wind drag coefficient over first year sea ice in the bering sea profiles of relative wind speed and temperature were collected from four levels over rough sea ice in the marginal ice zone of the bering sea and used to compute surface wind drag coefficients based upon 138 profiles for near constant ice conditions northeast winds of 3 15 m s 1 and near neutral stability the mean near neutral 10 m drag coefficient was 0 00309 0 00049 this is among the largest drag coefficients measured for neutral atmospheric conditions over sea ice sixty five percent of the variance of this estimate is explained by orientation of the ice floe to the wind an additional 5 of the variance is explained by wind speed dependence provided that diabatic atmospheric stability over the bering sea ice pack is well correlated with low wind speed the significant ice advecting wind stress on the ice is determined from the neutral value of the drag coefficient a function of ice roughness length alone the ice forecaster thus may use remote measurements or estimates of wind speed and surface roughness to assess the wind component of ice advection

a dynamical model for wind driven ice motion application to ice drift on the labrador shelf a three dimensional coupled ice ocean model has been developed to study short term ice motion over the eastern canadian continental shelf the model consists of a hibler ice model and a diagnostic ocean model ice is coupled to the ocean through a surface ekman layer the model is implemented for the labrador sea using 6 hourly winds and atmospheric pressures as input forcings the results show that the model is able to produce many desired features of ice motion and ocean currents including wind generated coastal currents an ice velocity field reflecting the influence of permanent and transient currents and an increased sea surface tilt and ice internal stress at the coast the model is used to simulate ice drift trajectories from six ice beacons deployed over the labrador and newfoundland shelves in 1992 in the subtidal frequency range the modeled and observed ice velocities are in excellent agreement model errors measured by the rms separation between the modeled and observed positions increase with time the increase is 10 km d 1 in the first 2 days and slower after 2 days the model results are compared with a model run without ice ocean coupling and a calculation using an empirical relationship and parameters speed ratio and turning angle the errors are 20 no ice ocean coupling and 70 empirical relationship larger than the errors in the coupled model in the first 2 days and much larger after several days

low frequency current regimes over the bering sea shelf abstract using direct current measurements made during the period 1975 81 we describe the general circulation over the southeastern bering sea and differentiate it by regimes related to depth and forcing mechanisms three regimes are present delineated by water depth z the coastal z 50 m the middle shelf 50 z 100 m and the outer shelf z 100 m these are nearly coincident with previously described hydrographic domains statistically significant mean flow 1 to 10 cm s 1 exists over the outer shelf generally directed toward the northwest but with a cross isobath component flow of similar magnitude 1 6 cm s 1 occurs in the coastal regime paralleling the 50 m isobath in a counterclockwise sense around the shelf mean flow in the middle shelf is insignificant kinetic energy at frequencies 0 5 cycle per day cpd is greater over the outer shelf than in the other two regimes suggesting that oceanic forcing is important there but does not affect the remainder of the shelf kinetic

wind driven ice drift in a shallow sea the free drift equations are solved for ice floes in a shallow sea of neutral stratification typical of many high latitude continental shelves solutions for ice drift and current velocity are obtained as a function of wind stress ice thickness and water depth the ocean is modeled by second order closure which allows continuous solutions from 5 m total depth to deep water results are presented with drag coefficients for the air ice ice water and water bottom interfaces specified from recent surveys from the bering sea shelf a region with broad areas of water depths between 20 and 50 m the solution shows little dependence on water depth for depths greater than 30 m this occurs because turbulent mixing is a decreasing function of water depth and offsets other influences of finite depth however for water depths less than 30 m ice velocities can change rapidly with wind speed and water depth and the presence of turbulence from tidal shear is very important for coupling wind driven ice drift to the bottom for the deep water limit the second order closure solution confirms analytic solutions that indicate an increase of 20 in the ratio of ice speed to wind speed as the wind speed increases from 10 to 25 m s

on the bering sea ice edge front an oceanographic field program was carried out along the bering sea ice edge in winter 1982 83 to investigate the temperature salinity front associated with and paralleling the winter ice edge currents were measured using taut wire moorings that were in place over winter and an intensive ctd survey was carried out of the frontal structure in midwinter february march the midwinter front separated cold 0 c more saline 32 5 outer shelf water the front had northwestward baroclinic currents paralleling the front ice edge with near surface speeds of 5 6 cm s and an associated transport of about 0 3 106 m3 s these baroclinic currents were superimposed on a regional barotropic along isobath flow resulting in north westward midwinter upper layer flows with monthly mean speeds exceeding 10 cm s an upper layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge the resulting low salinity meltwater was mixed vertically to maintain the front by wind acting across a highly mobile hydrodynamically rough ice cover subtidal fluctuations were not significantly affected by the front or the ice cover and local winds accounted for less than one quarter of the observed current variability the remainder being probably due to regional variations in the barotropic flow

mesoscopic faults in the bregaglia bergell massif central alps abstract the strike direction of dip and pitch of the striae along mesoscopic faults in the oligocene granodiorite tonalite of val masino val bregaglia bergell are analysed most fault planes are steeply dipping and show strike slip or oblique slip motion dominant strikes are nnw or nne a relative chronology of fault sets is suggested based on the presence of different minerals chlorite and epidote on fault planes the pattern of mesoscopic faults in the val masino val bregaglia massif does not follow the earlier tectonic trends of the pennidic nappe edifice nor even the trend of the nearby section of the insubric line considered at both regional and mesoscopic scales the mesoscopic analysis of the val masino val bregaglia massif thus reveals a fault system largely oblique to the major alpine lineaments the observed fault pattern does not reveal traces of thrusting referable to late alpine orogenic phases and can be related to subsequent deformation dominated by strike slip movements this pattern does not match the traditional schemes of extensional dip slip faulting following orogenesis it records a stage of tectonic evolution which follows nappe emplacement yet it precedes vertical or extensional post orogenic tectonics

processes controlling the advance and retreat of sea ice in the sea of okhotsk using defense meteorological satellite program dmsp special sensor microwave imager ssm i sea ice data and meteorological data we investigate processes controlling the advance and retreat of sea ice in the sea of okhotsk for this investigation we apply a new algorithm to the ssm i data which is capable of calculating ice concentration and distinguishing sea ice types this algorithm is confirmed by comparison with national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery our investigations show that there exists a locality for the areas of new ice formation and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly we also reveal that the speed of ice edge advance fairly coincides with that predicted by 2 of the geostrophic wind furthermore there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin we conclude that the advance of the ice cover in the sea of okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea ice extent can be interpreted by that in wind and air temperature conditions

mesoscale oceanographic features associated with the central bering sea ice edge february march 1981 midwinter 1981 observations from the central bering sea shelf showed a hydrographic structure which was two layered in temperature salinity and density this structure was confined to a 100 km wide band which coincided approximately with the ice edge the colder lower salinity upper layer was continuous in its t s properties with homogeneous water to the north beneath the ice the warmer more saline lower layer was similarly continuous with water to the south near the shelf break a northwestward baroclinic flow of the surface relative to 75 dbar was associated with the layered structure the layered structure and associated flow appear to be regular winter features associated with the ice edge in this region input of low salinity water from melting of ice along the edge is adequate to maintain the layered structure and its associated baroclinic circulation against the effects of tidal and wind mixing the resulting observed oceanographic features were similar to those which have been found in association with midshelf and shelf break fronts in other regions and appear to define a dynamically controlled boundary between the cold low salinity water on the northern shelf and the warmer more saline water near the shelf break

on the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the bering and okhotsk seas monthly and 3 day averaged nimbus 5 electrically scanning microwave radiometer sea ice data have been analyzed to document the fluctuations of the bering sea and sea of okhotsk ice covers for the four winters 1972 1973 through 1975 1976 on the short term seasonal and interannual time scales and to define those periods for which there is an out of phase relationship between the fluctuations of the two sea ice covers the sea ice fluctuations are shown to be related to changes in the position and intensity of quasi stationary high and low pressure systems associated with large scale standing wave patterns in the atmosphere through a comparison of the areal changes in ice cover with changes in the amplitude and phase of zonal harmonics 1 2 and 3 of the sea level pressure field on the seasonal time scale the sea level pressure for december the month of most rapid seasonal sea ice growth for both the bering and okhotsk seas is dominated by harmonic 2 which explains almost 60 of the total sea level pressure variance on average over the four winters the phase of harmonic 2 which is associated with the position of the aleutian low shifts from 156 e in 1972 1973 to 190 e in 1975 1976 thus providing a connection between the increasingly heavy bering sea ice cover over these four winters and the general circulation of the atmosphere on the short term episodes of midwinter bering sea ice retreat are generally preceded by or coincident with the breakdown of harmonic 1 and the intensification of harmonics 2 and 3 these episodes are also related to the coincidence of the phases of harmonics 2 and 3 with a mean position of 165 e this result is in excellent agreement with a study of the north pacific oscillation showing that the two modes of the oscillation are associated with the longitudinal position of the aleutian low it is suggested here that these two modes result from changes in the amplitudes and phases of atmospheric long waves 1 2 and 3 evidence is also presented indicating that the interaction of standing and transient components of wave 1 may play an important role in these fluctuations finally these results establish an observational connection relating climate dynamics to changes in ice covers in seasonal sea ice zones

beaufort chukchi seas summer and fall ice margin data from seasat conditions with similarities to the labrador sea the margin of the sea ice pack of the beaufort and chukchi seas is examined using the microwave data from seasat taken during the summer to early fall july 4 through october 8 1978 and the observations are compared to the analogous observations taken in limex 87 the sensors used are synthetic aperture radar sar the seasat a scatterometer system and the scanning multichannel microwave radiometer

modeling ice dynamics of coastal seas a coupled sea ice barotropic ocean model with a 1 km resolution and a seaward domain of 200 km quantifies three coastal processes coupling of ice motion to wind driven coastal currents ice thickness redistribution under compaction at the coast and formation of coastal shear zones the model consists of an ice momentum balance mass concentration and two parameter ice thickness distribution and equations for horizontal water motion and continuity using vertical structure functions an appropriate constitutive law appears to be a hardening plastic based on qualitative observations from alaskan continental shelves for first year sea ice strength is taken to be proportional to the square of ice thickness a north wind example of 10 m s with the coastline to the west shows the depth dependence of rotational shear in the sea ice ocean boundary layer and sea surface tilt which contributes an alongshore slope current there is slight convergence of sea ice over the shelf a coastal shear zone of 4 km and an alongshore ice speed seaward of the shear zone of 6 of the wind speed caused by the combination of an under ice shear layer and an alongshore slope current for an onshore wind ice is near free drift at 3 of the wind seaward of a ridging front which propagates seaward a square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness consistent with observations the hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast we conclude that 1 ice thickness motion feedback is important on scales less than 10 km 2 the observational base to discriminate between mesoscale constitutive laws is not yet available and 3 the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind

the partition of air ice ocean momentum exchange as a function of ice concentration floe size and draft a coupled sea ice ocean model is used to examine the relative magnitudes of terms in the sea ice momentum equation for ice concentrations less than 100 this numerical model for steady state horizontally homogeneous flow includes two terms that have previously been neglected in such quantitative models these are oceanic form drag and wave radiation pressure both of which are lateral forces that act on the sides of floes the former is generally decelerative while the latter is accelerative the model accepts as input variables average ice draft areal concentration and floe diameter it is found that form drag can be greater than or of the same order as skin friction drag for small thick floes at low concentrations an exception to this rule occurs when the effect of wakes between floes reduces the local form drag the higher net drag that generally exists at low concentrations implies lower ice floe speeds wave radiation pressure is negligible in all cases although this is sensitive to our choice of fetch parameterization ocean drag is often parameterized in numerical models of sea ice as a skin friction term alone with a constant drag coefficient between ice and prescribed geostrophic current velocities results from the present model are plotted in terms of such a drag coefficient which is a function of concentration floe size and draft this could be useful in future work where floe size data become regularly available for instance from radar satellite imagery

dynamical evaluation of the surface circulation using remote sensing of drifting ice floes an analysis of ice drift from consecutive landsat multispectral scanner images of the same area taken at 24 h interval allowed the calculation of the surface circulation using a dynamical approach comparison between calculated and measured values shows that this method leads to a good approximation of the surface circulation in a region where ice floes are free drifting on the other hand the sole use of the floe drift over time to evaluate the currents leads to results that are far from the measured values tests made using various air and ice drag coefficients and wind speeds and directions for different drift distances show that the error associated with these parameters is small although the values obtained using the numerical data involved considerably more effort and expense the results were not significantly better than those found using photographic products a good approximation of the surface circulation can thus be made using a simple digitization of the floe positions on photographic products application of the methodology to a set of four image pairs led to the recognition of two modes of circulation in southeastern hudson bay in spring 1985 this method can thus become a useful tool for rapid evaluations of surface currents in ice covered areas that can hardly be sampled otherwise

ice drift in the weddell sea in 1990 1991 as tracked by a satellite buoy ice drift in the weddell sea has been studied by using a satellite buoy deployed on an ice floe the buoy survived for a 20 month period indicating a drift trajectory of 10 000 km and yielding 13 months of marine meteorological data the drift of the ice floe was studied with respect to the winds measured by the buoy in the central weddell sea the mean drift speed of the ice floe was 0 15 m s which was about 3 of the wind speed more specifically the drift ratio was 3 4 in the marginal ice zone and 2 4 in the inner pack ice field on average the drift was directed 36 left of the wind direction but the turning angle was larger during the austral summer and smaller during the winter on time scales of days the drift was primarily wind dependent except for cases during winter periods of high ice concentration and internal ice resistance for time scales of several months purely wind based simulations of the drift resulted in a discrepancy between the observed and simulated trajectories but the inclusion of a slow 0 02 m s residual current made the simulations significantly better the geostrophic wind based on european centre for medium range weather forecasts pressure analyses was estimated for a 1 month period and the ice floe was found to drift almost parallel to the geostrophic wind with a speed of 2 of the geostrophic wind speed inertial type motion superimposed on the wind induced drift was found to be a characteristic feature in the marginal ice zone during the austral summer but it could not be found from the drift in winter when kinetic energy was transferred to larger scales of motion and dissipated into the ice field

investigation of the dynamic sea ice component of a coupled atmosphere sea ice general circulation model this paper discusses the development of a coupled atmospheric ice model with a comprehensive ice dynamics cavitating fluid rheology and an open water parameterization the results center on the ice thickness and concentration distribution in the arctic basin where the inclusion of ice rheology has maximum impact the influence of the wind stresses calculated by an atmospheric model with stability dependent surface drag coefficients is discussed along with the role of the ocean currents and ocean ice drag coefficient under winter wind stress conditions the model had a tendency to buildup ice on the siberian coast the introduction of a partial slip condition at land ice boundaries in the model designed to prevent this buildup is discussed and the best choice for the amplitude of the slip at the land boundaries in this model is found to be 0 4 the ice model results are compared with the available observational data sets on ice thickness concentration and ice velocity fields to test the validity of the model simulations

satellite passive microwave studies of the sea of okhotsk ice cover and its relation to oceanic processes 1978 1982 this paper describes the use of the nimbus 7 scanning multichannel microwave radiometer smmr satellite data to study the ice cover in the sea of okhotsk during the four winters of 1978 1982 the ice concentration estimates obtained from smmr are used to study two different polynyas one over the kashevarova bank and the other over the northwest continental shelf for the kashevarova polynya this study shows that the polynya which may be related to the upwelling observed in historic summer cruises occurs directly over the bank for the continental shelf which because of strong offshore winds and cold temperatures is a region of high ice production the polynya areas are combined with heat flux estimates from weather station data to yield the production rates of ice salt and dense shelf water as a previous study by kitani 1973 shows the mixing of this dense shelf water with pacific water yields a water mass unique to the okhotsk which is the layer of cold low salinity intermediate water between depths of 150 and 800 m from our calculations we estimate that the dense shelf water is produced at an annual rate of about 0 5 sv and that the intermediate water is produced at a rate of 1 2 sv which yields a renewal time for this layer of 10 40 years

response of sea ice drift to wind forcing on the northeastern newfoundland shelf observations of sea ice drift obtained with satellite tracked ice beacons in march april of 1988 and 1989 have been used to examine the response of sea ice drift to wind forcing over the northern newfoundland continental shelf the short term 5 20 days response of sea ice drift ranges from 2 6 to 5 4 of the local wind over much of the inner continental shelf which is comparable to that in the bering sea and the antarctic but larger than that in arctic sea ice drifts to the right of the local wind at angles ranging from 10 to 63 the response to wind forcing is largest near the ice edge both over the middle portions of the shelf and along the southern margins of the seasonal ice zone and during strong and steady wind of several days duration the large wind driven response of ice drift observed in this study in comparison with the arctic may result from 1 reduced levels of internal ice stress associated with the generally thin ice cover and lower areal concentration of sea ice 2 large atmospheric drag coefficients associated with the small ice floes in areas of comparatively higher ice concentration and 3 smooth ice bottom caused by melting in nearshore areas the ice to wind coupling is reduced owing to larger internal ice stresses experienced locally due to ice pileup

drag measurements for first year sea ice over a shallow sea for a free drift case a method is developed for simultaneously determining air ca and water cw drag coefficients by solving the vertically integrated stress balance equation for sea ice the method allows the algebraic determination of ca and cw from measurements of relative wind and relative current at single reference levels from estimates of the densities of all three fluids and ice thickness and from estimates of the accelerations caused by the nonsurface stress terms derived from position measurements the method treats the ice as a natural drag plate and therefore includes contributions from both skin and form drag one shortcoming of the technique is that if the relative wind and current are colinear then only the ratio of ca and cw can be determined another is that the accelerations caused by other forces need to be independently determined an experiment was conducted on a single floe in the eastern bering sea over the continental shelf during march 1981 the site was about 80 km from the ice edge and was occupied for approximately 3 days following the passage of a storm which had broken the pack into 10 20 m diameter floes both profile and slab inversion estimates of drag were made from the current meter and anemometer measurements at the site ca at 3 m was 4 55 10 3 by the profile method compared to 3 63 4 39 10 3 for slab depending on assumptions cw at 1 1 m by profile was 24 2 10 3 compared to 18 3 22 0 10 3 for slab the two methods gave results which were not statistically separable and which were among the highest drags observed for sea ice the instantaneous stress balance on the floe included contributions from material acceleration coriolis force the two surface stresses and sea surface tilt relative to mean current and tide

loitering of the retreating sea ice edge in the arctic seas each year the arctic sea ice edge retreats from its winter maximum extent through the seasonal ice zone siz to its summer minimum extent on some days this retreat happens at a rapid pace while on other days parts of the pan arctic ice edge hardly move for periods of days up to 1 5 weeks we term this stationary behavior ice edge loitering and identify areas that are more prone to loitering than others generally about 20 25 of the siz area experiences loitering most often only one time at any one location during the retreat season but sometimes two or more times the main mechanism controlling loitering is an interaction between surface winds and warm sea surface temperatures in areas from which the ice has already retreated when retreat happens early enough to allow atmospheric warming of this open water winds that force ice floes into this water cause melting thus while individual ice floes are moving the ice edge as a whole appears to loiter the time scale of loitering is then naturally tied to the synoptic time scale of wind forcing perhaps surprisingly the area of loitering in the arctic seas has not changed over the past 25 years even as the siz area has grown this is because rapid ice retreat happens most commonly late in the summer when atmospheric warming of open water is weak we speculate that loitering may have profound effects on both physical and biological conditions at the ice edge during the retreat season

a mixed layer beneath melting sea ice in the marginal ice zone using a one dimensional turbulent closure model a level 2 second order turbulent closure model is employed to study the surface mixed layer developing between sea ice and a relatively warmer background water in the marginal ice zone the model is driven by a suddenly imposed ice water stress and warming in the water the mixed layer rapidly develops in 1 day and afterwards is gradually eroded at its bottom mainly by an inertial oscillation the ice velocity is larger with the stronger stress but the mixed layer is thicker hence the length scale of ice travel before complete melting is nearly independent of the ice water stress higher temperature of the background water gives more heat to ice but produces a thinner mixed layer the product of the travel distance and the background temperature minus the freezing point is larger for the warmer water heat flux through the ice due to atmospheric forcing is a minor mechanism for melting in the marginal ice zone

northward flow in the bering and chukchi seas the ocean circulation on the bering and chukchi sea shelves is investigated using a barotropic numerical model in the presence of the winter seasonal wind stress from the northeast observed northward transport through bering strait of 0 6 sv for the 8 month winter season 1981 1982 can be driven by a sea level difference of 0 4 m between the pacific and arctic oceans this sea level difference between basins is in agreement with hydrographic estimates in the absence of wind stress a 0 4 m sea level difference drives a northward transport through bering strait of 1 1 sv maximum transport through bering strait is geostrophically limited not frictionally or inertially limited major qualitative circulation features of the region are evident in the simulations westward intensification of the northward transport across the bering sea shelf is confirmed with the major transport occurring in the relatively deep gulf of anadyr in the absence of wind anadyr strait contributes 72 of the northward transport through bering strait with northeasterly winds there is a net clockwise circulation around saint lawrence island within the 20 m isobath norton and kotzebue sounds are little influenced by the general circulation northward transport in the chukchi sea bifurcates in the vicinity of point hope the predominant branch is directed toward the northwest in a broad canyon feature south of herald shoal and the balance becomes the alaskan coastal current between cape lisburne and point barrow

sea ice drift near bering strait during 1982 six argos ice stations were deployed in the northeastern bering sea in january and february 1982 four moved north through bering strait and made between one and five passes through the strait before they sank or were crushed by the ice and two remained in western norton sound and shpanberg strait net winds in the region were directed toward the southwest and were relatively uniform geographically net currents were northward and both mean velocity and mean speed were greater at bering strait than at shpanberg strait norton sound contributed ice northward through bering strait in the mean during winter and spring there was also a net divergence of ice near cap lisburne a theory for open shelf shallow water ice drift is developed that adds terms for bottom drag and stress feedback from the water column a stress analysis for a station that remained in western norton sound and shpanberg strait showed that bottom drag did not contribute significantly but that stress feedback from the accelerated shallow water current can be of the same order as the coriolis force however the analysis contained a residual possibly associated with internal ice stress coastal setup or unknown measurement error which was of roughly the same order as the wind and current stress

atmospheric boundary layer structure and drag coefficients over sea ice this paper estimates the air sea drag coefficient for first year ice from recent aircraft measurements and reconciles the range of observed drag coefficients 103cd 1 2 3 7 referenced to 10 m for all sea ice types based on ice roughness and seasonal meteorology for the purpose of sea ice modeling it is necessary to define an effective drag coefficient which relates regional stress to regional wind because sea ice is heterogeneous on scales less than 20 km regional stress is influenced by the distribution of surface roughness the buoyancy flux from quasi periodic leads and external atmospheric conditions principally the inversion height 103cd is 1 3 1 5 for smooth ice but is much greater for nonflat surfaces for wind speeds greater than 5 m s and air temperatures below freezing the effective 103cd is 2 5 3 0 for nearly continuous pack ice such as first year ice in seasonal ice zones and central arctic basin the range of values of 103cd is 3 0 3 7 for unstable boundary layers typical of off ice winds in the marginal ice zone miz or even greater if the ice has been broken by a recent storm cd values at the lower end of these ranges are associated with low inversion heights these coefficients are confirmed by 103cd of 2 9 2 5 and 3 1 for first year sea ice calculated from gust probe data collected by the noaa p 3 aircraft interior to the inner miz in the bering sea during the marginal ice zone experiment mizex west in february 1983 and 103cd of 2 6 for the arctic calculated from arctic ice dynamics joint experiment aidjex aircraft data for february 1976 the effective drag coefficient with the presence of even a small concentration of sea ice is greater than the oceanic value as shown by a 103cd of 2 2 calculated from noaa p 3 gust probe data over a 40 km track of 0 4 ice concentration in the outer miz of the greenland sea in june 1984 during mizex 84 the relation of surface wind and stress to the geostrophic wind for shallow inversion heights typical of high latitudes is reviewed with a turbulent closure atmospheric boundary layer model the winter arctic is typified by low inversions 100 m low geostrophic drag coefficients and large geostrophic surface wind turning angles with low functional dependence on surface roughness seasonal ice zones are typified by a more modest influence of the inversion on boundary layer characteristics

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e