topographic controls on the surface energy balance of a high arctic valley glacier 1 this paper presents the results of a distributed two dimensional surface energy balance model used to investigate the spatial and temporal variations in the surface energy balance of midre lovenbreen a small valley glacier in northwest spitsbergen svalbard over the summer of 2000 we utilize high resolution airborne lidar data to derive a digital elevation model of the glacier and surrounding topography on which a surface energy balance is computed driven by meteorological data obtained from a meteorological station located on the glacier and a synoptic station maintained at the nearby ny alesund research base given the high resolution topographic data we focus particularly on whether the long duration of sunshine at high latitudes compensates for the higher solar zenith angles on the season long energy balance and whether shading by the surrounding topography plus glacier surface slope and aspect play an increased role in the patterns of solar radiation receipt and hence melt over the glacier surface the model results are validated using a combination of mass balance data from the glacier measured surface lowering at the glacier meteorological station and by comparing a derived energy balance component from the model with a measured energy flux overall the model performance is very good glacier topography is found to play a fundamental role in determining the surface energy balance topographic shading slope and aspect and correction of the surface albedo for high solar zenith angles are found to play a crucial role in determining spatial patterns of surface energy balance and therefore melt

modeling the instantaneous response of glaciers after the collapse of the larsen b ice shelf following the disintegration of the larsen b ice shelf antarctic peninsula in 2002 regular surveillance of its 20 tributary glaciers has revealed a response which is varied and complex in both space and time the major outlets have accelerated and thinned smaller glaciers have shown little or no change and glaciers flowing into the remnant scar inlet ice shelf have responded with delay in this study we present the first area wide numerical analysis of glacier dynamics before and immediately after the collapse of the ice shelf combining new datasets and a state of the art numerical ice flow model we simulate the loss of buttressing at the grounding line and find a good qualitative agreement between modelled changes in glacier flow and observations through this study we seek to improve confidence in our numerical models and their ability to capture the complex mechanical coupling between floating ice shelves and grounded ice

measurement and parameterization of albedo variations at haut glacier d arolla switzerland spatial and temporal variations of surface albedo on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described correlation and regression analyses are used to explain the albedo variations in terms of independent meteorological and surface property variables parameterizations are developed which allow estimation of albedo variation in surface energy balance models snow albedo is best estimated from accumulated daily maximum temperatures since snowfall on deep snow 0 5 cm w e depth a logarithmic function is used while on shallow snow 0 5 cm w e depth an exponential function is used to enable the albedo to decay to the underlying ice or debris albedo the transition from deep to shallow snow is calculated as a function of decreasing snow depth combined r 2 0 65 this new parameterization performs better than earlier schemes because accumulated daily maximum temperatures since snowfall correlate strongly with snow grain size and impurity concentration the main physical controls on snow albedo ice albedo may be parameterized by its relationship to elevation r 2 0 28 but this approach results in only a small improvement over the assumption of a constant mean ice albedo

modelling the evolution of supraglacial lakes on the west greenland ice sheet margin we present a model study investigating the summer evolution of supraglacial lakes on the greenland ice margin using a one dimensional 1 d model we calculate the surface ablation for a bare ice surface and beneath supraglacial lakes for 30 days in the summers of 1999 and 2001 the surface ablation beneath the lake was enhanced by 110 in 1999 and 170 in 2001 compared with the ablation for bare ice we then use the results from the 1 d model to further model the vertical and horizontal evolution of the supraglacial lakes the results of which are compared with satellite images within the region of the ice sheet where supraglacial lakes presently occur the area covered by supraglacial lakes is found to be more or less independent of the summer melt rate but controlled by topography we therefore predict that inside this region the area covered by supraglacial lakes will remain constant even in a warmer climate however in a warmer climate surface melting will occur higher on the ice sheet where small surface slopes favour formation of large supraglacial lakes enhanced surface melting beneath such lakes is a hitherto overlooked feedback mechanism related to climate warming

melting runoff and the formation of frozen lakes in a mixed snow and blue ice field in dronning maud land antarctica large scale melting phenomena such as meltwater drainage channels and meltwater accumulation basins of frozen lakes were surveyed on the land ice mass in jutulgryta dronning maud land antarctica during the norwegian antarctic research expedition in 1989 90 nare 1989 90 the largest frozen lake that was observed was close to 1 km in width these melting features were also detected in a landsat thematic mapper image recorded on 12 february 1990 then during nare 1993 94 a 5year glaciological programme was started in this area in spite of negative air temperatures and the presence of a frozen ice surface sub surface melting and runoff were found within the uppermost metre in blue ice fields the sub surface melting is a consequence of solar radiative penetration and absorption within the ice i e the solid state greenhouse effect temperatures in blue ice were about 6 c higher than for snow internal melt and meltwater transport were observed throughout the 1 month of measurements the conditions for active melting in jutulgryta are probably marginal a slight increase of air temperatures can result in more classical surface melting whereas a cooling may disable sub surface melting studies of how the extent and characteristics of the melting features change with time can be particularly valuable as indicators of climate change this ongoing programme clearly identifies the importance of analyzing how these melting features originate of mapping their present areal distribution of determining how sensitive they are to climate change and of studying changes in the past and possible changes in the future

supraglacial lakes on the larsen b ice shelf antarctica and at paakitsoq west greenland a comparative study we acknowledge the support of the u s national science foundation under grant ant 0944248

suitability of a constant air temperature lapse rate over an alpine glacier testing the greuell and bohm model as an alternative near surface air temperature typically measured at a height of 2 m is the most important control on the energy exchange and the melt rate at a snow or ice surface it is distributed in a simplistic manner in most glacier melt models by using constant linear lapse rates which poorly represent the actual spatial and temporal variability of air temperature in this paper we test a simple thermodynamic model proposed by greuell and bohm in 1998 as an alternative using a new dataset of air temperature measurements from along the flowline of haut glacier d arolla switzerland the unmodified model performs little better than assuming a constant linear lapse rate when modified to allow the ratio of the boundary layer height to the bulk heat transfer coefficient to vary along the flowline the model matches measured air temperatures better and a further reduction of the root mean square error is obtained although there is still considerable scope for improvement the modified model is shown to perform best under conditions favourable to the development of katabatic winds few clouds positive ambient air temperature limited influence of synoptic or valley winds and a long fetch but its performance is poor under cloudy conditions

spatial distribution of surface ablation in the terminus of rhonegletscher switzerland the spatial pattern of glacier surface melt was measured with a resolution of 20 100 m within a region extending 1 km up glacier from the terminus of rhonegletscher switzerland the melt rate was monitored from 6 july to 6 september 2009 using 44 ablation stakes we also measured the surface albedo near the stakes to investigate the importance of this parameter for the melt rate distribution the melt rate varied from 32 8 to 71 9 mm w e d 1 in the study area our measurements suggest that the spatial variation of the melt rate can be explained by 1 shading of the ice surface by neighbouring mountains 2 surface albedo and 3 effects of microclimate e g radiation from side walls on the surface energy balance the observed melt rate distribution was compared to the results of a temperature index melt model which takes into account shading of direct solar illumination but not the other two effects the model reproduces some important features of the field data but its spatial variations are generally less than the measured values our study shows the importance of albedo and other local conditions in the accurate estimation of the small scale melt rate distribution

