wind and thermodynamic retrieval from single doppler measurements of a gust front observed during phoenix ii abstract the adjoint method to retrieve the three dimensional wind and thermodynamic fields is applied to single doppler observations of a gust front measured during the phoenix ii experiment this method uses a fluid dynamics model and its adjoint and combines the retrieval with data assimilation into the prediction model the wind and thermodynamic variables are determined by minimizing the difference between the model solution and the observations experiments are conducted first with radial velocity alone and then with both radial velocity and reflectivity to examine the quality of the retrieval with respect to radar location boundary conditions length of assimilation data filtering smoothing enforced by penalty functions and model accuracy verification of these experiments is provided by a dual doppler analysis test results show that the adjoint method is able to retrieve the wind and thermodynamic fields of the gust front the retrieved horizontal wind agrees very well with the dual doppler

glacier calving rates due to subglacial discharge fjord circulation and free convection we would like to thank the new hampshire space grant consortium award nnx15ah79h for the training grant to fund kms the conocophillips ludin northern area program under the crios project and the dartmouth graduate studies travel fund for their financial support to conduct fieldwork and travel for data dissemination the polar geospatial center for arranging access to the worldview 2 imagery the uk natural environmental research council nerk oceans 2025 and northern sea program for mooring work support with further support from the research council of norway nfr projects circa 214271 cleopatra 178766 cleopatra ii 216537 and marine night 226471 alex hart and the geosciences mechanical workshop at the university of edinburgh for manufacturing the time lapse camera enclosure that was used in this study colin oriffiths for overseeing the collection of mooring data in kongsfjorden since 2002 esa for processing the copernicus sentinel data 2016

evolution of a surge type glacier in its quiescent phase kongsvegen spitsbergen 1964 95 kongsyegen is a 102 km 2 sub polar polythermal surge type glacier in northwest spitsbergen svalbard it surged just before 1948 and is currently in its quiescent phase measurements of surface geometry since 1966 show a retreat of the front and strong thinning of up to 75 m in the ablation area and a build up of up to 32 m in the accumulation area present day annual velocities along the glacier are low from 1 4 up to 3 6 m a 1 the measured mean net balance for the period 1987 94 and the balance reconstructed back to 1967 show a weak positive balance of about 0 1 m w e the measured actual ice flux is low and the mass transfer down glacier at the ela is only about 3 20 of that required for steady state thus the glacier is building up towards a new surge the total thickening rate on kongsvegen is somewhat higher than in other cases from svalbard but it is small compared with other well studied surge type glaciers in alaska and he pamirs this relatively low rate of change is a function of the low accumulation rate and the relatively cold climate compared to other areas and is common for surge type glaciers in svalbard

basal dynamics of kronebreen a fast flowing tidewater glacier in svalbard non local spatio temporal response to water input we evaluate the variability in basal friction for kronebreen svalbard a fast flowing tidewater glacier we invert 3 years 2013 15 of surface velocities at high temporal resolution generally 11 days to estimate the changing basal properties of the glacier our results suggest that sliding behaviour of kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another at present models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect for such ice masses with strong seasonal variations of surface melt the spatio temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and or time at least in a timescale of a few years basal sliding may not only be governed by local processes such as basal topography or summer melt but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation ice thickness changes or calving front geometry

geometry changes on svalbard glaciers mass balance or dynamic response the geometry of glaciers is affected by both the mass balance and the dynamics we present repeated gps measurements of longitudinal altitude profiles on three glaciers in svalbard and show that surface altitude changes alone cannot be used to assess the mass balance the three measured glaciers are in different dynamic modes and the observed changes in geometry are strongly affected by the dynamics nordenskioldbreen shows no significant change in the geometry indicating that the mass balance is in steady state with the dynamics on amundsenisen the surface has lowered by 1 5 2 0 m a 1 in the lower part of the accumulation area at 520 550 m a s l indicating that the ice flux is higher than the mass balance input probably due to a surge advance of the glacier further downstream affecting the higher part of the drainage area on kongsvegen the opposite situation was found here the geometry of the profile showed a clear build up of 0 5 m a 1 in the accumulation area and a lowering of 1 m a 1 in the lower part of the ablation area the ice velocity is very low giving a negligible vertical velocity component and an ice flux that is far smaller than the mass balance flux indicating that the glacier is building up towards a surge advance our results show that if mapping of height changes is to be used to monitor the response of the glaciers to climate change both surface net mass balance data and dynamic data are needed

spatial and temporal variability in the snowpack of a high arctic ice cap implications for mass change measurements interpretation of ice mass elevation changes observed by satellite altimetry demands quantification of the proportion of elevation change which is attributable to variations in firn densification detailed stratigraphic logging of snowpack structure and density was carried out at 1k m intervals along a 47 km transect on devon ice cap canada in spring pre melt and autumn during after melt 2004 and 2006 to characterize seasonal snowpack variability across the full range of snow facies simultaneous meteorological measurements were gathered spring pre melt snowpacks show low variability over large spatial scales with low magnitude changes in density the end of summer autumn density profiles show high variability in both 2004 and 2006 with vastly different melt regimes generating dissimilar patterns of ice layer formation over the two melt seasons dye tracing experiments from spring to autumn 2006 reveal that vertical and horizontal distribution of meltwater flow within and below the annual snowpack is strongly affected by the pre existing often subtle stratigraphic interfaces in the snowpack rather than its bulk properties strong interannual variability suggests that using a simple relationship between air temperature elevation and snowpack densification to derive mass change from measurements of elevation change across high arctic ice caps may be misguided melt timing and duration are important extrinsic factors governing snowpack densification and ice layer formation in summer rather than averaged air temperatures

modelling the long term mass balance and firn evolution of glaciers around kongsfjorden svalbard we analyse the long term 1961 2012 distributed surface mass balance and firn evolution of the kongsvegen and holtedahlfonna glacier systems in northwestern svalbard we couple a surface energy balance model to a firn model with forcing provided from regional climate model output in situ observational data are used to calibrate model parameters and validate the output the simulated area averaged surface mass balance for 1961 2012 is slightly positive 0 08 m w e a 1 which only fractionally compensates for mass loss by calving refreezing of percolating water in spring summer 0 13 m w e a 1 and stored water in fall winter 0 18 m w e a 1 provides a buffer for runoff internal accumulation i e refreezing below the previous year s summer surface in the accumulation zone peaks up to 0 22 m w e a 1 and is unaccounted for by stake observations superimposed ice formation in the lower accumulation zone ranges as high as 0 25 m w e a 1 a comparison of the periods 1961 99 and 2000 12 reveals 21 higher annual melt rates since 2000 and a 31 increase in runoff which can only in part be ascribed to recent warmer and drier conditions in response to firn line retreat both albedo lowering snow ice albedo feedback and lower refreezing rates refreezing feedback further amplified runoff

characterization of seasonal glacial seismicity from a single station on ice record at holtedahlfonna svalbard glacial seismicity provides important insights into glacier dynamic processes we study the temporal distribution of cryogenic seismic signals icequakes at holtedahlfonna svalbard between april

closing the mass budget of a tidewater glacier the example of kronebreen svalbard in this study we combine remote sensing in situ and model derived datasets from 1966 to 2014 to calculate the mass balance components of kronebreen a fast flowing tidewater glacier in svalbard

simulating climatic mass balance seasonal snow development and associated freshwater runoff in the kongsfjord basin svalbard 1980 2016 the kongsfjord basin in northwest svalbard is the site of a number of interdisciplinary studies concerned with the effect of fresh water from seasonal snow and glacier melt on the physical and biol

internal accumulation on storglaciaren sweden in a multi layer snow model coupled to a distributed energy and mass balance model to investigate the internal accumulation on storglaciaren sweden we couple a multilayer snow model to a distributed energy and mass balance model the snow model describes the temperature density and water content evolution of the snow ice pack and includes the processes of percolation and refreezing of water the model is run for the period 9 may 2 september 1999 and validated against weather station and mass balance observations on the glacier the model performs reasonably well with an average summer mass balance for the location of stake observations of 1 56 m w e compared to 1 59 m w e observed however the amount of melt is overestimated in the higher parts of the accumulation area and underestimated in the lower parts of the ablation area the modelled mass balance is most sensitive to the albedo parameterization the chosen momentum and scalar roughness lengths and all parameters related to snowfall the modelled internal accumulation is 0 25 m w e which amounts to about 20 of the winter accumulation and results in a positive net balance for 1999 of 0 23 m w e the modelled internal accumulation is most sensitive to the initial subsurface temperature profile and the irreducible water content

estimating the long term calving flux of kronebreen svalbard from geodetic elevation changes and mass balance modelling this study independently quantifies geodetic elevation change and models surface mass balance to solve the continuity equation the approach is tested on two dynamically different glaciers kongsvegen and kronebreen in northwest svalbard through two time epochs 1966 1990 95 i and 1990 95 2007 ii on kongsvegen a dynamically inactive glacier the residual term represents an error associated with determining elevation changes and surface mass balance it is apparent that centerline mass balance estimates are not representative of the entire glacier which we relate to center line accumulation being larger than the elevation bin average on kronebreen a fast flowing and actively calving glacier a significant part of the residual is identified with the long term calving flux for both glaciers the cumulative surface mass balance remained close to zero during the first epoch but became increasingly negative in the second epoch the long term calving flux of kronebreen is estimated to be 0 14 0 03 km3 w e a 1 during epoch i and 0 20 0 05 km3 w e a 1 in epoch ii

rapid loss of firn pore space accelerates 21st century greenland mass loss 1 mass loss from the two major ice sheets and their contribution to global sea level rise is accelerating in antarctica mass loss is dominated by increased flow velocities of outlet glaciers following the thinning or disintegration of coastal ice shelves into which they flow in contrast 55 of post 1992 greenland ice sheet gris mass loss is accounted for by surface processes notably increased meltwater runoff a subtle process in the surface mass balance of the gris is the retention and refreezing of meltwater currently preventing 40 of the meltwater to reach the ocean here we force a high resolution atmosphere snow model with a mid range warming scenario rcp4 5 1970 2100 to show that rapid loss of firn pore space by 50 at the end of the 21st century quickly reduces this refreezing buffer as a result gris surface mass loss accelerates throughout the 21st century and its contribution to global sea level rise increases to 1 7 0 5 mm yr 1 more than four times the current value

paleointensity during periods of rapid reversal a case study from the middle jurassic shamrock batholith western nevada paleointensity is one of the least deter mined parameters in geomagnetism yet this information has the potential to address many fundamental geophysical problems that bear on the evolution of the earth s core and lower mantle we test two important hy potheses that affect our understanding of how paleointensity has changed in earth s past 1 the mesozoic dipole low mdl hypoth esis and 2 the inverse relationship between geomagnetic polarity reversal rate and paleo intensity we report paleointensity results determined using both the coe modified thellier method and the izzi protocol on the medium grained hornblende biotite granite of the middle jurassic shamrock batholith in the southern singatse range western nevada usa previous zircon u pb dating gives an age of batholith emplacement at ca 165 8 0 4 ma this age estimate is coincident with a period of unusually high reversal frequency 10 reversals ma in the middle jurassic remanence in the shamrock batholith is held primarily by exsolved submicron magnetite inclusions in plagioclase the labora tory un blocking temperature range for the well de fined thermal remanent magnetization is nar row between 540 and 575 c and median destructive fields are between 40 and 50 mt thus we infer that the age of rema nence ac quisition is approximated by the u pb age estimate for pluton emplacement two sets of quality criteria were used to assess the paleo intensity results the first set yielded an 87 success rate while the second set using more stringent criteria resulted in only a 20 suc cess rate mean paleointensity values for the shamrock batholith using the loose and strict quality criteria are 34 0 6 4 t n 13 and 33 6 9 6 t n 3 respectively with errors reported at one standard deviation after correction for both remanence anisot ropy and cooling rate the mean values that pass loose and strict criteria are respec tively 17 9 2 7 t and 17 5 2 6 t the uncorrected and corrected paleointensity values for the strict estimates yield respec tive mean virtual dipole moments vdms of 62 7 18 zam 2 z 10 21 and 32 7 4 9 zam 2 the uncorrected value is within error of the vdms reported for plagioclase grains isolated from ca 160 ma basalts from ocean drilling program site 801 however these values have an absolute difference ranging from 6 to 20 zam 2 while the corrected vdm value is more consistent with the esti mated average jurassic field strength of 29 zam 2 using a recent estimate for the long term stable field strength of 42 zam 2 our corrected values add further credence to both the mdl and the inverse relationship between geomagnetic polarity reversal rate and dipole moment hypotheses

inverse estimation of snow accumulation along a radar transect on nordenskioldbreen svalbard we present an inverse modeling approach to reconstruct annual accumulation patterns from ground penetrating radar gpr data a coupled surface energy balance snow model simulates surface melt and the evolution of subsurface density temperature and water content the inverse problem consists of iteratively calibrating accumulation serving as input for the model by finding a match between modeled and observed radar travel times the inverse method is applied to a 16 km gpr transect on nordenskioldbreen svalbard yielding annual accumulation patterns for 2007 2012 accumulation patterns with a mean of 0 75 meter water equivalent mwe a 1contain substantial spatial variability with a mean annual standard deviation of 0 17 mwe a 1 and show only partial consistency from year to year in contrast to traditional methods accounting for melt water percolation refreezing and runoff facilitates accurate accumulation reconstruction in areas with substantial melt additionally accounting for horizontal density variability along the transect is shown to reduce spatial variability in reconstructed accumulation whereas incorporating irreducible water storage lowers accumulation estimates correlating accumulation to terrain characteristics in the dominant wind direction indicates a strong preference of snow deposition on leeward slopes whereas weaker correlations are found with terrain curvature sensitivity experiments reveal a nonlinear response of the mass balance to accumulation changes the related negative impact of small scale accumulation variability on the mean net mass balance is quantified yielding a negligible impact in the accumulation zone and a negative impact of 0 09 mwe a 1in the ablation area

synthetic dual doppler analysis of a winter mesoscale vortex abstract this article presents a detailed examination of the kinematic structure and evolution of the 5 december 1997 winter mesoscale vortex in the vicinity of lake michigan using the synthetic dual doppler sdd technique when such a mesoscale event propagates a distance large enough that the viewing angle from a single doppler radar changes by about 30 and the circulation is sufficiently steady during this time period then the sdd method can reveal reliable details about the circulation one such detail of the observed vortex was a pattern of convergence and divergence associated with radial bands where heavier snowfall was located another was the steadiness and vertical coherence of the derived vorticity and convergence patterns within the cyclonic circulation on 5 december 1997 the observed reflectivity field remained remarkably steady for nearly 2 5 h as the vortex moved southeastward allowing for the application of the sdd technique the reflectivity field exhibited a pronounced asymmetric c

spatial mapping of multi year superimposed ice on the glacier kongsvegen svalbard ground penetrating radar gpr and satellite ers 2 synthetic aperture radar sar are used to map the thickness and extent of the superimposed ice si zone on the surge type glacier kongsvegen svalbard gpr imagery shows sub horizontal si layers lying unconformably above a discrete boundary below this boundary the ice has a gpr signature similar to that of ice further down glacier in the ablation zone this boundary is posited to represent the closing of crevasses that were created during the last surge of kongsvegen in 1948 open crevasses would have interrupted the formation of sheet layers of si due to efficient vertical drainage of the snowpack aerial photographs suggest that the crevasses closed sometime in the period 1956 66 a classified sar image from 2003 is used to delineate the extent of the si zone the si extent in the sar image agrees well with the si zone mapped by gpr using the si spatial depth distribution we estimate the mean annual accumulation of superimposed ice to be 0 16 0 06 m w e a 1 locally up to 0 43 m a 1 w e this corresponds to 15 33 of the local winter balance and 5 10 of the total winter balance measured since 1987

retention of greenland runoff by refreezing implications for projected future sea level change melting produced at the surface of subfreezing permeable firn does not freely percolate but instead refreezes near its point of origin raising the firn temperature and decreasing the pore space if sufficient meltwater is introduced the firn will warm to 0 c and subsequent water will fill the remaining pore space without freezing only after the residual water content of the firn is exceeded will water flow through the firn and possibly escape as runoff this process prevents summer melt on high arctic glaciers and ice caps from escaping in its entirety and it must be accounted for in modeling glacier runoff on the basis of surface energy balance a model is presented here which describes in a simple way the transient process of infiltration refreezing and runoff in a future warming climate the model is applied to greenland for which predictions of runoff induced sea level rise that do not consider the refreezing process could be as much as 5 0 cm too high over 150 years

inhomogeneous precipitation distribution and snow transport in steep terrain 1 the inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface over topography we introduce and explain preferential deposition of precipitation as the deposition process without erosion of previously deposited snow and thus in absence of saltation a numerical model is developed describing the relevant processes of saltation suspension and preferential deposition the model uses high resolution wind fields calculated with a meteorological model arps the model is used to simulate a 120 h snow storm period over a steep alpine ridge for which snow distribution measurements are available the comparison to measurements shows that the model captures the larger scale snow distribution patterns and predicts the total additional lee slope loading well however the spatial resolution of 25 m is still insufficient to capture the smaller scale deposition features observed the model suggests that the snow distribution on the ridge scale is primarily caused by preferential deposition and that this result is not sensitive to model parameters such as turbulent diffusivity drift threshold or concentration in the saltation layer

multiphase formation of superimposed ice during a mass balance year at a maritime high arctic glacier meteorological and snow temperature data from midtre lovenbreen spitsbergen svalbard indicate two distinct annual phases of rapid snowpack warming and superimposed ice formation in 1998 99 short periods of positive air temperatures in early winter lasting up to 36 hours and often coinciding with rainfall caused rapid glacier wide melting percolating water froze to form superimposed ice on the lower half of the glacier and wetted refrozen snow and ice lenses at higher altitudes the second period of superimposed ice formation commenced in may june 1999 and continued for 5 weeks at low altitudes and throughout the summer at high altitudes these observations at midtre lovenbreen are typical of spitsbergen glaciers and reflect the unique climatology of the region they contrast with those from glaciers in more continental climatic settings where superimposed ice formation is confined to a single period during summer there are significant implications for glacier mass balance with superimposed ice locally comprising up to 20 of winter balances and accounting for 16 25 of the annual accumulation since projected climatic warming is greatest during the winter months in arctic regions superimposed ice may become an increasingly important component of the winter and potentially the net balance of spitsbergen glaciers

a high resolution hindcast of wind and waves for the north sea the norwegian sea and the barents sea 1 a combined high resolution atmospheric downscaling and wave hindcast based on the era 40 reanalysis covering the norwegian sea the north sea and the barents sea is presented the period covered is from september 1957 to august 2002 the dynamic atmospheric downscaling is performed as a series of short prognostic runs initialized from a blend of era 40 and the previous prognostic run to preserve the fine scale surface features from the high resolution model while maintaining the large scale synoptic field from era 40 the nested wam wave model hindcast consists of a coarse 50 km model covering the north atlantic forced with era 40 winds and a nested 10 11 km resolution model forced with downscaled winds a comparison against in situ and satellite observations of wind and sea state reveals significant improvement in mean values and upper percentiles of wind vectors and the significant wave height over era 40 improvement is also found in the mean wave period era 40 is biased low in wind speed and significant wave height a bias which is not reproduced by the downscaling the atmospheric downscaling also reproduces polar lows which cannot be resolved by era 40 but the lows are too weak and short lived as the downscaling is not capable of capturing their full life cycle

interannual variability in the spatial distribution of winter accumulation at a high arctic glacier finsterwalderbreen svalbard and its relationship with topography glacier mass balance and hydrology are strongly influenced by the distribution of snow accumulation at the start of the melt season two successive end of winter snow cover surveys at finsterwalderbreen svalbard are here used to investigate the interannual variability in the spatial distribution of accumulation and its relationship with topography 40 62 of the variance in snow depth was not determined by elevation assessed by linear regression of snow depth on surface elevation which could not therefore necessarily be used as a sole predictor of the spatial distribution of accumulation here principal components pc analysis of the topographic variables elevation slope north south and east west aspects shows that only two of six pcs determined for 2 years sampling locations had maximum loadings on altitude aspect was more important with maximum loadings on four pcs hierarchical cluster analysis was then applied to these pcs significant correlations with accumulation in each of two terrain clusters were given by 1 elevation and slope 2 east west aspect only 1999 1 elevation only 2 no significant correlations 2000 there is strong interannual variability not only in the magnitude of winter accumulation 0 41 m w e in 1999 0 58 m w e in 2000 but also in its spatial distribution and its relationship with topography

dynamic perennial firn aquifer on an arctic glacier ice penetrating radar and gps observations reveal a perennial firn aquifer pfa on a svalbard ice field similar to those recently discovered in southeastern greenland a bright widespread radar reflector separates relatively dry and water saturated firn this surface the phreatic firn water table is deeper beneath local surface elevation maxima shallower in surface lows and steeper where the surface is steep the reflector crosscuts snow stratigraphy we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases our observations indicate that pfas respond rapidly subannually to surface forcing and are capable of providing significant input to the englacial hydrology system

model study of the spatial distribution of the energy and mass balance of morteratschgletscher switzerland to investigate the spatial distribution of the energy and mass balance fluxes of a glacier a two dimensional mass balance model was developed and applied to morteratschgletscher switzerland the model is driven by meteorological input from four synoptic weather stations located in the vicinity of morteratschgletscher the model results were compared to observations made on the glacier the calculated mean specific mass balance is 0 47 m w e for 1999 and 0 23 m w e for 2000 net shortwave radiation shows a minimum at around 3350 m a s l due to the effects of shading slope aspect reflection from the slopes and obstruction of the sky ignoring these effects results in a 37 increase in the annual incoming shortwave radiation on the glacier causing 0 34 m w e more ablation a 1 c change in the air temperature results in a shift of 0 67 m w e in the mean specific mass balance while altering the precipitation by 10 causes a change of 0 17 m w e

flow field of kronebreen svalbard using repeated landsat 7 and aster data knowledge about the spatio temporal distribution of fast flowing arctic glaciers is still limited kronebreen svalbard in particular includes the confluence and the dynamic interplay of the fast flowing kronebreen and the currently slow flowing kongsvegen in this study image matching techniques on the basis of repeated landsat 7 enhanced thematic mapper plus etm pan and advanced spaceborne thermal emission and reflection radiometer aster satellite data are applied in order to derive surface velocity fields of the lowermost 10 km of kronebreen for the annual periods 1999 2000 2000 01 2001 02 and a 40 day period around july 2001 this work perfectly complements differential synthetic aperture radar interferometry dinsar studies available for kronebreen a complete surface velocity field is now available from combining the dinsar studies for the upper part of the glacier and the optical image matching study presented here the data obtained within this study are also compared to velocity data of 1964 1986 1990 and 1996 as also suggested by previous studies a significant spatio temporal variability of the spring summer and annual ice speeds becomes evident

formation of ice layers by infiltration and refreezing of meltwater melt layer frequency and magnitude in polar and sub polar ice cores have been interpreted as measures of past summer temperature and calibrations have been proposed relating frequency of occurrence of ice layers in ice cores to past summer temperatures but observations in the percolation facies in greenland and an analysis of the combined processes of meltwater infiltration and refreezing of water in snow indicate that in addition to unusually high rates of meltwater input formation of ice layers will also be facilitated by unusually cold initial conditions or early onset of melt uniform warming of both summer and winter conditions has the opposite effect and suppresses ice layer formation in favor of uniform wetting and refreezing of the snowpack numerical modeling of infiltration and refreezing at a stratigraphic fine to coarse transition allows quantification of the effects of significant parameters initial temperature grain size and density contrast across the stratigraphic transition water input rate and minimum impermeable layer thickness calculations are made to distinguish threshold values of parameters at which infiltration progresses faster than refreezing resulting in a break through of water across the stratigraphic transition from values leading to the formation of an ice layer when refreezing progresses faster than infiltration

the thermal regime of sub polar glaciers mapped by multi frequency radio echo sounding radio echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale radar signals of 320 370 mhz penetrate ice at sub freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water radar signals of 5 20 mhz on the other hand see through both the cold and the temperate ice down to the glacier bed radio echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in svalbard kongsvegen uversbreen midre lovenbreen and austre broggerbreen in the ablation area of kongsvegen a cold surface layer 50 160m thick was underlain by a warm basal layer which is advected from the temperate accumulation area the surface ablation of this cold layer may be compensated by freezing at its lower cold temperate interface this requires that the free water content in the ice at the freezing interface is about 1 of the volume the cold surface layer is thicker beneath medial moraines and where cold based hanging glaciers enter the main ice stream on uversbreen the thermal regime was similar to that of kongsvegen a temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between kongsvegen and uversbreen where meltwater accumulates during the summer near the subglacial lake setevatnet 250 m a s l lovenbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer up to 50m thick was fed by temperate ice from two cirques on austre broggerbreen a temperate basal layer was not detected by radio echo soundings but the basal ice was observed to be at the melting point in two boreholes

modeling the refreezing of meltwater as superimposed ice on a high arctic glacier a comparison of approaches 1 the refreezing of meltwater is known to be a critical factor when assessing the mass balance state of glaciers in the high arctic several different models of this process are widely used in numerical glacier simulations but as yet no attempt has been made to compare these approaches or to assess their relative performance against field measurements such models are likely to include implicit calibrations which may prove to be invalid under conditions different from those for which they were constructed we test a selection of six refreezing algorithms taken from the literature against field measurements of net mass balance and superimposed ice formation made at a high arctic glacier running these models for 1971 2002 using daily meteorological data and forward until 2050 using a range of future scenarios for the climate of svalbard we are able to make the following conclusions concerning mass balance modeling 1 the choice of meltwater refreezing model has a significant impact on the calculated net mass balance of a glacier 2 three of the models tested could with suitable tuning simultaneously reproduce both superimposed ice quantities and net mass balance measurements within their respective bounds of uncertainty while the other three could not 3 in situations where the model can be tuned to field measurements indicative of mass balance future predictions of mass balance are largely independent of the specific meltwater refreezing model used

wind and temperature retrievals in the 17 may 1981 arcadia oklahoma supercell ensemble kalman filter experiments abstract the feasibility of using an ensemble kalman filter enkf to retrieve the wind and temperature fields in an isolated convective storm has been tested by applying the technique to observations of the 17 may 1981 arcadia oklahoma tornadic supercell radial velocity and reflectivity observations from a single radar were assimilated into a nonhydrostatic anelastic numerical model initialized with an idealized horizontally homogeneous base state the assimilation results were compared to observations from another doppler radar the results of dual doppler wind syntheses and in situ measurements from an instrumented tower observation errors make it more difficult to assess enkf performance than in previous storm scale enkf experiments that employed synthetic observations and a perfect model nevertheless the comparisons in this case indicate that the locations of the main updraft and mesocyclone in the arcadia storm were determined rather accurately especially at midlevels the magnitudes of v

changes of glacier facies on hornsund glaciers svalbard during the decade 2007 2017 abstract changes in glacier facies glacier zones such as firn or superimposed ice si are good indicators of glacier response to climate change they are especially important for fast warming svalbard where only a few glaciers are under glaciological mass balance monitoring this paper presents a first study of changes of glacier facies extent for three tidewater glaciers located in southern spitsbergen svalbard and it is based on both satellite remote sensing and terrestrial data analysis covering two time spans 2007 2017 for hansbreen and 2012 2017 for storbreen and hornbreen satellite remote sensing analysis include unsupervised classification of synthetic aperture radar sar data from both decommissioned envisat asar and modern satellite missions radarsat 2 sentinel 1 the results of the sar classification are compared to the information on glacier zones retrieved from terrestrial data i e shallow cores and visual interpretation of 800 mhz ground penetrating radar gpr profiles in addition a novel application of the internal reflection power irp coefficient as an objective method of distinguishing glacier zones based on gpr data is discussed changes in glacier facies areas over time are analysed as well as their correlation to hansbreen s mass balance the main finding of the study is that firn and si of hansbreen storbreen and hornbreen significantly decreased over the study period for example due to continuous negative mass balance between 2010 and 2017 the contribution of firn area to hansbreen s total area decreased ca 14 cumulative firn area loss during that time 45 whereas since 2012 si has not been distinguished as a vast area on this glacier in addition an east west gradient of firn area loss was observed as a result of differences in local climate conditions therefore for the common time span i e 2012 2017 hansbreen recorded a ca 12 loss of firn contribution to glacier area whereas hornbreen recorded ca 9 finally application of the irp coefficient as an objective method of glacier zones discrimination by gpr data gave very good results so the method is recommended for future analysis of glacier zones instead or as a support to popular visual interpretation of the gpr profiles

