a cold path for the gulf stream troposphere connection abstractthe mechanism by which the gulf stream sea surface temperature sst front anchors a band of precipitation on its warm edge is still a matter of debate and little is known about how synoptic activity contributes to the mean state in the present study the influence of the sst front on precipitation is investigated during the course of a single extratropical cyclone using a regional configuration of the met office unified model the comparison of a control run with a simulation in which sst gradients were smoothed brought the following conclusions a band of precipitation is reproduced for a single extratropical cyclone and the response to the sst gradient is dominated by a change of convective precipitation in the cold sector of the storm several climatological features described by previous studies such as surface wind convergence on the warm edge or a meridional circulation cell across the sst front are also reproduced at synoptic time scales in the cold sector based on these results a s

lateral velocity variations in southern california i results for the upper crust from pg waves the plate boundary and major crustal blocks in southern california are imaged by a tomographic backprojection of the pg first arrivals recorded by the southern california array the method formulated specifically for local earthquake arrival times is a fast iterative alternative to direct least squares techniques with it we solve the combined problem of determining refractor velocity perturbations and source and station delays resolution and variance are found empirically by using synthetic examples a map showing lateral velocity variations at a depth of approximately 10 km is presented the results show a strong correlation with surface tectonic features clear velocity contrasts exist across the san andreas the san jacinto and the garlock faults the mojave region has the slowest velocities while the peninsula ranges have the highest the san jacinto block has velocities intermediate between mojave and peninsula range velocities and also has early station delays this may indicate that the san jacinto block has overridden mojave material on a shallow detachment surface no velocity variations are found associated with the transverse ranges which we interpret to mean that the surface batholithic rocks in this area do not extend to pg depths

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

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

air sea heat exchange along the northern sea surface temperature front in the eastern tropical pacific abstract the atmospheric response to the oceanic forcing in the eastern pacific along the northern equatorial sea surface temperature sst front is investigated in terms of sensible and latent heat flux during the 6 month period from 28 july 1999 to 27 january 2000 and the 7 month period from 28 june 2000 to 27 january 2001 of particular interest is the atmospheric boundary layer abl response to oceanic tropical instability waves tiws that distort the sst front during may january in normal years in previous studies time series of surface heat fluxes clearly show the influence of tiws but the relationship to spatial patterns of sst and wind speed has been inferred only from sparse in situ data in this study satellite observations are used as a basis for compositing in situ data from moorings to compensate for the lack of a spatially dense mooring array the variability in the position of the sst front caused by westward propagating tiws enables fixed mooring locations to measure the abl response

radar backscatter across the gulf stream sea surface temperature front ku band backscatter responses to frontal sea surface temperature sst changes are studied and applications of a high resolution scatterometer to remote sensing of an sst front are suggested ocean backscatter signatures were measured with an airborne ku band scatterometer across the gulf stream sst front during the surface wave dynamics experiment oceanic and atmospheric parameters were measured by buoys by the scanning radar altimeter and by the advanced very high resolution radiometer and the surface current fields analyzed by the fleet numerical meteorology and oceanography center were obtained vertical polarization backscatter difference across the sst front with an sst difference of 9 spl deg c is more than 5 db in several flight lines large horizontal polarization backscatter changes are also observed across the sst front with an sst difference approximately one half of that in the vertical polarization backscatter case corresponding wind speed differences cannot account for the large backscatter changes in view of seasat a satellite scatterometer sass geophysical model functions depending only on neutral wind velocity for both polarizations upwind backscatter on the cold side is smaller than or close to crosswind backscatter on the warm side for incidence angles larger than 20 spl deg and smaller than 60 spl deg this suggests that the sst front can be detected with backscatter measured by a spaceborne radar at a fixed azimuth angle even if wind directions are different over the cold and warm sides

ship observations and numerical simulation of the marine atmospheric boundary layer over the spring oceanic front in the northwestern south china sea the response of the marine atmospheric boundary layer mabl structure to an oceanic front is analyzed using global positioning system gps sounding data obtained during a survey in the northwestern south china sea nscs over a period of about 1 week in april 2013 the weather research and forecasting wrf model is used to further examine the thermodynamical mechanisms of the mabl s response to the front the wrf model successfully simulates the change in the mabl structure across the front which agrees well with the observations the spatially high pass filtered fields of sea surface temperature sst and 10 m neutral equivalent wind from the wrf model simulation show a tight positive coupling between the sst and surface winds near the front meanwhile the sst front works as a damping zone to reduce the enhancement of wind blowing from the warm to the cold side of the front in the lower boundary layer analysis of the momentum budget shows that the most active and significant term affecting horizontal momentum over the frontal zone is the adjustment of the pressure gradient it is found that the front in the nscs is wide enough for slowly moving air parcels to be affected by the change in underlying sst the different thermal structure upwind and downwind of the front causes a baroclinic adjustment of the perturbation pressure from the surface to the midlayer of the mabl which dominates the change in the wind profile across the front

