Snow accumulation and its moisture origin over Dome Argus, Antarctica

The spatial and temporal variability of snow accumulation near Dome Argus, Antarctica, is assessed using new snow pit and stake measurement data together with existing snow pit, ice core and automatic weather station records. Snow accumulation rate shows large inter-annual variations, but stable multi-decadal levels over the last seven centuries. Spatial variations in snow accumulation within the space of 50 km of Dome Argus are relatively small, probably thanks to the smooth topography. A comparison of theses accumulation observations with ECMWF reanalyses (ERA-40 and ERA-Interim) suggests ECMWF reanalysis captures the seasonal variations, but underestimates the overall snow accumulation at Dome Argus by ~50 %. The moisture sources for precipitation over Dome Argus are examined by means of a Lagrangian moisture source diagnostic, based on the tracing of specific humidity changes along air parcel trajectories, for the period 2000–2004 using operational ECMWF analysis data. Dome Argus mainly receives moisture from the mid-latitude (46 ± 4°S) South Indian Ocean, with a seasonal latitudinal shift of about 6°. Compared to other central East Antarctic deep ice core sites such as Dome F, Dome C, Vostok, and EPICA Dronning Maud Land, Dome Argus has a more southerly moisture origin, probably due to topographic influences on the moisture transport paths. These results have important implications for the interpretation of future ice cores at Dome Argus.     

Transport of Snow by the Wind: A Comparison Between Observations in Ad��lie Land, Antarctica, and Simulations Made with the Regional Climate Model MAR

For the first time a simulation of blowing snow events was validated in detail using one-month long observations (January 2010) made in Adélie Land, Antarctica. A regional climate model featuring a coupled atmosphere/blowing snow/snowpack model is forced laterally by meteorological re-analyses. The vertical grid spacing was 2 m from 2 to 20 m above the surface and the horizontal grid spacing was 5?km. The simulation was validated by comparing the occurrence of blowing snow events and other meteorological parameters at two automatic weather stations. The Nash test allowed us to compute efficiencies of the simulation. The regional climate model simulated the observed wind speed with a positive efficiency (0.69). Wind speeds higher than 12 m s ^?1 were underestimated. Positive efficiency of the simulated wind speed was a prerequisite for validating the blowing snow model. Temperatures were simulated with a slightly negative efficiency (?0.16) due to overestimation of the amplitude of the diurnal cycle during one week, probably because the cloud cover was underestimated at that location during the period concerned. Snowfall events were correctly simulated by our model, as confirmed by field reports. Because observations suggested that our instrument (an acoustic sounder) tends to overestimate the blowing snow flux, data were not sufficiently accurate to allow the complete validation of snow drift values. However, the simulation of blowing snow occurrence was in good agreement with the observations made during the first 20 days of January 2010, despite the fact that the blowing snow flux may be underestimated by the regional climate model during pure blowing snow events. We found that blowing snow occurs in Adélie Land only when the 30-min wind speed value at 2 m a.g.l. is >10 m s ^?1. The validation for the last 10 days of January 2010 was less satisfactory because of complications introduced by surface melting and refreezing.     

Detection of a katabatic wind event with GPS meteorology measurements at Scott Base Antarctica

A katabatic wind event which dramatically affects the polar climate has been detected using GPS meteorology measurements. GPS-derived precipitable water vapor (GPS PWV) variability and its relation to a katabatic event at Scott Base station, Antarctica was investigated. The investigations using the data gathered from 21 to 30 November of 2002. They showed that the water vapor profile exhibited an irregular pattern with a maximum PWV of 7.38?mm (~6?mm on average). This event was strongly influenced by relative humidity than by wind speed activity. The dominant wind flow during this period was from the North to Northeast (blowing from the Ross Sea) with a mean speed of 3.79?ms^?1. The PWV increased when the temperature was between ?15 and ?11°C. During the katabatic event identified between 21:30 UT of 28 November and 18:40 UT on 29 November, the wind blew from the Southeast to South direction (from the Ross Ice Shelf) with a maximum speed of 10.92?ms^?1. The PWV increased ~1.0?mm (23%) from the mean value accompanied by severe wind had pronounced effect on GPS observations.     

The contribution of snow condition trends to future ground climate

Global climate models predict that terrestrial northern high-latitude snow conditions will change substantially over the twenty-first century. Results from a Community Climate System Model simulation of twentieth and twenty-first (SRES A1B scenario) century climate show increased winter snowfall (+10–40%), altered maximum snow depth (?5 ± 6 cm), and a shortened snow-season (?14 ± 7 days in spring, +20 ± 9 days in autumn). By conducting a series of prescribed snow experiments with the Community Land Model, we isolate how trends in snowfall, snow depth, and snow-season length affect soil temperature trends. Increasing snowfall, by countering the snowpack-shallowing influence of warmer winters and shorter snow seasons, is effectively a soil warming agent, accounting for 10–30% of total soil warming at 1 m depth and ~16% of the simulated twenty-first century decline in near-surface permafrost extent. A shortening snow season enhances soil warming due to increased solar absorption whereas a shallowing snowpack mitigates soil warming due to weaker winter insulation from cold atmospheric air. Snowpack deepening has comparatively less impact due to saturation of snow insulative capacity at deeper snow depths. Snow depth and snow-season length trends tend to be positively related, but their effects on soil temperature are opposing. Consequently, on the century timescale the net change in snow state can either amplify or mitigate soil warming. Snow state changes explain less than 25% of total soil temperature change by 2100. However, for the latter half of twentieth century, snow state variations account for as much as 50–100% of total soil temperature variations.     

A return to wet conditions over Africa: 1995–2010

Climatic trends over sub-Saharan Africa are described using major river flows, European Community Medium-Range Weather Forecasts, Coupled Forecast System, global land surface data assimilation and National Center for Environmental Prediction reanalysis, Global Precipitation Climate Center gauge data, and satellite observations in the period 1995–2010. The Niger and Zambezi rivers reached flow levels last seen in the 1950s (2,000 and 5,000 m³ s^?1, respectively), and rainfall across the Congo Basin increased steadily ~+0.16 mm day^?1 year^?1. Weather events that contributed to flooding are studied and include the Zambezi tropical trough of 4 January 2008 and the Sahelian easterly wave of 19 July 2010. Diurnal summer rainfall increased threefold over the 1995–2010 period in conjunction with a strengthened land–sea temperature contrast, onshore flow, and afternoon uplift. 700 mb zonal winds over East Africa became easterly after 2001, so clean Indian Ocean air was entrained to the Congo, improving convective efficiency. Relationships between the African monsoon circulation and global teleconnections are explored. Zonal wind convergence around the Congo appears related with the tropical multi-decadal oscillation and signals in the Atlantic during the study period.     

Parametrization schemes of incident radiation in the North Water polynya

Abstract

An evaluation of the Canadian Land Surface Scheme (CLASS) 3.1 snow cover simulations at four sites included in the Snow Model Intercomparison Project (SnowMIP) revealed that CLASS was able to provide realistic representations of snow cover accumulation, melt and physical properties over a range of snow cover climates. The modified snow aging parametrization in CLASS 3.1 provided improved simulations of snowpack density which resulted in a marked reduction in the root‐mean‐square (rms) error for daily snow depth, and slight improvements in snow surface temperature. CLASS 3.1 still exhibited a tendency to overestimate snow cover duration which is attributed to the way shallow snow ablation is treated. CLASS provided generally realistic simulations of daily and seasonal variation in snow albedo although cold snow albedo was underpredicted by 0.10 to 0.15 at a site with a deep (> 2 m) cold snowpack. CLASS also exhibited a tendency to overpredict late spring snow albedo which was reduced by the addition of a snow layer subroutine that kept track of snow albedo by precipitation event. CLASS had a noticeable cold bias averaging 3°–4°C at two mountain sites included in the comparison. The bias was closely linked to atmospheric stability and could exceed 10°C under conditions of strong radiative cooling and low wind speeds. The CLASS energy deficit under these conditions was determined to be ～20–40 W m^?2 and was mostly accounted for by introducing a windless exchange coefficient into the calculation of sensible heat fluxes following the approach used in a number of other physical snowpack models. CLASS provided realistic simulations of daily snowmelt runoff with the exception of the Weissfluhjoch site which was characterized by a deep cold snowpack. A preliminary assessment of snow water equivalent (SWE) rms error for the 23 models participating in SnowMIP showed that CLASS was one of the better single layer snow models included in the comparison. CLASS performance was comparable to the multi‐layer CROCUS snowpack model in the evaluations carried out in this study.     

The effect of slope aspect on the response of snowpack to climate warming in the Pyrenees

The aim of this study was to analyse the effect of slope aspect on the response of snowpack to climate warming in the Pyrenees. For this purpose, data available from five automatic weather stations were used to simulate the energy and mass balance of snowpack, assuming different magnitudes of an idealized climate warming (upward shifting of 1, 2 and 3 °C the temperature series). Snow energy and mass balance were simulated using the Cold Regions Hydrological Modelling platform (CRHM). CRHM was used to create a model that enabled correction of the all-wave incoming radiation fluxes from the observation sites for various slope aspects (N, NE, E, SE, S, SW,W,NW and flat areas), which enabled assessment of the differential impact of climate warming on snow processes on mountain slopes. The results showed that slope aspect was responsible for substantial variability in snow accumulation and the duration of the snowpack. Simulated variability markedly increased with warmer temperature conditions. Annual maximum snow accumulation (MSA) and annual snowpack duration (ASD) showed marked sensitivity to a warming of 1 °C. Thus, the sensitivity of the MSA in flat areas ranged from 11 to 17 % per degree C amongst the weather stations, and the ASD ranged from 11 to 20 days per degree C. There was a clear increase in the sensitivity of the snowpack to climate warming on those slopes that received intense solar radiation (S, SE and SW slopes) compared with those slopes where the incident radiation was more limited (N, NE and NW slopes). The sensitivity of the MSA and the ASD increased as the temperature increased, particularly on the most irradiated slopes. Large interannual variability was also observed. Thus, with more snow accumulation and longer duration the sensitivity of the snowpack to temperature decreased, especially on south-facing slopes.     

Present and future near-surface wind climate of Greenland from high resolution regional climate modelling

The present and twenty-first century near-surface wind climate of Greenland is presented using output from the regional atmospheric climate model RACMO2. The modelled wind variability and wind distribution compare favourably to observations from three automatic weather stations in the ablation zone of southwest Greenland. The Weibull shape parameter is used to classify the wind climate. High values (κ > 4) are found in northern Greenland, indicative of uniform winds and a dominant katabatic forcing, while lower values (κ < 3) are found over the ocean and southern Greenland, where the synoptic forcing dominates. Very high values of the shape parameter are found over concave topography where confluence strengthens the katabatic circulation, while very low values are found in a narrow band along the coast due to barrier winds. To simulate the future (2081–2098) wind climate RACMO2 was forced with the HadGEM2-ES general circulation model using a scenario of mid-range radiative forcing of +4.5 W m^?2 by 2100. For the future simulated climate, the near-surface potential temperature deficit reduces in all seasons in regions where the surface temperature is below the freezing point, indicating a reduction in strength of the near-surface temperature inversion layer. This leads to a wind speed reduction over the central ice sheet where katabatic forcing dominates, and a wind speed increase over steep coastal topography due to counteracting effects of thermal and katabatic forcing. Thermally forced winds over the seasonally sea ice covered region of the Greenland Sea are reduced by up to 2.5 m s^?1.     

