air sea interactions over terra nova bay during winter simulation with a coupled atmosphere polynya model a preliminary simulation of the terra nova bay polynya has been performed with a coupled atmosphere polynya model the atmospheric model is a hydrostatic primitive equations model that has been validated previously by a simulation of the strong katabatic winds observed in that area the polynya model includes a representation of the free drift of frazil ice and simple sea ice dynamics and thermodynamics two and three dimensional experiments have been performed under polar night conditions two dimensional experiments show that an open warm water area influences significantly the atmospheric circulation in the antarctic coastal zone an additional ice breeze effect is simulated and is responsible for the strenghthening of the katabatic winds near the coast because of the important temperature difference between the continental air and the ice free ocean up to 40 c strong surface heat fluxes are simulated over the polynya finally a three dimensional experiment has been performed the integration domain includes terra nova bay the polynya observed in that region is well simulated it is found that heat losses from the polynya surface are stronger than previously thought but are probably constrained by the idealized representation of frazil ice which is assumed to be uniform in each grid box this stresses the need for having a better knowledge of frazil ice evolution in large polynyas

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

katabatic wind forcing of the terra nova bay polynya the terra nova bay polynya is a perennial winter feature in the western ross sea antarctica which occupies roughly 1000 km2 it is formed and maintained by the combined influence of persistent katabatic winds which advect newly formed bay ice eastward and the drygalski ice tongue which prevents northward drifting pack ice from entering terra nova bay existence of anomalously strong katabatic drainage along this coast is predicted by parish s 1982 simulation of wintertime airflow which reveals a pronounced confluence of surface winds upslope from the reeves glacier where the winds are further focused by local topography the simulation is strongly supported by regional sastrugi orientations average wintertime atmospheric conditions and ice sheet topography which control surface air drainage are stable on a climatic time scale therefore persistent wintertime katabatic winds should be an annual phenomenon further evidence comes from multi year landsat images which consistently show windswept snowfree areas on the reeves glacier in marked contrast to typical antarctic katabatic winds strong persistent winter winds are observed at sea level 25 km beyond the coastal slope break air probably descends as bora type winds and is likely to be significantly denser than the air at sea level conditions are not favorable for hydraulic jumps apparently typical of other katabatic regimes the horizontal density difference is maintained during airflow across the nansen ice sheet because relatively little air mass modification occurs there in contrast to situations where air moves over an ice laden ocean observations thus suggest that katabatic winds maintain their identity for some distance seaward of the coast qualitative trajectory calculations indicate that for representative geostrophic conditions this distance is on the order of the observed polynya width estimated ice freezing rates are 20 cm day 1 but wind generated waves and currents prevent ice from consolidating the blocking effect of the drygalski ice tongue is a consequence of its orientation with regard to western ross sea ice drift patterns ice tongue length controls polynya width absence of such blocking along other coasts experiencing strong katabatic outflow partly explains why similar polynyas do not form there

heat salt and freshwater budgets for a glacial fjord in greenland abstractin greenland s glacial fjords heat and freshwater are exchanged between glaciers and the ocean submarine melting of glaciers has been implicated as a potential trigger for recent glacier acceleration and observations of ocean heat transport are increasingly being used to infer the submarine melt rates the complete heat salt and mass budgets that underlie such methods however have been largely neglected here a new framework for exploring glacial fjord budgets is developed building on estuarine studies of salt budgets the heat salt and mass transports through the fjord are decomposed and new equations for calculating freshwater fluxes from submarine meltwater and runoff are presented this method is applied to moored records from sermilik fjord near the terminus of helheim glacier to evaluate the dominant balances in the fjord budgets and to estimate freshwater fluxes throughout the year two different regimes are found in the nonsummer months advective transports are balanced by

carbon sulphur iron variations and sulphur isotope patterns of silurian graptolite shales black shale horizons graptolithenschiefer in silurian and lower devonian strata of the franconian thuringian highlands frankenwald thuringer wald of germany have high metal concentrations e g u v mo organic carbon sulphur and iron contents degree of pyritization dop and sulphur isotope ratios from the lower graptolite shales along with faunal and sedimentological evidence show that the depositional environment was anoxic although some data e g c s plots do not suggest completely euxinic conditions the dop versus c plot indicates a black sea type environment from the sulphur isotope data the environment fluctuated between open and closed with respect to sulphate supply with higher carbon contents reflecting an increased bacterial reduction of the available sulphate diagenetic effects were responsible for somewhat unusual plots of c s ratios though iron availability may have been influential

factors controlling the near surface wind field in antarctica abstract using data from the regional atmospheric climate model racmo ant1 the momentum budget of the antarctic atmospheric surface layer sl taken as the lowest model layer located at 6 7 m above the surface is presented in july winter the katabatic pressure gradient force pgf dominates the sl momentum budget over the steep coastal slopes which results in strong 10 15 m s 1 and directionally constant katabatic winds farther inland where surface slopes are more gentle the large scale pgf may become equally important with the circumpolar pressure trough north of the antarctic coastline the large scale pgf acts along with the katabatic pgf in the downslope direction in wilkes land dronning maud land and on the western ross ice shelf the large scale pgf causes equivalent geostrophic winds in excess of 10 m s 1 thermal wind effects that oppose the downslope acceleration are especially strong in areas where large scale forcing is weak which allows cold air to pile up over the flat ice she

winter atmospheric buoyancy forcing and oceanic response during strong wind events around southeastern greenland in the regional arctic system model rasm for 1990 2010 abstractstrong mesoscale tip jets and barrier winds that occur along the southeastern greenland coast have the potential to impact deep convection in the irminger sea the self organizing map som training algorithm was used to identify 12 wind patterns that represent the range of winter november march ndjfm wind regimes identified in the fully coupled regional arctic system model rasm during 1990 2010 for all wind patterns the ocean loses buoyancy primarily through the turbulent sensible and latent heat fluxes haline contributions to buoyancy change were found to be insignificant compared to the thermal contributions patterns with westerly winds at the cape farewell area had the largest buoyancy loss over the irminger and labrador seas due to large turbulent fluxes from strong winds and the advection of anomalously cold dry air over the warmer ocean similar to observations rasm simulated typical ocean mixed layer depths mld of approximately 400 m throughout the irminger basin with indi

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

multi event analysis of the westerly greenland tip jet based upon 45 winters in era 40 the westerly greenland tip jet is an intense narrow and intermittent wind phenomenon located southeast of cape farewell that occurs frequently during the winter season using the era 40 reanalysis dataset a catalogue of 586 objectively detected westerly tip jet events is compiled for the winters 1957 2002 and an analysis is undertaken of the character of the jet and its accompanying atmospheric features it is shown that the tip jet frequency exhibits a significant positive correlation with both the nao index and the latitude of the icelandic low the peak wind speed and accompanying heat fluxes of the jet have values up to 30 m s 1 and 600 w m 2 respectively and are sustained for less than one day the air parcels constituting the tip jet are shown based upon a trajectory model and the era 40 dataset to have a continental origin and to exhibit a characteristic deflection and acceleration around southern greenland the events are almost invariably accompanied both by a notable coherence of the lower level tip jet with an overlying upper level jet stream and by a surface cyclone located to the lee of greenland it is also shown that the cyclone originates upstream of and is advected to the lee of greenland and thereby it both precedes in time and contributes dynamically to the formation of the tip jet on this basis it is suggested that the tip jet arises from the interplay of the synoptic scale flow evolution and the perturbing effects of greenland s topography upon the flow copyright 2009 royal meteorological society

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

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 dynamics of shelf forcing in greenlandic fjords abstractthe fjords that connect greenland s glaciers to the ocean are gateways for importing heat to melt ice and for exporting meltwater into the ocean the transport of heat and meltwater can be

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

subsurface iceberg melt key to greenland fjord freshwater budget liquid freshwater fluxes from the greenland ice sheet affect ocean water properties and circulation on local regional and basin wide scales with associated biosphere effects the exact impact however depends on the volume timing and location of freshwater releases which are poorly known in particular the transformation of icebergs which make up roughly 30 50 of the loss of the ice sheet mass to liquid freshwater is not well understood here we estimate the spatial and temporal distribution of the freshwater flux for the helheim sermilik glacier fjord system in southeast greenland using an iceberg melt model that resolves the subsurface iceberg melt by estimating seasonal variations in all the freshwater sources we confirm quantitatively that iceberg melt is the largest annual freshwater source in this system type we also show that 68 78 of the iceberg melt is released below a depth of 20 m and seasonally about 40 100 of that melt is likely to remain at depth in contrast with the usual model assumptions iceberg melt also peaks two months after all the other freshwater sources peak our methods provide a framework to assess individual freshwater sources in any tidewater system and our results are particularly applicable to coastal regions with a high solid ice discharge in greenland iceberg melt is the largest annual freshwater source in a south greenland fjord with release largely below 20 m depth according to iceberg model simulations furthermore iceberg melt peaks later in the year than other sources of freshwater

characteristics and dynamics of two major greenland glacial fjords the circulation regimes of two major outlet glacial fjords in southeastern greenland sermilik fjord sf and kangerdlugssuaq fjord kf are investigated using data collected in summer 2009 the two fjords show similar flow patterns with a time dependent vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input we show that this time dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth often referred to as intermediary circulation one difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three layer in kf in summer compared to two layer in sf outside each fjord large scale geostrophic currents dictate the stratification at the mouth although the way in which these large scale flows impinge on each fjord is distinct combining the observations with estimates from existing theories we find the magnitudes of the estuarine qe and intermediary qi circulation and show that qi qe although along fjord winds can also be significant we expect that the critical parameter determining qi qe is the sill depth compared to the fjord depth with shallower sills corresponding to weaker intermediary circulation finally we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries

wintertime surface winds over the greenland ice sheet abstract clear sky wintertime surface winds over the greenland ice sheet are simulated with a three dimensional mesoscale numerical model it is shown that the simulated winds blow from the broad gently sloped interior to the steep coastal margins this general wind pattern is similar to that found over antarctica due to the same governing dynamics the longwave radiational cooling of the sloping ice terrain is the key driving force of this cold airflow in some coastal areas the downslope winds converge into large fjords such as kangerlussuaq and sermilik this is consistent with the frequent presence in these areas of warm signatures on cloud free thermal infrared satellite images that are generated by katabatic winds the shape of the greenland ice sheet plays an important role in directing the flow of the surface winds the study demonstrates that the surface wind pattern is only moderately affected by climatological flow around and over the ice sheet the mass redistribution associated with the kat

shelf open ocean exchange forced by wind jets abstractthe general problem of exchange from a shallow shelf across sharp topography to the deep ocean forced by narrow cross shelf wind jets is studied using quasigeostrophic theory and an idealized primitive equation numerical model interest is motivated by katabatic winds that emanate from narrow fjords in southeast greenland although similar topographically constrained wind jets are found throughout the world s oceans because there is no net vorticity input by the wind the circulation is largely confined to the region near the forcing circulation over the shelf is limited by bottom friction for weakly stratified flows but stratification allows for much stronger upper layer flows that are regulated by weak coupling to the lower layer over the sloping topography the topographic beta effect limits the deep flow while for sufficient stratification the upper layer flow can cross the topography to connect the shelf to the open ocean this can be an effective transport mechanism even for short s

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

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

momentum budget of the atmospheric boundary layer over the greenland ice sheet and its surrounding seas 1 the atmospheric circulation patterns over the greenland ice sheet and its surrounding seas are studied by explicitly calculating the momentum budget components using data of a high resolution regional atmospheric climate model in winter djf the katabatic pressure gradient force pgf dominates the momentum budget of the atmospheric boundary layer abl over the ice sheet over the western slopes of the ice sheet the large scale pgf acts in the same direction as the katabatic pgf resulting in a strong southerly jet of up to 12 m s 1 in winter the accumulation of cold air over the sea ice along the northeast coast leads to a thermally induced northerly flow this circulation facilitates southward sea ice transport in this area and is enhanced by the large scale circulation along the west coast a similar west east temperature gradient also forces a northerly flow in the summer months sea ice is absent and thermal wind forcing is largely reduced over the ocean summer insolation also reduces katabatic forcing the large scale forcing dominates the abl momentum budget over the ice sheet heating of the abl over the snow free tundra induces thermal contrasts with the ice sheet and ocean forcing barrier winds in the coastal regions throughout the year strong surface layer winds along the southeast coast of greenland are forced by the large scale pgf

seasonal variability in warm water inflow toward kangerdlugssuaq fjord seasonal variability in pathways of warm water masses toward the kangerdlugssuaq fjord glacier system kf kg southeast greenland is investigated by backtracking lagrangian particles seeded at the fjord mouth in a high resolution regional ocean model simulation in the ice free and the ice covered seasons the waters at kf are a mixture of atlantic origin water advected from the irminger basin ff for faxafloi the deep waters from the denmark strait and the waters from the arctic ocean both represented by the kogur section ko below 200m depth the warm water is a mixture of ff and ko water masses and is warmer in winter than in summer we find that seasonal differences in pathways double the fraction of ff particles in winter causing the seasonal warming and salinification seasonal temperature variations at the upstream sections ff and ko have a negligible impact on temperature variations near the fjord successful monitoring of heat flux to the fjord therefore needs to take place close to the fjord and cannot be inferred from upstream conditions

the atlantic inflow in the western alboran sea abstract an extensive dataset collected in the alboran sea during the 1982 donde va experiment is used to characterize the kinematics and dynamics of the inflow of atlantic water into the mediterranean sea the veering of the inflow toward the ene after leaving the strait of gibraltar and the existence of an anticyclonic gyre that fills much of the western alboran sea in the upper 200 m are confirmed in the mean inflow variability with periods of 2 to 10 days is described particularly striking is one interval of about 9 days during which the gyre was not present and the inflow adopted a southerly course after leaving the strait the observations are interpreted in terms of vorticity conservation and in the light of earlier theoretical and numerical results

mesoscale structure of cape farewell tip jets abstractcape farewell greenland s southernmost point is characterized by a number of low level jets that are the result of topographic flow distortion associated with passing extratropical cyclones the heavy seas associated with these wind events are a hazard to maritime traffic in the region in addition the air sea heat flux associated with these weather systems plays an important role in the climate system by contributing to the forcing of the lower limb of the atlantic meridional overturning circulation in this paper the north american regional reanalysis will be used to generate a higher resolution climatology of these mesoscale jets as compared to previous studies through the use of a diagnostic that partitions the occurrence frequency of high speed wind events by wind direction the author shows that there are four different types of cape farewell tips jets that are characterized as having either northwesterly southwesterly northeasterly or southeasterly wind direction all four types hav

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

katabatic wind driven exchange in fjords the general issue of katabatic wind driven exchange in fjords is considered using an idealized numerical model theory and observations two regimes are identified for fjords narrower than a viscous boundary layer width the exchange is limited by a balance between wind and friction in lateral boundary layers for the nonlinear viscous parameterization used here this boundary layer thickness depends on the properties of the fjord such as stratification and length as well as on the wind stress and numerical parameters such as grid spacing and an empirical constant for wider fjords typical of east greenland the balance is primarily between wind the along fjord pressure gradient and acceleration in general agreement with previous two layer nonrotating theories it is expected that o 10 of the surface layer will be flushed out of the fjord by a single wind event application of the idealized model to a typical katabatic wind event produces outflowing velocities that are in general agreement with observations in sermilik fjord the presence of a sill has only a minor influence on the exchange until the sill penetrates over most of the lower layer thickness in which cases the exchange is reduced it is concluded that the multiple katabatic wind events per winter that are experienced by the fjords along east greenland represent an important mechanism of exchange between the fjord and shelf with implications for the renewal of warm salty waters at depth and for the export of glacial freshwater in the upper layer

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

subannual and seasonal variability of atlantic origin waters in two adjacent west greenland fjords greenland fjords provide a pathway for the inflow of warm shelf waters to glacier termini and outflow of glacially modified waters to the coastal ocean characterizing the dominant modes of variability in fjord circulation and how they vary over subannual and seasonal time scales is critical for predicting ocean heat transport to the ice here we present a 2 year hydrographic record from a suite of moorings in davis strait and two neighboring west greenland fjords that exhibit contrasting fjord and glacier geometry kangerdlugssuaq sermerssua and rink isbrae hydrographic variability above the sill exhibits clear seasonality with a progressive cooling of near surface waters and shoaling of deep isotherms above the sill during winter to spring renewal of below sill waters coincides with the arrival of dense waters at the fjord mouth warm salty atlantic origin water cascades into fjord basins from winter to midsummer we then use seaglider observations at davis strait along with reanalysis of sea ice and wind stress in baffin bay to explore the role of the west greenland current and local air sea forcing in driving fjord renewal these results demonstrate the importance of both remote and local processes in driving renewal of near terminus waters highlighting the need for sustained observations and improved ocean models that resolve the complete slope trough fjord ice system

comparison of wintertime mesoscale winds over the ocean around southeastern greenland in wrf and era interim strong mesoscale tip jets and barrier winds that occur over the ocean near southern greenland have the potential for impacting deep convection in the ocean the self organizing map som training algorithm was used to identify and classify the range of 10 m wind patterns present during ten winters 1997 2007 ndjfm in the ecmwf interim reanalysis era i and from a regional simulation using the weather research and forecasting wrf model at 50 km into a som the som is used to identify differences in the manifestation of westerly tip jets easterly tip jets and barrier flow the north atlantic oscillation nao index is well correlated with the type of tip jet present at cape farewell but the nao was not well correlated with the absence or presence of barrier flow wrf simulated patterns with strong barrier parallel flow more frequently than era i and wrf also had faster coastal winds than era i during all types of strong wind events the difference in coastal winds is likely related to model resolution and the resulting ability of each model to simulate strong mesoscale winds that are driven by greenland s steep terrain

trend and interannual variability in southeast greenland sea ice impacts on coastal greenland climate variability we describe the recent occurrence of a region of diminished sea ice cover or notch offshore of the kangerdlugssuaq fiord the site of the largest tidewater glacier along greenland s southeast coast the notch s location is consistent with a topographically forced flux of warm water toward the fiord and the decrease of the sea ice cover is shown to be associated with a regional warming of the upper ocean that began in the mid 1990s sea ice in the vicinity of the notch also exhibits interannual variability that is shown to be associated with a seesaw in surface temperature and sea ice between southeast and northeast greenland that is not describable solely in terms of the north atlantic oscillation we therefore argue that other modes of atmospheric variability including the lofoten low are required to fully document the changes to the climate that are occurring along greenland s east coast

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

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

interaction of katabatic flow with local thermal effects in a coastal region of adelie land east antarctica katabatic flows largely dominate the climate of the adelie land coastal region a detailed climatological data analysis of dumont d urville has been conducted results of this study support the idea that katabatic flow can be locally enhanced by the diurnal cycle of solar insolation and the temperature contrast between the continent and the ocean the interaction between katabatic wind and local thermal effects is expressed in terms of scale analysis except for surface stress all terms in the momentum equation for a katabatic flow in a coastal region of antarctica can reach the same order of magnitude the local circulation then is the result of a relatively tenuous force balance which can be disrupted even by a weak perturbation of any term to estimate the effect of the temperature contrast between the ocean and the continent on the katabatic flow two numerical experiments have been conducted the simulations consider an ocean free of sea ice representative of the summer months and another winter case with the ocean covered by thick sea ice these simulations show that with the ocean free of sea ice the katabatic flows extend only a limited distance over the open ocean during the day due to the local thermal effects with the ocean covered by sea ice the katabatic winds are not constrained and extend a considerable distance offshore

modelled variations of deep convection in the irminger sea during 2003 10 abstractresults from a high resolution ice ocean model are analyzed to understand the physical processes responsible for the interannual variability of ocean convection over the irminger sea the modeled convection in the open irminger sea for the winters of 2007 08 and 2008 09 is in good agreement with observations deep convection is caused by strong atmospheric forcing that increases the ocean heat loss through latent and sensible heat fluxes greenland tip jets are found to be the only strong wind events that directly affect the deep convection area and explain up to 53 of the total turbulent heat loss during active convection years deep convection is modeled where there is favorable preconditioning of the water column due to isopycnal doming inside the semienclosed irminger gyre the region of deep convection is also characterized by weak eddy kinetic energy finally an estimation of the surface forced water mass transformation confirms the irminger sea as a region of intermittent production of la

the freshwater composition of the fram strait outflow derived from a decade of tracer measurements the composition of the fram strait freshwater outflow is investigated by comparing 10 sections of concurrent salinity 18o nitrate and phosphate measurements collected between 1997 and 2011 the largest inventories of net sea ice meltwater are found in 2009 2010 and 2011 the 2009 2011 sections are also the first to show positive fractions of sea ice meltwater at the surface near the core of the egc sections from september 2009 2011 show an increased input of sea ice meltwater at the surface relative to older september sections this suggests that more sea ice now melts back into the surface in late summer than previously comparison of april july and september sections reveals seasonal variations in the inventory of positive sea ice meltwater with maximum inventories in september sections the time series of sections reveals a strong anti correlation between meteoric water and net sea ice meltwater inventories suggesting that meteoric water and brine may be delivered to fram strait together from a common source we find that the freshwater outflow at fram strait exhibits a similar meteoric water to net sea ice meltwater ratio as the central arctic ocean and siberian shelves suggesting that much of the sea ice meltwater and meteoric water at fram strait may originate from these regions however we also find that the ratio of meteoric water to sea ice meltwater inventories at fram strait is decreasing with time due to an increased surface input of sea ice meltwater in recent sections

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

atlantic water variability on the se greenland continental shelf and its relationship to sst and bathymetry 1 interaction of warm atlantic origin water aw and colder polar origin water pw advecting southward in the east greenland current egc influences the heat content of water entering greenland s outlet glacial fjords here we use depth and temperature data derived from deep diving seals to map out water mass variability across the continental shelf and to augment existing bathymetric products we compare depths derived from the seal dives with the ibcao version 3 bathymetric database over the shelf and find differences up to 300 m near several large submarine canyons in the vertical temperature structure we find two dominant modes a cold mode with the typical aw pw layering observed in the egc and a warm mode where aw is present throughout the water column the prevalence of these modes varies seasonally and spatially across the continental shelf implying distinct aw pathways in addition we find that satellite sea surface temperatures sst correlate significantly with temperatures in the upper 50 m r 0 54 but this correlation decreases with depth r 0 22 at 200 m and becomes insignificant below 250 m thus care must be taken in using sst as a proxy for heat content as aw mainly resides in these deeper layers sample unit level copyright

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

an easterly tip jet off cape farewell greenland ii simulations and dynamics an easterly tip jet that occurred on 21 february 2007 off cape farewell greenland is examined in part i of this article aircraft observations were described now in part ii numerical simulations and an analysis of the dynamical forcing mechanisms are presented the simulations make use of a limited area 12 km resolution configuration of the met office s unified model sea surface temperatures and sea ice concentrations have been replaced using the operational sea surface temperature and sea ice analysis ostia product addressing a boundary layer temperature bias while roughness lengths over sea ice have been updated addressing a wind speed bias these modifications ensured a reasonably accurate simulation generally within 1 2 k and 2 3 m s 1 when compared with dropsonde observations a momentum budget analysis along a curved locus through the core of the jet has been derived off southeast greenland the easterly tip jet was in cross jet geostrophic balance but was being accelerated downstream by an along jet pressure gradient over the curved part of the locus as the jet rounded cape farewell a cross jet residual suggests that the jet was unbalanced at the height of the jet core this residual decreases with height so that an approximate gradient wind balance applies in the upper part of the jet the anticyclonic curvature characteristic of easterly tip jets was caused by a dramatic decrease in the cross jet pressure gradient force at the end of the barrier after which the jet aligned with the synoptic scale isobars and returned to approximate geostrophic balance the momentum budget is shown to be robust and applicable to other cases copyright 2009 royal meteorological society