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

thermodynamic sea ice growth in the central weddell sea observed in upward looking sonar data upward looking sonar uls data were used to analyze thermodynamic sea ice growth the study was carried out for an ocean region in the central weddell sea for which data of sea ice thickness variability and of the oceanic heat flux through the ice are rare in the study area the contribution of sea ice deformation to vertical ice growth is relatively small in some years this provides the opportunity to simulate thermodynamic sea ice growth considering the influence of a snow cover and of the oceanic heat flux to this end a modified version of stefan s law was used the resulting ice thickness variations were then compared with the uls measurements for the investigated cases the best consistency between data and model results was obtained assuming a snow layer of less than 5 cm thickness and average oceanic heat fluxes between 6 and 14 w m 2 it is demonstrated that in conjunction with ice drift data and analytical models for thermal sea ice growth uls ice thickness measurements are useful for studying the seasonal cycle of growth and decay and for inferring the magnitude of the average oceanic heat flux under sea ice

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

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

intraseasonal variability of tropical atlantic sea surface temperature air sea interaction over upwelling fronts tropical atlantic sea surface temperatures ssts maximum intra seasonal variability isv and their interaction with local surface winds are investigated applying statistical analysis to observations and to a recent coupled reanalysis over the 2000 2009 decade five cores of strong isv emerge with standard deviation reaching about 1 c in frontal areas of the three main upwelling systems equatorial angola benguela and senegal mauritania the southern side of the canary upwelling west of 10 w along the equator a 20 60 day peak caused by tropical instability waves is shown to generate surface wind anomalies through the adjustment of the horizontal surface pressure gradient in addition to the modification of near surface atmospheric stratification east of 10 w along the equator an intense biweekly oscillation increases the ocean and atmosphere isv in the two coastal upwelling fronts intraseasonal sst anomalies resemble each other they are shown to be influenced by coastal kelvin waves in addition to large scale wind forcing over the angola benguela upwelling coastal wind bursts controlling the sst isv are associated with anomalously strong pressure patterns related to the madden julian oscillation the st helena anticyclone and the antarctic oscillation in the senegal mauritania upwelling the wind anomalies mainly linked to the azores anticyclone in the southern front during november to may appear to be connected to the saharan heat low in the northern front from june to september in all five regions and as expected for such upwelling regimes vertical oceanic mixing represents the dominant term in the mixed layer heat budget in the equatorial band as found in previous studies horizontal advection is equally important while it appears surprisingly weak in coastal fronts finally a striking result is the general lack of surface wind signal related to the sst isv in the coastal upwellings

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

sst front anchored mesoscale feature of surface wind in the southern indian ocean using 28 year satellite borne special sensor microwave imager observations features of high wind frequency hwf over the southern indian ocean are investigated climatology maps show that high winds occur frequently during austral winter located in the open ocean south of polar front in subpolar region warm flank of the subantarctic front between 55 e 78 e and south of cape agulhas where westerly wind prevails the strong instability of marine atmospheric boundary layer accompanied by increased sensible and latent heat fluxes on the warmer flank acts to enhance the vertical momentum mixing thus accelerate the surface winds effects of sea surface temperature sst front can even reach the entire troposphere by deep convection hwf also shows distinct interannual variability which is associated with the southern annual mode sam during positive phase of the sam hwf has positive anomalies over the open ocean south of polar front while has negative anomalies north of the sst front a phase shift of hwf happened around 2001 which is likely related to the reduction of storm tracks and poleward shift of westerly winds in the southern hemisphere

sea breeze like winds across the north wall of the gulf stream an analytical model sea breeze like winds have been observed on the warmer side of the gulf stream when synopticscale winds blow from cool shelf water toward a warm water surface sweet et al 1981 it is shown that a simple thermally driven analytical model can explain satisfactorily the increase in wind speed from the cold to the warmer water side as resulting from horizontal temperature gradient across the gulf stream

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

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

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

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

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

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

the influence of coastal shape on winter mesoscale air sea interaction abstract in the case of cold air outbreaks the combination of the coastal shape and the sea surface temperature sst pattern is shown to have a profound effect in establishing a low level mesoscale atmospheric circulation as a result of differential heating due to both variations in overwater path length and the sst a convergence or divergence line then forms along a line exactly downwind of the major bend in the coastline this is consistent with the structure of the cloud patterns seen in a high resolution landsat picture of the cloud streets the major features are also simulated well with a boundary layer model the dominant convergence line is marked by notably larger clouds to its cast the convective roll clouds grow downstream in accord with the deepening of the boundary layer to its west i e coastal side near the convergence line where the induced pressure field forces a strong westerly component in the boundary layer the wind shear across the inversion gives rise to kelvin helmholtz w

the influence of the marine atmospheric boundary layer on ers 1 synthetic aperture radar imagery of the gulf stream in september 1991 the ers 1 synthetic aperture radar sar collected a set of four colocated images over the western gulf stream gs the sar images were supplemented by satellite infrared imagery and measurements of the marine atmospheric boundary layer mabl from both a pair of surface buoys and a suite of instrument on the ukrainian research vessel r v vernadsky which between september 15 and 19 made six transects across the gs northern boundary within the sar swaths the influence of wind variations within the mabl was evident in each of the four sar images evidence for thermal wind effects is seen in the changing character of the imagery as the mean wind across the sea surface temperature boundary changed direction from pass to pass both in situ data and analytical models suggest that much of the day to day sar image variability was the result of changes in the character of the mabl especially evident near the northern gs boundary where the sign of the atmospheric stability fluctuated over short spatial scales because many of the governing parameters of the mabl rapidly decorrelate significant changes in the sar imagery occurred during the 3 days between passes nevertheless at least some manifestation of the gs was evident in the sar imagery on each of the four passes