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

calibration and evaluation of a high resolution surface mass balance model for paakitsoq west greenland modelling the hydrology of the greenland ice sheet including the filling and drainage of supraglacial lakes requires melt inputs generated at high spatial and temporal resolution here we apply a high spatial 100 m and temporal 1 hour mass balance model to a 450 km 2 subset of the paakitsoq region west greenland the model is calibrated by adjusting the values for parameters of fresh snow density threshold temperature for solid liquid precipitation and elevation dependent precipitation gradient to minimize the error between modelled output and surface height and albedo measurements from three greenland climate network stations for the mass balance years 2000 01 and 2004 05 best fit parameter values are consistent between the two years at 400 kg m 3 28c and 14 100 m 1 respectively model performance is evaluated first by comparing modelled snow and ice distribution with that derived from landsat 7 etm satellite imagery using normalized difference snow index classification and supervised image thresholding and second by comparing modelled albedo with that retrieved from the modis sensor mod10a1 product calculation of mass balance components indicates that 6 of surface meltwater and rainwater refreezes in the snowpack and does not become runoff such that refreezing accounts for 31 of the net accumulation

below surface ice melt on the coastal antarctic ice sheet in the jutulgryta area of dronning maud land antarctica subsurface melting of the ice sheet has been observed the melting takes place during the summer months in blue ice areas under conditions of below freezing air and surface temperatures adjacent snow covered regions having the same meteorological and climatic conditions experience little or no subsurface melting to help explain and understand the observed melt rate differences in the blue ice and snow covered areas a physically based numerical model of the coupled atmosphere radiation snow and blue ice system has been developed the model comprises a heat transfer equation which includes a spectrally dependent solar radiation source term the penetration of radiation into the snow and blue ice depends on the solar radiation spectrum the surface albedo and the snow and blue ice grain sizes and densities in addition the model uses a complete surface energy balance to define the surface boundary conditions it is run over the full annual cycle simulating temperature profiles and melting and freezing quantities throughout the summer and winter seasons the model is driven and validated using field observations collected during the norwegian antarctic research expedition nare 1996 97 the simulations suggest that the observed differences between subsurface snow and blue ice melting can be explained largely by radiative and heat transfer interactions resulting from differences in albedo grain size and density between the two mediums

breakup of the larsen b ice shelf triggered by chain reaction drainage of supraglacial lakes this research is supported by the u s national science foundation under grant geop ant 0944248 awarded to d r m and grants ant 0838811 and arc 0934534 awarded to o v s

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

areal melt and discharge modelling of storglaciaren sweden a grid based glacier melt and discharge model was applied to storglaciaren a small valley glacier 3 km 2 in northern sweden for the melt seasons of 1993 and 1994 the energy available for melt was estimated from a surface energy balance model using meteorological data collected by automatic weather stations on the glacier net radiation and the turbulent heat fluxes were calculated hourly for every grid point of a 30 m resolution digital terrain model using the measurements of temperature humidity wind speed and radiative fluxes on the glacier two different bulk approaches were used to calculate the turbulent fluxes and compared with respect to their impact on discharge simulations discharge of storglaciaren was simulated from calculated meltwater production and precipitation by three parallel linear reservoirs corresponding to the different storage properties of firn snow and ice the performance of the model was validated by comparing simulated discharge to measured discharge at the glacier snout depending on which parameterization of the turbulent fluxes was used the timing and magnitude of simulated discharge was in good agreement with observed discharge or simulated discharge was considerably underestimated in one year

glacier bed characteristics of midtre lovenbreen svalbard from high resolution seismic and radar surveying we conducted a seismic and radar survey of the central part of midtre lovenbreen a small polythermal valley glacier in svalbard we determined the physical properties of the material beneath the glacier by measuring the reflection coefficient of the bed by comparing the energy of the primary and multiple reflections and deriving the acoustic impedance by making reasonable assumptions about the properties of the basal ice we determined the acoustic impedance of the bed material as 6 78 1 53 x 10 6 kg m 2 s 1 we interpret the material beneath the glacier to be permafrost with up to 50 ice and we speculate that the material may be frozen talus similar to a deposit observed directly by others beneath another svalbard glacier the implication for midtre lovenbreen is that the basal material beneath the present glacier is not able to support fast flow we conclude that midtre lovenbreen has most likely had limited capability for faster flow in the past with motion dominated by internal deformation midtre lovenbreen is used as a study glacier for the scientific community in svalbard and a large number of studies have been based there our results show that it cannot be used as an analogue for larger glaciers in svalbard having distinct basal boundary conditions

reconstruction of former glacier surface topography from archive oblique aerial images abstract archive oblique aerial imagery offers the potential to reconstruct the former geometry of valley glaciers and other landscape surfaces whilst the use of structure from motion sfm photogrammetry with multiview stereopsis mvs to process small format imagery is now well established in the geosciences the potential of the technique for extracting topographic data from archive oblique aerial imagery is unclear here sfm mvs is used to reconstruct the former topography of two high arctic glaciers midtre and austre lovenbreen svalbard norway using three archive oblique aerial images obtained by the norwegian polar institute in 1936 the 1936 point cloud was produced using seven lidar derived ground control points located on stable surfaces in proximity to the former piedmont glacier termini to assess accuracy the 1936 data set was compared to a lidar data set using the m3c2 algorithm to calculate cloud to cloud differences for stable areas such as nonglacial surfaces vertical differences were detected between the two point clouds rms m3c2 vertical difference of 8 5 m with the outwash zones adjacent to the assessed glacier termini showing less extensive vertical discrepancies 94 of m3c2 vertical differences between 5 m this research highlights that historical glacier surface topography can be extracted from archive oblique aerial imagery but accuracy is limited by issues including the lack of camera calibration the quality and resolution of the archive imagery and by the identification of suitable ground control to demonstrate the value of historical glacier surfaces produced using oblique archive imagery the reconstructed glacier surface topography is used to investigate evidence of a potential former surge front at the high arctic valley glacier austre lovenbreen a glacier identified to have potentially exhibited surge type behaviour during the neoglacial a surface bulge of 15 20 m is resolved on the 1936 model however when compared with the now deglaciated former subglacial topography a surge origin for the surface feature becomes unclear the processed 1936 oblique imagery was also used to produce orthorectified nadir aerial imagery from which structural mapping was undertaken this adds to the existing 1948 1995 structural map series for these glaciers this research demonstrates the potential of sfm mvs for reconstructing historical glacier surfaces which is important for aiding our understanding of former glacier dynamics and enabling the rapid assessment of glacier change over time

parameter uncertainty refreezing and surface energy balance modelling at austfonna ice cap svalbard 2004 08 we apply a physically based coupled surface energy balance and snowpack model to a site close to the equilibrium line on austfonna ice cap svalbard over the 2004 08 melt seasons to explain contributions to the energy available for melting and to quantify the significance of refreezing the model is forced using in situ meteorological measurements and precipitation downscaled from erainterim reanalysis applying a monte carlo approach to determine the tunable parameters of the model we estimate the uncertainty related to the choice of parameter values multiple criteria are evaluated to identify well performing parameter combinations evaluating the model performance with respect to longwave outgoing radiation snow and ice temperatures and surface displacement on average over the investigated melt seasons 1 june to 15 september net radiation and sensible heat contributed 90 2 and 10 2 respectively to the mean energy available for melting snow and ice the energy consumed by subsurface heat exchange reduced runoff by 15 2 in 2004 and 49 3 in 2008 refreezing of meltwater and rain was estimated to be 0 37 0 04mw e a 1on average over the five seasons which represents a considerable reduction of mass loss during summer our findings suggest that refreezing potentially exerts a decisive control on glacier mass balance in persistently snow or firncovered areas

application of borehole optical televiewing to investigating the 3 d structure of glaciers implications for the formation of longitudinal debris ridges midre lovenbreen svalbard digital optical televiewing optv of hot water drilled boreholes is evaluated as a technique for the investigation of englacial ice and debris structures on the basis of six boreholes drilled in the terminus region of midre lovenbreen svalbard the resulting optv logs successfully reveal several visually distinctive englacial ice properties and deformation structures e g oblique englacial fractures imaged here for the first time combining these optv logs with surface mapping has resulted in the identification of eight separate structural elements several of which can be interpolated onto 3 d grids at a node spacing of 1 m vertically and 10 m horizontally basally derived englacial sediment layers are also found to be intercalated with primary stratification elevated into near vertical planes around a central fold axis by large scale lateral folding the analysis also allows supraglacial longitudinal debris ridges to be subclassified into two types a previously described type i form which are the exposed fold axes of large scale lateral folds and a new type ii form experiencing secondary deformation by small scale horizontal folding in association with vertical displacements across arcuate shear planes in response to longitudinally compressive stresses near the glacier terminus although using boreholes to investigate glacier structure is limited e g by parallelism with vertical planes applying optv to multiple boreholes at midre lovenbreen has successfully revealed a range of 3 d structural elements at high spatial resolution as such interpolating between multiple optv logs overcomes many of the problems associated with interpretations made solely on the basis of surface based structural mapping and combining the two techniques represents a powerful glaciological tool

influence of persistent wind scour on the surface mass balance of antarctica in the antarctic interior assessments of surface mass balance may overestimate accumulation because high winds remove some of the annual snowfall geophysical observations reveal localized zones of persistent wind scour where little or no snow accumulates that are predicted to occur across approximately 5 of the antarctic surface accurate quantification of surface snow accumulation over antarctica is a key constraint for estimates of the antarctic mass balance as well as climatic interpretations of ice core records1 2 over antarctica near surface winds accelerate down relatively steep surface slopes eroding and sublimating the snow this wind scour results in numerous localized regions 200 km2 with reduced surface accumulation3 4 5 6 7 estimates of antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes and overestimate the net mass input in wind scour zones3 here we combine airborne radar observations of unconformable stratigraphic layers with lidar derived surface roughness measurements to identify extensive wind scour zones over dome a in the interior of east antarctica the scour zones are persistent because they are controlled by bedrock topography on the basis of our dome a observations we develop an empirical model to predict wind scour zones across the antarctic continent and find that these zones are predominantly located in east antarctica we estimate that 2 7 6 6 of the surface area of antarctica has persistent negative net accumulation due to wind scour which suggests that across the continent the snow mass input is overestimated by 11 36 5 gt yr 1 in present surface mass balance calculations

surface temperature lapse rates over complex terrain lessons from the cascade mountains lapse rates of 3 9 5 2 c km 1 substantially smaller than the often assumed 6 5 c km 1 the data sets show similar seasonal and diurnal variability with lapse rates smallest 2 5 3 5 c km 1 in late summer minimum temperatures and largest 6 5 7 5 c km 1 in spring maximum temperatures geographic windward versus lee side differences in lapse rates are found to be substantial using a simple runoff model we show the appreciable implications of these results for hydrological modeling

widespread movement of meltwater onto and across antarctic ice shelves surface water and its drainage across the surface of antarctic ice is shown to be widespread large scale and to have persisted for decades melt ponds and streams form across antarctica but their full extent and the duration of their existence have remained unclear now jonathan kingslake et al show that surface drainage systems including interconnected ponds and streams have existed for decades as far as 85 s and up to 1 300 metres elevation they show that surface water can be transported more than 100 kilometres creating pond networks almost 80 kilometres long although the implications of the findings for ice sheet dynamics are not explored the study demonstrates that surface water drainage is more extensive than previously thought and is probably a persistent feature of the antarctic ice sheet elsewhere in this issue robin bell et al report on the influence of surface meltwater on antarctic ice shelf stability and find that it might not be a universally destructive force as was previously thought surface meltwater drains across ice sheets forming melt ponds that can trigger ice shelf collapse1 2 acceleration of grounded ice flow and increased sea level rise3 4 5 numerical models of the antarctic ice sheet that incorporate meltwater s impact on ice shelves but ignore the movement of water across the ice surface predict a metre of global sea level rise this century5 in response to atmospheric warming6 to understand the impact of water moving across the ice surface a broad quantification of surface meltwater and its drainage is needed yet despite extensive research in greenland7 8 9 10 and observations of individual drainage systems in antarctica10 11 12 13 14 15 16 17 we have little understanding of antarctic wide surface hydrology or how it will evolve here we show widespread drainage of meltwater across the surface of the ice sheet through surface streams and ponds hereafter surface drainage as far south as 85 s and as high as 1 300 metres above sea level our findings are based on satellite imagery from 1973 onwards and aerial photography from 1947 onwards surface drainage has persisted for decades transporting water up to 120 kilometres from grounded ice onto and across ice shelves feeding vast melt ponds up to 80 kilometres long large scale surface drainage could deliver water to areas of ice shelves vulnerable to collapse as melt rates increase this century while antarctic surface melt ponds are relatively well documented on some ice shelves we have discovered that ponds often form part of widespread large scale surface drainage systems in a warming climate enhanced surface drainage could accelerate future ice mass loss from antarctic potentially via positive feedbacks between the extent of exposed rock melting and thinning of the ice sheet

a simple energy balance model to calculate ice ablation at the margin of the greenland ice sheet apres avoir etabli les relations donnees climatiques taux d enlevement de la glace dans 2 glaciers du groenland un modele simple de bilan energetique est effectue pour calculer le taux d enlevement de la glace aux bordures du glacier

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

spatio temporal variability in elevation changes of two high arctic valley glaciers uncertainties in estimates of glacier and ice cap contribution to sea level rise exist in part due to poor quantification of mass balance errors particularly those resulting from extrapolation of sparse measurements centre line data are often assumed to be representative of the glacier as a whole with little attention paid to extrapolation errors or their effect on mass balance estimates here we present detailed digital elevation model dem measurements of glacier wide elevation changes over the last 40 years at two glaciers on svalbard norwegian arctic austre broggerbreen and midtre lovenbreen are shown to have lost 27 54 0 98 and 9 65 0 76 10 7 m 3 of ice respectively between 1966 and 2005 findings that we relate to trends in average summer air temperatures and winter accumulation these volume losses correspond to geodetic balances of 0 58 0 03 and 0 41 0 03 m w e a 1 respectively our analysis revealed high spatial complexity in patterns of elevation change varying between glaciers between measurement intervals and within and between elevation bins balances from extrapolated centre line geodetic data were the same within errors as those from full coverage dem differencing in the majority of comparisons yet significantly underestimated balance in three instances additionally field mass balance from centre line ablation stake data underestimated balances from full coverage geodetic measurements during three of six measurement periods these findings may support the hypothesis that field measurements under estimate svalbard glacier mass loss at least partly as a result of the failure of centre line measurements to account for glacier wide variations in ablation our results demonstrate the importance of deriving accurate interpolation functions and constraining extrapolation errors from sparse measurements

spatial and temporal variability of air temperature on a melting glacier atmospheric controls extrapolation methods and their effect on melt modeling juncal norte glacier chile 1 temperature data from three automatic weather stations and twelve temperature loggers are used to investigate the spatiotemporal variability of temperature over a glacier its main atmospheric controls the suitability of extrapolation techniques and their effect on melt modeling we use data collected on juncal norte glacier central chile during one ablation season we examine temporal and spatial variability in lapse rates lrs together with alternative statistical interpolation methods the main control over the glacier thermal regime is the development of a katabatic boundary layer kbl katabatic wind occurs at night and in the morning and is eroded in the afternoon lrs reveal strong diurnal variability with steeper lrs during the day when the katabatic wind weakens and shallower lrs during the night and morning we suggest that temporally variable lrs should be used to account for the observed change they tend to be steeper than equivalent constant lrs and therefore result in a reduction in simulated melt compared to use of constant lrs when extrapolating from lower to higher elevations in addition to the temporal variability the temperature elevation relationship varies also in space differences are evident between local lrs and including such variability in melt modeling affects melt simulations extrapolation methods based on the spatial variability of the observations after removal of the elevation trend such as inverse distance weighting or kriging do not seem necessary for simulations of gridded temperature data over a glacier

measuring glacier surface roughness using plot scale close range digital photogrammetry glacier roughness at sub metre scales is an important control on the ice surface energy balance and has implications for scattering energy measured by remote sensing instruments ice surface roughness is dynamic as a consequence of spatial and temporal variation in ablation to date studies relying on singular and or spatially discrete two dimensional profiles to describe ice surface roughness have failed to resolve common patterns or causes of variation in glacier surface morphology here we demonstrate the potential of close range digital photogrammetry as a rapid and cost effective method to retrieve three dimensional data detailing plot scale supraglacial topography the photogrammetric approach here employed a calibrated consumer grade 5 mpix digital camera repeatedly imaging a plot scale 25 m2 ice surface area on midtre lovenbreen svalbard from stereo pair images digital surface models dsms with sub centimetre horizontal resolution and 3 mm vertical precision were achieved at plot scales 4 m2 extraction of roughness metrics including estimates of aerodynamic roughness length z 0 was readily achievable and temporal variations in the glacier surface topography were captured close range photogrammetry with appropriate camera calibration and image acquisition geometry is shown to be a robust method to record sub centimetre variations in ablating ice topography while the dsm plot area may be limited through use of stereo pair images and issues of obliquity emerging photogrammetric packages are likely to overcome such limitations

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

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

meteorological conditions over antarctic blue ice areas and their influence on the local surface mass balance this paper addresses the causes of the prevailing meteorological conditions observed over an antarctic blue ice area and their effect on the surface mass balance over blue ice areas net accumulation is zero and ablation occurs mainly through sublimation sublimation rates are much higher than over adjacent snowfields the meteorological conditions favourable for high sublimation rates warm dry and gusty are due to the specific orographic setting of this blue ice area with usually a steep upwind mountainous slope causing strong adiabatic heating diabatic warming due to radiation and entrainment of warm air from aloft into the boundary layer augment the warming the prevailing warm dry conditions explain roughly 50 of the difference in sublimation and the different characteristics of blue ice mainly its lower albedo the other 50 most of the annual sublimation 70 takes place during the short summer mainly in daytime with winter ablation being restricted to occasional warm dry fohn like events the additional moisture is effectively removed by entrainment and horizontal advection which are maximum over the blue ice area low frequency turbulent motions induced by the upwind mountains enhance the vertical turbulent transports strong gusts and high peak wind speeds over blue ice areas cause high potential snowdrift transports which can easily remove the total precipitation thereby maintaining zero accumulation

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

sensitivity of mass balance of five swiss glaciers to temperature changes assessed by tuning a degree day model a degree day model is used to assess the sensitivity of the mass balance of five swiss glaciers to temperature changes the model uses temperature data extrapolated from nearby climate stations and is tuned by varying precipitation to make the model fit the observed distribution of mass balance with altitude once the model is tuned the effect of temperature change is simulated by recalculating the mass balance with the same parameters as before but with a temperature increase of 1 c throughout the year the largest mass balance changes involving increased ablation of 1 m w e a 1 c 1 occur at the snout with a progressively smaller increase with altitude the area averaged sensitivities for the five glaciers are 0 7 to 0 9 m w e a 1 c 1 if annual precipitation also increased by 20 it would partly offset the effect of the 1 c higher temperatures but could not compensate for it

glacial topographic interactions in the teton range wyoming 1 understanding interactions among tectonics topography climate and erosion is fundamental to studies of mountainous landscapes here we combine topographic analyses with modeled distributions of precipitation insolation and flexural isostasy to present a conceptual model of topographic evolution in the teton range wyoming and test whether efficient glacial relief production has contributed to summit elevations the conceptual model reveals a high degree of complexity inherent in even a relatively small glaciated mountain range back tilting has caused topographic asymmetry with the greatest relief characterizing eastern catchments in the center of the range two high summits grand teton and mount moran rise hundreds of meters above the surrounding landscape their elevations set by the threshold hillslope angle and the spacing between valleys hosting large erosionally efficient glaciers only basins 20 km2 held glaciers capable of eroding sufficiently rapidly to incise deeply and maintain shallow downvalley gradients on the eastern range flank glacial erosion here was promoted by 1 prevailing westerly winds transporting snow to high relief eastern basins leading to cross range precipitation asymmetry 2 the wind blown redistribution of snow from open western headwaters into sheltered eastern cirques with the associated erosion driven migration of the drainage divide increasing eastern accumulation areas and 3 tall steep hillslopes providing shading snow influx from avalanching and insulating debris cover from rockfalls to valley floor glaciers in comparison the topographic enhancement of glacial erosion was less pronounced in western and smaller eastern basins despite dramatic relief production insufficient rock mass is removed from the teton range to isostatically raise summit elevations

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

high resolution mapping of supra glacial drainage pathways reveals link between micro channel drainage density surface roughness and surface reflectance this paper reports on the use of a small unmanned aerial vehicle suav carrying a standard compact camera to construct a high resolution orthomosaic om and digital elevation model dem over the lower reaches of the glacier midtre lovenbreen svalbard structure from motion sfm techniques were used to build the om and dem and together these reveal insights into the nature of supra glacial drainage major meandering supra glacial drainage pathways show clear dynamism via meander cutoffs and abandoned channels in addition the imagery reveals a very extensive network of smaller channels that may well carry substantial amounts of water this network of channels is in part controlled by the structure of the glacier but in turn these channels have a significant impact on the ice surface roughness of the ice surface is higher where channels are most extensive in addition we find a relationship between channel density and surface reflectance such that greater channel density is associated with lower reflectance values given the role of surface reflectance and roughness in the energy balance of glaciers it is therefore apparent that extensive networks of small supra glacial channels across such glaciers have the potential to have an important impact on energy exchanges between the atmosphere and the ice surface copyright 2015 john wiley sons ltd

a distributed surface energy balance model for a small valley glacier i development and testing for haut glacier d arolla valais switzerland this paper describes the development and testing of a distributed surface energy balance model used to calculate rates of surface melting at haut glacier d arolla valais switzerland the model uses a digital elevation model dem of the glacier surface and surrounding topography together with meteorological data collected at a site in front of the glacier to determine hourly or daily totals of the energy balance components and hence of melting over the entire surface of the glacier with a spatial resolutio of 20 m the model can also be used to determine temporal and spatial variations in snow depth snow line position and glacier surface albedo calculations from the model are compared with observations made along the glacier centre line in 1990 and in general the model performs very well the correlation coefficients between calculated and measured snow line elevation albedo and ablation are 0 99 0 85 and 0 81 respectively the main source of error between modelled and measured values of these variables is probably inadequacies in the parameterization of albedo used in the model

modeling surface roughness solar ablation feedback application to small scale surface channels and crevasses of the greenland ice sheet surface roughness enhances the net ablation rate associated with direct solar radiation relative to smooth surfaces because roughness allows solar energy reflected from one part of the surface to be absorbed by another part in this study we examine the feedback between solar radiation driven ablation and growth of surface roughness on the greenland ice sheet using a numerical model of radiative transfer our experiments extend previous work by examining 1 the effects of diurnal and seasonal variation of solar zenith angle and azimuth relative to incipient roughness features 2 the evolution of roughness geometry in response to radiatively driven ablation and 3 the relative solar energy collection efficiencies of various roughness geometries and geographic locations and orientations a notable result of this examination is that the time evolution of the aspect ratio of surface features under solar driven ablation collapses onto a roughly universal curve that depends only on latitude not the detailed shape of the feature the total enhancement of surface melt relative to a smooth surface over a full ablation season varies with this ratio and this dependence suggests a way to parameterize roughness effects in large scale models that cannot treat individual roughness features overall our model results suggest that surface roughness at the latitudes spanned by the greenland ice sheet tends to dissipate as the ablation season progresses

including debris cover effects in a distributed model of glacier ablation 1 distributed glacier melt models generally assume that the glacier surface consists of bare exposed ice and snow in reality many glaciers are wholly or partially covered in layers of debris that tend to suppress ablation rates in this paper an existing physically based point model for the ablation of debris covered ice is incorporated in a distributed melt model and applied to haut glacier d arolla switzerland which has three large patches of debris cover on its surface the model is based on a 10 m resolution digital elevation model dem of the area each glacier pixel in the dem is defined as either bare or debris covered ice and may be covered in snow that must be melted off before ice ablation is assumed to occur each debris covered pixel is assigned a debris thickness value using probability distributions based on over 1000 manual thickness measurements locally observed meteorological data are used to run energy balance calculations in every pixel using an approach suitable for snow bare ice or debris covered ice as appropriate the use of the debris model significantly reduces the total ablation in the debris covered areas however the precise reduction is sensitive to the temperature extrapolation used in the model distribution because air near the debris surface tends to be slightly warmer than over bare ice overall results suggest that the debris patches which cover 10 of the glacierized area reduce total runoff from the glacierized part of the basin by up to 7

daily air temperature estimation on glacier surfaces in the tibetan plateau using modis lst data the moderate resolution imaging spectroradiometer modis land surface temperature lst data have been widely used for air temperature estimation in mountainous regions where station observations are sparse however the performance of modis lst in high elevation glacierized areas remains unclear this study investigates air temperature estimation in glacierized areas based on ground observations at four glaciers across the tibetan plateau before being used to estimate the air temperature modis lst data are evaluated at two of the glaciers which indicates that modis night time lst is more reliable than modis daytime lst data then linear models based on each of the individual modis lst products from two platforms terra and aqua and two overpasses night time and daytime are built to estimate daily mean minimum and maximum air temperatures in glacierized areas regional glacier surface rgs models mean mean square differences 3 3 3 0 and 4 8 c for daily mean minimum and maximum air temperatures respectively show higher accuracy than local non glacier surface models mean root mean square differences 4 2 4 7 and 5 7 c in addition the rgs models based on modis night time lst perform better to estimate daily mean minimum and maximum air temperatures than using temperature lapse rate derived from local stations

air temperature distribution and energy balance modelling of a debris covered glacier near surface air temperature is an important determinant of the surface energy balance of glaciers and is often represented by a constant linear temperature gradients tgs in models spatiotemporal variability in 2 m air temperature was measured across the debris covered miage glacier italy over an 89 d period during the 2014 ablation season using a network of 19 stations air temperature was found to be strongly dependent upon elevation for most stations even under varying meteorological conditions and at different times of day and its spatial variability was well explained by a locally derived mean linear tg mg tg of 0 0088 c m 1 however local temperature depressions occurred over areas of very thin or patchy debris cover the mg tg together with other air tgs extrapolated from both on and off glacier sites were applied in a distributed energy balance model compared with piecewise air temperature extrapolation from all on glacier stations modelled ablation using the mg tg increased by 4 using the environmental lapse rate ice melt under thick debris was relatively insensitive to air temperature while the effects of different temperature extrapolation methods were strongest at high elevation sites of thin and patchy debris cover

comparison of mass balances for vernagtferner oetzal alps as obtained from direct measurements and distributed modeling the direct comparison of modeled glacier mass balance distribution with field measure ments could be problematic as the methodology of determination and the processes considered at the point or catchment scale could differ strongly moreover direct measurements cover only small parts of a glacier and model performance is thus difficult to assess outside these regions remaining opportunities for model validation include comparison of snowlines as derived from remote sensing data and maps of the mass balance distribution as interpreted by observers with local knowledge this study compares such hand drawn maps of the vernagtferner oetzal alps mass balance with the modeled pattern as obtained from a distributed energy mass balance model of intermediate complexity the model is driven by measured daily values of temperature global radiation and precipitation from a nearby climate station and grids of mean daily potential global radiation and climatologic annual precipitation sums compared with the direct measurements the calculated mean mass balance and equilibrium line altitude agreed very well in both balance years although the spatial pattern of the mass balance distribution displayed larger deviations in regions influenced by snowdrift or local topographic undulations however compared with the remaining snow as visible on a satellite image from 1999 the modeled snowline pattern for a larger sample of glaciers is in very good agreement

climatogenic north south asymmetry of local glaciers in spitsbergen and other parts of the arctic although world glacier inventory wgi data for 241 local glaciers 1 km 2 in area in svalbard show a mean aspect of 014 24 their mid altitudes are lowest for an aspect of 109 46 which is inconsistent further data are generated here for the altitude length and source aspect of 205 local glaciers 0 3 6 0 km long in the main area of local glaciation in svalbard nordenskiold land all four mountain blocks have mean glacier source aspects of 356 to 018 the overall mean is 011 8 mid altitudes are lowest at 042 21 predicted to be 53 m lower than on opposite aspects lowest altitudes are predicted at 009 to 030 averaging 157 m lower than on opposite aspects these results show that local land terminating glaciers around 78 n are affected more by north south radiation receipt contrasts than by wind effects consistent with the trend found across most other arctic regions it is concluded that although weaker than in mid latitudes contrasts due to slope climates are substantial even in arctic glaciers this is apparent only when small steep glaciers are inventoried wgi data are incomplete and users need to check the thresholds of coverage

aerodynamic roughness of glacial ice surfaces derived from high resolution topographic data this paper presents new methods of estimating the aerodynamic roughness z0 of glacier ice directly from three dimensional point clouds and digital elevation models dems examines temporal variability of z0 and presents the first fully distributed map of z0 estimates across the ablation zone of an arctic glacier the aerodynamic roughness of glacier ice surfaces is an important component of energy balance models and meltwater runoff estimates through its influence on turbulent fluxes of latent and sensible heat in a warming climate these fluxes are predicted to become more significant in contributing to overall melt volumes ice z0 is commonly estimated from measurements of ice surface microtopography typically from topographic profiles taken perpendicular to the prevailing wind direction recent advances in surveying permit rapid acquisition of high resolution topographic data allowing revision of assumptions underlying conventional z0 measurement using structure from motion sfm photogrammetry with multi view stereo mvs to survey ice surfaces with millimeter scale accuracy z0 variation over 3 orders of magnitude was observed different surface types demonstrated different temporal trajectories in z0 through 3 days of intense melt a glacier scale 2 m resolution dem was obtained through terrestrial laser scanning tls and subgrid roughness was significantly related to plot scale z0 thus we show for the first time that glacier scale tls or sfm mvs surveys can characterize z0 variability over a glacier surface potentially leading to distributed representations of z0 in surface energy balance models

modelling seasonal and spatial variations in the surface energy balance of haut glacier d arolla switzerland the impact of spatial and temporal variations in the surface albedo and aerodynamic roughness length on the surface energy balance of haut glacier d arolla switzerland was examined using a semi distributed surface energy balance model arnold and others 1996 the model was updated to incorporate the glacier wide effects of albedo and aerodynamic roughness length variations using parameterizations following brock 1997 after the model s performance was validated the glacier wide patterns of the net shortwave turbulent and melt energy fluxes were examined on four days representative of surface conditions in late may june july and august in the model meteorological conditions were held constant on each day in order that the impact of albedo and aerodynamic roughness length variations could be assessed independently a late summer snowfall event was also simulated albedo and aerodynamic roughness length variations particularly those associated with the migration of the transient snowline and the decay of the winter snowpack were found to exert a strong influence on the magnitude of the surface energy fluxes the importance of meteorological conditions in suppressing the surface energy fluxes and melt rate following a fresh snowfall was highlighted

changes in clemenceau icefield and chaba group glaciers canada related to hypsometry tributary detachment length slope and area aspect relations we compiled a detailed glacier inventory of 176 glaciers in the clemenceau icefield group cig and adjacent chaba group ch canada based on 2001 landsat 7 and 2000 03 aster satellite imagery and natural resources canada digital elevation models we used this inventory to measure length and mass balance changes and their possible controls a classification of glacier hypsometry in the form of a hypsometric index was used to assess the sensitivity of different glacier systems to a unit rise in snowline the altitude and aar of possible steady state elas was derived using several methods and was compared to late summer snowlines of 2001 we further compared planar glacier area to slope corrected area and compared the effects on the shape of the hypsometric curves on the total glacier area and on the aspect area distribution in 2001 cig had a glaciated area of 271 km 2 and had lost 42 km 2 since the mid 1980s ch had a total area of 69 km 2 and had lost 28 km 2 average retreat rates are 14 m a 1 for the period 1850 2001 n 39 and 21 m a 1 for 1986 87 2001 n 23 indicating accelerated retreat larger glaciers and those that experience tributary detachment tend to retreat faster the difference between planar and slope corrected glacier areas ranges from 5 to 20 with a 6 increase for the entire cig ch region the area increase does not change the shape of the hypsometric curves

self similarity in glacier surface characteristics catchment wide information on glacier snow cover depth surface albedo and surface roughness is important input data for distributed models of glacier energy balance in this study we investigate the small scale mm to 100 m spatial variability in these properties with a view to better simulating this variability in such models data were collected on midre lovenbreen a 6 km 2 valley glacier in northwest svalbard the spatial variability of all three properties was found to be self similar over the range of scales under investigation snow depth and albedo exhibit a correlation length within which measurements were spatially autocorrelated late winter and summer properties of snow depth differed with smaller depths in summer due to melt and shorter correlation lengths similar correlation lengths for snow depth and surface albedo may suggest that snow depth variation is an important control on the small scale spatial variability of glacier surface albedo for surface roughness the data highlight a possible problem in energy balance studies which use microtopographic surveys to calculate aerodynamic roughness in that the scale of the measurements made affects the calculated roughness value this suggests that further investigations of the relationships between surface form and aerodynamic roughness of glacier surfaces are needed

centreline and cross glacier air temperature variability on an alpine glacier assessing temperature distribution methods and their influence on melt model calculations the spatio temporal distribution of air temperature over mountain glaciers can demonstrate complex patterns yet it is often represented simplistically using linear vertical temperature gradients vtgs extrapolated from off glacier locations we analyse a network of centreline and lateral air temperature observations at tsanteleina glacier italy during summer 2015 on average vtgs are steep 1 but they are shallow under warm ambient conditions when the correlation between air temperature and elevation becomes weaker published along flowline temperature distribution methods explain centreline observations well including warming on the lower glacier tongue but cannot estimate lateral temperature variability application of temperature distribution methods improves simulation of melt rates rmse in an energy balance model by up to 36 compared to the environmental lapse rate extrapolated from an off glacier station however results suggest that model parameters are not easily transferable to glaciers with a small fetch without recalibration such methods have potential to improve estimates of temperature across a glacier but their parameter transferability should be further linked to the glacier and atmospheric characteristics furthermore cold spots which can be 2 c cooler than expected for their elevation whose occurrence is not predicted by the temperature distribution models are identified at one quarter of the measurement sites

pattern of retreat and disintegration of larsen b ice shelf antarctic peninsula the retreat of the larsen b ice shelf antarctic peninsula and the collapse of its northern section are analyzed using satellite images acquired between january 1995 and may 2003 over 1 week during march 2002 after a period of steady retreat since 1995 2300 km 2 of the ice shelf broke up into many small icebergs this rapid collapse occurred at the end of an exceptionally warm summer and after a multi year period of decreasing surface net mass balance ice thinning flow acceleration and widening of rifts the ice shelf area decreased from 11 512 km 2 in january 1995 to 3463 km 2 in march 2002 and 2667 km 2 in april 2003 ers synthetic aperture radar sar images were used to identify ice shelf zones with different surface morphology which generated icebergs of different sizes and shapes the pattern of retreat and break up similar to that of larsen a in 1995 suggests that fracturing enhanced by abundant surface melt played a key role in addition the recent changes of grounded and residual floating ice north of larsen b are analyzed by means of envisat advanced synthetic aperture radar asar images up to summer 2003 showing significant loss of grounded ice upstream of those ice shelf sections which disintegrated in 1995 and 2002

response of surface topography to basal variability along glacial flowlines predicting the amplitude and distribution of surface undulations on ice sheets and glaciers is useful because of their influence on surface mass and energy balance atmospheric boundary layer processes and supraglacial meltwater routing we develop an approximate method of calculating the surface elevation response due to spatial perturbations in basal topography and slipperiness on two dimensional flow sections whose thickness surface slope and basal slip ratio vary along flow our main result is an integral expressing nonuniform transfer of basal variability to the surface it uses published fourier transfer functions derived through perturbing plane slab stokes flow but circumvents the need to sub window the spatial domain to estimate the response we test the method on ice flow synthesised by a finite element model of stokes flow with constant viscosity and known basal topography and slipperiness perturbations in this case it predicts the observed size and shape of the surface undulations well capturing more than 90 of their variance application of the method to the central flowline of columbia glacier alaska and a flowline on the greenland ice sheet ending on nordenskiold glacier using knowledge of the approximate bed topography and ignoring the unknown slipperiness forcing yields less faithful prediction of their surface undulations 40 50 of their variance but demonstrates the method s potential to reproduce their qualitative features we discuss the factors limiting the method s performance on real flowlines

modelling channelized surface drainage of supraglacial lakes supraglacial lakes can drain to the bed of ice sheets affecting ice dynamics or over their surface relocating surface water focusing on surface drainage we first discuss observations of lake drainage in particular for the first time lakes are observed to drain 70 km across the nivlisen ice shelf east antarctica inspired by these observations we develop a model of lake drainage through a channel that incises into an ice sheet surface by frictional heat dissipated in the flow modelled lake drainage can be stable or unstable during stable drainage the rate of lake level drawdown exceeds the rate of channel incision so discharge from the lake decreases with time this can prevent the lake from emptying completely during unstable drainage discharge grows unstably with time and always empties the lake model lakes are more prone to drain unstably when the initial lake area the lake input and the channel slope are larger these parameters will vary during atmospheric warming induced ablation area expansion hence the mechanisms revealed by our analysis can influence the dynamic response of ice sheets to warming through their impact on surface water routing and storage

the influence of dem resolution on simulated solar radiation induced glacier melt the influence of digital elevation model dem resolution to modelled glacier melt during peak melt production was evaluated by performing a clear sky gis radiation simulation over the peyto glacier in the canadian rockies dems were generated at eight resolutions ranging from 1 m to 1000 m grid spacing from airborne lidar data when applied to the planar area pa of the terrain it was found that total melt increased with dem resolution r2 0 63 by 4 over 3 orders of magnitude this systematic scaling effect was mitigated at the basin scale however when the dem slope variant area sva was used to account for the increased divergence from pa as resolution increases however even after the inclusion of sva in glacier surface melt simulations localized melt variations with scale were still evident in the ablation and accumulation zone observations in the ablation zone there was a systematic increase in simulated melt 4 as resolution decreased from 1 m to 1000 m r2 0 89 with the opposite effect in the accumulation zone r2 0 81 dem resolution also affected the diurnal melt cycle such that for the entire glacier there was a tendency for a morning over estimation and afternoon underestimation of melt rate with decreasing resolution for the accumulation zone there was an increased melt rate at low resolutions occurring in the afternoon while in the ablation zone there was a tendency for increasing melt rates with decreasing resolution throughout the day these localized spatio temporal variations in simulated melt are largely due to the lowering of ridges and raising of valley floors that occur as resolution decreases this scale dependence in the representation of terrain morphology directly controls the pattern and relative proportion of direct beam shadowing over actively melting surfaces and thereby has a systematic influence on the grid cell level hydrological balance it is recommended that gis based glacier melt modelling routines take into account the slope area of grid cells while noting that the choice of dem scale can have a discernible and systematic influence on modelled runoff magnitude it is important to note that while higher grid resolutions mitigate the effect of terrain smoothing on spatio temporal melt patterns lower resolutions actually mitigate the systematic error associated with assuming all surface areas are planar copyright 2010 john wiley sons ltd and her majesty the queen in right of canada

modeling of snow and ice melt at eth camp west greenland a study of surface albedo 1 the objective of this paper is to present the validation over greenland of a thermodynamic snow ice model that was complemented with the snow metamorphism and albedo parameterizations of the centre d etudes de la neige grenoble france in order to make the surface albedo variable and interactive special attention is given to the surface albedo since it is the most important parameter in energy exchanges with the atmosphere for snow and ice melt the development of an integrated snow ice and water albedo model takes into account the different surface types observed on an ice sheet and the snow albedo is calculated from the simulated surface snow grains the validation for a polar site has been done at eth camp west greenland 1155 m above sea level during the 1990 and 1991 summer seasons although both ablation seasons differed greatly in 1990 it showed a negative mass balance while in 1991 it ended with a positive mass balance a single model configuration was able to provide good results for both 1990 and 1991 these simulations show that the snow metamorphism laws included enable an accurate simulation of the surface albedo and henceforth of the surface mass balance for a polar site provided that the snow model is correctly forced at its surface level and that meltwater retention percolation and drainage are well represented in the snow model the model results are also compared with two other modeling approaches and differences between the three snow models are detailed

parameterization of the spatially averaged sky view factor in complex topography large scale meteorological land surface or climate models require precise subgrid parameterizations to reproduce unresolved subgrid processes this is particularly important in mountainous terrain where subgrid surface properties e g glacier area extent are used to illustrate the impact of global climate change the sky view factor is one of the most frequently used terrain characteristics to parameterize the influence of topography on the surface radiation balance in complex terrain a precise subgrid parameterization of sky view factors is therefore essential for accurate parameterizations of radiative fluxes such as shortwave diffuse sky and terrain reflected radiation while its computation is straightforward for a particular site a systematic characterization of the spatially averaged sky view factor is still missing we use gaussian random fields with a gaussian covariance as topography model and based on an analytical approximation we derive a parameterization for the spatially averaged sky view factor the sky view factor parameterization is solely based on computationally cheap terrain parameters namely the correlation length of subgrid topographic features and the mean squared slope in the grid cell of the large scale model for validation we compare parameterized to numerically exact sky view factors computed for real terrain of the swiss alps from a 25 m digital elevation model with subsequent averaging to varying target domain sizes we obtain a very good agreement when approaching the resolutions of regional climate models the parameterization also compares well for various real topographies from the u s

effects of digital elevation model spatial resolution on distributed calculations of solar radiation loading on a high arctic glacier high resolution airborne lidar data are used to produce digital elevation models dems of an arctic valley glacier midre lovenbreen svalbard at resolutions of 2 5 2000 m using three different interpolation schemes these data are used in a distributed model of solar radiation loading for glaciers when the mean of all lidar measurements within a dem cell is used to calculate cell height the differences between the finest 2 5 m and coarsest resolution 2000 m dems for the calculated annual whole glacier spatial means of total potential direct beam solar radiation potential duration of direct beam solar radiation and intensity of potential direct beam solar radiation are 20 56 and 23 of the 2 5 m dem values respectively a resolution change from 2 5 m to 200 m affects the whole glacier spatial mean summer net solar radiative flux by an average of 5 and the summer melt production from the glacier by an average of 3 compared with the 2 5 m dem values for the years 2001 03 these changes are largely driven by underestimation of shading by surrounding topography at coarser dem resolutions this dependency is reduced in the second and third interpolation schemes especially at resolutions finer than 50 m which use the maximum lidar height measurement in some or all dem cells these results suggest that resolutions of 50 m are the coarsest that should be adopted in high resolution glacier surface energy balance models for glaciers of similar size and in similar topographic situations to midre lovenbreen and that the impact of dem resolution on calculated solar radiation receipts can be reduced by an appropriate choice of dem interpolation scheme

climate sensitivity of a high precipitation glacier in new zealand the sensitivity of glaciers to climatic change is key information in assessing the response and sea level implications of projected future warming new zealand glaciers are important globally as an example of how maritime glaciers will contribute to sea level rise a spatially distributed energy balance model is applied to brewster glacier new zealand in order to calculate glacier mass balance run off and sensitivity to climate change the model successfully simulates four annual mass balance cycles close to half 52 of the energy available for melt on the glacier is supplied by turbulent heat fluxes with radiation less important except during the winter model sensitivity to temperature change is one of the largest reported on earth at 2 0 m w e a 1 8c 1 in contrast a 50 change in precipitation is required to offset the mass balance change resulting from a 18c temperature change meltwater run off sensitivity is also very high increasing 60 with a 18c warming the extreme sensitivity of mass balance to temperature change suggests that significant ice loss will occur with even moderate climate warming

mass balance gradients and climatic change it is generally assumed that the mass balance gradient on glaciers is more or less conserved under climatic change in studies of the dynamic response of glaciers to climatic change one of the following assumptions is normally made i the mass balance perturbation is independent of altitude or ii the mass balance profile does not change it simply shifts up and down observational evidence for such an approach is not convincing on some glaciers the inter annual changes in mass balance seem to be independent of altitude on others not at all moreover it is questionable whether inter annual variation can be projected on different climatic states to see what a physical approach might contribute we developed an altitude dependent mass balance model it is based on the energy balance of the ice snow surface where precipitation is included in a parameterized form and numerical integrations are done through an entire balance year with a 30 min time step atmospheric temperature snowfall and atmospheric transmissivity for solar radiation are all dependent on altitude so a mass balance profile can be calculated slope and exposure of the ice snow surface are taken into account and the effects of these parameters studied in general the calculations were done for 100 m elevation intervals climatological data from the sonnblick observatory austria 3106 m a s l and from vent 2000 m a s l oetztal alps austria served as input for a number of runs simulation of the mass balance profiles for hinterseisferner north easterly exposure and kesselwandferner southeasterly exposure yields reasonable results the larger balance gradient on kesselwandferner is produced by the model so exposure appears to be an important factor here sensitivity of mass balance profiles to shading effects different slope and exposure are systematically studied another section deals with the sensitivity to climatic change perturbations of air temperature cloudiness albedo and precipitation are imposed to see their effects on the mass balance profiles the results clearly show that in general mass balance perturbations depend strongly on altitude they generally increase down glacier and are not always symmetric about the reference state for typical climatic conditions in the alps we found that a 1 k temperature change leads to a change in equilibrium line altitude of 130 m three factors contribute to this large value turbulent heat flux longwave radiation from the atmosphere and fraction of precipitation falling as snow here the albedo feed back increases the sensitivity in a significant way

elevational changes in meteorological variables along a midlatitude glacier during summer during the summer of 1994 a glaciometeorological experiment was carried out on the pasterze a glacier in austria this paper reports on the data from six energy balance stations ranging in altitude from 2075 to 3225 m above sea level asl the wind regime was dominated by the glacier wind on the tongue directional constancies ranged between 0 94 and 0 97 mean 2 m wind speed and specifie humidity were almost constant along the glacier the variation in the 2 m temperature along the glacier cannot be described by the usually assumed constant decrease with elevation on the tongue the 2 m temperature even increased with elevation a much better description of the temperature distribution is given by a linear relation between the potential temperature and the distance along the flow line this can be understood from a simple thermodynamic analysis of the glacier wind layer it is further shown that changes in clear sky global radiation with elevation are due mainly to changes in local albedo and relief and hardly at all to changes in absolute optical path length and atmospheric water vapor and aerosol content on the tongue the laterally averaged ice albedo is almost constant with elevation the flux of incoming long wave radiation during clear sky conditions at u2 2310 m asl was 48 w m2 higher than the flux at u5 3225 m asl on average more than half of the difference was due to systematic differences in the shape of the temperature profile probably the inversion depth is larger at u2 the rest can be ascribed to higher 2 m temperatures and larger amounts of upper hemisphere slopes at u2 the distributions of the meteorological variables and the parameterizations described in this paper might be incorporated in surface energy balance models designed to simulate the surface mass balance

relative contribution of surface mass balance and ice flux changes to the accelerated thinning of the mer de glace alps over 1979 2008 by subtracting surface topographies from 1979 1994 2000 and 2008 we measured ice thinning rates increasing from 1 m a 1 1979 1994 to more than 4 m a 1 2000 2008 on the tongue of the mer de glace the relative contributions of changes in surface mass balance and ice fluxes to this acceleration in the thinning are estimated using field and remote sensing measurements between 1979 1994 and 2000 2008 surface mass balance diminished by 1 2 m w e a 1 mainly because of atmospheric warming mass balance changes induced by the growing debris covered area and the evolving glacier hypsometry compensated each other meanwhile the mer de glace slowed down and the ice fluxes through two cross sections at 2200 m a s l and 2050 m a s l decreased by 60 between 1979 1994 and 2000 2008 two thirds of the increase in the thinning rates was caused by reduced ice fluxes and one third by rising surface ablation however those numbers need to be interpreted cautiously given our inability to respect mass conservation below our upper cross section an important implication is that large errors would occur if one term of the continuity equation e g surface mass balance was deduced from the two others e g elevation and ice flux changes

integrated monitoring of mountain glaciers as key indicators of global climate change the european alps the internationally recommended multi level strategy for monitoring mountain glaciers is illustrated using the example of the european alps where especially dense information has been available through historical times this strategy combines in situ measurements mass balance length change with remote sensing inventories and numerical modelling it helps to bridge the gap between detailed local process oriented studies and global coverage since the 1980s mass balances have become increasingly negative with values close to 1 m w e a 1 during the first 5 years of the 21st century the hot dry summer of 2003 alone caused a record mean loss of 2 45 m w e roughly 50 above the previous record loss in 1998 more than three times the average between 1980 and 2000 and an order of magnitude more than characteristic long term averages since the end of the little ice age and other extended periods of glacier shrinkage during the past 2000 years it can be estimated that glaciers in the european alps lost about half their total volume roughly 0 5 a 1 between 1850 and around 1975 another 25 or 1 a 1 of the remaining amount between 1975 and 2000 and an additional 10 15 or 2 3 a 1 in the first 5 years of this century

calving fluxes and basal melt rates of antarctic ice shelves iceberg calving has been assumed to be the dominant cause of mass loss for the antarctic ice sheet with previous estimates of the calving flux exceeding 2 000 gigatonnes per year1 2 more recently the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3 4 5 so far however no study has reliably quantified the calving flux and the basal mass balance the balance between accretion and ablation at the ice shelf base for the whole of antarctica the distribution of fresh water in the southern ocean and its partitioning between the liquid and solid phases is therefore poorly constrained here we estimate the mass balance components for all ice shelves in antarctica using satellite measurements of calving flux and grounding line flux modelled ice shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas we obtain a total calving flux of 1 321 144 gigatonnes per year and a total basal mass balance of 1 454 174 gigatonnes per year this means that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1 2 7 in addition the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves we find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9 we suggest that basal mass loss is a valuable metric for predicting future ice shelf vulnerability to oceanic forcing

c swithinbank 1988 satellite image atlas of glaciers of the world antarctica washington dc united states government printing office united states geological survey professional paper 1386 b

effects of bed compaction on scour at piers in sand clay mixtures abstractscour at piers embedded in a bed of cohesive sediment mixture is investigated to quantify the effects of bed compaction experiments were conducted in a large rectangular laboratory flume with natural clay sediment collected from a stream located at the chilean coastal range nonintrusive and high resolution topographic measurements of scoured bed in the vicinity of piers were performed during the experimental runs with an installation of a laser distance sensor lds that was traversed by the precision step motors measurements were taken by the lds in different azimuthal half planes to study the spatiotemporal variation of the topography of evolving scour holes experiments were conducted over 40 h until an advanced stage of scour was reached with the approaching flow having a bed shear stress equaling 95 of the shields critical condition for the initiation of motion of sand in a sand clay mixture results show that the bed is successively scoured in three different forms chunks of aggregate

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis