http://www.the-cryosphere.net/ The Cryosphere Latest Articlesenhttp://www.the-cryosphere.net/7/933/2013/<b>Corrigendum to "Influence of ablation-related processes in the build-up of simulated Northern Hemisphere ice sheets during the last glacial cycle" published in The Cryosphere, 7, 681&ndash;698, 2013</b><br /><br />The Cryosphere, 7, 933-934, 2013<br /><br />Author(s): S. Charbit, C. Dumas, M. Kageyama, D. M. Roche, and C. Ritz<br /><br />No abstract available.Mon, 17 Jun 2013 00:00:00 +0200http://www.the-cryosphere.net/7/917/2013/<b>Seasonal controls on snow distribution and aerial ablation at the snow-patch and landscape scales, McMurdo Dry Valleys, Antarctica</b><br /><br />The Cryosphere, 7, 917-931, 2013<br /><br />Author(s): J. W. Eveland, M. N. Gooseff, D. J. Lampkin, J. E. Barrett, and C. D. Takacs-Vesbach<br /><br />Accumulated snow in the McMurdo Dry Valleys, while limited, has great ecological significance to subnivian soil environments. Though sublimation dominates the ablation process in this region, measurable increases in soil moisture and insulation from temperature extremes provide more favorable conditions with respect to subnivian soil communities. While precipitation is not substantial, significant amounts of snow can accumulate, via wind transport, in topographic lees along the valley bottoms, forming thousands of discontinuous snow patches. These patches have the potential to act as significant sources of local meltwater, controlling biogeochemical cycling and the landscape distribution of microbial communities. Therefore, determining the spatial and temporal dynamics of snow at multiple scales is imperative to understanding the broader ecological role of snow in this region. <br><br> High-resolution satellite imagery acquired during the 2009–2010 and 2010–2011 austral summers was used to quantify the distribution of snow across Taylor and Wright valleys. Extracted snow-covered area from the imagery was used as the basis for assessing inter-annual variability and seasonal controls on accumulation and ablation of snow at multiple scales. In addition to landscape analyses, fifteen 1 km² plots (3 in each of 5 study regions) were selected to assess the prevalence of snow cover at finer spatial scales, referred to herein as the snow-patch scale. Results confirm that snow patches tend to form in the same locations each year with some minor deviations observed. At the snow-patch scale, neighboring patches often exhibit considerable differences in aerial ablation rates, and particular snow patches do not reflect trends for snow-covered area observed at the landscape scale. These differences are presumably related to microtopographic influences acting on individual snow patches, such as wind sheltering and differences in snow depth due to the underlying topography. This highlights the importance of both the landscape and snow-patch scales in assessing the effects of snow cover on biogeochemical cycling and microbial communities.Tue, 11 Jun 2013 00:00:00 +0200http://www.the-cryosphere.net/7/905/2013/<b>Recent changes in spring snowmelt timing in the Yukon River basin detected by passive microwave satellite data</b><br /><br />The Cryosphere, 7, 905-916, 2013<br /><br />Author(s): K. A. Semmens and J. M. Ramage<br /><br />Spring melt is a significant feature of high latitude snowmelt dominated drainage basins influencing hydrological and ecological processes such as snowmelt runoff and green-up. Melt duration, defined as the transition period from snowmelt onset until the end of the melt refreeze, is characterized by high diurnal amplitude variations (DAV) where the snowpack is melting during the day and refreezing at night, after which the snowpack melts constantly until depletion. Determining trends for this critical period is necessary for understanding how the Arctic is changing with rising temperatures and provides a baseline from which to assess future change. To study this dynamic period, brightness temperature (<i>T</i>_b) data from the Special Sensor Microwave Imager (SSM/I) 37 V-GHz frequency from 1988 to 2010 were used to assess snowmelt timing trends for the Yukon River basin, Alaska/Canada. Annual <i>T</i>_b and DAV for 1434 Equal-Area Scalable Earth (EASE)-Grid pixels (25 km resolution) were processed to determine melt onset and melt refreeze dates from <i>T</i>_b and DAV thresholds previously established in the region. Temporal and spatial trends in the timing of melt onset and melt refreeze, and the duration of melt were analyzed for the 13 sub-basins of the Yukon River basin with three different time interval approaches. Results show a lengthening of the melt period for the majority of the sub-basins with a significant trend toward later end of melt refreeze after which the snowpack melts day and night leading to snow clearance, peak discharge, and green-up. Earlier melt onset trends were also found in the higher elevations and northernmost sub-basins (Porcupine, Chandalar, and Koyukuk rivers). Latitude and elevation displayed the dominant controls on melt timing variability and spring solar flux was highly correlated with melt timing in middle (&sim;600–1600 m) elevations.Wed, 05 Jun 2013 00:00:00 +0200http://www.the-cryosphere.net/7/889/2013/<b>Quantifying present and future glacier melt-water contribution to runoff in a central Himalayan river basin</b><br /><br />The Cryosphere, 7, 889-904, 2013<br /><br />Author(s): M. Prasch, W. Mauser, and M. Weber<br /><br />Water supply of most lowland cultures heavily depends on rain and melt water from the upstream mountains. Especially melt-water release of alpine mountain ranges is usually attributed a pivotal role for the water supply of large downstream regions. Water scarcity is assumed as consequence of glacier shrinkage and possible disappearance due to global climate change (GCC), in particular for large parts of Central and Southeast Asia. In this paper, the application and validation of a coupled modeling approach with regional climate model (RCM) outputs and a process-oriented glacier and hydrological model is presented for the central Himalayan Lhasa River basin despite scarce data availability. Current and possible future contributions of ice melt to runoff along the river network are spatially explicitly shown. Its role among the other water balance components is presented. Although glaciers have retreated and will continue to retreat according to the chosen climate scenarios, water availability is and will be primarily determined by monsoon precipitation and snowmelt. Ice melt from glaciers is and will be a minor runoff component in summer monsoon-dominated Himalayan river basins.Tue, 28 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/877/2013/<b>Density assumptions for converting geodetic glacier volume change to mass change</b><br /><br />The Cryosphere, 7, 877-887, 2013<br /><br />Author(s): M. Huss<br /><br />The geodetic method is widely used for assessing changes in the mass balance of mountain glaciers. However, comparison of repeated digital elevation models only provides a glacier volume change that must be converted to a change in mass using a density assumption or model. This study investigates the use of a constant factor for the volume-to-mass conversion based on a firn compaction model applied to simplified glacier geometries with idealized climate forcing, and two glaciers with long-term mass balance series. It is shown that the "density" of geodetic volume change is not a constant factor and is systematically smaller than ice density in most cases. This is explained by the accretion/removal of low-density firn layers, and changes in the firn density profile with positive/negative mass balance. Assuming a value of 850 &pm; 60 kg m^&minus;3 to convert volume change to mass change is appropriate for a wide range of conditions. For short time intervals (&leq;3 yr), periods with limited volume change, and/or changing mass balance gradients, the conversion factor can however vary from 0–2000 kg m^&minus;3 and beyond, which requires caution when interpreting glacier mass changes based on geodetic surveys.Mon, 27 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/867/2013/<b>Mass balance, runoff and surges of Bering Glacier, Alaska</b><br /><br />The Cryosphere, 7, 867-875, 2013<br /><br />Author(s): W. Tangborn<br /><br />The historical net, ablation and accumulation daily balances, as well as runoff of Bering Glacier, Alaska are determined for the 1951–2011 period with the PTAA (precipitation-temperature-area-altitude) model, using daily precipitation and temperature observations collected at the Cordova and Yakutat weather stations, together with the area-altitude distribution of the glacier. The model mean annual balance for this 61 yr period is −0.6 m w.e., the accumulation balance is +1.4 and the ablation balance is −2.0 m w.e. Average annual runoff is 2.5 m w.e. Periodic surges of this glacier transport large volumes of ice to lower elevations where the ablation rate is higher, producing more negative balances and increasing runoff. Runoff from Bering Glacier (derived from simulated ablation and precipitation as rain) is highly correlated with four of the glacier surges that have occurred since 1951. Ice volume loss for the 1972–2003 period measured with the PTAA model is 2.7 km³ w.e. a⁻¹ and closely agrees with losses for the same period measured with the geodetic method. It is proposed that the timing and magnitude of daily snow accumulation and runoff, both of which are controlled by the glacier's area-altitude distribution and are calculated with the PTAA model, can be used to determine the probability that a glacier will surge.Mon, 27 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/855/2013/<b>Radio-frequency probes of Antarctic ice at South Pole</b><br /><br />The Cryosphere, 7, 855-866, 2013<br /><br />Author(s): D. Besson and I. Kravchenko<br /><br />Using hardware developed for the ARA (Askaryan Radio Array) particle astrophysics experiment, we herein report on the amplitude and temporal characteristics of polarized surface radar echo data collected in South Polar ice using radio sounding equipment with 0.5-ns echo-time sampling. We observe strong echoes at 6, 9.6, 13.9, 17, and 19 μs following vertical pulse emission from the surface, corresponding to reflectors in the upper half of the ice sheet. The synchronicity of those echoes for all broadcast azimuthal polarizations affirms the lack of observable birefringence over the upper half of the ice sheet. Of the five strongest echoes, three exhibit an evident amplitude correlation with the local surface ice flow direction, qualitatively consistent with measurements in East Antarctica. Combined with other radio echo sounding data, we conclude that observed birefringent asymmetries at South Pole are generated entirely in the lower half of the ice sheet. By contrast, birefringent asymmetries are observed at shallow depths in East Antarctica.Thu, 16 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/841/2013/<b>Snow cover thickness estimation using radial basis function networks</b><br /><br />The Cryosphere, 7, 841-854, 2013<br /><br />Author(s): E. Binaghi, V. Pedoia, A. Guidali, and M. Guglielmin<br /><br />This paper reports an experimental study designed for the in-depth investigation of how the radial basis function network (RBFN) estimates snow cover thickness as a function of climate and topographic parameters. The estimation problem is modeled in terms of both function regression and classification, obtaining continuous and discrete thickness values, respectively. The model is based on a minimal set of climatic and topographic data collected from a limited number of stations located in the Italian Central Alps. Several experiments have been conceived and conducted adopting different evaluation indexes. A comparison analysis was also developed for a quantitative evaluation of the advantages of the RBFN method over to conventional widely used spatial interpolation techniques when dealing with critical situations originated by lack of data and limited <i>n</i>-homogeneously distributed instrumented sites. The RBFN model proved competitive behavior and a valuable tool in critical situations in which conventional techniques suffer from a lack of representative data.Tue, 14 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/823/2013/<b>Satellite-derived volume loss rates and glacier speeds for the Cordillera Darwin Icefield, Chile</b><br /><br />The Cryosphere, 7, 823-839, 2013<br /><br />Author(s): A. K. Melkonian, M. J. Willis, M. E. Pritchard, A. Rivera, F. Bown, and S. A. Bernstein<br /><br />We produce the first icefield-wide volume change rate and glacier velocity estimates for the Cordillera Darwin Icefield (CDI), a 2605 km² temperate icefield in southern Chile (69.6° W, 54.6° S). Velocities are measured from optical and radar imagery between 2001–2011. Thirty-six digital elevation models (DEMs) from ASTER and the SRTM DEM are stacked and a weighted linear regression is applied to elevations on a pixel-by-pixel basis to estimate volume change rates. <br><br> The CDI lost mass at an average rate of −3.9 ± 1.5 Gt yr⁻¹ between 2000 and 2011, equivalent to a sea level rise (SLR) of 0.01 ± 0.004 mm yr⁻¹ and an area-averaged thinning rate of −1.5 ± 0.6 m w.e.(water equivalent) yr⁻¹. <br><br> Thinning is widespread, with concentrations near the front of two northern glaciers (Marinelli, Darwin) and one western (CDI-08) glacier. Thickening is apparent in the south, most notably over the advancing Garibaldi Glacier. The northeastern part of the CDI has an average thinning rate of −1.9 ± 0.7 m w.e. yr⁻¹, while the southwestern part has an average thinning rate of −1.0 ± 0.4 m w.e. yr⁻¹. <br><br> Velocities are obtained over many of the CDI glaciers for the first time. We provide a repeat speed time series at the Marinelli Glacier. There we measure maximum front speeds of 7.5 ± 0.2 m day⁻¹ in 2001, 9.5 ± 0.6 m day⁻¹ in 2003 and 10 ± 0.3 m day⁻¹ in 2011. The maintenance of high front speeds from 2001 to 2011 supports the hypothesis that Marinelli is in the retreat phase of the tidewater cycle, with dynamic thinning governed by the fjord bathymetry.Tue, 14 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/817/2013/<b>Brief communication "Global glacier volumes and sea level &ndash; small but systematic effects of ice below the surface of the ocean and