statistical properties of the surface velocity field in the northern gulf of mexico sampled by glad drifters the grand lagrangian deployment glad used multiscale sampling and gps technology to observe time series of drifter positions with initial drifter separation of o 100 m to o 10 km and nominal 5 min sampling during the summer and fall of 2012 in the northern gulf of mexico histograms of the velocity field and its statistical parameters are non gaussian most are multimodal the dominant periods for the surface velocity field are 1 2 days due to inertial oscillations tides and the sea breeze 5 6 days due to wind forcing and submesoscale eddies 9 10 days and two weeks or longer periods due to wind forcing and mesoscale variability including the period of eddy rotation the temporal e folding scales of a fitted drifter velocity autocorrelation function are bimodal with time scales 0 25 0 50 days and 0 9 1 4 days and are the same order as the temporal e folding scales of observed winds from nearby moored national data buoy center stations the lagrangian integral time scales increase from coastal values of 8 h to offshore values of approximately 2 days with peak values of 3 4 days the velocity variance is large o 1 m2 s2 the surface velocity statistics are more anisotropic and increased dispersion is observed at flow bifurcations horizontal diffusivity estimates are o 103 m2 s in coastal regions with weaker flow to o 105 m2 s in flow bifurcations a strong jet and during the passage of hurricane isaac the gulf of mexico surface velocity statistics sampled by the glad drifters are a strong function of the feature sampled topography and wind forcing

rock avalanches and the pace of late quaternary development of river valleys in the karakoram himalaya we discuss the implications of a set of terrestrial cosmogenic nuclide tcn ages on blocky cross valley deposits of large rock avalanches along upper indus streams the dated deposits are key to understanding late quaternary events that play a major role in landscape evolution in the karakoram himalaya the landslides occurred between 3 and 8 ka ago challenging existing chronologies of events along indus streams the tcn ages may support a mid holocene climatic role in preparing slopes for failure but the balance of evidence suggests that large earthquakes triggered the landslides each landslide dammed the indus or a major tributary and controlled base level and sedimentation for millennia they produced landforms long regarded as characteristic of the region including extensive lacustrine deposits flights of river terraces epigenetic gorges and sediment fans until the 1990s most of the landslides were interpreted as moraines related lacustrine and other sediments continue to be attributed to glacial damming and stream terraces to tectonic processes generally they were seen to originate tens of thousands to hundreds of thousands of years earlier than the new ages require instead we argue that they record interactions among different geomorphic processes in landslide fragmented valleys during the holocene rather than being geomorphic markers of tectonic and climatic events the landslides have buffered or redirected climatic and tectonic forcing in such an active orogen millennia long episodes of zero net bedrock incision at each site are surprising however rates of sedimentation above landslide barriers and erosion controlled by their breaching are close to today9s high measured rates for geomorphic activity we propose that landslide fragmented rivers may in fact characterize interglaciations and future patterns of upper indus landscape evolution at time scales of 10 3 to 10 4 years

decay of the sea ice in the north water area observation of ice cover in landsat imagery the sea ice distribution in and around the north water was observed by using satellite imagery obtained by landsat the observed data for 1973 were used to describe the decay of the ice cover in the area the surface of the north water did not seem to be open throughout the winter but rather to be mostly covered by a thin layer of pack ice the entire decay began earlier in the spring because the ice present at the beginning of the decay period was relatively thin the sea surface in the north water lost ice cover earlier than the surrounding area open water was thus observed in spring when the ice cover at similar latitude was still complete the mechanism of decay itself did not indicate any peculiarity

a recent sea ice retreat west of the antarctic peninsula satellite passive microwave data show a record decrease in sea ice extent in the bellingshausen sea from mid 1988 through early 1991 the change coincides with more southerly surface winds increased cyclonic activity and rising surface air temperatures which reached historic highs along the west coast of the antarctic peninsula in 1989 preceded by high ice cover in 1986 87 the retreat was most evident during summer in the formerly perennial sea ice field over the continental shelf ocean heat storage probably contributed to the persistence and coastal propagation of this anomaly

