atmospheric vortex streets on a radarsat sar image we analyze the sea surface imprint of two atmospheric vortex streets avs s observed on a radarsat a canadian earth observation satellite synthetic aperture radar sar image of the aleutian islands in the western gulf of alaska acquired on may 5 1999 the radarsat sar instrument is operated in c band with hh polarization these avs s are interpreted as the atmosphere analog of classic von karman vortex streets the sar image along with radiosonde data and surface weather charts reveal that the avs lengths are 196 km and 111 km for avs 1 and avs 2 respectively there are five and two pairs of vortices within each avs the vortex shedding period is estimated to be between 35 and 48 minutes the vortex shedding started approximately 4 6 and 2 6 hours prior to the sar imaging time for avs 1 and avs 2 respectively there are seven and three pairs of vortices within the respective avs s the vortex tangential velocity is estimated to be between 1 7 and 2 3 m s and the energy dissipated during the vortex lifetime is estimated to be between 24 9 and 23 6 j m

reply to comments by h bjornsson et al on iceland as a heat island 1 bjornsson et al 2005 hereinafter referred to as bjj make two critical points about our paper on iceland douglass et al 2005 the first is that bjj s own analysis of temperature trends in iceland does not support our conclusions that recent temperature increases in iceland are due to variations in thermal heating the second is that one of bjj s maps is not the same as our corresponding map despite having originated in the same data set the authors first point is moot because they only reinforce our actual findings below we briefly discuss but do not immediately resolve the map problem 2 in the paper we note that iceland s considerable geothermal activity suggests a connection to the observed data but after pointing out the quantitative inadequacy of the geothermal hypothesis we state the temperature trends we observe must be due to complex persistent microclimate effects that do not conform to simple forcing theory and which involve quite large positive feedbacks even in our introduction we point out the quantitative results and refer to them as an unresolved puzzle bjj also refer to our observation of the extended nature of the warming trend as a contention that the geothermally enhanced warming extends over an area far larger than iceland emphasis ours this was neither said nor implied in our paper the large extent of the warming trend was presented as observed fact not contention and with no specific claim that the warming was geothermally enhanced the mapping discrepancy may be related to different methods of data conversions from the original gaussian grid to a 2 5 2 5 grid our published map was produced by a bilinear interpolation program gg2ll which is found at the web site containing the ncep data kistler et al 2001 data available at http dss ucar edu datasets ds090 2 data monthly we are looking into the discrepancy further and at this time can remark only that either version of the 2 m map under discussion is generally consistent with both our higher altitude maps and our conclusions 3 we welcome bjj s alternative hypothesis that changes in sea ice cover may have caused the large observed warming trend indeed one of the purposes of our paper was to call attention to this interesting anomaly one hopes that the extensive literature quoted by the authors can produce a quantitative explanation we are not ready to accept the authors hypothesis that the local anomaly is simply part of a global warming trend especially as it applies to the time period we studied as shown by douglass et al s 2005 figures 1a and 1b the anomaly in question is unique to latitudes at and above that of iceland 4 we take this opportunity to remind readers that the observed anomalies are not simply at the surface a finding that tends to be obscured by this discussion was that the 1979 1996 anomaly has an altitude effect whose existence implies a strong long term correlation in warming and cooling processes at different altitudes the sea ice hypothesis may be consistent with this but a quantitative explanation remains to be found

roll convection within an arctic cold air outbreak interpretation of in situ aircraft measurements and spaceborne sar imagery by a three dimensional atmospheric model abstract atmospheric roll convection within an arctic cold air outbreak was observed over the greenland sea during the arktis 1993 experiment on 24 march 1993 by in situ aircraft measurements and synthetic aperture radar sar imagery from the first european remote sensing satellite ers 1 inside a boundary layer heated from below two kinds of rolls were observed one aligned parallel and the other perpendicular to the mean wind direction the wind parallel rolls occupied the entire boundary layer whereas the wind perpendicular rolls were confined to a region around the top of the boundary layer where a strong vertical shear in the downstream wind component was observed a three dimensional numerical model has been applied to simulate the observed convective pattern it is shown that the model does not reproduce the observed pattern when using a height constant geostrophic wind profile however when adjusting the vertical wind profile to the one measured from the aircraft the model reproduces buoya

analysis and modeling of atmospheric gravity waves observed in radarsat sar images four case studies of radarsat synthetic aperture radar sar observations of atmospheric gravity waves are presented to demonstrate sar s capability to measure associated near surface wind field variations a brief review of the main characteristics and scales of atmospheric gravity waves agws first establishes their importance in atmospheric dynamics the shape and scale of the wave patterns observed in successive sar images are compared with those calculated from agw models there is agreement between the small scale wind variations across wave patterns in sar images and the larger scale wind field that plays a role in the generation of the observed waves

encounter of foehn wind with an atmospheric eddy over the black sea as observed by the synthetic aperture radar onboard envisat abstractfoehn wind blowing through the kolkhida kolkheti lowland in the southwestern caucasus western georgia was observed on an envisat synthetic aperture radar sar image as it encountered an atmospheric cyclonic eddy over the black sea on 13 september 2010 this sar image reveals unprecedented finescale features of the near surface wind fields that cannot be resolved by other sensors it shows among others the deflection of the foehn wind by the atmospheric eddy quantitative information on the near surface wind field over the sea is extracted from the sar image

coastal lee waves on ers 1 sar images alternative dark bright patterns on ers 1 synthetic aperture radar sar images of the west side of the taiwan strait taken on december 8 1994 were recognized to be the sea surface signature of a coastal lee wave such waves are called coastal lee waves because they occur along the lee side of the coast the coastal lee waves appeared in the form of a wave packet distributed within an offshore band 20 40 km wide the first packet which occurred in the northern portion of the observed area contained six waves with variable wavelengths defined as the spatial separation between two waves from 1 7 to 2 7 km the second packet in the middle contained 10 waves with a relatively uniform wavelength of 4 2 km the third packet in the southern portion contained 17 waves with an average wavelength of 2 0 km the crest lengths were from 20 to 80 km local meteorologic parameters observed simultaneously at fuzhou china close to the imaged area showed an offshore wind of 1 5 3 5 m s and a land surface air temperature of 19 c which was 4 c lower than the sea surface temperature sst thus the lower atmospheric boundary conditions at imaging time were very favorable both for generating the land breeze circulation and small wind waves on the sea surface which are in the bragg scattering wavelength band of the c band ers 1 sar a physical model of a three layer atmosphere was developed in order to explain how the land breeze circulation can generate the coastal lee waves the results showed that the vertical velocity disturbance caused by the wind convergence at the land breeze frontal zone is of vital importance for the generation of coastal lee waves and the model gave very good estimates of the processes observed the sar imaging mechanisms of the waves were analyzed in detail the differences between coastal lee waves and ocean internal waves which appear as similar alternative dark bright patterns on sar images were also discussed

