ALBERT

Description: The data set provides 3 years of almost continuous observation of water vapor in the air at 3 levels in the lowest 42 m above Dome C on the high antarctic plateau, 123° 21' E, 75° 06' S, 3233 m above sea level. Each data is an average over the previous ½ hour. The water vapor content is measured in a heated air flow to avoid that supersaturated air at ambient temperature deposits excess moisture (above 100% with respect to ice) before reaching the humidity sensor. In fact, many reports correspond to significant supersaturation (see references provided). HMP155 thermohygrometers are used, which for the hygrometer natively report relative humidity with respect to liquid water even below 0°C. This is the variable provided in the data set, along with temperature in the heated air flow and ambient temperature. There are several conversion formulae in the literature to convert to e.g. partial pressure and relative humidity with respect to ice. As there is no clear consensus on which should be preferred in the range of temperatures at Dome C, the user is left to carry our her/his own conversions.

Description: The data set provides 3 years of almost continuous observation of water vapor in the air at 3m height on the high antarctic plateau, 123° 21' E, 75° 06' S, 3233 m above sea level. Each data is an average over the previous ½ hour. The water vapor content is measured in a heated air flow to avoid that supersaturated air at ambient temperature deposits excess moisture (above 100% with respect to ice) before reaching the humidity sensor. In fact, many reports correspond to significant supersaturation (see references provided). HMP155 thermohygrometers are used, which for the hygrometer natively report relative humidity with respect to liquid water even below 0°C. This is the variable provided in the data set, along with temperature in the heated air flow and ambient temperature. There are several conversion formulae in the literature to convert to e.g. partial pressure and relative humidity with respect to ice. As there is no clear consensus on which should be preferred in the range of temperatures at Dome C, the user is left to carry our her/his own conversions.

Description: The data set provides 3 years of almost continuous observation of water vapor in the air at 42m height on the high antarctic plateau, 123° 21' E, 75° 06' S, 3233 m above sea level. Each data is an average over the previous ½ hour. The water vapor content is measured in a heated air flow to avoid that supersaturated air at ambient temperature deposits excess moisture (above 100% with respect to ice) before reaching the humidity sensor. In fact, many reports correspond to significant supersaturation (see references provided). HMP155 thermohygrometers are used, which for the hygrometer natively report relative humidity with respect to liquid water even below 0°C. This is the variable provided in the data set, along with temperature in the heated air flow and ambient temperature. There are several conversion formulae in the literature to convert to e.g. partial pressure and relative humidity with respect to ice. As there is no clear consensus on which should be preferred in the range of temperatures at Dome C, the user is left to carry our her/his own conversions.

Description: The data set provides 3 years of almost continuous observation of water vapor in the air at 18m height on the high antarctic plateau, 123° 21' E, 75° 06' S, 3233 m above sea level. Each data is an average over the previous ½ hour. The water vapor content is measured in a heated air flow to avoid that supersaturated air at ambient temperature deposits excess moisture (above 100% with respect to ice) before reaching the humidity sensor. In fact, many reports correspond to significant supersaturation (see references provided). HMP155 thermohygrometers are used, which for the hygrometer natively report relative humidity with respect to liquid water even below 0°C. This is the variable provided in the data set, along with temperature in the heated air flow and ambient temperature. There are several conversion formulae in the literature to convert to e.g. partial pressure and relative humidity with respect to ice. As there is no clear consensus on which should be preferred in the range of temperatures at Dome C, the user is left to carry our her/his own conversions.

Description: Water flowing below glaciers exerts a major control on glacier basal sliding. However, our knowledge of the physics of subglacial hydrology and its link with sliding is limited because of lacking observations. Here we use a 2-year-long dataset made of on-ice-measured seismic and in situ-measured glacier basal sliding speed on Glacier d'Argentière (French Alps) to investigate the physics of subglacial channels and its potential link with glacier basal sliding. Using dedicated theory and concomitant measurements of water discharge, we quantify temporal changes in channels' hydraulic radius and hydraulic pressure gradient. At seasonal timescales we find that hydraulic radius and hydraulic pressure gradient respectively exhibit a 2- and 6-fold increase from spring to summer, followed by comparable decrease towards autumn. At low discharge during the early and late melt season channels respond to changes in discharge mainly through changes in hydraulic radius, a regime that is consistent with predictions of channels' behaviour at equilibrium. In contrast, at high discharge and high short-term water-supply variability (summertime), channels undergo strong changes in hydraulic pressure gradient, a behaviour that is consistent with channels behaving out of equilibrium. This out-of-equilibrium regime is further supported by observations at the diurnal scale, which prove that channels pressurize in the morning and depressurize in the afternoon. During summer we also observe high and sustained basal sliding speed, which supports that the widespread inefficient drainage system (cavities) is likely pressurized concomitantly with the channel system. We propose that pressurized channels help sustain high pressure in cavities (and therefore high glacier sliding speed) through an efficient hydraulic connection between the two systems. The present findings provide an essential basis for testing the physics represented in subglacial hydrology and glacier sliding models.

Description: Supersaturation often occurs at the top of the troposphere where cirrus clouds form, but is comparatively unusual near the surface where the air is generally warmer and laden with liquid and/or ice condensation nuclei. One exception is the surface of the high Antarctic Plateau. One year of atmospheric moisture measurement at the surface of Dome C on the East Antarctic Plateau is presented. The measurements are obtained using commercial hygrometry sensors modified to allow air sampling without affecting the moisture content, even in the case of supersaturation. Supersaturation is found to be very frequent. Common unadapted hygrometry sensors generally fail to report supersaturation, and most reports of atmospheric moisture on the Antarctic Plateau are thus likely biased low. The measurements are compared with results from two models implementing cold microphysics parameterizations: the European Center for Medium-range Weather Forecasts through its operational analyses, and the Model Atmosphérique Régional. As in the observations, supersaturation is frequent in the models but the statistical distribution differs both between models and observations and between the two models, leaving much room for model improvement. This is unlikely to strongly affect estimations of surface sublimation because supersaturation is more frequent as temperature is lower, and moisture quantities and thus water fluxes are small anyway. Ignoring supersaturation may be a more serious issue when considering water isotopes, a tracer of phase change and temperature, largely used to reconstruct past climates and environments from ice cores. Because observations are easier in the surface atmosphere, longer and more continuous in situ observation series of atmospheric supersaturation can be obtained than higher in the atmosphere to test parameterizations of cold microphysics, such as those used in the formation of high-altitude cirrus clouds in meteorological and climate models.

Description: The response of very high elevation glaciated areas on Mont Blanc to climate change has been analyzed using observations and numerical modeling. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on the average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to snow accumulation changes and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching 1.5 °C at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modeling shows that glacier near-surface temperature warming is enhanced by increasing melt-frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.

Description: Supersaturations in the natural atmosphere are frequent at the top of the troposphere where cirrus clouds form, but are very infrequent near the surface where the air is generally warmer and laden with liquid and/or ice condensation nuclei. An exception is the surface of the high antarctic plateau. One year of atmospheric moisture measurement at the surface of Dome C on the East Antarctic plateau is presented and compared with results from 2 models implementing cold microphysics parametrizations: the European Center for Medium-range Weather Forecasts through its operational analyzes, and the Model Atmosphérique Régional. The measurements are obtained using commercial hygrometry sensors modified to allow air sampling without affecting the moisture content even in case of supersaturation. Supersaturations are very frequent in the observations and in the models, but the statistical distribution differs both between models and observations and between the 2 models, living much room for improvements in both models. Unadapted hygrometry sensors generally fail to report supersaturations, and most reports of atmospheric moisture on the antarctic plateau are thus likely biased low. This is unlikely to strongly affect estimations of surface sublimation because supersaturations are more frequent as temperature is lower, and moisture quantities and thus water fluxes are very small anyway. Ignoring supersaturation may be a more serious issue when considering water isotopes, a tracer of phase change and temperature, largely used to interpret snow and ice samples from the antarctic plateau and reconstruct past climates and environments from ice cores. Longer and more continuous in situ observation series to test parameterizations of cold microphysics, such as those used in the formation of cirrus clouds in climate models, can be obtained at surface levels than higher in the atmosphere.

Description: In the frame of the SUBGLACIOR project, a new type of casing has been installed for testing during the 2013/14 austral summer season at Dome Concordia station, Antarctica. The SUBGLACIOR probe requires a full fluid column up to the surface, in order to circulate fluid for ice-chips recovery. This makes it essential that the casing is leak-tight through the porous firn column. We have evaluated existing solutions before opting to test a new method. This new system is made of polyethylene pipes which are welded together at the surface while the casing pipes are lowered into the reamed borehole. It is simple and lightweight and allows the casing to be installed quickly with optimum chance of being leak-tight. The installed casing has been tested both with compressed air and drilling fluids and has proven to work.