air sea interactions during an arctic storm 1 the impacts of increased open water in the beaufort sea were investigated for a summer arctic storm in 2008 using a coupled atmosphere ice ocean model the storm originated in northern siberia and slowly moved into the beaufort sea along the ice edge in late july the maximum wind associated with the storm occurred when it was located over the open water near the beaufort sea coast after it had moved over the chukchi and beaufort seas the coupled model system is shown to simulate the storm track intensity maximum wind speed and the ice cover well the model simulations suggest that the lack of ice cover in the beaufort sea during the 2008 storm results in increased local surface wind and surface air temperature compared to enhanced ice cover extents such as occurred in past decades in addition due to this increase of open water the surface latent and sensible heat fluxes into the atmosphere are significantly increased however there were no significant impacts on the storm track the expanded open water and the loss of the sea ice results in increases in the surface air temperature by as much as 8 c although the atmospheric warming mostly occurs in the boundary layer there is increased atmospheric boundary turbulence and downward kinetic energy transport that reach to mid levels of the troposphere and beyond these changes result in enhanced surface winds by as much as 4 m s during the 2008 storm compared to higher ice concentration conditions typical of past decades the dominant sea surface temperature response to the storm occurs over open water storm generated mixing in the upper ocean results in sea surface cooling of up to 2 c along the southern beaufort sea coastal waters the ekman divergence associated with the storm caused a decrease in the fresh water content in the central beaufort sea by about 11 cm

the summer cyclone maximum over the central arctic ocean abstract a fascinating feature of the northern high latitude circulation is a prominent summer maximum in cyclone activity over the arctic ocean centered near the north pole in the long term mean this pattern is associated with the influx of lows generated over the eurasian continent and cyclogenesis over the arctic ocean itself its seasonal onset is linked to the following an eastward shift in the urals trough migration of the 500 hpa vortex core to near the pole and development of a separate region of high latitude baroclinicity the latter two features are consistent with differential atmospheric heating between the arctic ocean and snow free land variability in the strength of the cyclone pattern can be broadly linked to the phase of the summer northern annular mode when the cyclone pattern is well developed the 500 hpa vortex is especially strong and symmetric about the pole with negative sea level pressure slp anomalies over the pole and positive anomalies over middle latitudes net prec

the interaction of katabatic flow and mountain waves part ii case study analysis and conceptual model via numerical analysis of detailed simulations of an early september 1993 case night the authors develop a conceptual model of the interaction of katabatic flow in the nocturnal boundary layer with mountain waves mki a companion paper part i describes the synoptic and mesoscale observations of the case night from the atmospheric studies in complex terrain ascot experiment and idealized numerical simulations that manifest components of the conceptual model of mki presented herein the reader is also referred to part i for detailed scientific background and motivation the interaction of these phenomena is complicated and nonlinear since the amplitude wavelength and vertical structure of the mountain wave system developed by flow over the barrier owes some portion of its morphology to the evolving atmospheric stability in which the drainage flows develop simultaneously katabatic flows are impacted by the topographically induced gravity wave evolution which may include significantly changing wavelength amplitude flow magnitude and wave breaking behavior in addition to effects caused by turbulence including scouring perturbations to the leeside gravity wave structure at altitudes physically distant from the surface based katabatic flow layer can be reflected in the katabatic flow by transmission through the atmospheric column the simulations show that the evolution of atmospheric structure aloft can create local variability in the surface pressure gradient force governing katabatic flow variability is found to occur on two scales on the meso due to evolution of the mountain wave system on the order of one hour and on the microscale due to rapid wave evolution short wavelength and wave breaking induced fluctuations it is proposed that the mki mechanism explains a portion of the variability in observational records of katabatic flow

statistics and dynamics of aircraft encounters of turbulence over greenland abstract historical records of aviation turbulence encounters above greenland are examined for the period from 2000 to 2006 these data identify an important flow regime that contributes to the occurrence of aircraft turbulence encounters associated with the passage of surface cyclones that direct easterly or southeasterly flow over greenland s imposing terrain the result of this incident flow is the generation of mountain waves that may become unstable through interactions with the background directional wind shear it is shown that this regime accounted for approximately 40 of the significant turbulent events identified in the 7 yr database in addition two specific cases from the database are examined in more detail using a high resolution mesoscale model the model simulations highlight the important role of three dimensional gravity wave critical level interactions and demonstrate the utility of high resolution forecasts in the prediction of such events

an ice ocean coupled model an ice model an ocean model and a method of coupling the models are described the ice model is a synthesis with variations and extensions of previous modeling ideas ice thickness concentration velocity and internal energy are prognostic variables the ice thermodynamics are represented by temperatures at the snow surface ice surface the interior and the bottom surface melting and freezing rates are calculated at the ice atmosphere ice ocean and atmosphere ocean interfaces a prescribed portion of summer meltwater can be stored on the surface and refrozen in the fall the ocean model includes a second moment turbulence closure submodel and enables one to solve for oceanic heat flux the interfacial stress and subsurface properties in this paper the model is applied to one dimensional simulations but the equations are cited in a form for implementation by two and three dimensional models in a companion paper kantha and mellor this issue the model is used for two dimensional vertical plane simulations in the bering sea several one dimensional sensitivity studies are performed in the case where the ice model is decoupled from the ocean here the oceanic heat flux and sea surface temperature are prescribed constants the studies reveal the role and sensitivity of surface trapped meltwater ice concentration and ice divergence with the coupled ice ocean model the seasonally varying oceanic heat flux and mixed layer properties are determined by the model some comparisons with observations in the central arctic ocean are possible the role of the molecular sublayer immediately adjacent to the ice is examined frazi ice production is related to the large disparity in the molecular diffusivities for temperature and salinity the mixed layer model contains empirical constants which are known from turbulence data the molecular sublayer parameterization requires one empirical parameter b which is uncertain but from this study is assuredly greater than zero the value implicit in previous models the ice model requires the empirical parameters ci f and ci u to quantitatively account for freezing or melting processes in open leads their values are also uncertain but we present reasoning and sensitivity studies to suggest specific values finally an empirical parameter g is introduced it is the ratio of the value of the ice thickness used to represent average ice volume in the dynamic and thermodynamic equations to the value of the thickness needed in the heat conduction equation estimates of g are made from observed thickness distribution functions sensitivity studies show it to be an important parameter

another look at downslope windstorms part i the development of analogs to supercritical flow in an infinitely deep continuously stratified fluid abstract numerical simulations are conducted to examine the role played by different amplification mechanisms in the development of large amplitude mountain waves it is shown that when the static stability has a two layer structure the nonlinear response can differ significantly from the solution to the equivalent linear problem when the parameter nh u is as small as 0 3 in the cases where the nonlinear waves are much larger than their linear counterparts the highest stability is found in the lower layer and the flow resembles a hydraulic jump simulations of the 11 january 1972 boulder windstorm are presented which suggest that the transition to supercritical flow forced by the presence of a low level inversion plays an essential role in triggering the windstorm the similarities between breaking waves and nonbreaking waves which undergo a transition to supercritical flow are discussed

freshwater content variability in the arctic ocean 1 arctic ocean model simulations have revealed that the arctic ocean has a basin wide oscillation with cyclonic and anticyclonic circulation anomalies arctic ocean oscillation aoo that has a prominent decadal variability proshutinsky and johnson 1997 this study explores how the simulated aoo affects the arctic ocean stratification and its relationship to the sea ice cover variations the simulation uses the princeton ocean model coupled to sea ice hakkinen and mellor 1992 hakkinen 1999 the surface forcing is based on national centers for environmental prediction national center for atmospheric research reanalysis and its climatology of which the latter is used to force the model spin up phase our focus is to investigate the competition between ocean dynamics and ice formation melt on the arctic basin wide freshwater balance we find that changes in the atlantic water inflow can explain almost all of the simulated freshwater anomalies in the main arctic basin the atlantic water inflow anomalies are an essential part of aoo which is the wind driven barotropic response to the arctic oscillation ao the baroclinic response to ao such as ekman pumping in the beaufort gyre and ice melt freeze anomalies in response to ao are less significant considering the whole arctic freshwater balance

storm driven mixing and potential impact on the arctic ocean 1 observations of the ocean atmosphere and ice made by ice ocean environmental buoys indicate that mixing events reaching the depth of the halocline have occurred in various regions in the arctic ocean our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites in this study we analyzed these mixing events in the context of storm developments that occurred in the beaufort sea and in the general area just north of fram strait two areas with quite different hydrographic structures the beaufort sea is strongly influenced by inflow of pacific water through bering strait while the area north of fram strait is directly affected by the inflow of warm and salty north atlantic water our analyses of the basin wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different the buoy observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak this indicates the importance of stratification although the mixing itself was mechanically driven we also analyze the distribution of storms both the long term climatology and the patterns for each year in the past 2 decades the frequency of storms is also shown to be correlated but not strongly to arctic oscillation indices this study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline on the other hand synoptic scale storms can force mixing deep enough to the halocline and thermocline layer despite a very stable stratification associated with the arctic halocline the warm subsurface thermocline water is not always insulated from the mixed layer

origins of aircraft damaging clear air turbulence during the 9 december 1992 colorado downslope windstorm numerical simulations and comparison with observations results from numerical simulations of the colorado front range downslope windstorm of 9 december 1992 are presented although this case was not characterized by severe surface winds the event caused extreme clearair turbulence cat aloft as indicated by the severe structural damage experienced by a dc 8 cargo jet at 9 7 km above mean sea level over the mountains detailed measurements from the national oceanic and atmospheric administration environmental research laboratories environmental technology laboratory doppler lidar and wind profilers operating on that day and from the defense meteorological satellite program satellite allow for a uniquely rich comparison between the simulations and observations four levels of grid refinement were used in the model the outer domain used national centers for environmental prediction data for initial and boundary conditions the finest grid used 200 m in all three dimensions over a 48 km by 48 km section the range of resolution and domain coverage were sufficient to resolve the abundant variety of dynamics associated with a time evolving windstorm forced during a frontal passage this full range of resolution and model complexity was essential in this case many aspects of this windstorm are inherently three dimensional and are not represented in idealized models using either 2d or so called 2d 3d dynamics both the timing and location of wave breaking compared well with observations the model also reproduced cross stream wavelike perturbations in the jet stream that compared well with the orientation and spacing of cloud bands observed by satellite and lidar model results also show that the observed cat derives from interactions between these wavelike jet stream disturbances and mountain forced internal gravity waves due to the nearly east west orientation of the jet stream these two interacting wave modes were orthogonal to each other thermal gradients associated with the intense jet stream undulations generated horizontal vortex tubes hvts aligned with the mean flow these hvts remained aloft while they propagated downstream at about the elevation of the aircraft incident and evidence for such a vortex was seen by the lidar the model and observations suggest that one of these intense vortices may have caused the aircraft incident reports of strong surface gusts were intermittent along the front range during the period of this study the model showed that interactions between the gravity waves and flow aligned jet stream undulations result in isolated occurrences of strong surface gusts in line with observations the simulations show that strong shears on the upper and bottom surfaces of the jet stream combine to provide an episodic downburst of turbulence in the present case the perturbations of the jet stream provide a funnel shaped shear zone aligned with the mean flow that acts as a guide for the downward transport of turbulence resulting from breaking gravity waves the physical picture for the upper levels is similar to the surface gusts described by clark and farley resulting from vortex tilting the cat feeding into this funnel came from all surfaces of the jet stream with more than half originating from the vertically inclined shear zones on the bottom side of the jet stream visually the downburst of turbulence looks similar to a rain shaft plummeting to the surface and propagating out over the plains leaving relatively quiescent conditions behind

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

the effect of a storm on the 1992 summer sea ice cover of the beaufort chukchi and east siberian seas for the summer beaufort chukchi and east siberian seas a variety of active and passive microwave satellite data are used to determine the response of the ice edge and interior to a storm specifically the study concentrates on a low pressure system that passed over the region between august 14 and 20 1992 with peak geostrophic winds of about 18 m s 1 through the use of the ers 1 imaging radar and the special sensor microwave imager the ice response is examined at two locations at the ice edge for a nearly stationary location in the chukchi sea and in the ice interior along three swaths in the beaufort chukchi and east siberian seas the ice edge observations show that the storm fractures the large floes into small floes some of which are advected into the adjacent warm water the ice interior observations show that the storm caused an increase in the open water amount and a shift in the floe size distribution toward smaller floes in the ice interior application of the cumulative number distribution n d where n is the number of floes per unit area that are no smaller than some floe diameter d shows that for d 1 km n behaves like d where lies in the range 1 8 2 9 our analysis also shows that this slope is not affected by the storm and is slightly larger near the ice edge

influence of sea ice on ocean water vapor isotopes and greenland ice core records a warming climate results in sea ice loss and impacts to the arctic water cycle the water isotope parameter deuterium excess a moisture source proxy can serve as a tracer to help understand hydrological changes due to sea ice loss however unlocking the sea ice change signal of isotopes from ice cores requires understanding how sea ice changes impact deuterium excess which is unknown here we present the first isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values initial loss of sea ice extent leads to lower deuterium excess moisture sources and then values progressively increase with further ice loss our new process based interpretation suggests that past rapid 1 3 years greenland ice core changes in deuterium excess during warming might not be the result of abrupt atmospheric circulation shifts but rather gradual loss of sea ice extent at northern latitude moisture sources

what drove the dramatic retreat of arctic sea ice during summer 2007 1 a model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007 it is found that preconditioning anomalous winds and ice albedo feedback are mainly responsible for the retreat arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate during summer 2007 atmospheric changes strengthened the transpolar drift of sea ice causing more ice to move out of the pacific sector and the central arctic ocean where the reduction in ice thickness due to ice advection is up to 1 5 m more than usual some of the ice exited fram strait and some piled up in part of the canada basin and along the coast of northern greenland leaving behind an unusually large area of thin ice and open water thin ice and open water allow more surface solar heating because of a much reduced surface albedo leading to amplified ice melting the arctic ocean lost additional 10 of its total ice mass in which 70 is due directly to the amplified melting and 30 to the unusual ice advection causing the unprecedented ice retreat arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing

the interaction of katabatic flow and mountain waves part i observations and idealized simulations abstract the mutual interaction of katabatic flow in the nocturnal boundary layer nbl and topographically forced gravity waves is investigated due to the nonlinear nature of these phenomena analysis focuses on information obtained from the 1993 atmospheric studies in complex terrain field program held at the mountain canyon plains interface near eldorado canyon colorado and idealized simulations perturbations to katabatic flow by mountain waves relative to their more steady form in quiescent conditions are found to be caused by dynamic pressure effects based on a local froude number climatology case study analysis and the simulations the dynamic pressure effect is theorized to occur as gravity wave pressure perturbations are transmitted through the atmospheric column to the surface and through altered horizontal pressure gradient forcing to the surface based katabatic flows it is proposed that these perturbations are a routine feature in the atmospheric record and represent a significant p