snow instability patterns at the scale of a small basin spatial and temporal variations are inherent characteristics of the alpine snow cover spatial heterogeneity is supposed to control the avalanche release probability by either hindering extensive crack propagation or facilitating localized failure initiation though a link between spatial snow instability variations and meteorological forcing is anticipated it has not been quantitatively shown yet we recorded snow penetration resistance profiles with the snow micropenetrometer at an alpine field site during five field campaigns in eastern switzerland for each of about 150 vertical profiles sampled per day a failure initiation criterion and the critical crack length were calculated for both criteria we analyzed their spatial structure and predicted snow instability in the basin by external drift kriging the regression models were based on terrain and snow depth data slope aspect was the most prominent driver but significant covariates varied depending on the situation residual autocorrelation ranges were shorter than the ones of the terrain suggesting external influences possibly due to meteorological forcing to explore the causes of the instability patterns we repeated the geostatistical analysis with snow cover model output as covariate data for one case the observed variations of snow instability were related to variations in slab layer properties which were caused by preferential deposition of precipitation and differences in energy input at the snow surface during the formation period of the slab layers our results suggest that 3 d snow cover modeling allows reproducing some of the snow property variations related to snow instability but in future work all relevant micrometeorological spatial interactions should be considered

spatial variability of micropenetration resistance in snow layers on a small slope the mechanisms leading to dry snow slab release are influenced by the three dimensional variability of the snow cover we measured 113 profiles of penetration resistance with a snow micropenetrometer on an alpine snow slope seven distinct layers were visually identified in all snow micropenetrometer profiles the penetration resis tance of adjacent layers did not change abruptly but gradually across layer boundaries that were typically 2 mm thick in two layers penetration resistance varied around 200 over the grid possibly due to wind effects during or after layer deposition penetra tion resistance varied around 25 in five layers statistically significant slope scale linear trends were found for all layers the semivariogram was used to describe the spatial vari ation penetration resistance was autocorrelated but the scale of variation was layer spe cific a buried layer of surface hoar was the most critical weak layer it had little spatial variation the layers in the slab above had higher spatial variation the penetration resist ance of each snow layer had distinct geostatistical properties caused by the depositional processes

snow slope stability a probabilistic approach on determine une marge de securite difference entre la resistance de cisaillement basale et la contrainte statique appliquee pour des pentes neigeuses par un traitement probabiliste les modeles statistiques de vanmarcke sont appliques pour determiner la taille la plus probable du deficit requis pour le declenchement de l avalanche discussion des procedes statistiques pour l estimation des parametres de la marge de securite

star an efficient snow point sampling method the changeable variable and fragile nature of snow creates unique sampling challenges in this paper we present star an efficient field usable method for use in point sampling spatial studies we validate the accuracy of the star method using a comparative monte carlo simulation of 1024 detailed samples of elevation data as spatial snow studies generally attempt to find spatial continuity in layers and other properties we use variogram ranges to compare the ability of four sampling methods to accurately reveal such spatial correlation the three methods compared to star represent gridded gridded random and pure random methods star can be described as a linear random method the simulation shows star s accuracy to be comparable to both gridded and gridded random methods following this comparative process we introduce a new measure of appropriateness for sampling methods the correct convergence on a variogram model which we call correct spatial correlation detection this directly measures how many sampled areas become correctly classified with either spatially correlated or non correlated variance for a given variogram model fit in this measure star performs equivalently to the other methods and in correct convergence it performs as well as pure random sampling

numerical study on signatures of atmospheric convective cells in radar images of the ocean current and wind variations at the ocean surface can give rise to a modulation of the sea surface roughness and thus become visible in radar images the discrimination between radar signatures of oceanic and atmospheric phenomena can be quite difficult since signatures of different origin can have very similar shapes and magnitudes and are often superimposed upon each other in this work we employ a numerical radar imaging model for an investigation of typical properties of radar signatures of atmospheric convective cells and of theoretical differences between such atmospherically induced radar signatures and those of oceanic phenomena we show that main characteristics of observed multifrequency multipolarization radar signatures of atmospheric convective cells over the gulf stream are reproduced quite well by the proposed model this encourages us to vary wind and radar parameters systematically in order to get a general overview of the dependency of atmospherically induced radar signatures on these parameters finally we compare typical characteristics of radar signatures of atmospheric and oceanic phenomena and we present simulated radar images of a scenario of superimposed atmospheric convective cells and oceanic internal waves we show that the proposed model supports the experimental finding that radar signatures of oceanic phenomena are stronger at horizontal hh than at vertical vv polarization while atmospherically induced radar signatures are better visible at vv polarization

recording microscale variations in snowpack layering using near infrared photography deposition of snow from precipitation and wind events creates layering within seasonal snowpacks the thickness and horizontal continuity of layers within seasonal snowpacks can be highly variable due to snow blowing around topography and vegetation and this has important implications for hydrology remote sensing and avalanche forecasting in this paper we present practical field and post processing protocols for recording lateral variations in snow stratigraphy using near infrared nir photography a fuji s9100 digital camera modified to be sensitive to nir wavelengths was mounted on a rail system that allowed for rapid imaging of a 10 m long snow trench excavated on the north side of toolik lake alaska 68 3 n 149 36 w post processing of the images included removal of lens distortion and vignetting a tape measure running along the base of the trench provided known locations control points that permitted scaling and georeferencing snow layer heights estimated from the nir images compared well with manual stratigraphic measurements made at 0 2 m intervals along the trench n 357 r2 0 97 considerably greater stratigraphic detail was captured by the nir images than in the manually recorded profiles nir imaging of snow trenches using the described protocols is an efficient tool for quantifying continuous microscale variations in snow layers and associated properties

synthetic aperture radar observation of the sea surface imprints of upstream atmospheric solitons generated by flow impeded by an island 1 two cases of upstream propagation of atmospheric solitons generated by atmospheric flow over topography were identified on two radarsat 1 synthetic aperture radar sar images acquired near st lawrence island in the bering sea on 7 september 1997 and 6 june 2001 respectively in both cases a group of solitons was shown as three dark bright linear features on the sar images the soliton width and peak to peak distance measured from the two sar images are about 3 km and 4 5 km respectively simultaneous radiosonde measurements a surface weather map and operational weather model results confirm that these waves did not propagate on the lee side of the island as is commonly observed with island lee waves but indeed propagated against the flow in the upstream direction in the second case the same group of solitons was also identified as a wave like cloud pattern on a modis image taken about 4 5 hours later in this modis image the soliton train propagated further upstream with the leading crest reaching about 30 km north of the island and the number of crest trough features increased from three to seven in this study we describe the generation and evolution of upstream atmospheric solitons using the force kdv fkdv model with radiosonde and island topography data the numerical solution of the fkdv exhibits a sequence of solitons propagating upstream of the island both temporal and spatial scales of the solitons are in good agreement with that estimated from the successive sar and modis satellite images