drifter motion in the gulf of mexico constrained by altimetric lagrangian coherent structures 1 application of recent geometric tools for lagrangian coherent structures lcs shows that material attraction in geostrophic velocities derived from altimetry data imposed an important constraint to the motion of drifters from the grand lagrangian deployment glad in the gulf of mexico this material attraction is largely transparent to traditional eulerian analysis attracting lcs acted as approximate centerpieces for mesoscale patterns formed by the drifters persistently attracting lcs cores emerged 1 week before the development of a filament resembling the tiger tail of the deepwater horizon oil slick thereby anticipating its formation our results suggest that the mesoscale circulation plays a significant role in shaping near surface transport in the gulf of mexico

studies of antarctic sea ice concentrations from satellite data and their applications large regional and temporal changes in the global sea ice cover have been observed recently because of the relevance of such changes to climate change studies it is important that key ice concentration data sets currently used for evaluating such a phenomenon are assessed for accuracy and interpreted properly sea ice concentrations derived from passive microwave data using the bootstrap and nasa team algorithms are shown to be generally consistent but are also observed to differ by 10 35 in large areas within the ice pack especially in the weddell sea amundsen sea and ross sea regions comparative analyses of such passive microwave data with coregistered visible and infrared i e landsat avhrr and ols data show a predominance of thick consolidated ice in these areas and good agreement with the bootstrap algorithm results the relatively low values from the nasa team algorithm results are likely due to layering within the ice and snow and or surface flooding which are known to affect the polarization ratio large seasonality in the physical characteristics and emissivity of the ice cover is also observed and in predominantly new ice regions the ice concentrations from passive microwave data are usually lower than retrievals from landsat and ols data in which the thresholding technique is used the passive microwave results are biased because of relatively low emissivity of new ice but they may be more useful since the bias allows for the identification of areas of significant divergence and polynya activities such areas need to be identified since heat and salinity fluxes are proportionately increased in these areas compared to those from the thicker ice areas time series data from 1978 through 2000 also show a slight but insignificant positive trend of 0 17 0 33 decade in ice extent which is consistent with slight continental cooling during the period this is a big contrast to the observed negative trend of about 3 decade in the arctic sea ice cover it should be noted however that because the overlap period for key instruments is just 1 month the error due to changes in sensor characteristics calibration and threshold for the 15 ice edge may not be negligible

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

antarctic sea ice concentrations inferred from nimbus 5 esmr and landsat imagery a quantitative comparison is made of antarctic sea ice concentration derived from the nimbus 5 electrically scanning microwave radiometer esmr and from the landsat 1 and landsat 2 mss 7 near infrared band images the set of images includes regions near the ice edge and near the continental boundary during late winter or spring the ice covered areas in the southern ocean exhibit microwave brightness temperature predominantly characteristic of first year sea ice with emissivity of 0 92 the percentage ice cover is derived from the microwave data using an algorithm that uses this emissivity and interpolated climatological physical temperatures and that is not dependent on spatial resolution classification of ice floes and open water in cloud free landsat images provides an alternative determination of large scale ice concentrations but the limitations of this method are shown in various areas especially near the ice edge landsat data are limited in their ability to resolve individual ice floes a classification procedure for landsat data based on a threshold radiance level for water overestimates the ice concentration because this method tends to classify mixtures of open water and unresolved ice floes as fully ice covered a proportional classification based on observed reflectance gives better agreement with the esmr ice concentration values because it does not require that each open water area be resolved in the landsat imagery the derived ice concentrations from the esmr and landsat data using the proportional classification method agree to 15 with the largest uncertainties occurring in regions of low concentration

ross sea polynyas response of ice concentration retrievals to large areas of thin ice 1 for a 3 month period between may and july of 2005 we examine the response of the advanced microwave scanning radiometer amsr e enhanced nasa team 2 nt2 and amsr e bootstrap aba ice concentration algorithms to large areas of thin ice of the ross sea polynyas coincident envisat synthetic aperture radar sar coverage of the region during this period offers a detailed look at the development of the polynyas within several hundred kilometers of the ice front the high resolution imagery and derived ice motion fields show bands of polynya ice covering up to 105 km2 of the ross sea that are associated with wind forced advection in this study ice thickness from amsr e 36 ghz polarization information serves as the basis for examination of the response the quality of the thickness of newly formed sea ice 10 cm from amsr e is first assessed with thickness estimates derived from ice surface temperatures from the moderate resolution imaging spectroradiometer modis instrument the effect of large areas of thin ice in lowering the ice concentration estimates from both nt2 aba approaches is clearly demonstrated results show relatively robust relationships between retrieved ice concentrations and thin ice thickness estimates that differ between the two algorithms these relationships define the approximate spatial coincidence of ice concentration and thickness isopleths using the 83 aba and 91 nt2 isopleths as polynya boundaries we show that the computed coverage compares well with that using the estimated 10 cm thickness contour the thin ice response characterized here suggests that in regions with polynyas the retrieval results could be used to provide useful geophysical information namely thickness and coverage

submesoscale evolution of surface drifter triads in the gulf of mexico triangle shape metrics are analyzed to quantify the evolution of submesoscale 100 500 m initial separation surface drifter triplets released in the northern gulf of mexico the observations are compared to synthetic drifters advected by geostrophic velocity fields derived from satellite altimetry observed submesoscale triads evolve rapidly reaching highly elongated configurations on timescales of 6 hours to 2 days in contrast to 6 days or longer for altimetry derived synthetic data estimates of horizontal divergence and strain rate from the drifter triplets indicate the relative importance of divergence in the evolution of triangle shape horizontal divergence is scale dependent on the order of the local coriolis parameter and 2 to 3 times larger for initial 100 m scales compared to initial 500 m scales

passive microwave in situ observations of winter weddell sea ice the microwave radiative characteristics of antarctic sea ice during a winter period were investigated continuously from r v polarstern during the 1986 winter weddell sea project while the ship went through about 3000 km of ice from the marginal ice zone to the coastal region and back radiometer measurements at 6 10 18 37 and 90 ghz in vertical and horizontal polarizations were complemented by visual and video observations and measurements at 60 stations of ice thickness salinity temperature snow cover density and other physical characteristics two distinct types of ice cover were observed in the marginal ice zone small pancakes evenly distributed during the southbound leg and ice bands with wet pancakes during the northbound leg other ice types observed were first year ice covered by varying thicknesses and states of snow cover and new and young ice found mainly in leads and polynyas analysis of the data shows a large variability in the multispectral microwave emissivities of these ice types especially at 90 ghz over newly refrozen lead or polynya regions several forms of new ice appear radiometrically distinct while over thick consolidated ice with snow cover the brightness temperatures observed at 90 ghz varied by as much as 100 k overall however at 18 ghz and lower frequencies the emissivities of thick and cold first year ice are relatively stable with standard deviations of about 0 02 at the marginal ice zone the emissivity of the ice cover is a lot less predictable and could cause large uncertainties in ice concentration estimates the use of the 90 ghz channel in combination with a lower frequency channel shows strong potential for more detailed characterization of the ice cover including the identification of various forms of new ice and the quantification of varying snow cover and roughness

anomalous peak in antarctic sea ice area winter 1998 coincident with enso the results of an updated satellite analysis of hemispheric and regional antarctic sea ice cover are presented based on october 1987 september i999 special sensor microwave imager ssm i data these show an ongoing slight but significant hemispheric increase of 3 7 0 3 in extent and 6 6 1 5 in area in the two principal sectors weddell sea ice extent area decreased by 3 4 1 0 3 9 4 6 and ross sea ice extent area increased by 10 9 1 0 18 3 4 6 hemispheric ross sea and western pacific ocean ice peaks in september 1998 were anomalously high and may have been related to atmospheric and oceanic anomalies in the pacific ocean and beyond associated with that year s exceptionally strong enso preliminary comparison of antarctic sea ice concentration data with european centre for medium range weather forecasts ecmwf operational analyses fields suggests that the unusually extensive sea ice in winter 1998 was concomitant with an equatorward shift of the circumpolar westerly surface winds over the southern pacific ocean

reconstruction of submesoscale velocity field from surface drifters abstractthe extensive drifter deployment during the lagrangian submesoscale experiment laser provided observations of the surface velocity field in the northern gulf of mexico with high resolutio

diurnal cycling of submesoscale dynamics lagrangian implications in drifter observations and model simulations of the northern gulf of mexico abstractthe diurnal cycling of submesoscale circulations in vorticity divergence and strain is investigated using drifter data collected as part of the lagrangian submesoscale experiment laser

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

submesoscale impacts on horizontal and vertical transport in the gulf of mexico 1 impacts of submesoscale processes on transport are investigated numerically in an energetic mesoscale flow with an ocean model run at two horizontal resolutions 1 and 5 km the focus is the northwestern gulf of mexico where the loop current eddies are surrounded by smaller vortices by increasing the horizontal resolution the number and strength of submesoscale eddies and vorticity filaments within the mixed layer increase dramatically and with them the vertical velocities inside the coherent eddies and at their peripheries increased vertical velocities for increasing resolution are associated to near inertial motions and they are not limited to the mixed layer but are found at all depths horizontal velocities on the contrary are similar lagrangian isobaric tracers are deployed close to the surface and at 100 m and three dimensional neutrally buoyant particles are released close to the surface at the base of the mixed layer and at 100 m the modeled horizontal dispersion curves for each deployment depth are independent of the kind of particles and of horizontal resolution close to the ocean surface however convergence zones generated by submesoscale ageostrophic motions and resolved at 1 km resolution influence the details of the tracer distributions vertical dispersion increases by several folds for increasing resolution at all depths explored with the largest differences found close to the surface therefore submesoscales processes play a fundamental role in driving vertical transport in eddy dominated flows both within and below the mixed layer for times comparable to the eulerian time scale

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

passive microwave observations of the weddell sea during austral winter and early spring the results of multispectral passive microwave observations 6 7 to 90 ghz are presented from the cruises of the fs polarstern in the weddell sea from july to december 1986 this paper includes primarily the analysis of radiometric observations taken at ice station sites averaged emissivity spectra for first year fy ice were relatively constant throughout the experiment and were not statistically different from fy ice signatures in the arctic detailed ice characterization was carried out at each site to compare the microwave signatures of the ice with the physical properties absorption optical depths of fy ice were found to be sufficiently high that only the structure in the upper portions of the ice contributed significantly to interstation emissivity variations the emissivities at 90 ghz e 90 had the greatest variance both e 90 at vertical polarization and gr sub e 90 18 7 defined as e sub v 90 e sub v 18 7 e sub v 90 e sub v 18 7 depended on the scattering optical depth which is a function of the snow grain diameter and layer thickness the variance showed a latitude dependence and is probably due to an increase in the strength of snow metamorphism nearer the northern edge of the ice pack the contribution of variations of near surface brine volume to the emissivity was not significant over the range of values encountered at the station sites emissivity spectra are presented for a range of thin ice types unsupervised principal component analysis produced three significant eigenvectors and showed a separation among four different surface types open water thin ice fy ice and fy ice with a thick snow cover a comparison with smmr satellite data showed that average ice concentrations derived from the ship s ice watch log were consistent with the satellite concentrations the surface based emissivities for fy ice were also compared with emissivities calculated from scanning multichannel microwave radiometer smmr satellite radiances best agreement was found at 6 7 and 10 ghz while at 18 and 37 ghz smmr emissivities were slightly lower than surface based results for the three lower frequencies agreement was found within a confidence limit of 95 and for 37 ghz within about 90

further evidence of ice thinning in the arctic ocean a sea ice thickness profile obtained in september 1996 from the eurasian basin of the arctic ocean between fram strait and the north pole was compared with a profile obtained in the same region in september october 1976 a decline in mean ice draft of 43 was observed over the 20 year interval in agreement with changes observed in other parts of the arctic ocean by rothrock et al 1999

regional classes of sea ice cover in the east antarctic pack observed from satellite and in situ data during a winter time period abstract ice concentration data alone are often of limited use in many process and modeling studies as different ice regimes of approximately 100 concentration can have significantly different heat flux albedo and other surface properties current ice concentration algorithms perform poorly in regions of predominantly thin or highly fragmented ice which constitute a significant proportion of the pack in east antarctica the impact of the sea ice cover on high latitude air sea interactions and marine ecology depends not only on ice extent and concentration but also on the ice type composition of the pack an unsupervised ice classification scheme using data from four channels of the ssm i is presented and tested as a means of gaining important additional complementary information on surface type class interpretation is by comparison with avhrr ers 1 sar and near coincident digital aerial photography and in situ data the classification does a reasonable job at consistently differentiating the large scale constituent regimes including the outer marginal ice zone the interior pack and a transition zone separating the two given the short period of data analyzed the cluster maps appear to be generally coherent and consistent through time as the pack changes in response to synoptic scale atmospheric forcing although the robustness of the technique needs further testing over longer time periods an observed crossover in the meridional brightness temperature profiles is a dominant and consistent feature which marks the transition from unconsolidated and wet ice in the marginal ice zone to more consolidated ice with a thicker and drier snow cover in the interior pack ambiguities occur at the boundaries of some of these regimes due to sensor resolution limitations and the mixing of different ice types and open water also some ice classes like brash ice cannot be distinguished from forming pancake ice furthermore although the signature of the inner pack is usually distinct from that of the outer pack we observed one extraordinary swell propagation event which led to ice fracturing and surface wetting and significantly altered the surface classification the results of this multiparameter study underline the importance of using multisensor systems synergistically to improve interpretation of passive microwave data and better characterize the complex antarctic pack

ocean processes underlying surface clustering ageostrophic ocean processes such as frontogenesis submesoscale mixed layer instabilities shelf break fronts and topographic interactions on the continental shelf produce surface divergent flows that affect buoyant material over time this study examines the ocean processes leading to clustering i e the increase of material density over time on the ocean surface the time series of divergence along a material trajectory the lagrangian divergence ld is the flow property driving clustering to understand the impacts of various ocean processes on ld numerical ocean model simulations at different resolutions are analyzed although the relevant processes differ patterns in clustering evolution from the deep ocean and the continental shelf bear similarities smaller scale ocean features are associated with stronger surface divergence and the surface material clustering is initially dominated by these features over time the effect of these small scale features becomes bounded as material traverses small scale regions of both positive and negative divergence lower frequency flow phenomena however continue the clustering as a result clustering evolves from initial small scale to larger scale patterns

improved determination of the sea ice edge with ssm i data for small scale analyses a method to derive the sea ice edges from the 37 and 85 ghz channels of the spaceborne special sensor microwave imager ssm i with higher resolution than operational ice concentration analyses is developed a combined ice atmosphere model to evaluate atmospheric influences showed that under clear sky conditions the error of the ice edge position is 3 1 km on average the method performs well up to total liquid water content twc of 125 g m sup 2 and overestimates the ice extent when twc increases up to 250 g m sup 2 the algorithm is suitable to classify open water the interior ice pack and thin ice nilas or low ice concentrations caused by a mixture of open water and pancake ice simulations showed that interpolation and resolution matching techniques may improve the retrieval results with emphasis on interpolation validation of the algorithm with high resolution infrared data shows errors of the ice edge on average less than 5 km comparison with the nasa team ice concentration algorithm in the weddell sea antarctica shows best agreement with the contour line of 33 ice concentration the suitability of the method for mesoscale investigations is demonstrated with a time series of a meander structure in the marginal ice zone miz

antarctic sea ice microwave signatures and their correlation with in situ ice observations the general characteristics and microwave radiative properties of sea ice in the weddell sea region during the onset of spring are studied by using the nimbus 7 scanning multichannel microwave radiometer smmr and other satellite sensors in conjunction with in situ observations from the mikhail somov the position of the ice edge the gradient of ice concentration and the width of the marginal ice zone are inferred from the microwave data and are found to be consistent with ship observations especially at 18 ghz the sensitivities of the various smmr frequencies to surface and other effects are investigated by using multi spectral cluster analysis the results show considerable variability in emissivity especially at 37 ghz likely associated with varying degrees of surface wetness ice concentrations are derived by using two methods one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed by using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations