The 1979-2005 Greenland ice sheet melt extent from passive microwave data using an improved version of the melt retrieval XPGR algorithm

Analysis of passive microwave satellite observations over the Greenland ice sheet reveals a significant increase in surface melt over the period 1979-2005. Since 1979, the total melt area was found to have increased +1.22 x 10ˆ7 kmˆ2. An improved version of the cross-polarized gradient ratio (XPGR) technique is used to identify the melt from the brightness temperatures. The improvements in the melt retrieval XPGR algorithm as well as the surface melt acceleration are discussed with results from a coupled atmosphere-snow regional climate model. From 1979 to 2005, the ablation period increases everywhere over the melt zone except in the regions where the model simulates an increased summer snowfall. Indeed, more snowfall in summer decreases the liquid water content of the snowpack, raises the albedo and therefore reduces the melt. Finally, this melt acceleration over the Greenland ice sheet is highly correlated with both Greenland and global warming suggesting a continuing surface melt increase in the future.Peer reviewe

Evaluation of a high-resolution regional climate simulation over Greenland

A simulation of the 1991 summer has been performed over south Greenland with a coupled atmosphere–snow regional climate model (RCM) forced by the ECMWF re-analysis. The simulation is evaluated with in-situ coastal and ice-sheet atmospheric and glaciological observations. Modelled air temperature, specific humidity, wind speed and radiative fluxes are in good agreement with the available observations, although uncertainties in the radiative transfer scheme need further investigation to improve the model’s performance. In the sub-surface snow-ice model, surface albedo is calculated from the simulated snow grain shape and size, snow depth, meltwater accumulation, cloudiness and ice albedo. The use of snow metamorphism processes allows a realistic modelling of the temporal variations in the surface albedo during both melting periods and accumulation events. Concerning the surface albedo, the main finding is that an accurate albedo simulation during the melting season strongly depends on a proper initialization of the surface conditions which mainly result from winter accumulation processes. Furthermore, in a sensitivity experiment with a constant 0.8 albedo over the whole ice sheet, the average amount of melt decreased by more than 60%, which highlights the importance of a correctly simulated surface albedo. The use of this coupled atmosphere–snow RCM offers new perspectives in the study of the Greenland surface mass balance due to the represented feedback between the surface climate and the surface albedo, which is the most sensitive parameter in energy-balance-based ablation calculations.Peer reviewe

Modelling of large-scale melt parameters with a regional climate model in South-Greenland during the 1991 melt season

Large-scale positive degree-day based melt parameterisations for the Greenland ice sheet are highly sensitive to their parameters (standard temperature deviation, snow and ice degree-day factors). In this article, these parametrs have been simulated with a coupled atmosphere-snow regional climate model for the southern part of Greenland during the summer of 1991 forced at the lateral boundaries with ECMWF re-analysis. The calculated (from net ablation, i.e. ablation without refreezing) snow and ice positive degree-day factors vary considerably over the ice sheet. At low elevations, the modelled snow degree-day factor approaches closely the generally accepted value of 3 mm WE d-1 °C-1. Higher up the ice sheet, large values up to 15 mm WE d-1 °C-1 are simulated. In case of ice melt, maximum values until 40 mm WE d-1 °C-1 are found. The snow and ice positive degree-day factor distributions peak respectively at 3 and 8 mm WE d-1 °C-1. Refreezing is of small importance close to the ice sheet margin. Higher up the ice sheet, refreezing considerably lowers the amount of net ablation. The monthly simulated 2m air temperature standard deviation exhibits a strong seasonal cycle with the highest (between 3.0° and 5.0°C) values in May and June. July shows the lowest temperature fluctuations due to melting of the surface

Sea-ice simulations in the Weddell Sea

A model of sea-ice formation and movement has been developed and applied to a sector of the Southern Ocean including the Weddell Sea and the Drake Passage. This sea-ice model with leads is described in two parts : - the thermodynamical component, which represents the freezing and melting processes due to energy fluxes , between the atmosphere, ice, and ocean; - the dynamical component, presently limited to the computation of ice movement due to wind. Results from this model, including ice thickness, temperature. and spatial extent, will be presented and discussed for a particular point and for the whole area

Hantavirus-related acute interstitial nephritis in western Europe. Expansion of a world-wide zoonosis.

We report the clinical, biological and serological characteristics of 76 cases of Hantavirus-induced acute interstitial nephritis diagnosed in Belgium and France between 1977 and 1986. The disease is characterized by a fever of sudden onset promptly accompanied by pain in the loin or abdomen, nausea and vomiting, myalgias and occasionally with acute myopia and conjunctival injection. Within a week acute renal failure develops, necessitating haemo- or peritoneal dialysis in up to 10 per cent of patients. Transient proteinuria, microscopic haematuria and leukocyturia are observed simultaneously. Thrombocytopenia and mild elevations of hepatic enzymes, LDH and CPK, as well as biological signs of acute inflammatory reaction are observed, lasting for a few days. Spontaneous complete recovery is the rule. This picture is virtually identical with that of nephropathia epidemica, a Hantavirus nephropathy observed in northern Europe. This conclusion is supported by the observation of elevated antibody titres against the Puumala virus, the agent of nephropathia epidemica. This rodent-borne infection is markedly milder than that caused by other Hantaviruses such as the Hantaan or the Seoul virus in Asia. Acute interstitial disease due to Hantavirus should be included in the differential diagnosis of febrile acute renal failure