mechanisms of interannual to decadal scale winter labrador sea ice variability the variability of the winter sea ice cover of the labrador sea region and its links to atmospheric and oceanic forcing are investigated using observational data a coupled ocean sea ice model and a fully coupled model simulation drawn from the cmip5 archive a consistent series of mechanisms associated with high sea ice cover are found amongst the various data sets the highest values of sea ice area occur when the northern labrador sea is ice covered this region is found to be primarily thermodynamically forced contrasting with the dominance of mechanical forcing along the eastern coast of baffin island and labrador and the growth of sea ice is associated with anomalously fresh local ocean surface conditions positive fresh water anomalies are found to propagate to the region from a source area off the southeast greenland coast with a 1 month transit time these anomalies are associated with sea ice melt driven by the enhanced offshore transport of sea ice in the source region and its subsequent westward transport in the irminger current system by combining sea ice transport through the denmark strait in the preceding autumn with the greenland blocking index and the atlantic multidecadal oscillation index strong correlation with the labrador sea ice area of the following winter is obtained this relationship represents a dependence on the availability of sea ice to be melted in the source region the necessary atmospheric forcing to transport this offshore and a further multidecadal scale link with the large scale sea surface temperature conditions

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

an easterly tip jet off cape farewell greenland i aircraft observations an easterly tip jet event off cape farewell greenland is described and analysed in considerable detail in part i of this study this paper comprehensive aircraft based observations are described while in part ii of this study numerical simulations and a dynamical analysis are presented the easterly tip jet of 21 february 2007 took place during the greenland flow distortion experiment it resulted through the interaction of a barotropic synoptic scale low pressure system in the central north atlantic and the high topography of southern greenland in situ observations reveal a jet core at the coast with peak winds of almost 50 m s 1 about 600 800 m above the sea surface and of 30 m s 1 at 10 m the depth of the jet increased with wind speed from 1500 m to 2500 m as the peak winds increased from 30 to 50 m s 1 the jet accelerated and curved anticyclonically as it reached cape farewell and the end of the barrier the easterly tip jet was associated with a tongue of cold and dry air along the coast of southeast greenland general cloud cover to the east and cloud streets to the south of cape farewell precipitation was observed during the low level components of the flight the very high wind speeds generated a highly turbulent atmospheric boundary layer and resulted in some of the highest surface wind stresses ever observed over the ocean copyright c 2009 royal meteorological society

gale force winds over the irminger sea to the east of cape farewell greenland 1 high wind events that occur over the irminger sea to the east of cape farewell greenland are of interest as a result of the significant hazard they represent to maritime activity as well as their potential role in forcing deep ocean convection in the region in this paper the ncep reanalysis is used to develop a climatology of gale force wind events over the irminger sea in addition to the previously identified tip jet events that are characterized by strong westerly flow we show that there also exist reverse tip jet events that are characterized by strong easterly flow both types of events are associated with deep extra tropical cyclones that are undergoing an interaction with the high topography of southern greenland we also show that the frequency of both types of events is highest in the winter months and is modulated by the phase of the north atlantic oscillation nao

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

quantifying flow regimes in a greenland glacial fjord using iceberg drifters funded by the national science foundation grant numbers oce 1130008 arc 0909274 and the university of oregon

response of an antarctic peninsula fjord to summer katabatic wind events abstractfjords along the western antarctic peninsula are episodically exposed to strong winds flowing down marine terminating glaciers and out over the ocean these wind events could potentially be

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection