observations of temperature inversions over central arctic sea ice in summer we analysed high resolution tethersonde sounding data from the drifting ice station tara in the arctic ocean in april to august 2007 to a better understand the multiple processes affecting the generation and properties of arctic air temperature inversions and b to obtain insight into the vertical structure of the atmospheric boundary layer during the exceptional spring and summer 2007 which resulted in a historically low sea ice extent a total of 95 profiles up to the height of 2 km were measured on 39 days inversions were present in 88 of the data 13 of them being surface based compared to winter the occurrence and properties of summer inversions depended much less on surface net radiation and were mainly controlled by the surface melt and warm air advection inversions occuring during snow ice melt were located at low altitudes frequently based at the surface and were often as strong as winter inversions reported in previous studies in general the tara inversions were shallow and the deepest ones were observed when clouds occurred inside or partly above the inversion layer inversions were strongest under clear skies or in cases when the cloud top was above the inversion base related to cases of strong warm air advection up to 35 k day 1 in july exceptionally high temperatures around the inversion top caused maximum inversion strengths up to 13 k inversions of this magnitude at this time of the year have been rarely documented previously

arctic inversion strength in climate models recent work indicates that climate models have a positive bias in the strength of the wintertime low level temperature inversion over the high latitude northern hemisphere it has been argued this bias leads to underestimates of the arctic s surface temperature response to anthropogenic forcing here the bias in inversion strength is revisited the spatial distribution of low level stability is found to be bimodal in climate modelsandobservationalreanalysis products withlow levelinversionsrepresentedbyastableprimarymode over the interior arctic ocean and adjacent continents and a secondary unstable mode over the atlantic ocean averaging over these differing conditions is detrimental to understanding the origins of the inversion strength bias while nearly all of the 21 models examined overestimate the area average inversion strength conditionally sampling the two modes shows about half the models are biased because of the relative partitioning of the modes and half because of biases within the stable mode

snow distribution and melt modelling for glaciers in zackenberg river drainage basin north eastern greenland a physically based snow evolution modelling system snowmodel that includes four sub models micromet enbal snowpack and snowtran 3d was used to simulate eight full year evolutions of snow accumulation distribution sublimation and surface melt from glaciers in the zackenberg river drainage basin in north east greenland meteorological observations from two meteorological stations were used as model inputs and spatial snow depth observations snow melt depletion curves from photographic time lapse and a satellite image were used for model testing of snow and melt simulations which differ from previous snowmodel tests methods used on greenland glaciers modelled test period average end of winter snow water equivalent swe depth for the depletion area differs by a maximum of 14 mm w eq or 6 more than the observed and modelled test period average snow cover extent differs by a maximum of 5 or 0 8 km2 less than the observed furthermore comparison with a satellite image indicated a 7 discrepancy between observed and modelled snow cover extent for the entire drainage basin about 18 31 mm w eq of the solid precipitation was returned to the atmosphere by sublimation modelled mean annual snow melt and glacier ice melt for the glaciers in the zackenberg river drainage basin from 1997 through 2005 september august averaged 207 mm w eq year 1 and 1198 mm w eq year 1 respectively yielding a total averaging 1405 mm w eq year 1 total modelled mean annual surface melt varied from 960 mm w eq year 1 to 1989 mm w eq year 1 the surface melt period started between mid may and the beginning of june and lasted until mid september annual calculated runoff averaged 1487 mm w eq year 1 150 106 m3 1997 2005 with variations from 1031 mm w eq year 1 to 2051 mm w eq year 1 the model simulated a total glacier recession averaging 1347 mm w eq year 1 136 106 m3 1997 2005 which was almost equal to previous basin average hydrological water balance storage studies 244 mm w eq year 1 125 106 m3 1997 2003 copyright 2007 john wiley sons ltd

a crustal model for northern melville bay baffin bay the interpretation of seismic refraction and gravity data acquired in 2010 gives new insights into the crustal structure of the west greenland coast and the adjacent deep central baffin bay basin underneath melville bay the depth of the moho varies between 26 and 17 km stretched continental crust with a thickness of 25 to 14 km and deep sedimentary basins are present in this area the deep melville bay graben contains an up to 11 km thick infill of consolidated and unconsolidated sediments with velocities of 1 6 to 4 9 km s seaward at the 60 km wide transition between oceanic and stretched continental crust a mount shaped magmatic structure is observed which most likely formed prior to the initial formation of oceanic crust the up to 4 km high magmatic structure is underlain by a 2 km thick and 50 km wide high velocity lower crust more to the west in the oceanic part of the baffin bay basin we identify a two layered 3 5 to 6 km thin igneous oceanic crust with increasing thickness toward the shelf beneath the oceanic crust the depth of the moho ranges between 11 5 and 13 5 km in the western part of the profile oceanic layer 3 is unusually thin 1 5 km a possible explanation for the thin crust is accretion due to slow spreading although the basement is notably smooth compared to the basement of other regions formed by ultra slow spreading the oceanic crust is underlain by partly serpentinized upper mantle with velocities of 7 6 to 7 8 km s

the morphological characteristics of ribbed moraine abstract ribbed rogen moraines are large subglacially formed transverse ridges that cover extensive areas of the former laurentide scandinavian and irish ice sheets given their ubiquitous and conspicuous nature it is surprising that their characteristics are poorly understood to date most ribbed moraine studies have been spatially restricted and rely on small sample sizes thus published accounts of their characteristics are most likely unrepresentative of ribbed moraines generally this study addresses this deficit by producing the first representative data set on ribbed moraine size shape pattern and distribution and we describe their spatial characteristics various remote sensing and gis techniques were used to map ribbed moraines over a combined area of 81 000 km 2 in canada ireland and sweden producing a database of just over 33 000 individual landforms in all 25 082 ridges were mapped in two areas in central and northern quebec the lac naococane and river kaniapiskau regions 5637 in the lake rogen area of central sweden and 2500 in north central ireland in comparison against the published accounts of ribbed moraine we demonstrate that some widely held assertions are inaccurate or untrue and we show that ribbed moraine morphological characteristics are more complex than has been hitherto reported our data reveals they exist over a larger scale range than was previously stated this study concludes by presenting a list of ribbed moraine characteristics and argues that formational hypotheses must account for these if they are to remain valid explanations of ribbed moraine genesis

the spitsbergen south cape tip jet we investigated low level tip jets generated at the southern tip of the island of spitsbergen part of the svalbard archipelago in the arctic low level tip jets occur in many locations where airflow converges around obstacles such as islands they are often poorly resolved in forecasts or re analyses so it is important to document their locations and shed light on why they occur tip jets are the result of flow stagnation and flow splitting upstream of an obstacle both of these processes are dependent on the stability of the air column wind speed and direction upstream jets generated around sorkapp the southern cape of spitsbergen have been resolved previously in numerical studies but no climatology exists in this study we used the weather research and forecasting model wrf to demonstrate the influence of topography on the development of tip jets we used quikscat satellite derived surface wind data to identify tip jet events and compile climatologies and the era interim data to investigate the prevailing synoptic conditions during jet events and identify the main driving forces we found that tip jets can occur throughout the year associated with a negative surface level pressure anomaly moving in a northeast direction from the norwegian sea and towards the barents sea on average jets occurred just over 8 of days throughout the year the maximum 60 day running mean of occurrence was around 12 and occurred between february and march the results showed that negative wind speed and positive static stability anomalies were statistically significant upstream of the island group these anomalies remain significant when seasons of high middle and low occurrence were analysed separately we conclude therefore that wind direction persistence may play an important role in the seasonality of jet occurrences in the study region copyright 2011 royal meteorological society

the physiography of high arctic cross shelf troughs abstract a comprehensive inventory of high arctic cross shelf troughs is compiled from international bathymetric chart of the arctic ocean ibcao bathymetric data v 3 0 the location of 75 cross shelf troughs is presented alongside a synthesis of their key physiographic characteristics and available glacial geological evidence the troughs are interpreted to have been occupied intermittently and eroded by marine terminating ice streams that traversed the shelf during at least one and often many quaternary full glacial periods considerable variation in cross shelf trough physiography exists in the high arctic trough lengths range between 35 and 1400 km widths from 12 to 260 km and maximum depths from 200 to 1000 m the longest cross shelf troughs extend through inter island channels on the beaufort sea queen elizabeth islands and barents kara sea margins the gradient of the upper slope beyond high arctic glacial troughs which ranges between 0 3 and 13 is shown to have a negative relationship with palaeo ice stream drainage basin area and trough length glacial sedimentary depocentres or trough mouth fans tmfs are inferred on the basis of bathymetric and where available seismic evidence to exist beyond the majority of high arctic cross shelf troughs evidence of shelf progradation or tmf development is absent from the slope beyond several high arctic troughs probably as a result of limited sediment supply to the margin and or sediment by passing of the upper slope on the south greenland continental margin it is likely that steep slopes prevented the development of significant glacial sedimentary depocentres beyond cross shelf troughs or that glacigenic debris has been removed from the upper slope by submarine slope failure

basin seismic stratigraphy and aspects of prospectivity in the ne baffin bay northwest greenland abstract subsurface mapping in the northeastern part of baffin bay offshore northwest greenland indicates the presence of large basement structures and sedimentary basins we identify eight seismic stratigraphic units that can be genetically related to the regional geology and tectonic development the seismic interpretation includes the top of paleocene to eocene volcanic rocks which cover most parts of the southern and western study area using this horizon as a time marker the seismic units are divided into pre cenozoic and palaeogene to neogene strata based on comparison to equivalent units exposed onshore west greenland and canada and sampled by exploration wells farther south in the disko west offshore nuuk region our interpretation of the faults and tectonic elements suggest that the main extensional faults and basin formation took place mainly during the cretaceous and into the paleocene subsequent compressional tectonics and inversion were accompanied by strike slip faulting and local transtensional faults and flexures this last phase of deformation corresponds to the well documented eurekan orogeny in ellesmere island and northern greenland that developed as a result of northward motion and possible counterclockwise rotation of greenland relative to the north american plate we surmise that these tectonic phases exerted a strong control on basin infill by activation of hinterland sediment sources during cretaceous and palaeogene times the deep basins may include cretaceous and palaeogene organic rich sediments with hydrocarbon source potential we estimate that maturation could have started during the eocene

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

submarine geomorphology of northeast baffin bay and its implications for local paleo ice sheet dynamics abstract high resolution bathymetric data from close to the northwest greenland coast in northern melville bay northeast baffin bay reveal a range of glacial and nonglacial landforms the glacial landforms include crag and tails mega scale glacial lineations msgl rock drumlins and roche moutonnees that indicate paleo ice sheet dynamics the nonglacial landforms include steep ridges that are interpreted as volcanic dykes neoproterozoic thule dyke swarms and paleoproterozoic melville bugt dyke swarms these dykes are glacially overprinted and may have channeled ice and subglacial meltwater flow through narrow subglacial cavities some of the glacial landforms eroded into bedrock indicate a southward paleo ice stream orientation while other glacial landforms including the sedimentary depositional landforms indicate a westward paleo ice stream orientation the glacial landforms were likely produced during at least two epochs and under changing thickness of the ice streams the glacial landforms eroded into the bedrock are likely older than the sedimentary glacial landforms and were likely produced by a thin south southeastward ice stream that allowed cavity formation the westward oriented glacial landforms were likely produced by a thick ice stream that was probably active during the last glacial maximum lgm the different orientations of the glacial landforms indicate a reorganization of the ice streams that may have occurred during retreat and subsequent readvance this reorganization likely coincided with a migration of the ice divide from south to north

a diagnostic ice ocean model abstract a coupled ice ocean model suitable for simulating ice ocean circulation over a seasonal cycle is developed by coupling the dynamic thermodynamic sea ice model of hibler with a multilevel baroclinic ocean model bryan this model is used to investigate the effect of ocean circulation on seasonal sea ice simulations by carrying out a simulation of the arctic greenland and norwegian seas the ocean model contains a linear term that damps the ocean s temperature and salinity towards climatology the damping term was chosen to have a three year relaxation time equivalent to the adjustment time of the pack ice no damping however was applied to the uppermost layer of the ocean model which is in direct contact with the moving pack ice this damping procedure allows seasonal and shorter time scale variability to be simulated in the ocean but does not allow the model to drift away from ocean climatology on longer time scales for the standard experiment an initial integration of five years was per

hairpin erosional marks horseshoe vortices and subglacial erosion abstract crescentic erosional marks wrapped around obstacles and extending into straight grooves are termed hairpin erosional marks they are u shaped to semi circular in cross section are deepest around the upstream shoulders of the obstacles and range over seven orders of magnitude in scale some are asymmetrical with one groove better developed than the other the straight grooves may broaden and shallow rapidly in the downflow direction upstream grooves merge with rather than cross downstream crescentic marks grooves are distinct from glacial abrasion forms and many are not striated hairpin erosional marks are interpreted as being products of scour by horseshoe vortices in turbulent fluids this interpretation is supported by the close similarity of these marks to scours produced experimentally and in nature by horseshoe vortices estimated reynolds numbers show that such vortices are probable around obstacles in wind and flowing water but are extremely unlikely in ice aeolian hairpin erosional marks related to yardangs are illustrated to support this conclusion the surface texture cross sectional shapes and spatial patterns of hairpin erosional marks also discount formation by ice a model for the evolution of isolated erosional drumlins from an initial field of hairpin erosional marks extends earlier research on a meltwater hypothesis for drumlins

parametrizing turbulent exchange over summer sea ice and the marginal ice zone the surface of the arctic ocean in summer is a mix of sea ice and water in both leads and melt ponds here we use data collected at multiple sites during the year long experiment to study the surface heat budget of the arctic ocean sheba to develop a bulk turbulent flux algorithm for predicting the surface fluxes of momentum and sensible and latent heat over the arctic ocean during summer from readily measured or modelled quantities the distinctive aerodynamic feature of summer sea ice is that the leads and melt ponds create vertical ice faces that the wind can push against momentum transfer to the surface is thus enhanced through form drag in effect summer sea ice behaves aerodynamically like the marginal ice zone which is another surface that consists of sea ice and water in our bulk flux algorithm we therefore combine our sheba measurements of the neutral stability drag coefficient at a reference height of 10 m cdn10 with similar measurements from marginal ice zones that have been reported in the literature to create a unified parametrization for cdn10 for summer sea ice and for any marginal ice zone this parametrization predicts cdn10 from a second order polynomial in ice concentration our bulk flux algorithm also includes expressions for the roughness lengths for temperature and humidity introduces new profile stratification corrections for stable stratification and effectively eliminates the singularities that often occur in iterative flux algorithms for very light winds in summary this new algorithm seems capable of estimating the friction velocity u a surrogate for the momentum flux over summer sea ice with an absolute accuracy of 0 02 0 03 m s 1 the sensible heat flux with an accuracy of about 6 w m 2 and the latent heat flux with an accuracy of 3 5 w m 2 c opyright c 2010 royal meteorological society

a look at the surface based temperature inversion on the antarctic plateau data from radiosondes towers and a thermistor string are used to characterize the temperature inversion at two stations the amundsen scott station at the south pole and the somewhat higher and colder dome c station at a lower latitude ten years of temperature data from a 22 m tower at the south pole are analyzed the data include 2 and 22 m temperatures for the entire period and 13 m temperatures for the last 2 yr statistics of the individual temperatures and the differences among the three levels are presented for summer december and january and winter april september the relationships of temperature and inversion strength in the lowest 22 m with wind speed and downward longwave flux are examined for the winter months two preferred regimes one warming and one cooling are found in the temperature versus longwave flux data but the physical causes of these regimes have not been determined the minimum temperatures and the maximum inversions tend to occur not with calm winds but with winds of 3 5 m s 1 likely due to the inversion wind this inversion wind also explains why the near surface winds at south pole blow almost exclusively from the northeast quadrant temperature data from the surface to 2 m above the surface from south pole in the winter of 2001 are presented showing that the steepest temperature gradient in the entire atmosphere is in the lowest 20 cm the median difference between the temperatures at 2 m and the surface is over 1 0 k in winter under clear skies this difference increases to about 1 3 k monthly mean temperature profiles of the lowest 30 km of the atmosphere over south pole are presented based on 10 yr of radiosonde data these profiles show large variations in lower stratospheric temperatures and in the strength and depth of the surface based inversion the near destruction of a strong inversion at south pole durin g7ho n 8september 1992 is examined using a thermal conductivity model of the snowpack driven by the measured downward longwave flux the downward flux increased when a cloud moved over the station and it seems that this increase in radiation alone can explain the magnitude and timing of the warming near the surface temperature data from the 2003 04 and 2004 05 summers at dome c station are presented to show the effects of the diurnal cycle of solar elevation over the antarctic plateau these data include surface temperature and 2 and 30 m air temperatures as well as radiosonde air temperatures they show that strong inversions averaging 10 k between the surface and 30 m develop quickly at night when the sun is low in the sky but are destroyed during the middle of the day the diurnal temperature range at the surface was 13 k but only 3 k at 30 m

rossby wave propagation from the arctic into the midlatitudes does it arise from in situ latent heating or a trans arctic wave train abstractthe relationship between latent heating over the greenland barents and kara seas gbks hereafter and rossby wave propagation between the arctic and midlatitudes is investigated using glo

low level temperature inversions of the eurasian arctic and comparisons with soviet drifting station data abstract seasonal and regional variations in characteristics of the arctic low level temperature inversion are examined using up to 12 years of twice daily rawinsonde data from 31 inland and coastal sites of the eurasian arctic and a total of nearly six station years of data from three soviet drifting stations near the north pole the frequency of inversions the median inversion depth and the temperature difference across the inversion layer increase from the norwegian sea eastward toward the laptev and east siberian seas this effect is most pronounced in winter and autumn and reflects proximity to oceanic influences and synoptic activity possibly enhanced by a gradient in cloud cover east of novaya zemlya during winter inversions are found in over 95 of all soundings and tend to be surface based for all locations however inversions tend to he most intense during winter due to the large deficit in surface net radiation the strongest inversions are found over eastern siberia and reflect the ef

the vertical structure of the lower arctic troposphere analysed from observations and the era 40 reanalysis in situ atmospheric observations in the central arctic are few and mostly from near the surface a majorityare from coastal regions whereas soundings over the arctic ocean are rare this limits our

high resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain melville bay northwestern greenland abstract geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate melville bay in northwestern greenland contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings we present here the results of high resolution geomorphological mapping of the offshore and onshore landscapes in melville bay using multibeam sonar and satellite data at 5 and 10 m resolutions respectively the results show a similar areally scoured bedrock dominated landscape with a glacially modified cnoc and lochan morphology on the inner shelf 150 500 m depth and on the nearby exposed coast this is manifested by the presence of u shaped troughs moutonee type elongated landforms stoss and lee forms and streamlined features the submarine landscape shows features that are characteristic of bedrock in folded faulted and weathered metamorphic terrain and to a lesser extent glacially molded bedforms while coastal landforms exhibit higher relief irregular shaped basins and more subdued fracture valleys although generally similar the onshore and offshore landscapes contain examples of distinctly different landform patterns which are interpreted to reflect a longer exposure to long term deep weathering as well as to more recent periglacial weathering processes on land the spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock the lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the west greenland current flowing northward over the area in combination with limited sediment supply from long sea ice cover seasons the distribution and orientation of the landforms in the offshore part indicate ice movement toward the nw and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day melville bay trough

ribbed moraines in sweden distribution pattern and palaeoglaciological implications abstract a detailed map of ribbed moraines in central and northern sweden is presented they are frequent features over much of the mapped area and the distribution has well defined limits the most abundant ribbed moraines are situated in close connection to areas that are inferred to have been cold based during the retreat of the late weichselian ice sheet while outer fully warm based areas lack ribbed moraine observations have also been made on a more local scale where cold based patches grade into ribbed moraines via a zone of a broken up till cover a model of origin is presented which includes contracting of a frozen core area of a retreating ice sheet at the transition from non sliding to sliding conditions there will be high stresses resulting in local extensional flow at the base of the ice sheet a rising phase change surface frozen thawed material would cause detachment and boudinage like breaking up of a pre existing till cover thawed at the bedrock contact but still frozen to the ice sole the orientation of ice flow during the formation of the ribbed moraines closely matches the ice flow directions of the deglaciating late weichselian ice sheet thus ribbed moraines are considered to be deglaciation landforms typical of shrinking cold based zones of a retreating ice sheet

glacimarine sedimentary processes and depositional environments in an embayment fed by west greenland ice streams abstract the extent and behaviour of the central west greenland sector of the greenland ice sheet gis during the last glacial maximum lgm and the following deglaciation remains poorly constrained to investigate deglacial marine environments and sedimentary processes in an area fed by several lgm ice streams we now report findings from a 3 5 khz sub bottom profiler survey acquired in and around disko bay in 2009 sediment thicknesses and volumes in three glaciated areas disko bay southern vaigat and egedesminde dyb are fully constrained for the first time acoustic facies types and distributions were also mapped the largest sediment thicknesses 256 m and widest variation in acoustic character was observed in disko bay adjacent to the mouth of jakobshavns isfjord significant sediment thicknesses were also observed in isolated basins in the egedesminde dyb trough and in a trough in southern vaigat strait up to 110 m given low modern sedimentation rates these thick sediment packages are inferred to record the retreat of glaciers from the middle shelf through disko bay and into both the jakobshavns and torssukatak fjord systems in central west greenland our results highlight similarities in deglacial sedimentary processes across the study area when the margins of retreating glaciers supplied large volumes of sediment to the marine environment from sediment laden meltwater plumes and melting icebergs we estimate the sediment flux for the palaeo jakobshavn ice stream while the ice margin was stable at a fjord entrance sill to be 1 6 3 6 10 7 m 3 a 1 assuming a flux at the upper end of our range for the torssukatak fjord system requires the grounded ice margin to be stable for about 450 years during retreat the sediment fluxes we estimate are within the range of previously calculated fluxes for other arctic and antarctic ice streams and suggest that large volumes of meltwater and sediment were available at the base of the outlet glaciers during deglaciation even during periods of quasi stability retreat of the ice margins into the fjord systems is characterised by a rapid transition to ice distal sedimentation by rainout of iceberg rafted detritus ird and hemipelagic material accumulation rates drop to 2 mm a 1 this study demonstrates the variability in glacimarine processes and environments on high latitude continental margins and highlights the importance of local factors such as bedrock morphology as well as glacio dynamic factors on sedimentation

climatology of surface based inversions in the north american arctic the annual cycle of surface based inversions at nine arctic weather stations is examined based on a 20 year set of daily 1200 ut significant level radiosonde data all stations are at or near the coast inversions in winter months are primarily the result of strongly negative net radiation at the surface whereas in summer inversions more commonly result from near surface cooling of warm air masses inversion frequency is at a maximum in winter generally 70 of days when inversions range from approximately 400 to approximately 850 m in thickness inversion thickness and strength temperature change across the inversion are strongly related to surface temperature inversions may involve temperature changes of 30 degrees c in 6 degrees c 100 m sup minus 1 during periods of extreme warm air advection aloft midwinter inversions commonly persist for 2 4 days but may remain undisturbed for several weeks affecting lower tropospheric chemistry 9 refs 11 figs 5 tabs

modelling the vertical structure of the atmospheric boundary layer over arctic fjords in svalbard the vertical structure of the atmospheric boundary layer abl simulated with the mesoscale model weather research and forecasting wrf as well as with its polar optimized version polar wrf was compared to tethered balloon soundings and mast observations taken in march and april 2009 from two arctic fjords in svalbard from twelve short 48 h simulations the quasi normal scale elimination scheme for the abl and the noah land surface scheme for the surface were found to perform best and were selected for one long 16 day simulation the differences in performance of the standard wrf and polar wrf were marginal a warm bias especially near the surface was found in the modelled temperature profiles related to underestimated temperature inversion strength and depth the modelled humidity inversions were generally deeper but weaker than the observed and often occurred independently of temperature inversions the largest errors in temperature and humidity occurred under high pressure conditions multiple temperature and humidity inversions were usually not captured by wrf compared to the compact sea ice east of svalbard the modelled temperature and humidity inversions were weaker and less frequent over the fjords the biases in modelled wind speed profiles were closely related to low level jets lljs the modelled lljs were stronger and deeper and typically located at higher altitudes than the observed lljs errors in the near surface variables were notably reduced by applying post processing equations based on other modelled variables copyright 2012 royal meteorological society

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

seasonal variations in sea ice motion and effects on sea ice concentration in the canada basin drifting buoy data surface pressure and geostrophic wind analyses from the arctic ocean buoy program are used to examine seasonal features of the sea ice motion in the canada basin for 1979 1985 although the 7 year annual mean motion in this region is clockwise the month to month motion is highly variable in late summer to early autumn the circulation can become net anticlockwise for periods lasting at least 30 days results from a linear model demonstrate that these reversals of ice motion in the beaufort gyre are a wind driven response to persistent cyclonic activity that contrasts sharply with the predominantly anticyclonic regimes of spring late autumn and winter model predicted ice divergences of 0 5 or more per day which can occur during periods of anticlockwise ice motion are in good agreement with values calculated from optimally interpolated velocity gradient fields visible band imagery and passive microwave data confirm associated large areal reductions in ice concentration of approximately 20 data from under ice submarine sonar transects and surface pressure records prior to the study period point to frequent recurrences of these late summer to early autumn ice conditions

holocene history of the larsen a ice shelf constrained by geomagnetic paleointensity dating a sedimentary record collected from beneath the former lar sen a ice shelf reveals the holocene history of the larsen a re gion the record begins with the transition from grounded ice to a floating ice shelf completed by 10 7 6 0 5 ka and ends with the modern recession the record contains several late holocene dia tomaceous ooze layers that suggest proximity to productive open water events radiocarbon ages obtained from these sediments were complicated by the presence of detrital and reworked carbon we have eliminated these complications and constructed a chro nology for the larsen a ice shelf history via tuning of the geo magnetic field paleointensity record with a reference curve this approach provides chronological control to sediment sequences that lack appropriate material for radiocarbon dating geomag netic paleointensity features with wavelengths of 2 3 k y can be recognized and interhemispherically correlated illustrating the po tential to use geomagnetic paleointensity variations as a global cor relation and dating tool at sub milankovitch time scales

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

does the summer arctic frontal zone influence arctic ocean cyclone activity abstractextratropical cyclone activity over the central arctic ocean reaches its peak in summer previous research has argued for the existence of two external source regions for cyclones contributing to this summer maximum the eurasian continent interior and a narrow band of strong horizontal temperature gradients along the arctic coastline known as the arctic frontal zone afz this study incorporates data from an atmospheric reanalysis and an advanced cyclone detection and tracking algorithm to critically evaluate the relationship between the summer afz and cyclone activity in the central arctic ocean analysis of both individual cyclone tracks and seasonal fields of cyclone characteristics shows that the arctic coast and therefore the afz is not a region of cyclogenesis rather the afz acts as an intensification area for systems forming over eurasia as these systems migrate toward the arctic ocean they experience greater deepening in situations when the afz is strong at midtropospheric levels

assessment of the uncertainties in arctic low level temperature inversion characteristics in radio occultation observations the variation of low level inversion characteristics is one of the important factors for arctic amplification radiosonde rs observations are one of the reliable tools to study arctic inversions however they provide limited information on the spatial distribution of temperature inversions the radio occultation ro technique can provide accurate all weather high vertical resolution atmospheric parameter profiles over both land and ocean in this paper the ro technique is investigated to estimate the inversions and their uncertainties are assessed via comparing with the rs inversions results show that the inversions base depth and strength from rs and ro observations are lower deeper and stronger in winter than in autumn spring and summer moreover comparisons of spatiotemporally synchronized ro and rs inversions i e scheme i during 2007 2013 reveal that the former are higher deeper and weaker than the latter further comparisons of rs and 5 circ times 5 circ gridded ro inversions i e scheme ii show smaller overall standard deviations than scheme i indicating that the gridded ro observations can better describe the large scale spatial structure of temperature inversions furthermore corrections of the observed remarkable systematic differences between ro and rs inversions in both the schemes are also made the results show that the ro inversions can be well calibrated and that greater improvements in ro inversions calibration are achieved in scheme ii than in scheme i therefore the ro technique could be a potential tool to study the arctic low level temperature inversions as well as improve our understanding of arctic climate change