measurement and simulation of snow and superimposed ice at the kongsvegen glacier svalbard spitzbergen 1 multiyear glaciometeorological data have been collected at about the equilibrium line of kongsvegen glacier in svalbard during the first summer of the investigation period about 0 6 m of superimposed ice si was built up because of effective meltwater refreeze upon the former glacier surface thus winter accumulation is completely retained from runoff and latent heat is released equivalent to 27 of july net radiation this ice layer as well as part of the former year s ice disappeared during the subsequent summer using a physically based snow model the evolution of the snow pack properties as well as the observed amount of si is successfully reproduced however the latter is only possible by modifying the model s water transport routine to also treat effects of ponding water which have been observed two distinct phases of si formation can be distinguished a first one 15 cm is initiated as soon as meltwater has penetrated to the underlying cold glacier ice toward the end of the melt period however the remaining body of si is rapidly formed because of intense atmospheric cooling the availability of ponding water plays an essential role in this context during the following summer the initial refreezing phase was terminated by exposure of the newly built si at the surface the whole amount of the actual year and the major part of the former year s si was melted then a positive ice albedo feedback process plays an additional role there sensitivity studies prove that the model results and their interpretation do not critically depend on possible uncertainties of input data and model parameters despite their local nature these studies are valuable steps toward understanding the regional distribution of si on arctic glaciers as well as their climate sensitivity remote sensing studies indicate that si presently covers 35 of kongsvegen s surface area

internal accumulation in firn and its significance for the mass balance of storglaciaren sweden the discussion on global change has led to increased interest in glacier mass balance since glaciers can be used as climatic indicators to meet the need for high quality mass balance data requires critical examination of traditional mass balance methods and their possible errors one issue regarding mass balance measurements that has received little attention is internal accumulation our study shows that internal accumulation in the firn layer of storglaciaren sweden significantly affects the mass balance of the glacier this occurs because the winter cold wave penetrates below the previous year s summer surface and into underlying firn we estimated internal accumulation from measurements of temperature and water content in firn the depth of the 0 c isotherm correlated with snow depth and air temperature so that low snow depth and low air temperature separately cause a deeper 0 c isotherm we determined irreducible gravimetric water content in firn to 2 3 which corresponds to an irreducible water saturation of 6 8 our value for firn is relatively high compared with that for snow probably due to trapped water in isolated firn pores refreezing of percolating meltwater in spring accounted for 30 of annual internal accumulation the remaining 70 was due to refreezing of retained capillary water in firn pores during winter disregarding internal accumulation would lead to underestimation of annual net mass balance by 0 04 0 06 m w e corresponding to 3 5 of annual accumulation of the entire glacier in an average year hence internal accumulation potentially becomes a source for systematic error if not accounted in mass balance measurements

using a low order model to detect and characterize tornadoes in multiple doppler radar data a new multiple doppler radar analysis technique is presented for the objective detection and characterization of tornado like vortices the technique consists of fitting radial wind data from two or more radars to a simple analytical model of a vortex and its near environment the model combines a uniform flow linear shear flow linear divergence flow all of which compose a broadscale flow and a modified combined rankine vortex representing the tornado the vortex and its environment are allowed to translate the parameters in the low order model are determined by minimizing a cost function that accounts for the discrepancy between the model and observed radial winds since vortex translation is taken into account the cost function can be evaluated over time as well as space and thus the observations can be used at the actual times and locations where they were acquired the technique is first tested using analytically simulated observations whose wind field and error characteristics are systematically varied an advanced regional prediction system arps high resolution numerical simulation of a supercell and associated tornado is then used to emulate an observation dataset the method is tested with two virtual radars for several radarsampling strategies finally the technique is applied to a dataset of real dual doppler observations of a tornado that struck central oklahoma on 8 may 2003 the method shows skill in retrieving the tornado path and radar grid scale features of the horizontal wind field in the vicinity of the tornado the best results are obtained using a two step procedure in which the broadscale flow is retrieved first

wind influence on snow depth distribution and accumulation over glaciers 1 in mountain regions wind is known to cause snow redistribution while physically based models of snow redistribution have been developed for flat to gently rolling terrain extension of these findings to steep terrain has been limited by the complexity of wind fields in such areas in this study we applied a nonhydrostatic and compressible atmospheric prediction model to steep alpine topography and compared the results to a fully distributed data set of snow depth estimations the results show reduced horizontal wind velocity as well as an increasing downward vertical wind velocity over areas with the largest winter accumulation which are mostly glacierized we show that the wind velocity normal to the local surface which should be zero in a nondivergent flow field and is a direct measure of increased or decreased local deposition is a function of small scale features of local topography the correlation between wind fields snow accumulation and glacierization suggests that accurate modeling of wind fields over glacierized areas in complex terrain is a key factor for understanding the mass balance distribution of glaciers