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

numerical simulations of an observed gravity current and gravity waves in an environment characterized by complex stratification and shear abstract numerical simulations of a gravity current in an environment characterized by complex stratification and vertical wind shear have been performed using a nonhydrostatic two dimensional dry primitive equation model data from one of the most complete documentations to date of gravity waves associated with a gravity current presented in an earlier study are used both to prescribe the gravity current s environment and for validation of the simulated gravity current and its associated gravity waves these comparisons indicate that the gravity current observed by a doppler wind profiler and sodars was well simulated in terms of depth density contrast and propagation speed and that the model produced a variety of gravity waves similar in many ways to these observed because uncertainties remained concerning the gravity wave generation mechanisms derived from the observations e g wavelengths were not observed the validated simulations are used to test these tentative hypotheses the simulatio

the impact of resolution on the representation of southeast greenland barrier winds and katabatic flows southern greenland is characterized by a number of low level high wind speed weather systems that are the result of topographic flow distortion these systems include barrier winds and katabatic flow that occur along its southeast coast global atmospheric reanalyses have proven to be important tools in furthering our understanding of these orographic winds and their role in the climate system however there is evidence that the mesoscale characteristics of these systems may be missed in these global products here we show that the arctic system reanalysis a higher resolution regional reanalysis is able to capture mesoscale features of barrier winds and katabatic flow that are missed or underrepresented in era i a leading modern global reanalysis this suggests that our understanding of the impact of these wind systems on the coupled climate system can be enhanced through the use of higher resolution regional reanalyses or model data

the role of wave dynamics and small scale topography for downslope wind events in southeast greenland abstractin ammassalik in southeast greenland downslope winds can reach hurricane intensity and represent a hazard for the local population and environment they advect cold air down the ice sheet and over the irminger sea where they drive large ocean atmosphere heat fluxes over an important ocean convection region earlier studies have found them to be associated with a strong katabatic acceleration over the steep coastal slopes flow convergence inside the valley of ammassalik and in one instance mountain wave breaking yet for the general occurrence of strong downslope wind events the importance of mesoscale processes is largely unknown here two wind events one weak and one strong are simulated with the atmospheric weather research and forecasting wrf model with different model and topography resolutions ranging from 1 67 to 60 km for both events but especially for the strong one it is found that lower resolutions underestimate the wind speed because they misrepresent the steepness of the

dynamics of the mackenzie river plume on the inner beaufort shelf during an open water period in summer abstract the oceanographic conditions of the mackenzie river plume in the arctic ocean were examined during a 12 day period in august 2007 field observations in the river channel and the delta region 2 6 m depth ship based observations on the shelf and satellite observations of sea surface temperatures indicate that movements of plume density fronts cause changes in water temperatures of over 10 c over a few days we used a 1d model to compare the strength of stratification versus surface wind stress and a 3d numerical model to simulate the plume motions under forcing from the river flows local wind and water level variations from tides and wind driven surge the results indicate that the coastal region is stratified with a 2 m thick surface plume even in water depths of 3 4 m resulting in strong vertical variation of horizontal currents moderate easterly winds of 5 10 m s are sufficient to induce offshore transport of the surface plume and onshore transport of the deeper shelf water leading to large fluctuations in temperature and salinity in the coastal region this study examined a period of offshore transport and mean water level set down and indicates the rapid response of the plume to wind over the shallow delta

strong downslope wind events in ammassalik southeast greenland abstractammassalik in southeast greenland is known for strong wind events that can reach hurricane intensity and cause severe destruction in the local town yet these winds and their impact on the nearby fjord and shelf region have not been studied in detail here data from two meteorological stations and the european centre for medium range weather forecasts interim re analysis era interim are used to identify and characterize these strong downslope wind events which are especially pronounced at a major east greenland fjord sermilik fjord within ammassalik their local and regional characteristics their dynamics and their impacts on the regional sea ice cover and air sea fluxes are described based on a composite of the events it is concluded that wind events last for approximately a day and seven to eight events occur each winter downslope wind events are associated with a deep synoptic scale cyclone between iceland and greenland during the events cold dry air is advected down the ice sheet

modeling the seasonal variation of sea ice in the labrador sea with a coupled multicategory ice model and the princeton ocean model we use a multicategory sea ice model coupled to the princeton ocean model which is driven by monthly climatological atmospheric forcing to study the seasonal variation of ice cover in the labrador sea initial ocean conditions are derived from a gridded objectively analyzed temperature salinity data set that provides improved resolution of gradients in the vicinity of the shelf break the model produces a realistic seasonal variation of sea ice there is ice growth over the inner shelf and ice melt over the outer shelf and slope over the inner shelf advection and diffusion decrease the ice mass over the outer shelf advection and diffusion increase the ice mass which maintains the location of the ice edge near the offshore ice edge the melt rate exceed s1mp er month and the heat to melt ice together with the heat lost to the atmosphere exceeds 500 wm 22 the heat lost at the ocean surface is compensated for by advection of heat from an offshore convective region the dominant heat source for the spring retreat of ice in the south is shortwave radiation over the open water fraction marginal ice zones are regions of dynamic interaction be tween atmosphere ice and ocean in the labrador marginal ice zone the ice edge is located near the labrador current and its associated shelf break front wintertime convection in the western labrador sea is thought to form labrador intermedi ate water clarke and gascard 1983 since the ice edge bor ders the convective region it is important to clarify the pro cesses that limit the ice extent and to examine the heat and salt fluxes in the vicinity of the ice edge in this study we investigate the seasonal evolution of sea ice over the labrador shelf with a coupled ice ocean model our objective is to assess the capability of the model in simulating the evolution of the ice cover and to identify model deficien cies we examine the processes that limit the ice extent labrador sea ice has been the subject of a number of studies with numerical models most recently ikeda et al 1996 cou pled a two category ice model hibler 1979 with the geo physical fluid dynamics laboratory gfdl ocean model bryan 1969 cox 1984 there was overall agreement with the seasonal cycle as well as with interannual variations the re sults showed that shoreward advection of relatively warm off shore water is an important source of heat to melt ice how ever the model ice decayed too rapidly partly because the two category ice model underestimates ice concentration there are a number of differences between the present model and the model of ikeda et al 1996 we have imple mented a multicategory ice model and used the sigma coordi nate princeton ocean model blumberg and mellor 1987 mel lor 1996 with its embedded turbulence closure submodel we use a climatology from the national centers for environmen tal prediction ncep national center for atmospheric re

an analysis of the nonhydrostatic dynamics in numerically simulated antarctic katabatic flows abstract a series of two dimensional numerical experiments was conducted in order to describe the role of nonhydrostatic dynamics in simple antarctic katabatic flows the results presented include a comparison of the thermodynamic and dynamic fields produced by hydrostatic and nonhydrostatic numerical simulations the source of the differences in the simulations was diagnosed based on an analysis of the model equation tendencies as well as calculated components of the pressure gradient force over most of the terrain slope the nonhydrostatic effects were found to be insensitive to the model horizontal resolution for a grid spacing ranging from 5 to 100 km

tip jets and barrier winds a quikscat climatology of high wind speed events around greenland the high topography of greenland results in a number of orographically induced high wind speed flows along its coast that are of interest from both a severe weather and climate perspective here the surface wind field dataset from the nasa jpl seawinds scatterometer on board the quick scatterometer quikscat satellite is used to develop a wintertime climatology of these flows the high spatial resolution and the twice daily sampling of the seawinds instrument allows for a much more detailed view of the surface winds around greenland than has been previously possible three phenomena stand out as the most distinctive features of the surface wind field during the winter months the previously identified tip jets and reverse tip jets as well as the hitherto unrecognized barrier flows along its southeast coast in the vicinity of the denmark strait peak surface wind speeds associated with these phenomena can be as large as 50 m s 1 with winds over 25 m s 1 occurring approximately 10 15 of the time at each location a compositing technique is used to show that each type of flow is the result of an interaction between a synoptic scale parent cyclone and the high topography of greenland in keeping with previous work it is argued that tip jets are caused by a combination of conservation of the bernoulli function during orographic descent and acceleration due to flow splitting as stable air passes around cape farewell while barrier winds are a geostrophic response to stable air being forced against high topography it is proposed that reverse tip jets occur when barrier winds reach the end of the topographic barrier and move from a geostrophic to a gradient wind balance becoming supergeostrophic as a result of their anticyclonic curvature

momentum budget of the east antarctic atmospheric boundary layer results of a regional climate model output of a regional atmospheric climate model is used to quantify the average january and july momentum budget of the atmospheric boundary layer abl over the east antarctic ice sheet and the surrounding oceans results are binned in nine elevation intervals over the ice sheet and six distance intervals over the ocean in january when surface cooling is weak the large scale pressure gradient force dominates the abl momentum budget in july under conditions of strong surface cooling a shallow katabatic jet develops over the gentle slopes of the interior ice sheet and a strong deep jet over the steep coastal slopes in the coastal regions the abl thickens considerably caused by the piling up of cold air over the adjacent sea ice and ice shelves this represents the main opposing force for the katabatic winds horizontal and vertical advection are generally small in the cross slope direction the momentum budget represents a simple balance between surface drag and coriolis turning intraseasonal variability of the large scale wind field in the abl can be explained in terms of the strength of the polar vortex the background baroclinicity and the topography of the ice sheet subsidence is found over the interior ice sheet and rising motion in the coastal zone reflecting the acceleration and deceleration of the katabatic circulation however vertical velocities are generally small because the downslope mass flux in the abl is confined to a shallow layer below the wind speed maximum