characteristics of ocean surface winds in the lee of an isolated island observed by synthetic aperture radar abstractcharacteristics of ocean surface winds around an isolated island are examined in relation to atmospheric stability using a synthetic aperture radar sar and rawinsonde sounding observations the sar derived winds on 22 may 2009 indicate a low level jet extending over 30 km behind the island around the time of sar acquisition winds intensified on the leeward side in association with the stabilization of stratified flows which suggests the connection of the sar derived jet with downslope winds a number of sar derived winds elucidate typical wind patterns and their transitions depending on the nondimensional mountain height for cases of large 2 a wake is formed in the lee of the island and low level jets produce strong wind shear on both sides of the wake for cases of relatively small 1 75 although a weak wind region is formed behind the mountain no wind jets develop as a transition of the above two cases a low level jet develops in the lee of the island as in the case on 22 may

sub mesoscale ocean vortex trains in the luzon strait 1 this study uses the argos satellite tracked surface drifter trajectory data and envisat european satellite asar advanced synthetic aperture radar images to illustrate the ocean vortex trains ovt in the luzon strait two cases that occurred in the northwest of babuyan island are observed the first train of three cyclonic vortices showed up on drifter trajectories from 20 to 20 5 n and from 120 to 121 e and the second consisting of five pairs of cyclonic anticyclonic vortices occurred on the upstream side of the first one from 19 5 to 20 0 n and from 121 0 to 122 0 e and showed up on the asar images acquired on 19 november 2006 the total length of the vortex train axis reaches about 250 km all vortices propagate northwestward 315 tn the mean angular velocity is 2 07 0 18 10 5 s 1 theoretical models of ocean vortex radar image derived from radar imaging theories are used to extract dynamical parameters from asar imagery signatures which include the distance between two consecutive vortices and that between two rows of vortices of 22 6 1 9 km and 8 2 1 2 km respectively the maximum rotational velocity radius as 4 70 km and the vortex rotational angular velocity 3 10 5s 1 dynamical analyses give the mean velocity of the current of 0 65 ms 1 and the propagation velocity of the vortex 0 58 ms 1 the vortex shedding rate is estimated as 2 57 10 5 s 1 the reynolds number is estimated as 50 to 500 for the individual vortex and the vortex train the rossby numbers are o 0 4 and o 0 5 respectively implying that both vortex and vortex train observed in the luzon strait have a sub mesoscale nature this study also reveals a strong current with an average surface current velocity of around 0 7 ms 1 and the direction of around 315 tn flowing directly from the pacific to scs passing through the southern luzon strait the mean flow velocity can be calculated using methods developed in this study and ovt dynamical models this information may provide more insight to the circulation systems in the area including the origin of kuroshio

integrating spatial patterns into a snow avalanche cellular automata model 1 snow avalanches are a major mountain hazard that kills hundreds of people and causes millions of dollars in damage worldwide annually yet the relationship between the well documented spatial variability of the snowpack and the avalanche release process is not well understood we utilize a cellular automata model to show that the spatial structure of shear strength may be critically important for avalanche fracture propagation fractures through weak layers with large scale spatial structure are much more likely to propagate over large areas than fractures through weak layers with smaller scale spatial structure our technique of integrating spatial structure into the model can improve many cellular automata models that aim to explain and predict other natural hazards such as forest fires landslides and earthquakes

sar observation and numerical modeling of tidal current wakes at the east china sea offshore wind farm a terrasar x ts x synthetic aperture radar sar image acquired at the east china sea offshore wind farm presents distinct wakes at a kilometer scale on the lee of the wind turbines the presumption was that these wakes were caused by wind movement around turbine blades however wind analysis using spaceborne radiometer data numerical weather prediction and in situ measurements suggest that the prevailing wind direction did not align with the wakes by analyzing measurement at the tidal gauge station and modeling of the tidal current field these trailing wakes are interpreted to have formed when a strong tidal current impinged on the cylindrical monopiles of the wind turbines a numerical simulation was further conducted to reproduce the tidal current wake under such conditions comparison of the simulated surface velocity in the wake region with the ts x sea surface backscatter intensity shows a similar trend consequently turbulence intensity t i of the tidal current wakes over multiple piles is studied using the ts x observation it is found that the t i has a logarithmic relation with distance furthermore another case study showing wakes due to wind movement around turbine blades is presented to discuss the differences in the tidal current wakes and wind turbine wakes the conclusion is drawn that small scale wakes formed by interaction of the tidal current and the turbine piles could be also imaged by sar when certain conditions are satisfied the study is anticipated to draw more attentions to the impacts of offshore wind foundations on local hydrodynamic field

stability algorithm for snow micro penetrometer measurements information on snow cover stability is important for predicting avalanche danger traditionally stability evaluation is based on manual observations of snow stratigraphy and stability tests which are time consuming the snowmicropen smp is a high resolution constant speed penetrometer to measure penetration resistance we have analysed the resistance signal to derive snow stability the proposed stability algorithm was developed by comparing 68 smp force distance profiles with the corresponding manual profiles including stability tests the algorithm identifies a set of four potentially weak layers by taking into account changes in structure and rupture strength of microstructural elements that make up snow layers as derived from the smp signal in 90 of the cases one of the four potentially weak layers proposed by the algorithm coincided with the failure layer observed in the stability test to select the critical layer from the four potential weaknesses was more difficult with fully automatic picking of the critical layer agreement with the failure layer observed in the stability test was reached in 60 of the cases to derive a stability classification we analysed weak layer as well as slab properties these predictor variables allow the smp signal to be classified into two stability classes poor and fair to good with an accuracy of 75 when compared with observed stability the smp in combination with the proposed algorithm shows high potential for providing snow cover stability information at high resolution in time and space

atmospheric front over the east china sea studied by multisensor satellite and in situ data 1 a frontal feature visible on a synthetic aperture radar sar image acquired by the radarsat satellite over the east china sea on 19 november 2000 is analyzed in conjunction with data acquired by quikscat topex poseidon tropical rain measurement mission trmm defense meteorological satellite program dmsp and national oceanic and atmospheric administration noaa satellites and with data obtained from ship measurements although this frontal feature is located close to the kuroshio front it is demonstrated that it is not a sea surface manifestation of an oceanic front but rather of an atmospheric front extending over 800 km from an area of the pacific ocean northeast of taiwan to the southern coast of korea it is a cold front moving in the southeast direction with a speed of approximately 45 50 km hour and associated with a 40 km wide rainband trailing the front the radarsat image which has a resolution of 50 m reveals fine scale structures of the atmospheric front in particular small scale convective rain cells embedded in the front conclusion is drawn that accurate interpretation of frontal features in sar images requires use of additional meteorological and remote sensing data and information

evolution of an atmospheric karman vortex street from high resolution satellite winds guadalupe island case study vortex streets formed in the stratocumulus capped wake of mountainous islands are the atmospheric analogues of the classic karman vortex street observed in laboratory flows past bluff bodies the q

a model of variations in the north atlantic oscillation 1 the major source of interannual variability in the atmospheric circulation over the north atlantic ocean is the north atlantic oscillation nao which is associated with the strength of the winter surface westerly winds over the ocean during the last century the nao has shown pronounced multi annual and multi decadal variations fluctuations that have been accompanied by changes in the marine and terrestrial ecosystems of the north atlantic region this paper presents a simple model which reproduces the major trends in the nao index from 1866 to 2004 the model is based on climatic resonators that are forced by the global mean temperature and the southern oscillation of the pacific ocean so the ocean component of the model shows similar variations to time series from the north atlantic

coexistence of atmospheric gravity waves and boundary layer rolls observed by sar abstractboth atmospheric gravity waves agw and marine atmospheric boundary layer mabl rolls are simultaneously observed on an environmental satellite envisat advanced synthetic aperture radar asar image acquired along the china coast on 22 may 2005 the synthetic aperture radar sar image covers about 400 km 400 km of a coastal area of the yellow sea the sea surface imprints of agw show the patterns of both a transverse wave along the coastal plain and a diverging wave in the lee of mount laoshan 1133 m peak which indicate that terrain forcing affects the formation of agw the agw have a wavelength of 8 10 km and extend about 100 km offshore model simulation shows that these waves have an amplitude over 3 km finer scale 2 km brushlike roughness features perpendicular to the coast are also observed and they are interpreted as mabl rolls the fft analysis shows that the roll wavelengths vary spatially the two way interactive triply nested grid 9 3 1 km weather research and forecasti

on the remote sensing of oceanic and atmospheric convection in the greenland sea by synthetic aperture radar 1 in this paper we discuss characteristic properties of radar signatures of oceanic and atmospheric convection features in the greenland sea if the water surface is clean no surface films or ice coverage oceanic and atmospheric features can become visible in radar images via a modulation of the surface roughness and their radar signatures can be very similar for an unambiguous interpretation and for the retrieval of quantitative information on current and wind variations from radar imagery with such signatures theoretical models of current and wind phenomena and their radar imaging mechanisms must be utilized we demonstrate this approach with the analysis of some synthetic aperture radar sar images acquired by the satellites ers 2 and radarsat 1 in one case an ers 2 sar image and a radarsat 1 scansar image exhibit pronounced cell like signatures with length scales on the order of 10 20 km and modulation depths of about 5 6 db and 9 10 db respectively simulations with a numerical sar imaging model and various input current and wind fields reveal that the signatures in both images can be explained consistently by wind variations on the order of 2 5 m s but not by surface current variations on realistic orders of magnitude accordingly the observed features must be atmospheric convection cells this is confirmed by visible typical cloud patterns in a noaa avhrr image of the test scenario in another case the presence of an oceanic convective chimney is obvious from in situ data but no signatures of it are visible in an ers 2 sar image we show by numerical simulations with an oceanic convection model and our sar imaging model that this is consistent with theoretical predictions since the current gradients associated with the observed chimney are not sufficiently strong to give rise to significant signatures in an ers 2 sar image under the given conditions further model results indicate that it should be generally difficult to observe oceanic convection features in the greenland sea with ers 2 or radarsat 1 sar since their signatures resulting from pure wave current interaction will be too weak to become visible in the noisy sar images in most cases this situation will improve with the availability of future high resolution sars such as radarsat 2 sar in fine resolution mode 2004 and terrasar x 2005 which will offer significantly reduced speckle noise fluctuations at comparable spatial resolutions and thus a much better visibility of small image intensity variations on spatial scales on the order of a few hundred meters index terms 3314 meteorology and atmospheric dynamics convective processes 4275 oceanography general remote sensing and electromagnetic processes 0689 4279 oceanography general upwelling and convergences 4255 oceanography general numerical modeling

wind jets and wind waves off the pacific coast of northern japan under winter monsoon captured by combined use of scatterometer synthetic aperture radar and altimeter 1 wind jets and wind waves off the pacific coast of northern japan under the east asian winter monsoon are investigated using scatterometer synthetic aperture radar sar and altimeters first we depict two prevailing wind flow patterns associated with the northwesterly winter monsoon they are derived by averaging quikscat wind vectors when the 850 hpa pressure level wind directions are within 260 290 and 290 330 respectively wind jets and wakes are formed in different regions depending on the approach angle of wind to the topographic features second using high resolution satellite observations of quikscat and ers 2 sar for wind and topex poseidon and ers 2 radar altimeter for significant wave height we present two case studies corresponding to the two prevailing wind flow patterns in order to investigate wind wave development under orographically modified winds combined use of quikscat and sar allows us to capture the surface wind transition from the shore to the offshore they verify that the wind jets and wakes are extensions of terrestrial gaps and blockages variations of significant wave height observed by the altimeters are compared with those of surface wind derived from quikscat and sar along the altimeter ground tracks the positions of local maxima and minima of significant wave height and squares of wind speeds coincide with each other this demonstrates an important role of coastal topography in wind modification and the resulting offshore wind wave development

spatial scales of snow texture as indicator for snow class a method for automated and fast classification of snow texture would be useful for applications where snow structure must be quantified large numbers of field measurements were carried out on natural snow in order to investigate small scale variations of the micro penetration force snow characterization was done for snow from the himalaya and the alps using a high resolution snow penetrometer snowmicropen measurements of snow resistance at equal intervals of 4 mm were geostatistically evaluated the range parameter correlation length or cl of penetration force was estimated for all major snow classes from the sample semivariogram average cl was lowest for new snow and highest for melt freeze snow for major snow classes cl was found to increase with snow density ground perpendicular and ground parallel snow profiles were also obtained for homogeneous snow and cl was estimated along these directions new snow showed larger cl in the ground parallel direction and depth hoar snow showed larger cl in the ground perpendicular direction based on cl the directional anisotropy was calculated an attempt was also made to show the relationship between cl and texture index the semivariogram was used to estimate the fractal dimension both cl and fractal dimension were found to be potential parameters to describe snow

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

convergence fronts in tidally forced rotating estuaries in situ observation and remote sensing imagery reveal the presence of longitudinal velocity convergences over bathymetric channels in tidal estuaries we present the results of numerical experiments designed to investigate the cause of these convergences for channels possessing shallow shoal regions and a deeper central region the equations of motion for a homogeneous fluid on a rotating earth are solved using a fully spectral code in the across estuary i e the vertical or x z plane while no along estuary flow variations in the y direction are permitted a gaussian shaped bottom bathymetry is chosen in the along channel y direction we impose a pressure gradient which is the sum of constant and fluctuating parts to simulate the steady and tidally oscillating parts of the estuarine flow the details of the transient response can be complicated but we observe that for most 80 of the tidal cycle there exists a cross estuary recirculation cell colocated with a localized along channel jet both of these are situated over the bottom bathymetric groove the circulation is always clockwise when facing down current this feature results from the generation of stream wise vorticity through the tilting of planetary vorticity by the vertical shear of the along estuary flow a surface convergence divergence pair is associated with the flow the maximum value of each is seen to occur on the edge of the bathymetric feature but may migrate toward or away from the center as long as the current continues in the same direction when the tide reverses the feature reappears on the opposite shoal and the migration of the convergence and divergence extrema begins again we also find that the responses are qualitatively similar for all bathymetric grooves even asymmetrically situated ones provided that the estuary width to depth ratio is of order 100 or larger the rossby numbers are of order unity and the ekman layer thickness to channel depth ratio is greater than 0 65

role of the supraglacial snowpack in mediating meltwater delivery to the glacier system as inferred from dye tracer investigations the supraglacial snowpack plays an important role in mediating the delivery of meltwater produced at the snowpack surface to the rest of the glacier system with potential implications for both proglacial hydrograph form and the timing and magnitude of glacier movement induced by changes in subglacial water pressure however there remain few field observations of the hydrological behaviour of supraglacial snowpacks and its seasonal evolution during the melt season data collected during the 2004 melt season at haut glacier d arolla valais switzerland uses both qualitative and quantitative dye tracing techniques to enhance our understanding of supraglacial snowpack hydrology observations of the movement of dye stained water show the complexity of flow patterns and the influence of ice layers and preferential flow zones in controlling percolation through the snowpack and fluorometric techniques yield average flow rates for percolation through the snowpack of between 0 13 and 0 49 m h the changing form of dye return curves and increasing percolation rates reflect an increase over the course of the melt season in the efficiency with whichthesnowpacktransmitsmeltwater snowpackpermeabilitywasfoundtobesignificantlylower 1 67x10 m on average than that assumed in previous modelling studies of glacial hydrology showing the need for improved information about snowpack hydrology if its importance in controlling runoff is to be fully appreciated

gap winds and wakes sar observations and numerical simulations the nature of terrain induced gap winds and wakes in the atmosphere is examined using surface wind data from synthetic aperture radar sar and the shallow water equations the shallow water model is used to predict the types of wake jet wind patterns that might occur behind an idealized pair of bell shaped hills with a gap between them a regime diagram is constructed based on the width of the gap and the upstream froude number specific predictions of the model are found to compare moderately well with sar data from four examples of airflow near unimak island in the aleutian chain the model predicts the observed wakes and jets including jets that exceed the upstream speed theoretical analysis considers the relative importance of rising terrain and narrowing valley walls in the acceleration of gap winds wind speeds in the wake region are controlled by the bernoulli function and regional pressure gap winds therefore are streams of air that have avoided bernoulli loss over the terrain by passing through gaps the speed of gap winds can exceed the upstream speed only in ridgelike situations when the regional leeside pressure is lower than the upstream pressure

an ers 1 synthetic aperture radar image of atmospheric lee waves an ers 1 synthetic aperture radar sar image of the island hopen shows a distinct 7 6 km wavelength wave phenomenon near the island this wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves the pattern is visible in the sar image since the lee waves modulate the horizontal wind speed near the ocean surface which in turn modulates the surface roughness and the radar cross section the physical setting for the observation is presented and discussed the lower bound on horizontal wind speed modulation is estimated to range from 3 2 ms 1 for the wind speed minima to 12 2 ms 1 for the wind speed maxima based upon the observed radar cross section modulation and the ers 1 scatterometer wind retrieval model cmod4 the wavelength and wind speed modulation are consistent with linear lee wave model predications the model uses an atmosphere with an exponential profile of the scorer parameter ratio of buoyancy frequency to wind speed to represent a shallow ground based inversion layer observed at bear island and a bell shaped barrier to represent the forcing effects of hopen

three dimensional microstructure and numerical calculation of elastic properties of alpine snow with a focus on weak layers abstract the microstructure and stratigraphy of a snowpack determine its physical behaviour weaklayers or weak interfaces buried under a slab are prerequisites for the formation of dry snow slabavalanches and a precise characterization of weak layers or interfaces is essential to assess stability yettheir exact geometry and micromechanical properties are poorly known we cast weak layers and theiradjacent layers in the field during two winters and reconstructed their three dimensional microstructureusing x ray microcomputer tomography the high resolution of 10 20 m m allowed us to study snowstratigraphy at the microstructural scale we quantified the microstructural variability for 32centimetre sized layered samples and we calculated young s modulus and poisson s ratio bytomography based finite element simulations layers in a sample could therefore be differentiatednot only by a change in morphology or microstructure but also by a change in mechanical properties we found a logarithmic correlation of young s modulus with density for two different density ranges consistent with previous studies by calculating the relative microstructural changes within our samples we showed that a large change could indicate a potential weak layer but only when the weak layer andboth adjacent layers i e the sandwich were considered keywords

direct influence of gravity waves on surface layer stress during a cold air outbreak as shown by synthetic aperture radar abstract synthetic aperture radar sar images of oceans and the great lakes have provided a highly detailed means of observing atmospheric boundary layer phenomena such as convection land breezes and internal gravity waves this is possible because the backscattered radiation detected by sar can be dominated by scattering from wind driven capillary waves whose spatial variation is visible as patterns in the sar images in this paper we present two case studies in which sar images taken over lake superior demonstrate spatial variability in the surface wind stress created over the lake by coincident gravity waves and boundary layer convection during cold air outbreaks of particular interest is the direct influence of the gravity waves on the lake surface stress despite the intervening highly convective atmosphere as well as the detailed view of the fetch dependence of that stress

investigation of the island induced ocean vortex train of the kuroshio current using satellite imagery abstract in this study we used satellite imagery to conduct a statistical study of the ocean vortex train induced by the kuroshio current on the leeward side of green island taiwan the spatial scale and characteristics of the ocean vortex train were analyzed using image datasets from five different high resolution satellites including optical imagery from the satellite pour l observation de la terre and the formosat 2 satellites and synthetic aperture radar imagery from the european remote sensing satellite advanced land observing satellite and sentinel 1 satellite altimetry data and a moored acoustic doppler current profiler adcp were used to calculate the velocity of the kuroshio current the adcp data suggest that the velocity increases on the western side of the vortex train when it is formed on the leeward side of green island data from the moderate resolution imaging spectroradiometer modis showed that the sea surface temperature of the recirculation water was over 2 c colder and the chlorophyll a concentration was two times higher than that of the surrounding waters these phenomena suggested upwelling mixing processes and an island mass effect wind forcing had a pronounced effect on the characteristics of the vortex train high resolution satellite images indicate that the averaged aspect ratio of the vortex train is 2 09 and the dimensionless width is 2 02 under southerly winds compared to 1 91 and 2 76 respectively under northerly winds

coastal katabatic winds imaged by sar 1 sea surface imprints of coastal katabatic winds are observed on a radarsat 1 synthetic aperture radar sar standard mode image off the u s west coast taken on january 21 2003 the katabatic wind pattern is shown in the sar image as a striking finger like bright dark region that mirrors the coastal mountain topography we simulate the low level atmospheric circulation using the numerical weather model mm5 with a triply nested grid technique the model simulation reproduces the finger like katabatic wind pattern at the sar imaging time katabatic wind is strongest in the morning when the surface temperature gradient between ocean and land reaches a maximum the sea surface wind simulated by the mm5 model and that derived from the calibrated sar normalized radar cross section are in good agreement the katabatic wind variation along the coastline is between 5 8 ms 1 and the longest wind finger stretches over 20 km offshore

on optimal stability test spacing for assessing snow avalanche conditions assessing snow stability requires a holistic approach relying on avalanche snowpack and weather observations part of this assessment utilizes stability tests but these tests can be unreliable due in part to the spatial variability of test results conducting more than one test can help to mitigate this uncertainty though it is unclear how far apart to space tests to optimize our assessments to address this issue we analyze the probability of sampling two relatively strong test results over 25 spatial datasets collected using a variety of stability tests our results show that the optimal distance for spacing stability tests varies by dataset even when taking the sampling scheme and stability test type into account this suggests that no clear rule currently exists for spacing stability tests our work further emphasizes the spatial complexity of snow stability measurements and the need for holistic stability assessments where stability tests are only one part of a multifaceted puzzle

footprints of storms on the sea a view from spaceborne synthetic aperture radar synthetic aperture radar sar on board seasat observed images of stormlike echoes on the sea in 1978 the core of these images is usually an echo free hole which is attributed to the damping of the short 30 cm radar detectable gravity waves by the intense rain in the storm core although the beating down of waves by rain is consistent with observations by seafarers and with the first scientific explanation of the phenomenon by reynolds 1875 neither theory nor experiment has provided definitive support one experiment appears to provide the key it shows that the kinetic energy of the rain produces sufficient turbulence in a thin fresh water layer to damp 30 cm waves in 10 20 s thus producing the echo free hole a sequence of positive feedbacks then serves to damp the longer waves the angular dependence of the sea surface echo cross sections seen by seasat sar outside the echo free hole indicates winds diverging from the downdraft induced by the intense rain core the wind generated waves and associated echoes extend out to a sharply defined gust front the sea surface footprint thus mimics the features of a storm microburst the variations in surface radar cross section due to a combination of rain and wind effects impacts spaceborne measurements of surface winds by scatterometry and rainfall measurements by radar portions of this synthesis remain speculative but serve as hypotheses for further research

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

iceland as a heat island 1 iceland is a strong localized source of non eruptive volcanic warming and cooling temperature trend maps show that this phenomenon is localized to an area of about twice that of iceland with altitude the area remains constant but the phenomenon weakens and changes sign upon passing through the tropopause the effect s magnitude implies a large positive feedback according to a conventional climate forcing estimate this phenomenon is unique in that it is not observed for the other major volcanic islands

instruments and methods recording microscale variations in snowpack layering using near infrared photography deposition of snow from precipitation and wind events creates layering within seasonal snowpacks the thickness and horizontal continuity of layers within seasonal snowpacks can be highly variable due to snow blowing around topography and vegetation and this has important implications for hydrology remote sensing and avalanche forecasting in this paper we present practical field and post processing protocols for recording lateral variations in snow stratigraphy using near infrared nir photography a fuji s9100 digital camera modified to be sensitive to nir wavelengths was mounted on a rail system that allowed for rapid imaging of a 10 m long snow trench excavated on the north side of toolik lake alaska 68838 0 n 149836 0 w post processing of the images included removal of lens distortion and vignetting a tape measure running along the base of the trench provided known locations control points that permitted scaling and georeferencing snow layer heights estimated from the nir images compared well with manual stratigraphic measurements made at 0 2 m intervals along the trench n 357 r 2 0 97 considerably greater stratigraphic detail was captured by the nir images than in the manually recorded profiles nir imaging of snow trenches using the described protocols is an efficient tool for quantifying continuous microscale variations in snow layers and associated properties

on polarimetric characteristics in sar images of mesoscale cellular convection in the marine atmospheric boundary layer 1 convection is an important phenomenon in the marine atmospheric boundary layer mabl previous spaceborne radar studies of such have been limited to single polarization data and therefore their focus was on the variation in intensity of the radar return which was constrained by the existence of a single polarization image pattern representing different atmospheric and oceanic phenomena in this paper we study the polarimetric characteristics of mesoscale cellular convection mcc in the mabl using high resolution data from fully polarimetric hh vv hv and vh radarsat 2 rs 2 synthetic aperture radar sar images in conjunction with closely collocated mesoscale atmospheric model simulations to identify the mcc signatures to compare the polarimetric characteristics of mcc with those of the ocean surface our analysis also includes 641 open ocean surface quad polarization rs 2 sar images collocated with 52 national data buoy center buoys the open ocean surface sar images exhibit different polarimetric characteristics from those of mcc thus we differentiate mcc from other open ocean phenomena based on identifiable polarimetric sar characteristics

katabatic wind fields in coastal areas studied by ers 1 synthetic aperture radar imagery and numerical modeling synthetic aperture radar sar images acquired over mediterranean coastal waters from the first european remote sensing satellite ers 1 showing sea surface manifestations of katabatic wind fields are presented in particular sea surface roughness patterns generated by katabatic winds blowing from 1800 in high mountains through a broad valley at the western coast of calabria southern italy into the gulf of gioia is investigated the ers 1 sar images show that their areal extent and shape vary strongly depending on the meteorological conditions the roughness pattern sometimes has the form of a mushroom an elongated tongue a broad blob or a narrow truncated band for one event september 8 1992 we have simulated the wind field at the sea surface by using a nonhydrostatic mesoscale atmospheric model and then compared it with the wind field derived from the ers 1 sar image by using the c band wind scatterometer model cmod4 the comparison shows that the atmospheric model reproduces quite well the mushroom like form of the wind field pattern while the wind speed is obtained somewhat lower than the one inferred from the sar image this study demonstrates that sar images acquired over coastal waters are well suited to study local wind fields in coastal areas and to test numerical models that describe local wind fields which extend from the coast onto the sea

an observational study of vortex spacing in island wake vortex streets abstract vortex streets are a frequent occurrence in stratocumulus topped flow downwind of mountainous islands theoretical studies dating back to von karman supported by laboratory and numerical studies have yielded similarity theories for the size and spacing of these vortices behind bluff bodies despite dynamical differences between such two dimensional flows and the three dimensional flow past isolated islands satellite case studies suggest these geometric similarities may also hold for the atmospheric case in this study two of the resulting dimensionless ratios are measured using satellite imagery one is the aspect ratio between cross street and along street spacing of the vortices the second is the ratio of the cross street spacing to the crosswind width of the island a 30 image sample from the aqua and terra moderate resolution imaging spectroradiometer satellites is analyzed to obtain these ratios the resulting set of values for the two dimensionless ratios is tested against the values f

boundary layer roll statistics from sar the atmospheric boundary layer abl mean flow frequently consists of an organized secondary circulation in the form of counter rotating rolls embedded in it theory predicts this is the case for a range of thermodynamic conditions although generally associated with the formation of cloud streets numerical and theoretical studies suggest that rolls should be present whenever there is sufficient shear to organize the convection including cloud free conditions through their association with clouds and their modification of the mean low level flow abl rolls alter air sea interaction processes surface energy fluxes and the earth radiational balance despite their potential importance to climate there exist no prior studies that can establish the extent and statistical frequency of roll occurrence synthetic aperture radar sar can detect abl roll signature on the ocean surface a first regional climate scale attempt to construct abl roll frequency statistics from the radarsat sar observations is described

the spatial variability of snow resistance on potential avalanche slopes since snow avalanches are believed to release from zones of localized weakness knowledge of snow strength patterns is important for determining slope stability and for applying effective avalanche control measures in this study the spatial variability of snow resistance an index of snow strength and depth were measured and compared with terrain features on two inclined slopes a refined instrument allowed the strength of an entire snow slab to be characterized in a short time the spatial pattern of trees appeared to affect the pattern of snow depth at one site where a significant linear relationship was found between snow depth and average snow resistance these results suggest that localized snow depth variations may be important in snow strength genesis although a linear relationship existed at that site additional factors may be critically relevant a second site with more complex terrain features and less localized wind drifting did not show a linear relationship between depth and average resistance instead complex patterns of resistance demonstrated that many factors contribute to snow resistance in particular the snow overlying rocks was found to have significantly weaker resistance than that in adjacent areas not over rocks

field observations on spatial variability of surface hoar at the basin scale inclination and wind exposure within an area of about 3 km 2 four automatic weather stations were located within the study area one on level terrain and three across a ridge despite the good instrumentation the correlation between surface hoar growth and calculated sublimation rate was poor distinct spatial patterns of surface hoar growth were found surface hoar crystals were frequently larger at the ridge site than in the surroundings of the automatic weather station on level terrain the variation in surface hoar formation was mainly due to different prevailing wind regimes during the formation periods the surroundings of the automatic weather station on level terrain were under the influence of local katabatic winds that dried up the air so that growth conditions were locally less favorable our observations suggest that predicting surface hoar formation for complex alpine terrain on the basis of data from an automatic weather station the standard procedure in avalanche forecasting seems nearly impossible unless at least the local wind regime is known at high resolution 10 m for both surface hoar formation and surface hoar destruction observations suggest wind conditions to be most crucial for spatial variation

density specific surface area and correlation length of snow measured by high resolution penetrometry precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular the area wide acquisition of structural parameters at high spatial resolution from state of the art methods is however still cumbersome since the time required for a single profile is a serious practical limitation as a remedy we have developed a statistical model to extract three major snow structural parameters density correlation length and specific surface area ssa solely from the snowmicropen smp a high resolution penetrometer which allows a meter profile to be measured with millimeter resolution in less than 1 min the model was calibrated by combining smp data with 3 d microstructural data from microcomputed tomography which was used to reconstruct full depth snow profiles from different snow climates alpine arctic and antarctic density correlation length and ssa were derived from the smp with a mean relative error of 10 6 16 4 and 23 1 respectively for validation we compared the density and ssa derived from the smp to traditional measurements and near infrared profiles we demonstrate the potential of our method by the retrieval of a two dimensional stratigraphy at kohnen station antarctica from a 46 m long smp transect the result clearly reveals past depositional and metamorphic events and our findings show that the smp can be used as an objective high resolution tool to retrieve essential snow structural parameters efficiently in the field

variations in snow surface properties at the snowpack depth the slope and the basin scale variations of snow surface and snowpack properties affect avalanche formation in up to four north facing slopes above the tree line near davos switzerland snow surface properties were characterized penetration resistance was measured with a snow micro penetrometer the sampling scheme was designed to allow a multi scale approach covering the snowpack depth scale 0 5 5 m the slope scale 5 100 m and the basin scale 100 1000 m observations and measurements were compared to the data of a nearby automatic weather station aws the aws data were also used to model snow cover stratigraphy and its evolution with the numerical snow cover model snowpack comparing the four slopes showed that surface properties observed manually were similar among the three slopes that were sheltered and often different from the slope that was wind exposed however the penetration resistance of the surface layer was in most cases significantly different among slopes although most values were 0 1 n indicating very low hardness these seemingly contradictory results follow from the different measurement support of the two methods it is presently unclear which amount of variation at a given scale is relevant for avalanche formation the geostatistical analysis and an analysis aimed at identifying the causes of variability were not conclusive no patterns emerged that would allow conclusions regarding the effect on avalanche formation finding the causes of variability seems to require high resolution terrain and weather models that are presently not readily available

synergistic use of satellite observations and numerical weather model to study atmospheric occluded fronts synthetic aperture radar sar images reveal the surface imprints of atmospheric occluded fronts an occluded front is characterized as a low wind zone located between and within two zones of higher winds blowing in the opposite directions on the left and right sides of the occluded front a group of four sar images reveal that the width of an individual occluded frontal zone and the wind magnitudes outside fronts vary greatly from case to case in this paper we performed a case study to analyze an occluded front observed by an environmental satellite envisat advanced sar and ascat scatterometer along the west coast of canada on november 24 2011 the two way interactive triply nested grid 9 3 1 km weather research and forecasting wrf model was utilized to simulate the evolution of the occluded front the occluded front moved toward the east during a 24 h model simulation and the movement between 18 00 and 21 00 utc matched the occluded front positions derived from the concurrently collected surface weather maps from the national oceanic and atmospheric national weather service archives the wrf simulated low wind zone associated with the occluded front and ocean surface wind speed match well with the sar and scatterometer wind retrievals high wind outside the front zone became weaker during the front evolution whereas the width of the occluded frontal zone was contracted laterally analysis of the wrf model derived potential temperature field suggests that the occlusion process occurred below the 800 mb level the structure of the occluded front studied here not only follows the conventional conceptual model and also supports the findings of a novel wrap up conceptual model for an atmospheric frontal occlusion process

an unusual aerial photograph of an eddy circulation in marine stratocumulus clouds abstractan aerial photograph of a cyclonic von karman like vortex in the marine stratocumulus clouds off the california coast taken by a commercial pilot near grover beach is presented it is believed that this is the first photograph of such an eddy taken from an airplane to appear in publication the eddy occurred with a strong inversion above a shallow marine boundary layer in the lee of high inversion penetrating terrain tower and surface wind measurements plotted on satellite imagery demonstrate that the grover beach eddy was not just a cloud level feature but extended through the marine atmospheric boundary layer mabl to the surface evolution of the flow during the formation of the eddy appears similar to idealized numerical simulations of blocked mabl flow from the literature the tower measurements sampled the northern part of the eddy circulation during its formation just offshore the 2 3 c temperature increases and then decreases during and after the eddy passage may be indicative o

sentinel 1 interferometric sar mapping of precipitable water vapor over a country spanning area this paper presents a methodology to generate maps of atmosphere s precipitable water vapor pwv over large areas with a length of hundreds of kilometers and a width of about 250 km based on the use of interferometric sentinel 1a b c band synthetic aperture radar sar data with a high spatial resolution of 5 times 20 text m 2 and the revisiting time of six days an algorithm to calibrate and merge pwv maps from different swaths of sentinel 1 acquired along the same track using global navigation satellite system gnss measurements is described the proposed methodology is tested on sentinel 1a sar images acquired over the iberian peninsula along both descending and ascending tracks the assessment with an independent set of gnss measurements shows a mean difference of a fraction of millimeter and a dispersion lower than 2 mm both the use of sentinel 1a b sar images and the proposed methodology open new perspectives on the application of sar meteorology for the high resolution mapping of pwv over large region spanning areas and the assimilation of interferometric sar data into numerical weather models

sea surface imprints of coastal mountain lee waves imaged by synthetic aperture radar 1 a group of mountain lee waves is observed on an envisat advanced synthetic aperture radar sar image on the lee side of mountain laoshan 1133 m along the yellow sea coast of china the lee waves are shown as alternating bright and dark patterns on the sar image indicating the ocean surface wind oscillation associated with the atmospheric wavefield the horizontal wind variation between wave crest and trough is from 7 to 17 m s a moderate resolution imaging spectroradiometer image acquired about 8 5 h prior to the sar pass also showed the same group of standing lee waves the cloud pattern matches the high wind pattern in the sar derived wind image the mesoscale weather research and forecasting wrf model is used to simulate the lee wave phenomenon we run the triply nested grid model with the highest horizontal resolution of 1 km the wrf model successfully captures the characteristics of the lee wave the waves are generated by the terrain forcing and the wave induced perturbation propagates very strongly upward to the 500 hpa level the event lasts about 24 h based on the wrf model wind results we run a radar imaging model to simulate the sar observation the normalized radar cross section nrcs variations induced by the lee wave are compared between the radar simulation and the actual sar observation reasonable agreement is reached

spatial patterns of surface hoar properties and incoming radiation on an inclined forest opening avalanche hazard evaluation relies in part on representative snowpack stability obser vations thus understanding the spatial patterns of snowpack instabilities and their environmental determinants is crucial this case study integrates intensive field observations with spatial modeling to identify associations between incoming radiation surface hoar development and its subsequent shear strength across an inclined forest opening we examined a buried surface hoar layer in southwest montana usa over five sampling days collecting 824 snowmicropen resistance profiles and performing 352 shear frame tests spatial models of incoming long and shortwave radiation were generated for the surface hoar formation period using modeled hemispheric sky visibility physically based parameters and the bird clear sky radiation model in a geographic information system before burial the surface hoar persisted despite moderate winds and relatively high air temperatures the buried surface hoar layer thickness varied between 3 and 21 mm within a distance of 30 m modeled incoming radiation explained spatial variations in layer thickness and shear strength in areas exposed to large amounts of radiation the surface hoar layer was strong and thin while areas with limited incoming radiation due to high sky visibility and shading possessed a thicker surface hoar layer that sheared more easily this demonstrates the usefulness of microclimate modeling for slope scale avalanche hazard evaluation we also identify that over the 3 week sample period strengthening occurred without thinning of the surface hoar layer

estimating alpine snowpack properties using fmcw radar large variations in both snow water equivalent swe and snow slope stability are known to exist in the alpine snowpack caused by wind topographic and microclimatic effects this variability makes extrapolation of point measurements of snowpack properties difficult and prone to error but these types of measurements are used to estimate swe and stability across entire mountain ranges radar technology provides a promising alternative to point measurements because large areas can be covered quickly and non intrusively there is great potential for obtaining information on a large spatial scale from airborne applications frequency modulated continuous wave fmcw radar measurements were made from the ground in several different alpine snowpacks along with manual and in situ electrical measurements the surface and ground reflections from the radar data combined with an average density estimate can provide a useful estimate of swe in addition the locations of internal reflections are highly correlated with both visually identified layers and measured changes in in situ dielectric properties

experimental analysis of snow micropenetrometer smp cone penetration in homogeneous snow layers the cone penetration test cpt is widely used to determine in situ soil and snow characteristics and stratigraphy for avalanche forecasting knowledge about snow stratigraphy is of crucial import

case study of a coastal jet at spitsbergen comparison of sar and model estimated wind a combination of in situ ship measurements synthetic aperture radar sar imagery and high resolution numerical modeling was used to investigate a mesoscale coastal jet radiating out from hinlopenstretet norway on 14 august 1996 in the meteorological analysis a light breeze and high static stability were found upstream of svalbard by studying results of numerical simulations in relation to the topography upstream stagnation flow splitting and downstream jets and wakes were identified in the hinlopenstretet area this flow pattern was confirmed by in situ ship measurements and the sar estimated wind through investigations of sensitivity simulations it was found that the low level jet mainly was a result of stratified flow around dynamically steep isolated topography while the channeling effect of hinlopenstretet had a minor influence in the core of the jet the velocity was increased by a factor of about 3 compared to the upstream velocity

viewing a cold air outbreak using satellite based synthetic aperture radar and advanced very high resolution radiometer imagery in this phenomenological study we compare nearly simultaneous visible wavelength advanced very high resolution radiometer avhrr and synthetic aperture radar sar images of a cold air outbreak that occurred off the ice pack in the bering sea the visible image shows the spatial evolution of the cloud structure from the ice edge to several hundred kilometers offshore near the ice edge the clouds form regular linear features known as cloud streets these streets are spaced about 5 km apart 5 times the depth of the boundary layer by 200 km offshore the visible image shows nascent closed cell mesoscale cellular convection mcc with connected disks and smears of white clouds surrounded by arcs and rings of dark cloud free regions the diameters of the disks range between 10 and 15 km the sar image shows the same broadly defined spatial pattern but with a substantial increase in detail uncorrelated with the avhrr image in the area of the cloud streets shown in the avhrr image are two dimensional elongated regions of enhanced radar backscatter called sar streaks with the same cross wind spacing as the cloud streets this suggests the presence of quasi two dimensional roll vortices in the atmospheric boundary layer downstream in the area of proto mcc are broadly spaced expanses of enhanced backscatter that form two dimensional patterns such as connected arcs that have structure and scales similar to the spaces between the clouds the spatial evolution of the streaks and streets broadly conforms to the patterns of downdrafts and updrafts respectively exhibited in modeling studies of cold air outbreaks however the comparison with modeling studies is more successful for the cloud streets than for the sar streaks we suggest that this difference is because the clouds in the avhrr images give a time integrated signal of large scale quasi two dimensional atmospheric turbulence whereas mesoscale radar patterns of surface roughness give a relatively instantaneous view of fundamentally three dimensional structure within the atmospheric boundary layer