies and partially compensated by wind shear anomalies a momentum balance analysis shows that wind speed anomalies are created by stress shear anomalies near surface pressure gradient anomalies have a negligible contribution because of the back pressure effect related to the air temperature inversion as mixing coefficients are mainly unchanged between summer and winter the stronger coupling in winter is due to the enhanced large scale wind shear that enables a more efficient action of the turbulent stress perturbations this mechanism is robust as it does not depend on the choice of planetary boundary layer parameterization

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

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

observed variations of the atmospheric boundary layer and stratocumulus over a warm eddy in the kuroshio extension abstracta research vessel sailing across a warm eddy in the kuroshio extension on 13 april 2016 captured an abrupt development of stratocumulus under synoptic high pressure shipboard observations

a succession of miocene rodent assemblages from fissure fillings in southern france palaeoenvironmental interpretation and comparison with spain abstract an early to late miocene sequence of rodent assemblages from southern france has been quantitatively studied the resulting pattern seems very similar to a contemporary sequence from central spain calatayud teruel basin the fossil mammal bearing localities are of different types mainly karst infills in france and localities situated in sedimentary basins in spain in order to interpret the fossil record a comparison has been made between southern france faunas of similar age but collected in karst infills and in basin deposits there seems to be no difference between the two kinds of faunas and thus there is no indication that karst infills systematically give a picture of drier and more open environments both types of localities may give a similar relative abundance of taxa and when differences exist they can be attributed to local conditions the comparison between southern france and the calatayud teruel basin central spain shows that 1 similar trends occurred in the two areas 2 differences between spectra were more important during the late early miocene than during the middle miocene 3 the shift between the late early miocene and the middle miocene environments in southern france does not seem to be correlated with a general drop in temperatures as inferred from the analysis of central spain faunas

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

latest oligocene late miocene lacustrine systems of the north central part of the ebro basin spain sedimentary facies model and palaeogeographic synthesis abstract in the central part of the ebro basin spain north of the ebro river three allostratigraphic or tectosedimentary units differentiated within the latest oligocene late miocene upper agenian vallesian interval are sedimentologically characterized these deposits represent carbonate and sulphate lacustrine environments fed by pyrenean alluvial systems luna system and huesca system in each unit several facies associations or lithofacies were mapped these interfinger through time gypsum lithofacies occupy the southernmost part of the study area and are surrounded by carbonate and or detrital lithofacies to the north each lithofacies consists of different carbonate sulphate and or detrital facies arranged in simple sequences decimetres to metres thick the four types of sequences characterized reflect a complex shallowing evolution involving carbonate or sulphate contexts thus each lithofacies represents the sedimentation in a particular lacustrine or alluvial subenvironment a single lacustrine system is proposed for the central part of the basin its evolution followed cycles of water level variations which caused kilometre scale migrations of the lake shoreline in this model two distinct situations or lakes alternated through time a one represents high levels associated with a single body of dilute carbonate water where massive carbonate facies formed influenced by organism proliferation these lakes had wide palustrine vegetated margins in which bioturbated facies developed b the other represents low levels that correspond to a playa lake model laminated sulphate deposits formed in the lake waters while nodular gypsum originated in the surrounding saline mud flats and within the exposed previously deposited carbonate sediments transitions from one situation to the other including minor water level fluctuations within carbonate sedimentation conditions were marked by the development of laminated and stromatolitic facies lake level variations were caused by climatic cycles and gave rise to the simple sequences and to the lithofacies lateral relationships recognized in this study correlation among tectosedimentary units in the studied pyrenean domain and in the iberian domain of the ebro basin shows that for units n1 and n2 the facies that resulted from dilute carbonate waters are rare in the lacustrine areas of the iberian margin this indicates that a strong hydrological contrast existed between both regions on this basis a theoretical asymmetrical facies model is proposed for the single lacustrine basin that extended over these regions

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

patterns and average rates of late neogene recent uplift of the betic cordillera se spain abstract the facies distribution in the sedimentary units infilling a series of neogene basins has been used to reconstruct the relief generation and uplift across the internal zone of the betic cordillera in southern spain uplift amounts and average rates can be estimated using the current elevation of the outcrops of well dated deposits indicative of ancient sea level positions coral reefs and coastal conglomerates record the initial development of emergent betic relief during the langhian continental and marginal marine deposits indicate the existence of a large island centred on the present sierra nevada sierra de los filabres chain by the end of the middle miocene the precursor of the sierra nevada sierra de los filabres chain originally part of this large island remained emerged whilst the surrounding areas were re invaded by the sea during the early tortonian at the end of the tortonian the inland basins granada and guadix basins became continental while the sierras de la contraviesa sierra de gador and sierra alhamilla emerged separating the alboran basin from the alpujarra tabernas and sorbas basins which became narrow passages of the mediterranean sea in contrast the sierra cabrera emerged during the late messinian suggesting a progressive uplift from west to east of the sierras south of the sierra nevada sierra de los filabres chain during the pliocene only the low areas closest to the present day coast remained as marine basins and progressively emerged throughout this stage the highest average uplift rate recorded is 280 m ma for the sierra de gador although the average uplift rates of upper neogene coastal marine rocks since depositon have maximum values of approximately 200 m ma most of the uplift of the betic mountains took place before the early pliocene the recorded uplift of neogene rocks was highest at the margins of western sierra nevada where peaks higher than 3000 m occur the average rates of uplift were lower to the east of this major relief the main sierras and depressions in the present day landscape correspond respectively to the emergent land in which uplift was concentrated and to the marine basins that existed before the final emergence of the region the altitude of the sierras reflects the time at which they became emergent the highest mountains being the first to rise above sea level

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

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

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

mesoscale coastal processes during gale iop 2 abstract during intensive observation period 2 of the genesis of atlantic lows experiment a number of mesoscale phenomena were observed with special and conventional observing systems over the land and coastal waters this study involved analysis of these data for the period 24 26 january 1986 in order to define the structure and dynamics of three features the coastal front a shallow cyclone that propagated along the coastal front modifying it as it moved northward and a low level jet that formed in the strong coastal pressure gradient field the coastal front formed in an existing pressure trough over the gulf stream as a result of both ageostrophic deformation and differential diabatic heating there existed considerable variability in the frontal strength and position on both the mesoalpha and mesobeta scales the level of strongest frontogenesis was near the surface with frontolysis calculated above 950 mb the marine atmospheric boundary layer mabl over the gulf stream was conducive to cyclon

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

dynamical analyses of marine atmospheric boundary layer structure near the gulf stream oceanic front the effects of the sea surface temperature s s t front at the edge of the gulf stream on the marine atmospheric boundary layer mabl are investigated using a numerical model to study the modification effects of an oceanic front on the mabl structure the situation simulated is flow from over cold shelf water to over the warm water of the gulf stream the initial temperature and humidity profiles of the air are specified to be near neutral over the cold water and are therefore typical of undisturbed conditions the differential in s s t across the oceanic front creates a horizontal variation in the surface perturbation pressure and the stability the surface perturbation pressure and turbulent fluxes modulate the flow and produce horizontal variations in horizontal wind components with associated vertical motions a thermally direct cell is produced as a result of the s s t difference across the front the isotherms slope upward towards the warm water entrainment of inversion layer air and upward vertical motion over the warm water cause the mabl to be deeper there a layer of cloud forms over warm water and is associated with mixed layer deepening rather than lowering of the condensation level turbulent fluxes in the mabl show considerable spatial variation surface stress is much larger over the front and over the warm water than over the cold water this is mostly caused by wind speed changes associated with the front changes in the drag coefficient due to changes in surface roughness and stability are much less important mean budgets for temperature and total water indicate that there is a balance between horizontal advection and turbulent flux divergence the u momentum budget shows that once the geostrophic balance terms are subtracted the balance is mainly between the pressure gradient force associated with the induced temperature field and turbulent friction with horizontal advection and the coriolis force acting on the geostrophic departure playing minor roles the v momentum budget shows a balance between horizontal advection coriolis force and friction although there are few data for comparison the results are in qualitative agreement with observations in the area this study shows that the s s t front at the gulf stream edge produces marked local changes in the nearby atmospheric surface layer

syntectonic burial and post tectonic exhumation of the southern pyrenees foreland fold thrust belt in the oligocene to earliest miocene the entire southern pyrenean foreland fold and thrust belt was backfilled and buried in up to 3 km of syntectonic continental conglomerates from the range9s own erosional debris then starting in the mid to late miocene the pyrenees were exhumed by erosional excavation to their present relief a model is proposed for this unusual development whereby late eocene oligocene tectonic uplift of the margins of the ebro basin raised local base level and blocked normal dispersal of erosional debris to adjacent oceans thus causing the basin to fill then backfill northwards across the entire southern flank of the pyrenees subsequent miocene rifting of the catalan mediterranean margin and the messinian salinity crisis lowered base level allowing the ebro river to cut headward capture the ebro basin and re excavate the pyrenees

numerical simulation of boundary layer structure and cross equatorial flow in the eastern pacific abstract recent observations from spaceborne microwave sensors have revealed detailed structure of the surface flow over the equatorial eastern pacific in the boreal fall season a marked acceleration of surface wind across the northern sea surface temperature sst front of the cold tongue is a prominent feature of the regional climate previous studies have attributed the acceleration to the effect of enhanced momentum mixing over the warmer waters a high resolution numerical model is used to examine the cross frontal flow adjustment in a comprehensive comparison the model agrees well with many observed features of cross equatorial flow and boundary layer structure from satellite tropical atmosphere ocean tao moorings and the recent eastern pacific investigation of climate processes epic campaign in particular the model simulates the acceleration across the sst front and the change from a stable to unstable boundary layer analysis of the model momentum budget indicates that the hydrostatic

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

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

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

mixed layer lateral eddy fluxes mediated by air sea interaction abstract the modulation of air sea heat fluxes by geostrophic eddies due to the stirring of temperature at the sea surface is discussed and quantified it is argued that the damping of eddy temperature variance by such air sea fluxes enhances the dissipation of surface temperature fields depending on the time scale of damping relative to that of the eddying motions surface eddy diffusivities can be significantly enhanced over interior values the issues are explored and quantified in a controlled setting by driving a tracer field a proxy for sea surface temperature with surface altimetric observations in the antarctic circumpolar current acc of the southern ocean a new tracer based diagnostic of eddy diffusivity is introduced which is related to the nakamura effective diffusivity using this the mixed layer lateral eddy diffusivities associated with i eddy stirring and small scale mixing and ii surface damping by air sea interaction is quantified in the acc a diffusivity associated with su

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

low long term erosion rates in high energy mountain belts insights from thermo and biochronology in the eastern pyrenees abstract we relate the high elevation of flat topography in the eastern pyrenees to the resurrection of a mountain belt which prior to 12 ma was a low relief landscape or peneplain bevelling eroded stumps of the pyrenean compressional orogen new apatite fission track and u th he data together demonstrate the consistently young age