an overview of barrier winds off southeastern greenland during the greenland flow distortion experiment during the greenland flow distortion experiment barrier flow was observed by an instrumented aircraft on 1 2 5 and 6 march 2007 off southeastern greenland during this time period the barrier flow increased from a narrow jet 15 m s 1 to a jet filling almost the whole of the denmark strait with maximum wind speed exceeding 40 m s 1 dropsonde observations show that the barrier flow was capped by a sharp temperature inversion below mountain height below the inversion was a cold and dry jet with a larger northerly wind component than that of the flow above which was also warmer and more moist thus the observations indicate two air masses below mountain height a cold and dry barrier jet of northern origin and above this a warmer and moister air mass that was of cyclonic origin numerical simulations emphasize the non stationarity of the greenland barrier flow and its dependence on the synoptic situation in the greenland iceland region they show that the barrier jet originated north of the denmark strait and was drawn southward by a synoptic scale cyclone with the strength and location of the maximum winds highly dependent on the location of the cyclone relative to the orography of greenland experiments without greenland s orography suggest a 20 m s 1 enhancement of the low level peak wind speeds due to the presence of the barrier thus the greenland barrier flows are not classic geostrophically balanced barrier flows but have a significant ageostrophic component and are precisely controlled by synoptic scale systems copyright c 2009 royal meteorological society

strong winter cooling over the irminger sea in winter 2014 2015 exceptional deep convection and the emergence of anomalously low sst deep convection is presumed to be vital for the north atlantic meridional overturning circulation even though observational evidence for the link remains inconclusive modeling studies have suggested thatconvection will weaken as a result of enhanced freshwater input the emergence of anomalously low seasurface temperature in the subpolar north atlantic has led to speculation that this process is already at work hereweshow that strong atmospheric forcing in the winter of 2014 2015 associated with a high north atlanticoscillation nao index produced record mixed layer depths in the irminger sea local mixing removed thestratification of the upper 1400mand ventilated the basin to middepths resembling a state similar to themid 1990s when a positive nao also prevailed we show that the strong local atmospheric forcing ispredominantly responsible for the negative sea surface temperature anomalies observed in the subpolar northatlantic in 2015 and that there is no evidence of permanently weakened deep convection

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

changes in ocean temperature in the barents sea in the twenty first century abstractpossible modifications to ocean temperature in the barents sea induced by climate change are explored the simulations were performed with a coupled ice ocean model ciom driven by the surface fields from the canadian regional climate model crcm simulations ciom can capture the observed water volume inflow through the barents sea opening the ciom simulation and observations suggest an increase in the atlantic water volume inflow and heat transport into the barents sea in recent decades resulting from enhanced storm activity while seasonal variations of sea ice and sea surface temperature in ciom simulations are comparable with observations ciom results underestimate the sea surface temperature but overestimate ice cover in the barents sea consistent with an underestimated heat transport through the barents sea opening under the sres a1b scenario the loss of sea ice significantly increases the surface solar radiation and the ocean surface heat loss through turbulent heat fluxes and longwa

the overamplification of gravity waves in numerical solutions to flow over topography abstract the tendency of high resolution numerical weather prediction nwp models to overpredict the strength of vertically propagating mountain waves is explored discrete analytic mountain wave solutions are presented for the classical problem of cross mountain flow in an atmosphere with constant wind speed and stability time dependent linear numerical solutions are also obtained for more realistic atmospheric structures on one hand using second order accurate finite differences on an arakawa c grid to model nonhydrostatic flow over what might be supposed to be an adequately resolved 8 x wide mountain can lead to an overamplification of the standing mountain wave by 30 40 on the other hand the same finite difference scheme underestimates the wave amplitude in hydrostatic flow over an 8 x wide mountain increasing the accuracy of the advection scheme to the fourth order significantly reduces the numerical errors associated with both the hydrostatic and nonhydrostatic discrete solutions the coupl

the role of katabatic winds on the antarctic surface wind regime abstract antarctica is known for its strong and persistent surface winds that are directed along topographic pathways surface winds are especially strong during the winter period the high directional constancy of the wind and the close relationship of the wind direction to the underlying terrain can be interpreted as evidence of katabatic wind activity observations show that the directional constancy of the antarctic surface wind displays little seasonal variation summertime winds cannot be expected to contain a significant katabatic component owing to enhanced solar heating of the ice slopes observations also show that the coastal environs are subjected to wide variation in atmospheric pressure associated with frequent cyclone activity the robust unidirectional nature of the antarctic surface wind throughout the year implies that significant topographic influences other than those from katabatic forcing must be acting idealized numerical simulations have been performed to illustrate the potential

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

seasonal variability in the dynamics of marine terminating outlet glaciers in greenland recent studies indicate that the dynamics of fast flowing marine terminating outlet glaciers of the greenland ice sheet may be sensitive to climate and ocean forcing on sub annual timescales observations of seasonal behavior of these glaciers at such high temporal resolution however are currently few here we present observations of front position flow speed near surface air temperature and ocean conditions for six large marine terminating glaciers in the uummannaq region of west greenland to investigate controls on short term glacier dynamics as proposed by other studies we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange our data suggest that high sea surface temperature anomalously low sea ice concentration and reduced melange formation in early 2003 have triggered multi year retreat of several glaciers in the study area which is consistent with other regions in greenland of the stable glaciers only rink isbrae exhibits a seasonal speed variation that correlates with variations in front position with the others undergoing mid summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution drainage of supraglacial lakes and water filled crevasses results in substantial decreases in speed 40 60 on fast flowing glaciers our results demonstrate that attempts to model ice sheet evolution must take into account short timescale flow dynamics resulting from drainage events and oceanographic conditions

late paleozoic deformation of the cratonic carbonate cover of eastern north america paleozoic carbonates that cover the eastern half of the north american craton preserved a bedding parallel shortening fabric up to 800 km away from the appalachian ouachita orogenic front as recorded by mechanical twins in calcite a strain fabric is present in 29 of 31 samples from three traverse within the flat lying cratonic cover sequence jasper arkansas to minneapolis bluefield west virginia to madison wisconsin and albany new york to hamilton ontario twinning is found only in paleozoic carbonates and is absent in cretaceous limestones in the two southernmost traverses the orientation of the principal shortening axis e1 is perpendicular to the thrust front and parallel to the thrusting direction of the southern appalachians and the ouachitas the magnitude of calcite shortening strain 6 and the calculated differential stress 90 mpa decrease exponentially away from the orogenic front until twinning is absent the northernmost traverse shows greater complexity probably because of its location in the bend of the appalachian trend the authors conclude that the regional strain fabric preserved in the cratonic cover sequence of eastern north american was produced by late paleozoic orogenic stresses of the appalachian ouachita orogeny and that compressive stresses were transmitted over distances greater than 1200 km awaymore from the active plate margin less

lidar observations of a breaking mountain wave associated with extreme turbulence observations from a doppler lidar which are enhanced by stratospheric aerosols from mount pinatubo s eruption provide unique measurements of mountain waves over the rocky mountains including nearly instantaneous observations of wave breaking in the lower stratosphere the wave breaking is revealed by a flow reversal aloft that marks a localized critical layer created when the wave amplitude was great enough to cause overturning the altitude spatial scale and duration of this wave induced critical layer are documented the mountain waves led to turbulence affecting commercial aircraft including one accident in which a cargo jet lost an engine and part of a wing in extreme turbulence at the same time the lidar was making observations nearby although earlier observations of mountain wave drag assumed wave stationarity over 3 5 h significant changes over less than 2 h are documented here such nonstationarity could contribute to discrepancies remaining between observations and simulations of mountain wave drag

arctic system reanalysis improvements in topographically forced winds near greenland southern greenland is home to a number of weather systems characterized by high speed low level winds that are the result of topographic flow distortion these systems include tip jets barrier winds and katabatic flows global atmospheric reanalyses have proven to be important tools in furthering our understanding of these systems and their role in the climate system however there is evidence that their mesoscale structure may be poorly resolved in these global products here output from the regional arctic system reanalysis asrv1 30 km and asrv2 15 km grid resolutions are compared to the global era interim reanalysis era i 80 km grid resolution focusing on their ability to represent winds in the vicinity of southern greenland comparisons are made to observations from surface and upper air stations as well as from research aircraft flights during the greenland flow distortion experiment gfdex the era i reanalysis has a tendency to underestimate high wind speeds and overestimate low wind speeds which is reduced in asrv1 and nearly eliminated in asrv2 in addition there is generally a systematic reduction in the root mean square error between the observed and the reanalysis wind speeds from era i to asrv1 to asrv2 the exception being low level marine winds where the correspondence is similar in all reanalyses case studies reveal that mesoscale spatial features of the wind field are better captured in asrv2 as compared to the era i or asrv1 these results confirm that a horizontal grid size on the order of 15 km is needed to characterize the impact that greenland s topography has on the regional wind field and climate however even at this resolution there are still features of the wind field that are under resolved

