cryosphere applications of nscat data though designed to measure vector winds over the ocean new imaging techniques facilitate the use of nasa scatterometer data nscat in cryosphere studies nscat provides data of unprecedented coverage resolution and quality which when coupled with the scatterometer image reconstruction with filtering sirf algorithm enables images of spl sigma sup o at resolutions approaching 8 km over stationary targets such images are useful in ice mapping and classification and multidecadal studies are possible by comparison with seasat scatterometer sass data the utility of nscat data in polar ice studies is illustrated through a review of two cryosphere applications of nscat data 1 sea ice mapping and tracking and 2 ice sheet change in greenland and antarctica the wide swath and frequent revisit coupled with incidence and azimuth angle diversity makes nscat data very effective in mapping the extent of sea ice in greenland snow and ice facies are clearly delineated on the basis of the seasonally dependent radar backscattering cross section due to sensitivity of radar backscatter to diagenetic changes occurring at and beneath the surface comparison of nscat and sass data enables study of change in greenland between 1978 and 1996

detection of snowmelt regions on the greenland ice sheet using diurnal backscatter change snowmelt regions on greenland ice are mapped daily with the seawinds wideswath ku band 13 4 ghz scatterometer on the quikscat satellite the approach exploits the high temporal resolution of seawinds quikscat data for the melt mapping using diurnal backscatter change independent of the absolute calibration the results reveal several pronounced melting and refreezing events and effects of topography are evident in the melt patterns the spatial resolution is sufficient to identify melt features on the sukker toppen iskappe west of the main ice sheet an anomalous warming event caused by downward mixing of warm air is detected in late september 1999 over the west flank of the southern greenland ice sheet time series images of melt regions are presented over the period from summer to the fall freeze up the satellite observations are verified with in situ measurements from the greenland climate network stations

integrated pan arctic melt onset detection from satellite active and passive microwave measurements 2000 2009 1 an integrated pan arctic melt onset data set is generated for the first time by combining estimates derived from active and passive microwave satellite data using algorithms developed for the northern high latitude land surface ice caps large lakes and sea ice the data set yields new insights into the spatial and temporal patterns of mean melt onset date mmod and the associated geographic and topographic controls for example in the terrestrial arctic tree fraction and latitude explain more than 60 of the variance in mmod with the former exerting a stronger influence on mmod than the latter elevation is also found to be an important factor controlling mmod with most of the arctic exhibiting significant positive relationships between mmod and elevation with a mean value of 24 5 m d 1 melt onset progresses fastest over land areas of uniform cover or elevation 40 80 km d 1 or both and slows down in mountainous areas on ice caps and in the forest tundra ecotones over sea ice melt onset advances very slowly in the marginal seas while in the central arctic the rate of advance can exceed 100 km d 1 comparison of the observed mmod with simulated values from the third version of the canadian coupled global climate model showed good agreement over land areas but weaker agreement over sea ice particularly in the central arctic where simulated mmod is about 2 3 weeks later than observed because of a cold bias in simulated surface air temperatures over sea ice

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

monitoring ice sheet behavior from space satellite remote sensing has revolutionized ice sheet research a variety of instruments sensitive to different parts of the electromagnetic spectrum take what the human eye detects as a flat white desert and provide data sets rich in scientific information image based maps of ice sheets are becoming commonplace and have become an integral component of field work more than a pretty picture the digital character of the satellite data from these instruments has become fundamental to the production of elevation motion accumulation and reflectance data sets visible imagery shows the scientist a wealth of features that offer clues to the history and current behavior of the ice sheet radar and microwave imagery provide information from beneath the surface and have been used to estimate snow accumulation rates interferometry principles have recently been applied to measure surface topography and ice motion with unparalleled precision nonimaging instruments also keep a watchful eye monitoring the ice sheet for indications of growth or shrinkage further expansion of the uses of satellite data is anticipated in the future

importance of seasonal and annual layers in controlling backscatter to radar altimeters across the percolation zone of an ice sheet radar altimeters are one of the main tools for measuring elevation changes across the antarctic and greenland ice sheets and larger ice caps a ground based radar was deployed in autumn 2004 and spring 2006 in the percolation zone of the greenland ice sheet this radar is a high bandwidth system operating in the ku band the same frequency as several satellite altimeters measurements were made over an elevation range of 1795 to 2350 m along with snow pit and shallow core studies these measurements demonstrate the spatial and temporal variations in the backscatter relative strengths of surface and volume reflections change dramatically between spring and autumn and there is also high spatial variability across the percolation zone the extent of percolation will affect elevation estimates made by radar altimeters

variability in ice phenology on great bear lake and great slave lake northwest territories canada from seawinds quikscat 2000 2006 abstract the temporal evolution of the backscatter coefficient sigma nought from quikscat was evaluated for monitoring ice phenology on great bear lake 66 n 121 w and great slave lake 61 40 n 114 w northwest territories canada results indicated that from quikscat can be used to detect melt onset water clear of ice and freeze onset dates on both lakes an ice phenology algorithm was then developed to assess the spatiotemporal variability on both lakes from quikscat for the period 2000 2006 results showed that for great slave lake the average melt onset date occurred on year day yd 123 the average water clear of ice date was on yd164 and the average freeze onset date was on yd330 on great bear lake the average melt onset date occurred on yd139 the average water clear of ice date was yd191 and the average freeze onset date was yd321 ice cover remained present for at least five weeks longer on great bear lake than on great slave lake and most of the difference can be explained by earlier ice melt on great slave lake spatially on great bear lake melt onset took place first in the eastern arm water clear of ice occurred first in southeastern and western arms and freeze onset appeared first in the northern arm and along the shorelines on great slave lake melt onset began first in the central basin and then progressed to the northern and eastern arms later in the season the central basin of great slave lake cleared earlier than the periphery due to the discharge from the slave river freeze onset on great slave lake occurred first within the east arm closely followed by the north and west arms and then finally in the centre of the main basin

a ground based radar backscatter investigation in the percolation zone of the greenland ice sheet abstract satellite radar altimeters and scatterometers deployed over ice sheets experience backscatter from the surface and from within the snowpack termed surface and volume backscatter respectively in order to assess the errors in satellite altimeter measurements it is vital to know where the return is originating from in the snowpack this return can vary spatially and temporally seasonal variations in the volume backscatter can be a major complicating factor in the radar return from the percolation zone ground based step frequency radar was deployed in the percolation zone of the greenland ice sheet at 1945 m elevation 69 51n 47 15w previous measurements in this area made by scientists from the byrd polar research centre and the university of kansas undertaken prior to summer melt events have shown the strongest backscatter from ice features at around 1 m depth buried beneath the previous end of summer surface in autumn 2004 radar measurements in the ku band with bandwidths of 1 and 8 ghz were made alongside detailed stratigraphic observations within a 1 km 2 site the radar results revealed no continuous reflecting horizons in the upper 3 5 m of the firn shallow cores and snowpits also indicated that there were no spatially continuous stratigraphic horizons across the study site an average electromagnetic wave velocity of 2 11 0 05 10 8 m s 1 was determined for the upper metre of the firn surface and volume backscatter at vertical incidence were calculated using a standard model the contribution of the surface backscatter to the total backscatter was on average 6 db higher than that of the volume backscatter however at the higher 8 ghz bandwidth the strongest return frequently originated not from the surface but from within the upper 30 cm of the snowpack most probably from thin ice layers at 1 ghz bandwidth these ice layers were not always resolved their return merged with the surface return causing it to broaden with the peak and leading edge moving down modelling using density and thickness measurements from shallow cores and snowpits showed that the backscatter from these shallow thin ice layers could be stronger than the surface return owing to constructive interference from the top and base of the layers

elevation change of the antarctic ice sheet 1995 2000 from ers 2 satellite radar altimetry we analyzed antarctic ice sheet elevation change dh dt from 1995 to 2000 using 123 million elevation change measurements from european remote sensing 2 ice mode satellite radar altimeter data covering an area of about 7 2 million km sup 2 almost all drainage basins in east antarctica had average dh dt values within spl plusmn 3 0 cm year whereas drainage basins in west antarctica had substantial spatial variability with average dh dt values ranging between 11 to 12 cm year the east antarctic ice sheet had a five year trend of 1 spl plusmn 0 6 cm year where 13 out of the 14 basins had either a positive trend or a trend that was not significantly different than zero the west antarctic ice sheet had a five year trend of 3 6 spl plusmn 1 0 cm year due largely to strong negative trends of around 10 cm year for basins in marie byrd land along the pacific sector of the antarctic coast the continent as a whole had a five year dh dt trend of 0 4 spl plusmn 0 4 cm year finally time series constructed for the pine island thwaites de vicq and land glaciers in west antarctic showed five year dh dt trends from 26 to 135 cm year that were significantly more negative than the average dh dt trends in their respective basins the strongly negative dh dt values for these coastal glacier outlets are consistent with recently reported results indicating increased basal melting at these glaciers grounding lines caused by ocean thermal forcing

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

satellite derived melt season surface temperature of the greenland ice sheet 2000 2005 and its relationship to mass balance 1 mean clear sky surface temperature of the greenland ice sheet was measured for each melt season from 2000 to 2005 using moderate resolution imaging spectroradiometer modis derived land surface temperature lst data product maps during the period of most active melt the mean clear sky surface temperature of the ice sheet was highest in 2002 8 29 5 29 c and 2005 8 29 5 43 c compared to a 6 year mean of 9 04 5 59 c in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005 surface temperature variability shows a correspondence with the dry snow facies of the ice sheet a reduction in area of the dry snow facies would indicate a more negative mass balance surface temperature variability generally increased during the study period and is most pronounced in the 2005 melt season this is consistent with surface instability caused by air temperature fluctuations

radar measurements of melt zones on the greenland ice sheet surface based microwave radar measurements were performed at a location on the western flank of the greenland ice sheet here firn metamorphosis is dominated by seasonal melt which leads to marked contrasts in the vertical structure of winter and summer firn this snow regime is also one of the brightest radar targets on earth with an average backscatter coefficient of 0 db at 5 3 ghz and an incidence angle of 25 by combining detailed observations of firn physical properties with ranging radar measurements we find that the glaciological mechanism associated with this strong electromagnetic response is summer ice lens formation within the previous winter s snow pack this observation has important implications for monitoring and understanding changes in ice sheet volume using space borne microwave sensors

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

mapping of ice layer extent and snow accumulation in the percolation zone of the greenland ice sheet 1 the greenland ice sheet underwent record extensive melt in 2002 and prolonged melt in 2003 the severe melting created a significant and extensive ice layer over the greenland ice sheet an innovative approach is developed to detect the ice layer formation using data acquired by the seawinds scatterometer on the quikscat satellite quikscat backscatter together with in situ data from automatic weather stations of the greenland climate network are used to map the extent of ice layer formation the results reveal areas of extensive ice layer formed by the 2002 melt which is consistent with the maximum melt extent in 2002 moreover during freezing seasons quikscat data show a linear decrease in backscatter in decibels or db that is related to the amount of snow accumulation in the ice layer formation region this snow accumulation signature is caused by the attenuation of radar waves in the snow layer accumulating since the last major melt event whose thickness appears as an exponential function in relation to the backscatter signature we use the greenland climate network data to calibrate the quikscat accumulation rate in order to estimate and map snow accumulation quikscat results capture the extreme snowfall in mid april 2003 which deposited more than 0 5 m of snow in a day as measured by the automated weather station at the nasa south east site large scale quikscat results show an anomalous increase of snow accumulation over the southeast region of greenland during the 2002 2003 freezing season

variations in snowpack melt on the greenland ice sheet based on passive microwave measurements a simple microwave emission model is used to simulate 37 ghz brightness temperatures associated with snowpack melt conditions for locations across the greenland ice sheet the simulated values are utilized as threshold values and compared to daily gridded smmr and ssm i passive microwave data in order to reveal regions experiencing melt the spatial extent of the area classified as melting is examined on a daily monthly and seasonal may august basis for 1979 91 the typical seasonal cycle of melt coverage shows melt beginning in late april a rapid increase in the melting area from mid may to mid july a rapid decrease in melt extent from late july through mid august and cessation of melt in late september seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3 8 annually significant at the 95 confidence interval this increase is dominated by statistically significant positive trends in melt coverage during july and august in the west and southwest of the ice sheet we find that a linear correlation between microwave derived melt extent and a surface measure of ablation rate is significant in june and july but not august so caution must be exercised in using the microwave derived melt extents in august nevertheless knowledge of the variability of snowpack melt on the greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the arctic and examining the impact of climate change on the ice sheet

progressive increase in ice loss from greenland 1 laser altimeter measurements over greenland show increasing thickening rates above 2000 m reflecting increasing snowfall in a warming climate but near coastal thinning rates have increased substantially since the mid 1990s and net mass loss more than doubled from an average of 4 50 gt yr 1 between 1993 4 and 1998 9 to 57 105 gt yr 1 between 1998 9 and 2004 this increasing trend is very similar to findings from independent mass budget studies but differs widely from ers radar altimeter results this may result from limitations associated with the large ers footprint over sloping and undulating surfaces that typify fast narrow glaciers where thinning is most pronounced

improved elevation change measurement of the southern greenland ice sheet from satellite radar altimetry a new analysis of seasat and geosat satellite radar altimeter measurements over the greenland ice sheet was performed to determine surface elevation change the new analysis includes twice as many measurements and has 50 greater spatial coverage than the authors previous study in addition a precise global ocean reference network created from four years of topex poseidon altimeter data is used to obtain improved estimates of altimeter orbit errors and measurement system biases the results show that the average elevation change of the southern greenland ice sheet above 2000 m from 1978 to 1988 is not significantly different than zero this contradicts earlier and even more recent studies that reported positive ice sheet growth rates and suggested increased precipitation due to a warmer polar climate

snow and ice facies variability and ice layer formation on canadian arctic ice caps 1999 2005 1 time series of enhanced resolution data from the seawinds scatterometer aboard quikscat were used to map the distribution of snow and ice surface facies and ice layer formation in the percolation zone on ice caps in the queen elizabeth islands during the period 1999 2005 iterative self organizing data analysis classification of the mean postfreeze up biweekly average 0 signal for the 7 year period resulted in the delineation of four snow and ice surface facies interpreted as the percolation saturation superimposed ice and glacier ice zones analysis with national centers for environmental prediction national center for atmospheric research reanalysis reveals that changes in geopotential height in the troposphere 700 500 and 300 hpa and air temperature 700 hpa level are positively negatively correlated with area changes in the glacier ice percolation and saturation zones and changes in facies boundary elevation the change in biweekly averaged backscatter following the freeze up periods between successive autumns was used to map changes in the distribution of ice layers formed by meltwater percolation and refreezing in the snowpack within the percolation zone strongly positive air temperature anomalies at the 700 hpa level in 2001 and 2005 are consistent with extensive ice layer formation in the percolation zones of all ice caps such large interannual changes in ice layer formation are likely associated with large changes to the density profile of the snowpack and may be associated with surface elevation changes that are unrelated to changes in surface mass balance

early last interglacial greenland ice sheet melting and a sustained period of meridional overturning weakening a model analysis of the uncertainties proxy data suggest that the last interglacial lig 130 116 ka bp climate was characterized by higher temperatures a partially melted greenland ice sheet gis and a changed atlantic meridional overturning circulation amoc notwithstanding the uncertainties in lig palaeoclimatic reconstructions this setting potentially provides an opportunity to evaluate the relation between gis melt and the amoc as simulated by climate models however first we need to assess the extent to which a causal relation between early lig gis melt and the weakened amoc is plausible with a series of transient lig climate simulations with the loveclim earth system model we quantify the importance of the major known uncertainties involved in early lig gis melt scenarios based on this we construct a specific scenario that is within the parameter space of uncertainties and show that it is physically consistent that early lig gis melting kept the amoc weakened notwithstanding this scenario is at the extreme end of the parameter space assuming that proxy based reconstructions of early lig amoc weakening offer a realistic representation of its past state this indicates that either 1 the amoc weakening was caused by other forcings than early lig gis melt or 2 the early lig amoc was less stable than indicated by our simulations and a small amount of gis melt was sufficient to keep the amoc in the weak state of a bi stable regime we argue that more intensive research is required because of the high potential of the early lig to evaluate model performance in relation to the amoc response to gis melt

seasonal and interannual variations of firn densification and ice sheet surface elevation at the greenland summit seasonal and interannual variations in surface elevation at the greenland summit are modeled using a new temperature dependent formulation of firn densification and are compared with elevations from european remote sensing satellite ers 1 2 radar altimetry the rate constant and activation energy usually set as constants in the arrhenius type relation are strongly temperature dependent based on measurements of crystal growth rates a multiplicative factor in the densification rate accounts for differences between densification and grain growth rates and is chosen to match the modeled and measured density profiles from 0 to 40 m the stronger temperature dependence produces a significant seasonal cycle in the densification rate in the upper firn much of the densification and consequent surface lowering occur within 3 months in late spring early summer followed by a build up from accumulation modeled elevation changes using automatic weather station measurements of temperature and accumulation and modeled precipitation agree well with observations the respective seasonal amplitudes are 18 and 25 cm peak to peak with minima in mid summer the minimum elevation in 1995 is driven mainly by a temporary accumulation decrease and secondarily by warmer temperatures increased compaction driven by a summer warming trend decreases the modeled elevation 1992 99 by 20 cm but accumulation increases in latter years dominate the overall 4 2 cm a 1 trend

changes in greenland ice sheet elevation attributed primarily to snow accumulation variability the response of grounded ice sheets to a changing climate critically influences possible future changes in sea level recent satellite surveys over southern greenland show little overall elevation change at higher elevations but large spatial variability using satellite studies alone it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability here we derive changes in ice sheet elevation in southern greenland for the years 1978 88 using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation our patterns of accumulation driven elevation change agree closely with contemporaneous satellite measurements of ice sheet elevation change and we therefore attribute the changes observed in 1978 88 to variability in snow accumulation similar analyses of longer ice core records show that in this decade the greenland ice sheet exhibited typical variability at high elevations well within the long term natural variability our results indicate that a better understanding of ice sheet mass changes will require long term measurements of both surface elevation and snow accumulation

greenland ice sheet increased coastal thinning repeated laser altimeter surveys and modelled snowfall summer melt show average ice loss from greenland between 1997 and 2003 was 80 12 km3 yr 1 compared to about 60 km3 yr 1 for 1993 4 1998 9 half of the increase was from higher summer melting with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation velocities of one large glacier almost doubled between 1997 and 2003 resulting in net loss from its drainage basin by about 20 km3 of ice between 2002 and 2003 copyright 2004 by the american geophysical union

a five year record of summer melt on eurasian arctic ice caps abstract climatologies and annual anomaly patterns 2000 04 of melt season duration and dates of melt onset freeze up on eurasian arctic ice masses were derived from quick scatterometer quikscat backscatter data severnaya zemlya russia has later melt onset earlier freeze up and shorter melt seasons than svalbard norway novaya zemlya russia in all three archipelagos 2001 was the longest melt season and 2000 was the shortest anomalously long short melt seasons on svalbard were associated with negative positive sea ice concentration anomalies along the north coast in june and august annual mean melt duration was strongly correlated with the mean june august ncep ncar reanalysis 850 hpa air temperature allowing reconstruction of melt durations for the period of 1948 2005 the 2000 04 pentad had the second or third longest mean melt duration of all pentads in the 1950 2004 epoch while the 1950 54 pentad probably had the longest integration of these results with previous results from gre

snowmelt on the greenland ice sheet as derived from passive microwave satellite data abstract the melt extent of the snow on the greenland ice sheet is of considerable importance to the ice sheet s mass and energy balance as well as arctic and global climates by comparing passive microwave satellite data to field observations variations in melt extent have been detected by establishing melt thresholds in the cross polarized gradient ratio xpgr the xpgr defined as the normalized difference between the 19 ghz horizontal channel and the 37 ghz vertical channel of the special sensor microwave imager ssm i exploits the different effects of snow wetness on different frequencies and polarizations and establishes a distinct melt signal using this xpgr melt signal seasonal and interannual variations in snowmelt extent of the ice sheet are studied the melt is found to be most extensive on the western side of the ice sheet and peaks in late july moreover there is a notable increasing trend in melt area between the years 1979 and 1991 of 4 4 per year which came to an abrupt halt in 1

using the magmatic record to constrain the growth of continental crust the eoarchean zircon hf record of greenland abstract southern west greenland contains some of the best studied and best preserved magmatic eoarchean rocks on earth and these provide an excellent vantage point from which to view long standing questions regarding the growth of the earliest continental crust in order to address the questions surrounding early crustal growth and complementary mantle depletion we present laser ablation split stream lass analyses of the u pb and hf isotope compositions of zircon from eleven samples of the least altered meta igneous rocks from the itsaq amitsoq gneisses of the isukasia and nuuk regions of southern west greenland this analytical technique allows a less ambiguous approach to determining the age and hf isotope composition of complicated zircon results corroborate previous findings that eoarchean zircon from the itsaq gneiss 3 85 ga to 3 63 ga were derived from a broadly chondritic source in contrast to the sm nd whole rock isotope record for southern west greenland the zircon lu hf isotope record provides no evidence for early mantle depletion nor does it suggest the presence of crust older than 3 85 ga in greenland utilizing lass u pb and hf data from the greenland zircons studied here we demonstrate the importance of focusing on the magmatic rather than detrital zircon record to more confidently understand early crustal growth and mantle depletion we compare the greenland hf isotope data with other eoarchean magmatic complexes such as the acasta gneiss complex nuvvuagittuq greenstone belt and the gneissic complexes of southern africa and all lack zircons with suprachondritic hf isotope compositions in total these data suggest only a very modest volume of crust was produced during or survived from the hadean and earliest eoarchean there remains no record of planet scale early earth mantle depletion in the hf isotope record prior to 3 8 ga

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

accumulation map for the greenland ice sheet 1971 1990 an updated accumulation map for the greenland ice sheet for the period 1971 1990 based on kriging of accurate point estimates developed during the past decade at over 40 points plus over 200 historical points shows an average water accumulation of 30 g cm 2yr 1 average uncertainty standard deviation in estimates of point accumulation for the interior part of the ice sheet where the kriging drift surface is well constrained is approximately 7 g cm 2yr 1 or 24 of mean accumulation because there are multiple cores in most regions the regional uncertainty in accumulation should be considerably lower than the 7 g cm 2yr 1 average uncertainty at a point there are still many areas on the ice sheet including northwest and southern greenland where annual accumulation remains poorly constrained

melt season duration on canadian arctic ice caps 2000 2004 1 the extent and duration of summer melt on ice caps in the queen elizabeth islands qei nunavut canada in 2000 2004 were mapped using enhanced resolution quikscat qscat scatterometer images the mean melt duration depends mainly on surface elevation and distance from baffin bay over most ice caps inter annual variations in melt duration and the variation in melt duration with elevation are closely related to variations in the july 500 hpa height over the qei pressure related variability in the vertical gradient of near surface air temperature appears to be a major control on the inter annual variations in average melt duration

variations of near surface firn density in the lower accumulation area of the greenland ice sheet pâkitsoq west greenland firn density variations have been studied in the lower accumulation area of the greenland ice sheet 1440 1620 m a s l near p kitsoq west greenland the main control on density in the near surface firn layer of 5 10 m thickness is the formation of ice layers by the refreezing of meltwater that reaches depths of 2 4 m below the surface the density variations are described by the ratio of annual surface melt m to the annual accumulation c the ratio m c is about 0 6 at the run off limit at about 1400 m a s l in the study area where refreezing of meltwater transforms snow into impermeable ice the mean density of near surface firn decreases with elevation reflecting a decrease in melt with elevation there is a surprising decrease in firn density at depths of more than about 4 m below the 1991 summer surface which reflects lower melt rates and or higher accumulation in the early 1980s and late 1970s when this firn was passing through the surface layer the formation of such low density firn may have partially contributed to the 1978 85 thickening of the ice sheet observed by satellite radar altimetry near surface firn density is therefore very sensitive to climate change and might be an attractive target for climate monitoring

melt season duration and ice layer formation on the greenland ice sheet 2000 2004 1 time series of enhanced resolution quikscat images were used to map the extent and duration of surface melt and the distribution of ice layer formation on the greenland ice sheet in the period 2000 2004 apart from the bare ice and the mixed pixels 10 along the ice sheet margin where melt cannot be determined reliably annual melt duration and melt anomaly maps were produced across the ice sheet 90 for each summer over the 5 year period the mean melt duration for the ice sheet ranged from 14 3 to 20 5 d the proportion of the ice sheet that experienced melting in a given year ranged from 44 2 to 79 2 extensive melt in 2002 was caused by a single melt event of a few days duration this event was associated with the intrusion of a ridge of high pressure from the north atlantic ocean that brought warm air onto the ice sheet the change in biweekly averaged backscatter between the freeze up periods in the current and previous falls was used to identify changes in the distribution of ice layers in snow between successive melt seasons the year 2002 had the maximum melt extent and duration and ice layer formation extended to higher elevations than in other years interannual changes in the distribution of ice layer formation may be associated with changes in surface height that are not necessarily indicative of mass balance changes mapping of ice layer formation is thus potentially useful for interpreting both real and apparent height changes measured by altimetry

embryonic rifting zone revealed by a high density survey on the southern margin of the southern okinawa trough offshore northern ishigaki jima island in the southern okinawa trough offers outstanding opportunities to explore the rifting stage of a backarc system we report the results of integrated marine

elevation change of the southern greenland ice sheet seasat and geosat satellite altimeter measurements for the greenland ice sheet south of 72 degreesn latitude show that surface elevations above 2000 meters increased at an average rate of only 1 5 0 5 centimeters per year from 1978 to 1988 in contrast elevation changes varied regionally from 15 to 18 centimeters per year seasonally by 15 centimeters and interannually by 8 centimeters the average growth rate is too small to determine if the greenland ice sheet is undergoing a long term change due to a warmer polar climate

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

mass changes of the greenland and antarctic ice sheets and shelves and contributions to sea level rise 1992 2002 changes in ice mass are estimated from elevation changes derived from 10 5 years greenland and 9 years antarctica of satellite radar altimetry data from the european remote sensing satellites ers 1 and 2 for the first time the dh dt values are adjusted for changes in surface elevation resulting from temperature driven variations in the rate of firn compaction the greenland ice sheet is thinning at the margins 42 2g t a 1 below the equilibrium line altitude ela and growing inland 53 2g t a 1 above the ela with a small overall mass gain 11 3g t a 1 0 03 mm a 1 sle sea level equivalent the ice sheet in west antarctica wa is losing mass 47 4g t a 1 and the ice sheet in east antarctica ea shows a small mass gain 16 11 gt a 1 for a combined net change of 31 12 gt a 1 0 08 mm a 1 sle the contribution of the three ice sheets to sea level is 0 05 0 03 mm a 1 t he antarctic ice shelves show corresponding mass changes of 95 11 gt a 1 in wa and 142 10 gt a 1 in ea thinning at the margins of the greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate the marked thinnings in the pine island and thwaites glacier basins of wa and the totten glacier basin in ea are probably ice dynamic responses to long term climate change and perhaps past removal of their adjacent ice shelves the ice growth in the southern antarctic peninsula and parts of ea may be due to increasing precipitation during the last century

resolution enhancement of spaceborne scatterometer data a method for generating enhanced resolution radar images of the earth s surface using spaceborne scatterometry is presented the technique is based on an image reconstruction technique that takes advantage of the spatial overlap in scatterometer measurements made at different times to provide enhanced imaging resolution the reconstruction algorithm is described and the technique is demonstrated using both simulated and actual seasat a scatterometer sass measurements the technique can also be used with ers 1 scatterometer data the sass derived images which have approximately 4 km resolution illustrate the resolution enhancement capability of the technique which permits utilization of both historic and contemporary scatterometer data for medium scale monitoring of vegetation and polar ice the tradeoff between imaging noise and resolution inherent in the technique is discussed