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Climate modeling of ice supersaturation and haze at Dome C, Antarctica

Authors and Institute Affiliations : J-B Madeleine (LMD), H. Gallée (IGE), R. Forbes (ECMWF), D. Veron (University of Delaware), C. Genthon (IGE), F. Hourdin (LMD), F. Lemonnier (LMD), L. Piard (IGE)

Ice supersaturation is usually found at high altitudes where cirrus clouds form. At such altitudes, continuous and detailed measurement of the different steps leading to cloud formation and their comparison to climate models is difficult. The Concordia station on the Antarctic plateau offers an opportunity to document supersaturation and cloud formation in similar thermodynamical conditions and over the long term. The 40-m meteorological mast at Dome C was therefore instrumented with two special hygrometers, one at the top and one at the bottom, and haze formation was detected via visibility measurements. Ice supersaturation is found in all seasons and a RHi of up to 200% is measured. During summer, in the evening, the RHi often reaches 120% and sometimes precedes the formation of haze and a drop in visibility (for more detail, see Genthon et al., this conference). This timing of events is examined in four atmospheric models: the ECMWF IFS, the MAR limited area model, PolarWRF and the IPSL Climate Model, for which the parameterization of supersaturation is being developed. The models predict realistic supersaturations but the detailed diurnal cycle and statistical distributions differ from the observations. Haze is predicted and compared in detail with the observations. The use of the mast also gives access to the vertical gradients of humidity. The strengths and weaknesses of the models are compared, and pave the way to improvements in the different parameterizations.