dramatic interannual changes of perennial arctic sea ice linked to abnormal summer storm activity 1 the perennial september arctic sea ice cover exhibits large interannual variability with changes of over a million square kilometers from one year to the next here we explore the role of changes in arctic cyclone activity and related factors in driving these pronounced year to year changes in perennial sea ice cover strong relationships are revealed between the september sea ice changes and the number of cyclones in the preceding late spring and early summer in particular fewer cyclones over the central arctic ocean during the months of may june and july appear to favor a low sea ice area at the end of the melt season years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks they lack the normal maximum in cyclone activity over the central arctic ocean and cyclones that track from eurasia into the central arctic are largely absent fewer storms are associated with above average mean sea level pressure strengthened anticyclonic winds an intensification of the transpolar drift stream and reduced cloud cover all of which favor ice melt it is also shown that a strengthening of the central arctic cyclone maximum helps preserve the ice cover although the association is weaker than that between low cyclone activity and reduced sea ice the results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season

effect of a sheared flow on iceberg motion and melting icebergs account for approximately half the freshwater flux into the ocean from the greenland and antarctic ice sheets and play a major role in the distribution of meltwater into the ocean global climate models distribute this freshwater by parameterizing iceberg motion and melt but these parameterizations are presently informed by limited observations here we present a record of speed and draft for 90 icebergs from sermilik fjord southeastern greenland collected in conjunction with wind and ocean velocity data over an 8 month period it is shown that icebergs subject to strongly sheared flows predominantly move with the vertical average of the ocean currents if as typical in iceberg parameterizations only the surface ocean velocity is taken into account iceberg speed and basal melt may have errors in excess of 60 these results emphasize the need for parameterizations to consider ocean properties over the entire iceberg draft

large amplitude mountain wave breaking over greenland abstract a large amplitude mountain wave generated by strong southwesterly flow over southern greenland was observed during the fronts and atlantic storm track experiment fastex on 29 january 1997 by the noaa g iv research aircraft dropwindsondes deployed every 50 km and flight level data depict a vertically propagating large amplitude wave with deep convectively unstable layers potential temperature perturbations of 25 k that deformed the tropopause and lower stratosphere and a vertical velocity maximum of nearly 10 m s 1 in the stratosphere the wave breaking was associated with a large vertical flux of horizontal momentum and dominated by quasi isotropic turbulence the coupled ocean atmosphere mesoscale prediction system coamps nonhydrostatic model with four nested grid meshes with a minimum resolution of 1 7 km accurately simulates the amplitude location and timing of the mountain wave and turbulent breakdown finescale low velocity plumes that resemble wakelike structures emanate from highl

the arctic frontal zone as seen in the ncep ncar reanalysis abstract calculations of a thermal front parameter using ncep ncar reanalysis data over the period 1979 98 reveal a relative maximum in frontal frequencies during summer along northern eurasia from about 60 to 70 n best expressed over the eastern half of the continent a similar relative maximum is found over alaska which is present year round although best expressed in summer these high latitude features can be clearly distinguished from the polar frontal zone in the midlatitudes of the pacific basin and collectively resemble the summertime arctic frontal zone discussed in several early studies while some separation between high and midlatitude frontal activity is observed in all seasons the summer season is distinguished by the development of an attendant mean baroclinic zone aligned roughly along the arctic ocean coastline and associated wind maxima in the upper troposphere the regions of maximum summer frontal frequency correspond to preferred areas of cyclogenesis and to where the summertime

the response of the sea ice edge to atmospheric and oceanic jet formation abstractthe sea ice edge presents a region of many feedback processes between the atmosphere ocean and sea ice maslowski et al here the authors focus on the impact of on ice atmospheric and oceanic flows at the sea ice edge mesoscale jet formation due to the coriolis effect is well understood over sharp changes in surface roughness such as coastlines hunt et al this sharp change in surface roughness is experienced by the atmosphere and ocean encountering a compacted sea ice edge this paper presents a study of a dynamic sea ice edge responding to prescribed atmospheric and oceanic jet formation an idealized analytical model of sea ice drift is developed and compared to a sea ice climate model the los alamos sea ice model cice run on an idealized domain the response of the cice model to jet formation is tested at various resolutions it is found that the formation of atmospheric jets at the sea ice edge increases the wind speed parallel to the sea ice edge and results in the formation of a

arctic sea ice retreat in 2007 follows thinning trend the minimum of arctic sea ice extent in the summer of 2007 was unprecedented in the historical record a coupled ice ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective it is found that even though the 2007 ice extent was strongly anomalous the loss in total ice mass was not rather the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987 since then the simulated mean september ice thickness within the arctic ocean has declined from 3 7 to 2 6 m at a rate of 0 57 m decade 1 both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing the combined impact of these two trends caused a large reduction in the september mean ice concentration in the arctic ocean this created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the pacific side to the atlantic side of the basin and more than usual into the greenland sea this exposed large areas of open water resulting in the record ice extent anomaly

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen