greenland flow variability from ice sheet wide velocity mapping using radarsat synthetic aperture radar data we have mapped the flow velocity over much of the greenland ice sheet for the winters of 2000 01 and 2005 06 these maps provide a detailed view of the ice sheet flow including that of the hundreds of glaciers draining the interior the focused patterns of flow at the coast suggest a strong influence of bedrock topography differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes the overall pattern is one of speed up accompanied by terminus retreat but there are also several instances of surge behavior and a few cases of glacier slowdown comprehensive mappings such as these at regular intervals provide an important new observational capability for understanding ice sheet variability

basal conditions and ice dynamics inferred from radar derived internal stratigraphy of the northeast greenland ice stream we analyze the internal stratigraphy in radio echo sounding data of the northeast greenland ice stream to infer past and present ice dynamics in the upper reaches of the ice stream we propose that shear margin steady state folds in internal reflecting horizons irhs form due to the influence of ice flow over spatially varying basal lubrication irhs are generally lower in the ice stream than outside likely because of greater basal melting in the ice stream from enhanced geothermal flux and heat of sliding strain rate modeling of irhs deposited during the holocene indicates no recent major changes in ice stream vigor or extent in this region downstream of our survey irhs are disrupted as the ice flows into a prominent overdeepening when combined with additional data from other studies these data suggest that upstream portions of the ice stream are controlled by variations in basal lubrication whereas downstream portions are confined by basal topography

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

change in surface debris cover on mont blanc massif glaciers after the little ice age termination because of insulation by supraglacial debris the dynamics of debris covered glaciers differ from those of clean glaciers thus changes in debris cover have to be taken into account when interpreting glacier fluctuations in terms of climate forcing three large glaciers in the mont blanc massif were investigated for the period since the termination of the little ice age lia using historical and scientific documents of the eighteenth and nineteenth centuries although debris cover was limited to its frontal area until the 1840s miage glacier exhibited a continuous debris cover in the first decades after the lia increasing to its present extent by the 1930s on the mer de glace a partial debris cover formed by coalescence of two of the four medial moraines at the close of the lia until 1890 these moraines have formed the present veine noire black vein in contrast brenva glacier had a continuous debris cover at the end of the eighteenth century possibly following a rock avalanche in 1767 fo

basal melt at northgrip modeled from borehole ice core and radio echo sounder observations from temperature measurements down through the 3001 m deep borehole at the north greenland icecore project northgrip drill site it is now clear that the ice at the base 3080 m below the surface is at the pressure melting point this is supported by the measurements on the ice core where the annual layer thicknesses show there is bottom melting at the site and upstream from the borehole surface velocity measurements internal radio echo layers borehole and ice core data are used to constrain a time dependent flow model simulating flow along the north northwest trending ice ridge flow line leading to the northgrip site also time dependent melt rates along the flowline are calculated with a heat flow model the results show the geothermal heat flow varies from 50 to 200 mw m 2 along the 100km section of the modeled flowline the melt rate at the northgrip site is 0 75 cm a 1 but the deep ice in the northgrip core originated 50 km upstream and has experienced melt rates as high as 1 1 cm a 1

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

coherent radar ice thickness measurements over the greenland ice sheet we developed two 150 mhz coherent radar depth sounders for ice thickness measurements over the greenland ice sheet we developed one of these using connectorized components and the other using radio frequency integrated circuits rfics both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice we used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers we operated both radar systems on the nasa p 3b aircraft equipped with gps receivers radar data are tagged with gps derived location information and are collected in conjunction with laser altimeter measurements we have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of program for regional climate assessment parca investigations and the north greenland ice core project radar echograms and derived ice thickness data are placed on a server at the university of kansas http tornado rsl ukans edu greenlanddata htm for easy access by the scientific community we obtained good ice thickness information with an accuracy of 10 m over 90 of the flight lines flown as a part of the parca initiative in this paper we provide a brief description of the system along with samples of data over the interior along the 2000 m contour line in the south and from a few selected outlet glaciers

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

transmission of solar radiation through clouds on melting glaciers a comparison of parameterizations and their impact on melt modelling we explore the robustness and transferability of parameterizations of cloud radiative forcing used in glacier melt models at two sites in the swiss alps we also look at the rationale behind some of the most commonly used approaches and explore the relationship between cloud transmittance and several standard meteorological variables the 2 m air temperature diurnal range is the best predictor of variations in cloud transmittance however linear and exponential parameterizations can only explain 30 50 of the observed variance in computed cloud transmittance factors we examine the impact of modelled cloud transmittance factors on both solar radiation and ablation rates computed with an enhanced temperature index model the melt model performance decreases when modelled radiation is used the reduction being due to an underestimation of incoming solar radiation on clear sky days the model works well under overcast conditions we also seek alternatives to the use of in situ ground data however outputs from an atmospheric model 2 2 km horizontal resolution do not seem to provide an alternative to the parameterizations of cloud radiative forcing based on observations of air temperature at glacier automatic weather stations conversely the correct definition of overcast conditions is important

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

tracer transport in the greenland ice sheet three dimensional isotopic stratigraphy abstract polar ice cores can provide both a record of climate history and a sharp test of the performance of numerical ice dynamics models the stratigraphic structure of an ice sheet is an expression of its full depositional and dynamic history and thus presents a greater challenge to computer models than merely matching the contemporary ice thickness and areal extent we describe a coupled model of ice and tracer dynamics that is realized by adding a semi lagrangian tracer transport scheme to a conventional thermomechanical ice dynamics model model skill is demonstrated by using ice core data from the grip site near summit greenland to successfully predict the isotopic stratigraphy of ice cores at other deep drilling sites the success of this effort indicates that when compensated for the effects of ice flow and elevation all the deep cores relate a coherent glacial history over the past 120 000 years according to the simulation results the oldest greenland ice lies beneath the grip gisp2 and northgrip sites although comparably old ice may also be found in north greenland and east central greenland

surface roughness and bulk heat transfer on a glacier comparison with eddy correlation more than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice the results proved to be extremely sensitive to measurement height which is difficult to define precisely on the hummocky terrain of a glacier therefore aerodynamic roughness lengths were estimated from the microtopography of the surface yielding 2 46 mm for ice and 5 5 mm for snow despite the indeterminate nature of the profile analysis it did support the view that the thermal roughness length must decrease as the roughness reynolds number increases a relationship which has been modelled in the literature good agreement between bulk transfer estimates and eddy correlation measurements of fhe sensible heat flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length

backwasting rate on debris covered koxkar glacier tuomuer mountain china a physically based energy balance model with improved parameterization of solar radiation for a sloped ice surface has been developed to estimate the backwasting rate of an ice cliff in a debris covered area the model has been tested against observations between 5 august and 5 september 2008 on 38 ice cliffs in the debris covered area of koxkar glacier tuomuer mountain china we calculated that the energy balance model gave a good estimate of the backwasting rates with errors in the range 1 96 cm d 1 and root mean square errors of 0 99 cm d 1 errors arising from setting of surface albedo and turbulent flux parameterization were limited we found that shortwave radiation is the most important heat source for ice cliff ablation contributing about 76 of the total heat available for ice melt while the sensible heat flux provides nearly 24 of the total heat for ice cliff wastage the latent heat flux and net longwave radiation are comparatively small according to the model calculation the mean backwasting rate of ice cliffs in the debris covered area of koxkar glacier is estimated at 7 64 m a 1 when the winter ablation is neglected with this annual backwasting rate and given a mean slope angle of 46 48 the backwasting of ice cliffs produces about 1 60 10 6 m 3 of meltwater accounting for about 7 3 of the total melt runoff from the debris covered area

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

ice ablation and meteorological conditions on the debris covered area of baltoro glacier karakoram pakistan during the recent italian expedition k2 2004 50 years later june july 2004 on baltoro glacier karakoram pakistan glaciological field experiments were carried out on the debris covered area of this high elevation glacier the aim was to investigate the ice ablation and its relations with debris thermal properties and meteorological conditions ablation measurements along the glacier up to about 5000 m and within a dedicated test field were combined with meteorological data from two automatic weather stations located at urdukas 4022 m a s l and at k2 base camp 5033 m a s l in addition temperature measurements of the debris cover at different depth levels along the glacier allowed the calculation of debris surface temperature and of the debris thermal resistance r using the air temperature the local mean lapse rate 0 00758 cm 1 and the measured ablation the degree day factors k at different locations on the glacier were calculated the ice ablation rates were related to debris thickness and elevation they are typically on the order of 4 cm d 1 during the observation period however it was found that the surface topography slope aspect has an influence on the total ablation similar to that of the debris thickness thermal resistance of the debris cover and its distribution over the glacier were estimated finally a best guess estimate of the total meltwater production was calculated from available climate data

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

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

highly variable aerodynamic roughness length z0 for a hummocky debris covered glacier the aerodynamic roughness length z0 is an essential parameter in surface energy balance studies but few literature values exist for debris covered glaciers we use microtopographic and aerodynamic methods to assess the spatial variability of z0 for lirung glacier nepal we apply structure from motion to produce digital elevation models for three nested domains five 1 m2 plots a 21 300 m2 surface depression and lower 550 000 m2 of the debris mantled tongue wind and temperature sensor towers were installed in the vicinity of the plots within the surface depression in october 2014 we calculate z0 according to a variety of transect based microtopographic parameterisations for each plot then develop a grid version of the algorithms by aggregating data from all transects this grid approach is applied to the surface depression dem to characterize z0 spatial variability the algorithms reproduce the same variability among transects and plots but z0 estimates vary by an order of magnitude between algorithms across the study depression results from different algorithms are strongly correlated using monin obukov similarity theory we derive z0 values from the meteorological data using different stability criteria we derive median values of z0 between 0 03 m and 0 05 m but with considerable uncertainty due to the glacier s complex topography considering estimates from these algorithms results suggest that z0 varies across lirung glacier between 0 005 m gravels to 0 5 m boulders future efforts should assess the importance of such variable z0 values in a distributed energy balance model

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

a physically based method for estimating supraglacial debris thickness from thermal band remote sensing data in order to account for the effects of debris cover in model scenarios of the response of glaciers to climate change and water resource planning it is important to know the distribution and thickness of supraglacial debris and to monitor its change over time previous attempts to map surface debris thickness using thermal band remote sensing have relied upon time specific empirical relationships between surface temperature and thickness limiting their general applicability in this paper we develop a physically based model that utilizes advanced spaceborne thermal emission and reflection radiometer aster thermal band remotely sensed imagery and is based on a solution of the energy balance at the debris surface the model is used to estimate debris thickness on miage glacier italy and is validated using field debris thickness measurements and a previously published debris thickness map the temporal transferability of the model is demonstrated through successful application to a separate aster image from a different year using reanalysis meteorological input data this model has the potential to be used for regional scale supraglacial debris thickness mapping and monitoring for debris up to at least 0 50 m thickness but improved understanding of the spatial patterns of air temperature aerodynamic roughness length and thermal properties across debriscovered glaciers is needed

flow of ice sheets in the vicinity of subglacial peaks although changes of surface slope across a subglacial peak can be explained at least semi quantitatively on a two dimensional basis in terms of gradients of longitudinal and shear stresses along a flow line we lack appreciation of flow in the third dimension which may tend to cause lower layers to flow around rather than over a sharp peak this paper collects and surveys evidence relevant to flow in the third dimension and discusses the processes involved particularly the evidence from radio echo layering and also discusses possible reasons for the lack of radio echo layers near the base of the antarctic ice sheet

observation and analysis of ice flow in the largest greenland ice stream we have applied satellite radar interferometry methods to map the velocity field of the recently discovered northeast greenland ice stream we have used these data in conjunction with ice thickness and accumulation data to determine that the ice stream is in balance within the measurement errors we used control methods to invert a finite element model of ice sheet flow constrained by the data to infer the ice stream s basal shear stress distribution our results reveal that flow in a section of the downstream end has much in common with the streaming flow of the ross ice streams of west antarctica e g a weak bed and fast flow in the presence of low driving stresses for several hundred kilometers along the middle of the ice stream the basal shear stress balances the driving stress in the upstream area where the ice stream is first visible in the velocity data the bed appears to be weak which may contribute to the initiation of the ice stream

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

ice stream related patterns of ice flow in the interior of northeast greenland ice flow in the interior of the ne quadrant of the greenland ice sheet is focused on the large ice stream draining the north side of the summit dome the rapid ice flow in the stream is apparent in the surface features in the stream and at the margins in the broad scale topography that drives ice flow and in satellite derived ice motion information the patterns of ice flow in the upper half of the stream are remarkable for their level of organization simple geometry and effects on local surface topography the stream begins less than 100 km from the ice divide as a current 15 km wide and then broadens symmetrically downstream by the addition of ice from the sides to a width of more than 60 km elevation data and visible band imagery show that the stream has marginal troughs tens of meters deep in its upper reach which are coincident with regions of high shear strain rate the topography of the margins and undulating surface of the stream is generated by the ice flow the surface undulations in the stream are fixed in location and shape over the 5 year period from 1994 to 1999 the enhanced flow presents a challenge for researchers trying to understand the history of ice discharge from a significant area in the interior of the ice sheet

analysis of deep penetrating radar surveys of west antarctica us itase 2001 1 we collected 1850 km of ground based radio echo sounding res data in west antarctica along the 2001 us leg of the international trans antarctic scientific expedition traverse us itase these data represent the first high resolution measurements of ice thickness and internal stratigraphy for portions of this area that bear on questions about the stability of the west antarctic ice sheet wais internal layers depicting isochrones have been traced continuously for much of the profile length and a date from the byrd deep core is ascribed to one of these isochrones from which we estimate vertical velocities across the traverse route comparison of our ice thickness measurements with bedmap show good agreement in regions where the database is well constrained by data coverage where the bedmap dataset was forced to interpolate differences are as high as 45 of the ice thickness

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

inference of accumulation rate patterns from deep layers in glaciers and ice sheets the spatial pattern of accumulation rate can be inferred from internal layers in glaciers and ice sheets non dimensional analysis determines where finite strain can be neglected shallow layer approximation or approximated with a local one dimensional flow model local layer approxima tion and where gradients in strain rate along particle paths must be included deep layers we develop a general geophysical inverse procedure to infer the spatial pattern of accumulation rate along a steady state flowband using measured topography of the ice sheet surface bed and a deep layer a variety of thermomechanical ice flow models can be used in the forward problem to calculate surface topography and ice velocity which are used to calculate particle paths and internal layer shapes an objective tolerance criterion prevents over fitting the data after making site specific simplifications in the thermomechanical flow algorithm we find the accumulation rate along a flowband through taylor mouth a flank site on taylor dome antarctica using a layer at approximately 100 m depth or 20 of the ice thickness accumulation rate correlates with ice surface curvature at this site gradients along flow paths critically impact inference of both the accumulation pattern and the depth age relation in a 100 m core

2 m temperatures along melting mid latitude glaciers and implications for the sensitivity of the mass balance to variations in temperature in calculations of the variation in the 2 m temperature along glaciers the lapse rate is generally assumed to be constant this implies that the ratio of changes in the 2 m temperature above a glacier to changes in the temperature outside the thermal regime of that glacier climate sensitivity is equal to 1 however data collected during the ablation season on several mid latitude glaciers show that this sensitivity is smaller than 1 the lowest measured value 0 3 was obtained on the tongue of the pasterze a glacier in austria the measured temperature distribution along the pasterze cannot be described by a constant lapse rate either however there is almost a linear relationship between potential temperature and the distance along die glacier this paper introduces a simple analytical thermodynamic glacier wind model which can be applied to melting glaciers and which explains the observed climate sensitivities and temperature distributions much better than calculations based on a constant lapse rate this way of modelling the 2 m temperatures has implications for the sensitivity of the surface mass balance to atmospheric warming outside the thermal regime of the glacier the magnitude of this sensitivity is computed with a surface energy balance model applied to the pasterze when a constant lapse rate is used instead of the proposed glacier wind model to compute changes in the 2 m temperature along the glacier the negative change in mass balance due to 1 c warming is overestimated by 22

longitudinal and topographic variations in north atlantic tidal and inertial energy around latitudes 30 10 n 1 open ocean kinetic energy is investigated at dominant inertial and semidiurnal tidal frequencies using historic current observations from the north atlantic ocean around midlatitudes focus is on possible energy variations due to major topography changes between the eastern canary and western hatteras sohm basins thereby crossing the mid atlantic ridge mar while in open basins on both sides of mar semidiurnal kinetic energy drops in magnitude by some 50 between latitudes 20 n 28 n in agreement with tpxo elevation data an even larger longitudinal dependence is observed west of mar semidiurnal energy is up to 30 times less than east of it inertial kinetic energy is either decreasing by a factor of 2 4 westward or more or less independent of longitude this contrasts strongly with westward intensified near surface inertial energy fluxes previously found the latter fluxes also did not show an increase by a factor of 5 10 for 25 n 30 n as observed here for inertial energy in both basins west of mar the internal wave background level for frequencies up to sixth diurnal is much less by a factor of 3 10 at tidal inertial interaction frequencies than east of mar no significant atmospheric or large scale vorticity influence or seasonal variations therein is found on inertial energy content across the basin as no individual peaks are observed at frequencies k1 o1 and m1 s1 direct diurnal tidal forcing and subharmonic resonance must be accompanied by nonlinear interactions in possibly enhancing inertial energy at the critical diurnal latitude

supraglacial ice cliffs and ponds on debris covered glaciers spatio temporal distribution and characteristics ice cliffs and ponds on debris covered glaciers have received increased attention due to their role in amplifying local melt however very few studies have looked at these features on the catchment scale to determine their patterns and changes in space and time we have compiled a detailed inventory of cliffs and ponds in the langtang catchment central himalaya from six high resolution satellite orthoimages and dems between 2006 and 2015 and a historic orthophoto from 1974 cliffs cover between 1 4 0 4 in the dry and 3 4 0 9 in the wet seasons and ponds between 0 6 0 1 and 1 6 0 3 of the total debris covered tongues we find large variations between seasons as cliffs and ponds tend to grow in the wetter monsoon period but there is no obvious trend in total area over the study period the inventory further shows that cliffs are predominately north facing irrespective of the glacier flow direction both cliffs and ponds appear in higher densities several hundred metres from the terminus in areas where tributaries reach the main glacier tongue on the largest glacier in the catchment 10 of all cliffs and ponds persisted over nearly a decade

high resolution radar mapping of internal layers at the north greenland ice core project existing accumulation maps with reported errors of about 20 are determined from sparsely distributed ice cores and pits a more accurate accumulation rate might be obtained by generating continuous profiles of dated layers from high resolution radar mapping of near surface internal layers in the ice sheet isochrones to generate such profiles we designed and developed an ultrawideband radar for high resolution mapping of internal layers in the top 200 m of ice and tested it at the north greenland ice core project drill site reflection profiles of 2 and 10 km length reveal horizons that we correlate with electrical conductivity measurement ecm recordings our results show that the radar determined depth of internal layers is within 2 m of that in an ice core collected at a nearby location preliminary frequency analyses of layer reflections reveal that the reflections are strongest at the 500 1000 mhz frequency range long term accumulation rate computed from radar data is within 5 of that obtained from snow pits

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

modeling 2 m air temperatures over mountain glaciers exploring the influence of katabatic cooling and external warming air temperature is one of the most relevant input variables for snow and ice melt calculations however local meteorological conditions complex topography and logistical concerns in glacierized regions make the measuring and modeling of air temperature a difficult task in this study we investigate the spatial distribution of 2 m air temperature over mountain glaciers and propose a modification to an existing model to improve its representation spatially distributed meteorological data from haut glacier d arolla switzerland place canada and juncal norte chile glaciers are used to examine approximate flow line temperatures during their respective ablation seasons during warm conditions off glacier temperatures well above 0 c observed air temperatures in the upper reaches of place glacier and haut glacier d arolla decrease down glacier along the approximate flow line at juncal norte and haut glacier d arolla an increase in air temperature is observed over the glacier tongue while the temperature behavior over the upper part can be explained by the cooling effect of the glacier surface the temperature increase over the glacier tongue may be caused by several processes induced by the surrounding warm atmosphere in order to capture the latter effect we add an additional term to the greuell and bohm gb thermodynamic glacier wind model for high off glacier temperatures the modified gb model reduces root mean square error up to 32 and provides a new approach for distributing air temperature over mountain glaciers as a function of off glacier temperatures and approximate glacier flow lines

comparison of the meteorology and surface energy fluxes of debris free and debris covered glaciers in the southeastern tibetan plateau knowledge of debris free and debris covered glaciers is important for understanding the varying response of glaciers to climate change measurements at the debris free parlung no 4 glacier and the debris covered 24 k glacier in the southeastern tibetan plateau were carried out to compare the meteorology and surface energy fluxes and to understand the factors controlling the melting process the meteorological comparisons displayed temporally synchronous fluctuations in air temperature relative humidity and incoming longwave radiation l in but notable differences in precipitation incoming shortwave radiation s in and wind speed under the prevailing regional precipitation and debris conditions more l in 42 w m 2 was supplied from warmer and more humid air and more s in 58 w m 2 was absorbed at the 24 k glacier the relatively high energy supply led mainly to an increased energy output via turbulent heat fluxes and outgoing longwave radiation rather than glacier melting beneath the thick debris the sensitivity experiment showed that melt rates were sensitive to energy supply at debris thicknesses similar to 10 cm in contrast energy supply to the parlung no 4 glacier mainly resulted in snow ice melting the magnitude of which was significantly influenced by energy supplied by s in and the sensible heat flux

assessing ice cliff backwasting and its contribution to total ablation of debris covered miage glacier mont blanc massif italy continuous surface debris cover strongly reduces the ablation of glaciers but high melt rates may occur at ice cliffs that are too steep to hold debris this study assesses the contribution of ice cliff backwasting to total ablation of miage glacier mont blanc massif italy in 2010 and 2011 based on field measurements physical melt models and mapping of ice cliffs using a high resolution 1 m digital elevation model dem short term model calculations closely match the measured melt rates a model sensitivity analysis indicates that the effects of cliff slope and albedo are more important for ablation than enhanced longwave incidence from sun warmed debris or reduced turbulent fluxes at sheltered cliff bases analysis of the dem indicates that ice cliffs account for at most 1 3 of the 1 m pixels in the glacier s debris covered zone but application of a distributed model indicates that ice cliffs account for 7 4 of total ablation we conclude that ice cliffs make an important contribution to the ablation of debris covered glaciers even when their spatial extent is very small

deformation of till beneath ice stream b west antarctica the behaviour and possible instability of the west antarctic ice sheet depend fundamentally on the dynamics of the large ice streams which drain it model calculations show that most ice stream velocity arises at the bed1 2 and radar sounding has shown the bed to be wet3 but the basal boundary condition is not well understood seismic evidence from the upstream b camp upb on the siple coast of west antarctica4 shows that the ice stream there rests on a layer of unconsolidated sediment averaging 5 or 6 m thick in which the water pressure is only 50 kpa less than the overburden pressure because this thin layer occurs well inland beneath an active ice sheet and rests on a surface showing flutes4 characteristic of glacial erosion5 we presume that it is glacial till we propose here that deformation within the till is the primary mechanism by which the ice stream moves and we discuss implications of this hypothesis

well posed boundary conditions for limited domain models of transient ice flow near an ice divide when an ice flow model is constrained by data that exist over only a section of an ice sheet it is computationally advantageous to limit the model domain to only that section for example a limited domain near an ice core site might cross an ice divide and have no termini accurately calculating ice sheet evolution in response to spatial and temporal variations in climate and ice flow depends on accurately calculating the transient ice flux crossing the limited domain boundaries in the absence of information from outside the limited domain this is an ill posed problem boundary conditions based only on information from inside the limited domain can produce ice sheet evolution incompatible with the full ice sheet within which we suppose it to exist we use impulse response functions to provide boundary values that are informed by the external ice sheet without conventionally nesting the limited domain in a full ice sheet model evolution within a limited domain can then be consistent with evolution of the full ice sheet our treatment of limited domain boundary conditions is designed for future use in an inverse problem in which external changes that affected the limited domain can be inferred from data from within the limited domain

distributed glacier mass balance modelling as an important component of modern multi level glacier monitoring modern concepts of worldwide glacier monitoring include numerical models for 1 interconnecting the different levels of observations local mass balance representative length change glacier inventories for global coverage and 2 extrapolations in space coupling with climate models and time backward and forward in this context one important new tool is distributed mass balance modelling in complex mountain topography this approach builds on simplified energy balance models and can be applied for investigating the spatio temporal representativity of the few mass balance measurements for estimating balance values at the tongue of unmeasured glaciers in order to derive long term average balance values from a great number of glaciers with known length change and for assessing special effects such as the influence of sahara dust falls on the albedo and mass balance or autocorrelation effects due to surface darkening of glaciers with strongly negative balances experience from first model runs in the swiss alps and from applications to the extreme conditions in summer 2003 provides evidence about the usefulness of this approach for glacier monitoring and analysis of glacier changes in high mountain regions the main difficulties concern the spatial variability of the input parameters e g precipitation snow cover and surface albedo and the uncertainties in the parameterizations of the components of the energy balance field measurements remain essential to tie the models to real ground conditions

fast flow signature in the stagnated kamb ice stream west antarctica among the major ice streams that drain west antarctica kamb ice stream formerly called ice stream c is unique in that it stagnated 150 yr ago but its former fast flow conditions are virtually unknown here we presentsurface based radar profiles of the ice stream s undulating internal stratigraphy which records these conditions our analysis of the profiles indicates that pre stagnation flow velocities averaged over a period 740 yr exceeded 350 m yr 1 in the trunk of the ice stream this velocity constraint would be lower if the ice had been thickening higher if thinning but suggests mass loss from the ice stream catchment that is of sufficient magnitude to reverse the gain estimated for today s siple coast region analysis of other ice streams would allow comparison of velocities over millennial time scales with observations of present day velocities useful for evaluating how west antarctic ice drainage has evolved

effect of sedimentation on ice sheet grounding line stability sedimentation filling space beneath ice shelves helps to stabilize ice sheets against grounding line retreat in response to a rise in relative sea level of at least several meters recent antarctic changes thus cannot be attributed to sea level rise strengthening earlier interpretations that warming has driven ice sheet mass loss large sea level rise such as the 100 meter rise at the end of the last ice age may overwhelm the stabilizing feedback from sedimentation but smaller sea level changes are unlikely to have synchronized the behavior of ice sheets in the past

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

an energy balance model for debris covered glaciers including heat conduction through the debris layer extensive covers of supraglacial debris are often present in glacier ablation areas and it is essential to assess exactly how the debris affects glacier melt rates this paper presents a physically based energy balance model for the surface of a debris covered glacier the model is driven by meteorological variables and was developed using data collected at miage glacier italy during the ablation seasons of 2005 2006 and 2007 the debris surface temperature is numerically estimated by considering the balance of heat fluxes at the air debris interface and heat conduction through the debris is calculated in order to estimate melt rates at the debris ice interface the predicted hourly debris surface temperatures and debris internal temperatures provide a good fit to temperatures measured on rock covered miage glacier r 2 0 94 and the tephra covered glacier on villarrica volcano chile r 2 0 82 the model can also be used to reproduce observed changes in melt rates below debris layers of varying types and thicknesses an important consideration for the overall mass balance of debris covered glaciers

the internal layering of pine island glacier west antarctica from airborne radar sounding data this paper presents an overview of internal layering across pine island glacier west antarctica as measured from airborne radar data acquired during a survey conducted by the british antarctic survey and the university of texas in the 2004 05 season internal layering is classified according to type continuous discontinuous missing and the results compared with insar velocities several areas exhibit disruption of internal layers that is most likely caused by large basal shear stresses signs of changes in flow were identified in a few inter tributary areas but overall the layering classification and distribution of layers indicate that only minor changes in ice flow regime have taken place this is supported by bed topography data that show the main trunk of the glacier as well as some of the tributaries are topographically controlled and located in deep basins

ice sheet grounding zone stabilization due to till compaction 1 based on modeling motivated by new gps and radio echo sounding surveys a few kilometers long zone of whillans ice stream west antarctica just inland of the grounding line has higher basal shear stress than the ice farther upstream or the freely slipping ice shelf downstream data from this zone show a few meter high upwarp of the surface overlying a large fold extending through all internal radar layers observed flowband modeling shows that the fold can be generated by decreased basal lubrication beneath the upwarp basal topography alone cannot create this fold physical modeling and available data suggest that low amplitude tidal flexure of the ice shelf extends a few kilometers inland downward flexing of this grounded ice from the rising tide would compact subglacial till resulting in higher basal shear stress this result suggests that important processes influencing grounding line stability are not included in modern whole ice sheet models

a distributed energy balance melt model of an alpine debris covered glacier distributed energy balance melt models have rarely been applied to glaciers with extensive supraglacial debris cover this paper describes the development of a distributed melt model and its application to the debris covered miage glacier western italian alps over two summer seasons sub debris melt rates are calculated using an existing debris energy balance model deb model and melt rates for clean ice snow and partially debris covered ice are calculated using standard energy balance equations simulated sub debris melt rates compare well to ablation stake observations melt rates are highest and most sensitive to air temperature on areas of dirty crevassed ice on the middle glacier here melt rates are highly spatially variable because the debris thickness and surface type varies markedly melt rates are lowest and least sensitive to air temperature beneath the thickest debris on the lower glacier debris delays and attenuates the melt signal compared to clean ice with peak melt occurring later in the day with increasing debris thickness the continuously debris covered zone consistently provides 30 of total melt throughout the ablation season with the proportion increasing during cold weather sensitivity experiments show that an increase in debris thickness of 0 035 m would offset 1 c of atmospheric warming

variability of air temperature over a debris covered glacier in the nepalese himalaya estimates of melt from debris covered glaciers require distributed estimates of meteorological variables and air temperature in particular meteorological data are scarce for this environment and spatial variability of temperature over debris is poorly understood based on multiple measurements of air and surface temperature from three ablation seasons 2012 14 we investigate the variability of temperature over lirung glacier nepal in order to reveal how air temperature is affected by the debris cover and improve ways to extrapolate it we investigate how much on glacier temperature deviates from that predicted from a valley lapse rate lr analyse on glacier lrs and test regression models of air temperature and surface temperature air temperature over the debris covered glacier tongue is much higher than what a valley lr would prescribe so an extrapolation from off glacier stations is not applicable an on glacier lr is clearly defined at night with strong correlation but not during the day when the warming debris disrupts the elevation control an alternative to derive daytime air temperature is to use a relationship between air and surface temperature as previously suggested we find strong variability during daytime that should be accounted for if these regressions are used for temperature extrapolation

longitudinal variations in glacial flow theory and test using data from the byrd station strain network antarctica application de la theorie de budd 1970 des effets du lit sur les variations d ecoulement du glacier aux observations de la calotte de glace a la station byrd on utilise une rheologie visqueuse lineaire et on resout une equation biharmonique des variations des efforts et des vitesses de deformation les conditions aux limites comportent une topographie du fond avec ondulations glissements et cisaillements

influence of subglacial geology on the position of a west antarctic ice stream from seismic observations ice streams drain much of the interior west antarctic ice sheet and buffer the main ice reservoir from oceanic influences1 2 the slow flowing interior feeds the floating ross ice shelf with ice via fast flowing ice streams3 that are believed to modulate sea level change through their control of inland ice storage understanding ice stream behaviour and predicting the response to climate change4 requires a better knowledge of the subglacial geology5 6 it is known that a thawed ice bed and high pressure basal water are necessary but not sufficient conditions to cause ice streaming7 8 moreover it has been hypothesized that a soft sedimentary bed is also required because of its intrinsic low frictional resistance to flow9 and owing to its high erodibility so as to generate till that can deform and lubricate ice motion10 11 or to bury rough features and smooth the bed for sliding here we use seismic observations to provide evidence that one margin of the upglacier part of an ice stream is directly above the boundary of a basin with such sedimentary fill the ice stream is within the basin and the ice outside the basin is slow flowing the basin fill presents an order of magnitude lower frictional resistance to ice flow than the subglacial material outside the basin we conclude that the ice stream position is dependent on subglacial geology

changes in the configuration of ice stream flow from the west antarctic ice sheet surface based ice penetrating radar profiles on the northeast flank of siple dome support the hypothesis that a curvilinear scar first observed in advanced very high resolution radiometer satellite imagery represents the margin of a formerly active ice stream the scar defines the southwestern boundary of an ice stream flowing from ice stream c to ice stream d close to where it enters the ross ice shelf our studies show that the scar coincides with a trough and upward step in surface topography approximately 5 km across underlain by a zone of disturbed internal stratigraphy revealed by the radar burial depth of the disturbed zone enables us to calculate the time of shutdown as occurring prior to approximately 1 3 ka the configuration of the ice streams draining the west antarctic ice sheet into the ross ice shelf evidently changes with time and attempts to predict the evolution of the ice sheet must incorporate this observation

annual accumulation for greenland updated using ice core data developed during 2000 2006 and analysis of daily coastal meteorological data an updated accumulation map for greenland is presented on the basis of 39 new ice core estimates of accumulation 256 ice sheet estimates from ice cores and snow pits used in previous maps and reanalysis of time series data from 20 coastal weather stations the period 1950 2000 is better represented by the data than are earlier periods ice sheetwide accumulation was estimated based on kriging the average accumulation 95 confidence interval or 2 times standard error over the greenland ice sheet is 30 0 2 4 g cm 2 a 1 with the average accumulation above 2000 m elevation being essentially the same 29 9 2 2 g cm 2 a 1 at higher elevations the new accumulation map maintains the main features shown in previous maps however there are five coastal areas with obvious differences southwest northwest and eastern regions where the accumulation values are 20 50 lower than previously estimated and southeast and northeast regions where the accumulation values are 20 50 higher than previously estimated these differences are almost entirely due to new coastal data the much lower accumulation in the southwest and the much higher accumulation in the southeast indicated by the current map mean that long term mass balance in both catchments is closer to steady state than previously estimated however uncertainty in these areas remains high owing to strong gradients in precipitation from the coast inland a significant and sustained precipitation measurement program will be needed to resolve this uncertainty copyright 2009 by the american geophysical union

discovery of till deposition at the grounding line of whillans ice stream we report on the discovery of a grounding line sedimentary wedge till delta deposited by whillans ice stream west antarctica our observation is that grounding line deposition serves to thicken the ice and stabilize the position of the grounding line the ice thickness at the grounding line is greater than that of floating ice in hydrostatic equilibrium thus the grounding line will tend to remain in the same location despite changes in sea level until sea level rises enough to overcome the excess thickness that is due to the wedge further our observation demonstrates the occurrence of rapid subglacial erosion sediment transport by distributed subglacial till deformation and grounding line sedimentation which have important implications for ice dynamics numerical modeling of ice flow and interpretation of the sedimentation record