of new local lakes on land"</b><br /><br />The Cryosphere, 7, 817-821, 2013<br /><br />Author(s): W. Haeberli and A. Linsbauer<br /><br />The potential contribution of glaciers and ice caps to sea level rise is usually calculated by comparing the estimated total ice volume with the surface area of the ocean. Part of this total ice volume, however, does not contribute to sea level rise because it is below the surface of the ocean or below the levels of future lakes on land. The present communication points to this so far overlooked phenomenon and provides a first order-of-magnitude estimate. It is shown that the effect is small (most likely about 1 to 6 cm sea level equivalent) but systematic, could primarily affect earlier stages of global glacier vanishing, and should therefore be adequately considered. Now-available techniques of slope-related high-resolution glacier bed modelling have the potential to provide more detailed assessments in the future.Wed, 08 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/797/2013/<b>Speedup and fracturing of George VI Ice Shelf, Antarctic Peninsula</b><br /><br />The Cryosphere, 7, 797-816, 2013<br /><br />Author(s): T. O. Holt, N. F. Glasser, D. J. Quincey, and M. R. Siegfried<br /><br />George VI Ice Shelf (GVIIS) is located on the Antarctic Peninsula, a region where several ice shelves have undergone rapid breakup in response to atmospheric and oceanic warming. We use a combination of optical (Landsat), radar (ERS 1/2 SAR) and laser altimetry (GLAS) datasets to examine the response of GVIIS to environmental change and to offer an assessment on its future stability. The spatial and structural changes of GVIIS (ca. 1973 to ca. 2010) are mapped and surface velocities are calculated at different time periods (InSAR and optical feature tracking from 1989 to 2009) to document changes in the ice shelf's flow regime. Surface elevation changes are recorded between 2003 and 2008 using repeat track ICESat acquisitions. We note an increase in fracture extent and distribution at the south ice front, ice-shelf acceleration towards both the north and south ice fronts and spatially varied negative surface elevation change throughout, with greater variations observed towards the central and southern regions of the ice shelf. We propose that whilst GVIIS is in no imminent danger of collapse, it is vulnerable to ongoing atmospheric and oceanic warming and is more susceptible to breakup along its southern margin in ice preconditioned for further retreat.Mon, 06 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/779/2013/<b>High-resolution interactive modelling of the mountain glacier–atmosphere interface: an application over the Karakoram</b><br /><br />The Cryosphere, 7, 779-795, 2013<br /><br />Author(s): E. Collier, T. Mölg, F. Maussion, D. Scherer, C. Mayer, and A. B. G. Bush<br /><br />The traditional approach to simulations of alpine glacier mass balance (MB) has been one-way, or offline, thus precluding feedbacks from changing glacier surface conditions on the atmospheric forcing. In addition, alpine glaciers have been only simply, if at all, represented in atmospheric models to date. Here, we extend a recently presented, novel technique for simulating glacier–atmosphere interactions without the need for statistical downscaling, through the use of a coupled high-resolution mesoscale atmospheric and physically-based climatic mass balance (CMB) modelling system that includes glacier CMB feedbacks to the atmosphere. We compare the model results over the Karakoram region of the northwestern Himalaya with remote sensing data for the ablation season of 2004 as well as with in situ glaciological and meteorological measurements from the Baltoro glacier. We find that interactive coupling has a localized but appreciable impact on the near-surface meteorological forcing data and that incorporation of CMB processes improves the simulation of variables such as land surface temperature and snow albedo. Furthermore, including feedbacks from the glacier model has a non-negligible effect on simulated CMB, reducing modelled ablation, on average, by 0.1 m w.e. (−6.0%) to a total of −1.5 m w.e. between 25 June–31 August 2004. The interactively coupled model shows promise as a new, multi-scale tool for explicitly resolving atmospheric-CMB processes of mountain glaciers at the basin scale.Mon, 06 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/763/2013/<b>Mapping radiation transfer through sea ice using a remotely operated vehicle (ROV)</b><br /><br />The Cryosphere, 7, 763-777, 2013<br /><br />Author(s): M. Nicolaus and C. Katlein<br /><br />Transmission of sunlight into and through sea ice is of critical importance for sea-ice associated organisms and photosynthesis because light is their primary energy source. The amount of visible light transferred through sea ice contributes to the energy budget of the sea ice and the uppermost ocean. However, our current knowledge on the amount and distribution of light under sea ice is still restricted to a few local observations, and our understanding of light-driven processes and interdisciplinary interactions is still sparse. The main reasons are that the under-ice environment is difficult to access and that measurements require large logistical and instrumental efforts. Hence, it has not been possible to map light conditions under sea ice over larger areas and to quantify spatial variability on different scales. Here we present a detailed methodological description for operating spectral radiometers on a remotely operated vehicle (ROV) under sea ice. Recent advances in ROV and radiation-sensor technology have allowed us to map under-ice spectral radiance and irradiance on floe scales within a few hours of station time. The ROV was operated directly from the sea ice, allowing for direct relations of optical properties to other sea-ice and surface features. The ROV was flown close to the sea ice in order to capture small-scale variability. Results from the presented data set and similar future studies will allow for better quantification of light conditions under sea ice. The presented experiences will support further developments in order to gather large data sets of under-ice radiation for different ice conditions and during different seasons.Thu, 02 May 2013 00:00:00 +0200http://www.the-cryosphere.net/7/741/2013/<b>Intercomparison of retrieval algorithms for the specific surface area of snow from near-infrared satellite data in mountainous terrain, and comparison with the output of a semi-distributed snowpack model</b><br /><br />The Cryosphere, 7, 741-761, 2013<br /><br />Author(s): A. Mary, M. Dumont, J.-P. Dedieu, Y. Durand, P. Sirguey, H. Milhem, O. Mestre, H. S. Negi, A. A. Kokhanovsky, M. Lafaysse, and S. Morin<br /><br />This study compares different methods to retrieve the specific surface area (SSA) of snow from satellite radiance measurements in mountainous terrain. It aims at addressing the effect on the retrieval of topographic corrections of reflectance, namely slope and aspect of terrain, multiple reflections on neighbouring slopes and accounting (or not) for the anisotropy of snow reflectance. Using MODerate resolution Imaging Spectrometer (MODIS) data for six different clear sky scenes spanning a wide range of snow conditions during the winter season 2008–2009 over a domain of 46 × 50 km in the French Alps, we compared SSA retrievals with and without topographic correction, with a spherical or non-spherical snow reflectance model and, in spherical case, with or without anisotropy corrections. The retrieved SSA values were compared to field measurements and to the results of the detailed snowpack model Crocus, fed by driving data from the SAFRAN meteorological analysis. It was found that the difference in terms of surface SSA between retrieved values and SAFRAN-Crocus output was minimal when the topographic correction was taken into account, when using a retrieval method assuming disconnected spherical snow grains. In this case, the root mean square deviation was 9.4 m² kg⁻¹ and the mean difference was 0.1 m² kg⁻¹, based on 3170 pairs of observation and simulated values. The added-value of the anisotropy correction was not significant in our case, which may be explained by the presence of mixed pixels and surface roughness. MODIS retrieved data show SSA variations with elevation and aspect which are physically consistent and in good agreement with SAFRAN-Crocus outputs. The variability of the MODIS retrieved SSA within the topographic classes of the model was found to be relatively small (3.9 m² kg⁻¹). This indicates that semi-distributed snowpack simulations in mountainous terrain with a sufficiently large number of classes provides a representation of the snowpack variability consistent with the scale of MODIS 500 m pixels.Mon, 29 Apr 2013 00:00:00 +0200http://www.the-cryosphere.net/7/719/2013/<b>Transient thermal modeling of permafrost conditions in Southern Norway</b><br /><br />The Cryosphere, 7, 719-739, 2013<br /><br />Author(s): S. Westermann, T. V. Schuler, K. Gisnås, and B. Etzelmüller<br /><br />Thermal modeling is a powerful tool to infer the temperature regime of the ground in permafrost areas. We present a transient permafrost model, CryoGrid 2, that calculates ground temperatures according to conductive heat transfer in the soil and in the snowpack. CryoGrid 2 is forced by operational air temperature and snow-depth products for potential permafrost areas in Southern Norway for the period 1958 to 2009 at 1 km² spatial resolution. In total, an area of about 80 000 km² is covered. The model results are validated against borehole temperatures, permafrost probability maps from "bottom temperature of snow" measurements and inventories of landforms indicative of permafrost occurrence. The validation demonstrates that CryoGrid 2 can reproduce the observed lower permafrost limit to within 100 m at all validation sites, while the agreement between simulated and measured borehole temperatures is within 1 K for most sites. The number of grid cells with simulated permafrost does not change significantly between the 1960s and 1990s. In the 2000s, a significant reduction of about 40% of the area with average 2 m ground temperatures below 0 °C is found, which mostly corresponds to degrading permafrost with still negative temperatures in deeper ground layers. The thermal conductivity of the snow is the largest source of uncertainty in CryoGrid 2, strongly affecting the simulated permafrost area. Finally, the prospects of employing CryoGrid 2 as an operational soil-temperature product for Norway are discussed.Thu, 25 Apr 2013 00:00:00 +0200http://www.the-cryosphere.net/7/707/2013/<b>Ikaite crystal distribution in winter sea ice and implications for CO₂ system dynamics</b><br /><br />The Cryosphere, 7, 707-718, 2013<br /><br />Author(s): S. Rysgaard, D. H. Søgaard, M. Cooper, M. Pu&cacute;ko, K. Lennert, T. N. Papakyriakou, F. Wang, N. X. Geilfus, R. N. Glud, J. Ehn, D. F. McGinnis, K. Attard, J. Sievers, J. W. Deming, and D. Barber<br /><br />The precipitation of ikaite (CaCO₃ &sdot; 6H₂O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74&deg; N, 20&deg; W) of NE Greenland. Ikaite crystals, ranging in size from a few μm to 700 μm, were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surface-ice values of 700–900 μmol kg⁻¹ ice (~25 × 10⁶ crystals kg^&minus;1) to values of 100–200 μmol kg⁻¹ ice (1–7 × 10⁶ crystals kg^&minus;1) near the sea ice–water interface, all of which are much higher (4–10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration, whereas TA concentrations in the lower half of the sea ice were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolve in layers below. Melting of sea ice and dissolution of observed concentrations of ikaite would result in meltwater with a <i>p</i>CO₂ of <15 μatm. This value is far below atmospheric values of 390 μatm and surface water concentrations of 315 μatm. Hence, the meltwater increases the potential for seawater uptake of CO₂.Tue, 23 Apr 2013 00:00:00 +0200http://www.the-cryosphere.net/7/699/2013/<b>New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery</b><br /><br />The Cryosphere, 7, 699-705, 2013<br /><br />Author(s): W. N. Meier, D. Gallaher, and G. G. Campbell<br /><br />Visible satellite imagery from the 1964 Nimbus I satellite has been recovered, digitized, and processed to estimate Arctic and Antarctic sea ice extent for September 1964. September is the month when the Arctic sea ice reaches its minimum annual extent and the Antarctic sea ice reaches its maximum. Images from a three-week period were manually analyzed to estimate the location of the ice edge and then composited to obtain a hemispheric estimate. Uncertainties were based on limitations in the image analysis and the variation of the ice cover over the three-week period. The 1964 Antarctic extent is higher than estimates from the 1979–present passive microwave record, but is in accord with previous indications of higher extents during the 1960s. The Arctic 1964 extent is near the 1979–2000 average from the passive microwave record, suggesting relatively stable summer extents during the 1960s and 1970s preceding the downward trend since 1979 and particularly the large decrease in the last decade. These early satellite data put the recently observed record into a longer-term context.Tue, 23 Apr 2013 00:00:00 +0200http://www.the-cryosphere.net/7/681/2013/<b>Influence of ablation-related processes in the build-up of simulated Northern Hemisphere ice sheets during the last glacial cycle</b><br /><br />The Cryosphere, 7, 681-698, 2013<br /><br />Author(s): S. Charbit, C. Dumas, M. Kageyama, D. M. Roche, and C. Ritz<br /><br />Since the original formulation of the positive-degree-day (PDD) method, different PDD calibrations have been proposed in the literature in response to the increasing number of observations. Although these formulations generally provide a satisfactory description of the present-day Greenland geometry, they have not all been tested for paleo ice sheets. Using the climate-ice sheet model CLIMBER-GRISLI coupled with different PDD models, we evaluate how the parameterisation of the ablation may affect the evolution of Northern Hemisphere ice sheets in the transient simulations of the last glacial cycle. Results from fully coupled simulations are compared to time-slice experiments carried out at different key periods of the last glacial period. We find large differences in the simulated ice sheets according to the chosen PDD model. These differences occur as soon as the onset of glaciation, therefore affecting the subsequent evolution of the ice system. To further investigate how the PDD method controls this evolution, special attention is given to the role of each PDD parameter. We show that glacial inception is critically dependent on the representation of the impact of the temperature variability from the daily to the inter-annual time scale, whose effect is modulated by the refreezing scheme. Finally, an additional set of sensitivity experiments has been carried out to assess the relative importance of melt processes with respect to initial ice sheet configuration in the construction and the evolution of past Northern Hemisphere ice sheets. Our analysis reveals that the impacts of the initial ice sheet condition may range from quite negligible to explaining about half of the LGM ice volume depending on the representation of stochastic temperature variations which remain the main driver of the evolution of the ice system. The main findings of this paper underline the need for conducting studies with high resolution climate models coupled to detailed snow models to better constrain the temporal and spatial variations of the PDD parameters. The development of such approaches could improve the calibration of the PDD formulation which is still widely used in climate-ice sheet studies.Thu, 18 Apr 2013 00:00:00 +0200http://www.the-cryosphere.net/7/667/2013/<b>An approach to derive regional snow lines and glacier mass change from MODIS imagery, western North America</b><br /><br />The Cryosphere, 7, 667-680, 2013<br /><br />Author(s): J. M. Shea, B. Menounos, R. D. Moore, and C. Tennant<br /><br />We describe a method to calculate regional snow line elevations and annual equilibrium line altitudes (ELAs) from daily MODIS imagery (MOD02QKM) on large glaciers and icefields in western North America. An automated cluster analysis of the cloud-masked visible and near-infrared bands at 250 m resolution is used to delineate glacier facies (snow and ice) for ten glacierized regions between 2000–2011. For each region and season, the maximum observed value of the 20th percentile of snow-covered pixels (<i>Z</i>_<i>S</i>(20)) is used to define a regional ELA proxy (ELA_est). Our results indicate significant increases in the regional ELA proxy at two continental sites (Peyto Glacier and Gulkana Glacier) over the period of observation, though no statistically significant trends are identified at other sites. To evaluate the utility of regional ELA proxies derived from MOD02QKM imagery, we compare standard geodetic estimates of glacier mass change with estimates derived from historical mass balance gradients and observations of <i>Z</i>_<i>S</i>(20) at three large icefields. Our approach yields estimates of mass change that more negative than traditional geodetic approaches, though MODIS-derived estimates are within the margins of error at all three sites. Both estimates of glacier mass change corroborate the continued mass loss of glaciers in western North America. Between 2000 and 2009, the geodetic change approach yields mean annual rates of surface elevation change for the Columbia, Lillooet, and Sittakanay icefields of −0.29 ± 0.05, −0.26 ± 0.05, and −0.63 ± 0.17 m a⁻¹, respectively. This study provides a new technique for glacier facies detection at daily timescales, and contributes to the development of regional estimates of glacier mass change, both of which are critical for studies of glacier contributions to streamflow and global sea level rise.Thu, 18 Apr 2013 00:00:00 +0200http://www.the-cryosphere.net/7/657/2013/<b>Theoretical study of solar light reflectance from vertical snow surfaces</b><br /><br />The Cryosphere, 7, 657-666, 2013<br /><br />Author(s): O. V. Nikolaeva and A. A. Kokhanovsky<br /><br />The influence of horizontal and vertical inhomogeneity of snow surfaces on solar light reflectance is studied using the radiative transfer theory (RTT). We compared 1-D RTT and 2-D RTT and found that large errors are produced if the 1-D RTT is used for the calculation of the snow reflection function (and, therefore, also in the retrievals of the snow grain radii) in 2-D measurement geometries. Such 2-D geometries are common in the procedures for the determination of the effective snow grain radii using near-infrared photography and spectroscopy of vertical snow walls. In particular, we have considered three cases for the numerical calculations: (1) the case with no black film; (2) the case with a black film at the pit's bottom; (3) the case with a black film at the pit's bottom and also at one of the vertical snow walls.Fri, 05 Apr 2013 00:00:00 +0200