The Thermodynamic Effects of Sublimating, Blowing Snow in the Atmospheric Boundary Layer

A seasonal snowcover blankets much of Canada during wintertime. In such an environment, the frequency of blowing snow events is relatively high and can have important meteorological and hydrological impacts. Apart from the transport of snow, the thermodynamic impact of sublimating blowing snow in air near the surface can be investigated. Using a time or fetch-dependent blowing snow model named 'PIEKTUK' that incorporates prognostic equations for a spectrum of sublimating snow particles, plus temperature and humidity distributions, it is found that the sublimation of blowing snow can lead to temperature decreases of the order of 0.5 °C and significant water vapour increases in the near-surface air. Typical predicted snow removal rates due to sublimation of blowing snow are several millimetres snow water equivalent per day over open Arctic tundra conditions. The model forecast sublimation rates are most sensitive to humidity, as well as wind speed, temperature and particle distributions, with a maximum value in sublimation typically found approximately 1 km downstream from blowing snow initiation. This suggests that the sublimation process is self-limiting despite ongoing transport of snow by wind, yielding significantly lower values of blowing snow sublimation rates (nearly two-thirds less) compared to situations where the thermodynamic feedbacks are neglected. The PIEKTUK model may provide the necessary thermodynamic inputs or blowing snow parameterizations for mesoscale models, allowing the assessment of the contribution of blowing snow fluxes, in more complex situations, to the moisture budgets of high-latitude regions.     

Observation and Numerical Simulation of Cold Clouds and Snow Particles in the Yeongdong Region

The Yeongdong region of the Korean Peninsula is vulnerable to high-impact weather events, because of its complicated geographical characteristics and East Sea effect, such that heavy snowfall episodes have frequently occurred in winter. Snow crystal play an important role in cloud and precipitation physics because it is an essential element for improvement of numerical model, and remote sensing retrieval such as radar and satellite. In this study, the high-temporal resolution (3-hourly) dataset of radiosonde soundings and snow particle photographs during the intensive observation period for 2013–2016 has been used to understand characteristics of snow particles for the different meteorological conditions in the Yeongdong region. We also attempt to simulate two episodes that occurred on 23–24 February and 13–14 December 2016; one has a single-layered cloud and the other has two-layered cloud structure. This study demonstrates that the rimed particles in the first period tend to shift to aggregates of dendrites with the decrease of 850-hPa temperature. In general, the low-level clouds in the Yeongdong region are observed along with the distinctive wind shear and strong inversion in equivalent potential temperature around 2 ~ 3 km above the sea level. The simulation successfully represents the variations of the characteristics of snow particles as well as different cloud structure for both episodes. The observation and model simulations clearly suggest that snow particles primarily depend on the 850-hPa temperature.     

High-resolution modelling of the Antarctic surface mass balance, application for the twentieth, twenty first and twenty second centuries

About 75 % of the Antarctic surface mass gain occurs over areas below 2,000 m asl, which cover 40 % of the grounded ice-sheet. As the topography is complex in many of these regions, surface mass balance modelling is highly dependent on horizontal resolution, and studying the impact of Antarctica on the future rise in sea level requires physical approaches. We have developed a computationally efficient, physical downscaling model for high-resolution (15 km) long-term surface mass balance (SMB) projections. Here, we present results of this model, called SMHiL (surface mass balance high-resolution downscaling), which was forced with the LMDZ4 atmospheric general circulation model to assess Antarctic SMB variability in the twenty first and the twenty second centuries under two different scenarios. The higher resolution of SMHiL better reproduces the geographical patterns of SMB and increase significantly the averaged SMB over the grounded ice-sheet for the end of the twentieth century. A comparison with more than 3200 quality-controlled field data shows that LMDZ4 and SMHiL reproduce the observed values equally well. Nevertheless, field data below 2,000 m asl are too scarce to efficiently show the added value of SMHiL and measuring the SMB in these undocumented areas should be a future scientific priority. Our results suggest that running LMDZ4 at a finer resolution (15 km) may give a future increase in SMB in Antarctica that is about 30 % higher than by using its standard resolution (60 km) due to the higher increase in precipitation in coastal areas at 15 km. However, a part (～15 %) of these discrepancies could be an artefact from SMHiL since it neglects the foehn effect and likely overestimates the precipitation increase. Future changes in the Antarctic SMB at low elevations will result from the competition between higher snow accumulation and runoff. For this reason, developing downscaling models is crucial to represent processes in sufficient detail and correctly model the SMB in coastal areas.     

Future surface mass balance of the Antarctic ice sheet and its influence on sea level change, simulated by a regional atmospheric climate model

A regional atmospheric climate model with multi-layer snow module (RACMO2) is forced at the lateral boundaries by global climate model (GCM) data to assess the future climate and surface mass balance (SMB) of the Antarctic ice sheet (AIS). Two different GCMs (ECHAM5 until 2100 and HadCM3 until 2200) and two different emission scenarios (A1B and E1) are used as forcing to capture a realistic range in future climate states. Simulated ice sheet averaged 2 m air temperature (T_2m) increases (1.8–3.0 K in 2100 and 2.4–5.3 K in 2200), simultaneously and with the same magnitude as GCM simulated T_2m. The SMB and its components increase in magnitude, as they are directly influenced by the temperature increase. Changes in atmospheric circulation around Antarctica play a minor role in future SMB changes. During the next two centuries, the projected increase in liquid water flux from rainfall and snowmelt, together 60–200 Gt year^?1, will mostly refreeze in the snow pack, so runoff remains small (10–40 Gt year^?1). Sublimation increases by 25–50 %, but remains an order of magnitude smaller than snowfall. The increase in snowfall mainly determines future changes in SMB on the AIS: 6–16 % in 2100 and 8–25 % in 2200. Without any ice dynamical response, this would result in an eustatic sea level drop of 20–43 mm in 2100 and 73–163 mm in 2200, compared to the twentieth century. Averaged over the AIS, a strong relation between $\Updelta$ SMB and $\Updelta\hbox{T}_{2{\rm m}}$ of 98 ± 5 Gt w.e. year^?1 K^?1 is found.     

New estimations of precipitation and surface sublimation in East Antarctica from snow accumulation measurements

Surface mass balance (SMB) distribution and its temporal and spatial variability is an essential input parameter in mass balance studies. Different methods were used, compared and integrated (stake farms, ice cores, snow radar, surface morphology, remote sensing) at eight sites along a transect from Terra Nova Bay (TNB) to Dome C (DC) (East Antarctica), to provide detailed information on the SMB. Spatial variability measurements show that the measured maximum snow accumulation (SA) in a 15 km area is well correlated to firn temperature. Wind-driven sublimation processes, controlled by the surface slope in the wind direction, have a huge impact (up to 85% of snow precipitation) on SMB and are significant in terms of past, present and future SMB evaluations. The snow redistribution process is local and has a strong impact on the annual variability of accumulation. The spatial variability of SMB at the kilometre scale is one order of magnitude higher than its temporal variability (20–30%) at the centennial time scale. This high spatial variability is due to wind-driven sublimation. Compared with our SMB calculations, previous compilations generally over-estimate SMB, up to 65% in some areas.     

Snow precipitation at four ice core sites in East Antarctica: provenance, seasonality and blocking factors

Snow precipitation is the primary mass input to the Antarctic ice sheet and is one of the most direct climatic indicators, with important implications for paleoclimatic reconstruction from ice cores. Provenance of precipitation and the dynamic conditions that force these precipitation events at four deep ice core sites (Dome C, Law Dome, Talos Dome, and Taylor Dome) in East Antarctica were analysed with air mass back trajectories calculated using the Lagrangian model and the mean composite data for precipitation, geopotential height and wind speed field data from the European Centre for Medium Range Weather Forecast from 1980 to 2001. On an annual basis, back trajectories showed that the Atlantic-Indian and Ross-Pacific Oceans were the main provenances of precipitation in Wilkes Land (80%) and Victoria Land (40%), respectively, whereas the greatest influence of the ice sheet was on the interior near the Vostok site (80%) and in the Southwest Ross Sea (50%), an effect that decreased towards the coast and along the Antarctic slope. Victoria Land received snowfall atypically with respect to other Antarctica areas in terms of pathway (eastern instead of western), seasonality (summer instead of winter) and velocity (old air age). Geopotential height patterns at 500 hPa at low (>10 days) and high (2–6 days) frequencies during snowfall cycles at two core sites showed large positive anomalies at low frequencies developing in the Tasman Sea-Eastern Indian Ocean at higher latitudes (60–70°S) than normal. This could be considered part of an atmospheric blocking event, with transient eddies acting to decelerate westerlies in a split region area and accelerate the flow on the flanks of the low-frequency positive anomalies.     

Measurements of stratospheric ozone at a mid-latitude observing station Valentia, Ireland (51.94° N, 10.25° W), using ground-based and ozonesonde observations from 1994 to 2009

Sixteen years (1994 – 2009) of ozone profiling by ozonesondes at Valentia Meteorological and Geophysical Observatory, Ireland (51.94^° N, 10.23^° W) along with a co-located MkIV Brewer spectrophotometer for the period 1993–2009 are analyzed. Simple and multiple linear regression methods are used to infer the recent trend, if any, in stratospheric column ozone over the station. The decadal trend from 1994 to 2010 is also calculated from the monthly mean data of Brewer and column ozone data derived from satellite observations. Both of these show a 1.5 % increase per decade during this period with an uncertainty of about ±0.25 %. Monthly mean data for March show a much stronger trend of?~?4.8 % increase per decade for both ozonesonde and Brewer data. The ozone profile is divided between three vertical slots of 0–15 km, 15–26 km, and 26 km to the top of the atmosphere and a 11-year running average is calculated. Ozone values for the month of March only are observed to increase at each level with a maximum change of +9.2?±?3.2 % per decade (between years 1994 and 2009) being observed in the vertical region from 15 to 26 km. In the tropospheric region from 0 to 15 km, the trend is positive but with a poor statistical significance. However, for the top level of above 26 km the trend is significantly positive at about 4 % per decade. The March integrated ozonesonde column ozone during this period is found to increase at a rate of ~6.6 % per decade compared with the Brewer and satellite positive trends of ~5 % per decade.     

Increased photosynthesis compensates for shorter growing season in subarctic tundra—8 years of snow accumulation manipulations

This study was initiated to analyze the effect of increased snow cover on plant photosynthesis in subarctic mires underlain by permafrost. Snow fences were used to increase the accumulation of snow on a subarctic permafrost mire in northern Sweden. By measuring reflected photosynthetic active radiation (PAR) the effect of snow thickness and associated delay of the start of the growing season was assessed in terms of absorbed PAR and estimated gross primary production (GPP). Six plots experienced increased snow accumulation and six plots were untreated. Incoming and reflected PAR was logged hourly from August 2010 to October 2013. In 2010 PAR measurements were coupled with flux chamber measurements to assess GPP and light use efficiency of the plots. The increased snow thickness prolonged the duration of the snow cover in spring. The delay of the growing season start in the treated plots was 18 days in 2011, 3 days in 2012 and 22 days in 2013. Results show higher PAR absorption, together with almost 35 % higher light use efficiency, in treated plots compared to untreated plots. Estimations of GPP suggest that the loss in early season photosynthesis, due to the shortening of the growing season in the treatment plots, is well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons. This compensation is likely to be explained by increased soil moisture and nutrients together with a shift in vegetation composition associated with the accelerated permafrost thaw in the treatment plots.     

Physical and chemical impacts of a major storm on a temperate lake: a taste of things to come?

Extreme weather can have a substantial influence on lakes and is expected to become more frequent with climate change. We explored the influence of one particular extreme event, Storm Ophelia, on the physical and chemical environment of England’s largest lake, Windermere. We found that the substantial influence of Ophelia on meteorological conditions at Windermere, in particular wind speed, resulted in a 25-fold increase (relative to the study-period average) in the wind energy flux at the lake-air interface. Following Ophelia, there was a short-lived mixing event in which the Schmidt stability decreased by over 100 Jm^?2 and the thermocline deepened by over 10 m during a 12-h period. As a result of changes to the strength of stratification, Ophelia also changed the internal seiche regime of Windermere with the dominant seiche period increasing from ~?17 h pre-storm to ~?21 h post-storm. Following Ophelia, there was an upwelling of cold and low-oxygenated waters at the southern-end of the lake. This had a substantial influence on the main outflow of Windermere, the River Leven, where dissolved oxygen concentrations decreased by ~?48%, from 9.3 to 4.8 mg L^?1, while at the mid-lake monitoring station in Windermere, it decreased by only ~?3%. This study illustrates that the response of a lake to extreme weather can cause important effects downstream, the influence of which may not be evident at the lake surface. To understand the impact of future extreme events fully, the whole lake and downstream-river system need to be studied together.     

The Effect of Coherent Structures in the Atmospheric Surface Layer on Blowing-Snow Transport

While turbulent bursts are considered critical for blowing-snow transport and initiation, the interaction of the airflow with the snow surface is not fully understood. To better characterize the coupling of turbulent structures and blowing-snow transport, observations collected in natural environments at the necessary high-resolution time scales are needed. To address this, high-frequency measurements of turbulence, blowing-snow density and particle velocity were made in the Canadian Rockies. During blowing-snow storms, modified variable-interval time averaging enabled identification of periods of near-surface blowing-snow coupling with shear-stress-producing motions in the lowest 2 m of the atmospheric surface layer. The identification of those turbulent motions responsible for blowing snow yields a better understanding of the event-driven mechanics of initiation and sustained transport. The type of coherent structures generating the Reynolds stress are just as important as the magnitude of the Reynolds stress in initiating and sustaining near-surface blowing snow. Our results suggest that blowing-snow models driven by merely the time-averaged shear stress lack physical realism in the near-surface region. The next phase of the development of blowing-snow models should incorporate parametrizations of coherent turbulent structures.     

Influence of weather conditions and spatial variability on glacier surface melt in Chilean Patagonia

In order to clarify how differences in weather conditions affect the surface heat balance of a large maritime glacier, meteorological observations were carried out in the ablation area of Glaciar Exploradores in the Chilean Patagonia during the austral summer of 2006/2007. Under cloudy/rainy weather, when the air temperature and wind speed were high due to advection, the average melting heat was 18.8 MJ m^?2 day^?1 and the turbulent heat fluxes contributed 35% of the total melt. During clear weather, the average melting heat was 16.9 MJ m^?2 day^?1 and 13% of the total was the turbulent heat fluxes. A decrease in air temperature due to the development of the glacier boundary layer on clear days will lead to an overestimation of the melt using the air temperature at a weather station outside of the glacier.     

Snowpack model estimates of the mass balance of the Greenland ice sheet and its changes over the twentyfirst century

The performance of a snow cover model in capturing the ablation on the Greenland ice sheet is evaluated. This model allows an explicit calculation of the formation of melt water, of the fraction of melt water which re-freezes, and of runoff in the ablation region. The input climate variables to the snowpack model come from two climate models. While the higher resolution general circulation model (ECHAM 4), is closest to observations in its estimate of accumulation, it fails to give accurate results in its predictions of runoff, primarily in the southern half of the ice sheet. The two-dimensional low-resolution climate model (MIT 2D LO) produces estimates of runoff from the Greenland ice sheet within the range of uncertainty of the Inter governmental Panel on Climate Change (IPCC1) 1995 estimates. Both models reproduce some of the characteristics of the extent of the wet snow zone observed with satellite remote sensing; the MIT model is closer to observations in terms of areal extent and intensity of the melting in the southern half of the ice-sheet in July and August while the ECHAM model reproduces melting in the northern half of the ice sheet well. Changes in runoff from Greenland and Antarctica are often cited as one of the major concerns linked to anthropogenic changes in climate. Because it is based on physical principles and relies on the surface energy balance as input, the snow cover model can respond to the current climatic forcing as well as to future changes in climate on the century time scale without the limitations inherent in empirical parametrizations. For a reference climate scenario similar to the IPCC's IS92a, the model projects that the Greenland ice sheet does not contribute significantly to changes in the level of the ocean over the twenty-first century. Increases in accumulation over the central portion of the ice sheet offset most of the increase in melting and runoff, which takes place along the margins of the ice sheet. The range of uncertainty in the predictions of sea-level rise is estimated by repeating the calculation with the MIT model for seven climate change scenarios. The range is –0.5 to 1.7 cm.