For most parts of the year the Antarctic Plateau has a surface temperature inversion with strengthc. 20 K. Under such conditions the warmer air at the top of the inversion layer contributes more to the clearsky atmospheric longwave radiation at surface level than does the colder air near the ground. Hence, it ismore appropriate to relate longwave irradiance (LWI) to the top of the inversion layer temperature (T_m) than to the ground level temperature (T_g ). Analysis of radio soundings carried out at Dome C and SouthPole during 2006-08 shows that the temperature at 400 m above the surface (T_400 ) is a good proxy for T_m and is linearly related to T_g with correlation coefficients greater than 0.8. During summer, radiosondemeasurements show almost isothermal conditions, hence T 400 still remains a good proxy for the lowertroposphere maximum temperature. A methodology is presented to parameterize the clear sky effectiveemissivity in terms of the troposphere maximum temperature, using ground temperature measurements. Thepredicted LWI values for both sites are comparable with those obtained using radiative transfer models,while for Dome C the bias of 0.8 W m^-2 and the root mean square (RMS) of 6.2 W m^-2 are lower than thosecalculated with previously published parametric equations.

Over the past few years a major effort has been put into the exploration of potential sites for the deployment of submillimetre astronomical facilities. Amongst the most important sites are Dome C and Dome A on the Antarctic Plateau, and the Chajnantor area in Chile. In this context, we report on measurements of the sky opacity at 200 ?m over a period of three years at the French-Italian station, Concordia, at Dome C, Antarctica. We also present some solutions to the challenges of operating in the harsh polar environment. Methods. The 200-?m atmospheric opacity was measured with a tipper. The forward atmospheric model MOLIERE (Microwave Observation LIne Estimation and REtrieval) was used to calculate the atmospheric transmission and to evaluate the precipitable water vapour content (PWV) from the observed sky opacity. These results have been compared with satellite measurements from the Infrared Atmospheric Sounding Interferometer (IASI) on Metop-A, with balloon humidity sondes and with results obtained by a ground-based microwave radiometer (HAMSTRAD). In addition, a series of experiments has been designed to study frost formation on surfaces, and the temporal and spatial evolution of thermal gradients in the low atmosphere. Results. Dome C offers exceptional conditions in terms of absolute atmospheric transmission and stability for submillimetre astronomy. Over the austral winter the PWV exhibits long periods during which it is stable and at a very low level (0.1 to 0.3 mm). Higher values (0.2 to 0.8 mm) of PWV are observed during the short summer period. Based on observations over three years, a transmission of around 50% at 350 ?m is achieved for 75% of the time. The 200-?m window opens with a typical transmission of 10% to 15% for 25% of the time. Conclusions. Dome C is one of the best accessible sites on Earth for submillimetre astronomy. Observations at 350 or 450 ?m are possible all year round, and the 200-?m window opens long enough and with a sufficient transparency to be useful. Although the polar environment severely constrains hardware design, a permanent observatory with appropriate technical capabilities is feasible. Because of the very good astronomical conditions, high angular resolution and time series (multi-year) observations at Dome C with a medium size single dish telescope would enable unique studies to be conducted, some of which are not otherwise feasible even from space. © 2011 ESO.

The Dome C (Concordia) station in Antarctica (75°06?S, 123°21?E, 3233 m above mean sea level) has a unique opportunity to test the quality of remote-sensing measurements and meteorological analyses because it is situated well inside the Eastern Antarctic Plateau and is less affected by local phenomena. Measurements of tropospheric temperature and water vapour (H2O) together with the integrated water vapour (IWV) performed in 2010 are statistically analysed to assess their quality and to study the yearly correlation between temperature and H2O over the entire troposphere. The statistical tools include yearly evolution, seasonally-averaged mean and bias, standard deviation and linear Pearson correlation. The datasets are made of measurements from the ground-based microwave radiometer H2O Antarctica Microwave Stratospheric and Tropospheric Radiometer (HAMSTRAD), radiosonde, in situ sensors, the space-borne infrared sensors Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp-A platform and the Atmospheric InfraRed Sounder (AIRS) on the Aqua platform, and the analyses from the European Centre for Medium-Range Weather Forecast (ECMWF). Despite some obvious biases within all these datasets, our study shows that temperature and IWV are generally measured with high quality whilst H2O measurement quality is slightly worse. The AIRS and IASI measurements do not have the vertical resolution to correctly probe the lowermost troposphere, whilst HAMSTRAD loses sensitivity in the upper troposphere-lower stratosphere. Within the entire troposphere over the whole year, it is found that the time evolution of temperature and H2O is highly correlated (> 0.8). This suggests that, in addition to the variability of solar radiation producing an obvious diurnal cycle in the planetary boundary layer in summer and an obvious seasonal cycle over the year, the H2O and temperature intra-seasonal variabilities are affected by the same processes, e.g. related to the long-range transport of air masses. © Antarctic Science Ltd 2013.

The Concordiasi project was undertaken in Antarctica to reduce uncertainties in diverse and complementary fields in Antarctica science. Some of the objectives of the project involved investigations of precipitation to constrain the mass budget over Antarctica and stratospheric ozone depletion. The project was a joint French-United States initiative that started during the International Polar Year (IPY). The project was undertaken over Antarctica during September-November, 2008, December, 2009, and was expected to continue between September-December, 2010. It was undertaken as part of the IPY-The Observing System Research and Predictability Experiment. Participants in the project included scientists from France, the US, Italy, and Australia, along with international organizations such as the European Center for Medium-Range Weather Forecasts (ECMWF).

The lower atmospheric boundary layer at Dome C on the Antarctic plateau has been continuously monitored along a 45-m tower since 2009. Two years of observations (2009 and 2010) are presented. A strong diurnal cycle is observed near the surface in summer but almost disappears at the top of the tower, indicating that the summer nocturnal inversion is very shallow. Very steep inversions reaching almost 1 °C m^-1 on average along the tower are observed in winter. They are stronger and more frequent during the colder 2010 winter, reaching a maximum in a layer ~10-15 m above the surface. Winter temperature is characterized by strong synoptic variability. An extreme warm event occurred in July 2009. The temperature reached -30 °C, typical of midsummer weather. Meteorological analyses which agree with the observations near the surface confirm that heat is propagated downward from higher elevations. A high total water column indicates moist air masses aloft originating from the lower latitudes. The coldest temperatures and strongest inversions are associated with characteristic synoptic patterns and a particularly dry atmosphere. Measurement of moisture in the clean and cold Antarctic plateau atmosphere is a challenging task. Supersaturations are very likely but are not revealed by the observations. This is possibly an instrumental artifact that would affect other moisture measurements made in similar conditions. In spite of this, such observations offer a stringent test of the robustness of the polar boundary layer in meteorological and climate models, addressing a major concern raised in the IPCC 2007 report. Key-points Two years of continuous 45-m ABL observation at Dome C Antarctica Observed high interannual and synoptic variability and extreme inversions Supersaturation likely but not reported, common instrumental limitation ©2013. American Geophysical Union. All Rights Reserved.