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The atmospheric properties above three sites (Dome C, Dome A and the South Pole) on the Internal Antarctic Plateau are investigated for astronomical applications using the monthly median of the analyses from ECMWF (the European Centre for Medium‐Range Weather Forecasts). Radiosoundings extended on a yearly time‐scale at the South Pole and Dome C are used to quantify the reliability of the ECMWF analyses in the free atmosphere as well as in the boundary and surface layers, and to characterize the median wind speed in the first 100 m above the two sites. Thermodynamic instability properties in the free atmosphere above the three sites are quantified with monthly median values of the Richardson number. We find that the probability to trigger thermodynamic instabilities above 100 m is smaller on the Internal Antarctic Plateau than on mid‐latitude sites. In spite of the generally more stable atmospheric conditions of the Antarctic sites compared to mid‐latitude sites, Dome C shows worse thermodynamic instability conditions than those predicted above the South Pole and Dome A above 100 m. A rank of the Antarctic sites done with respect to the strength of the wind speed in the free atmosphere (ECMWF analyses) as well as the wind shear in the surface layer (radiosoundings) is presented.

SUMMARYThe data collected during three contrasting Intensive Observing Periods (IOPs) of the Mesoscale Alpine Programme (MAP) were used to assess the performance of the Meso-NH model with particular emphasis on precipitation and microphysical processes. The model was able to reproduce the intense and moderate convective rain of IOPs 2A and 3, respectively, and also the stratiform precipitation associated with IOP 8. Microphysical budget computations were used to derive the mean vertical distribution of the hydrometeors and to quantify the relationships among the different water species. The results of IOP 8 exhibit a shallow stratiform system in which the dominant ice hydrometeor is snow, growing efficiently by vapour deposition. In contrast, the results of IOP 2A show a much deeper system in which graupel and its associated growth modes play an important role. These results are consistent with the two conceptual models of orographic rain that were derived from the MAP radar observations.

One of the main goals of the feasibility study MOSE (MOdelling ESO Sites) is to evaluate the performances of a method conceived to forecast the optical turbulence above the ESO sites of the Very Large Telescope and the European-Extremely Large Telescope in Chile. The method implied the use of a dedicated code conceived for the optical turbulence (OT) called Astro-Meso-Nh. In this paper we present results we obtained at conclusion of this project concerning the performances of this method in forecasting the most relevant parameters related to the optical turbulence (C 2 N , seeing ε, isoplanatic angle θ 0 and wavefront coherence time τ 0 ). Numerical predictions related to a very rich statistical sample of nights uniformly distributed along a solar year and belonging to different years have been compared to observations and different statistical operators have been analyzed such as the classical bias, RMSE, σ and more sophisticated statistical operators derived by the contingency tables that are able to quantify the score of success of a predictive method such as the percentage of correct detection (PC) and the probability to detect a parameter within a specific range of values (POD). The main conclusions of the study tell us that the Astro-Meso-Nh model provides performances that are already very good to definitely guarantee a not negligible positive impact on the Service Mode of top-class telescopes and ELTs. A demonstrator for an automatic and operational version of the Astro-Meso-Nh model will be soon implemented on the sites of VLT and E-ELT.

In recent years, ground-based astronomy has been looking towards Antarctica, especially its summits and the internal continental plateau, where the optical turbulence appears to be confined in a shallow layer close to the icy surface. Preliminary measurements have so far indicated rather good values for the seeing above 30-35 m: around 0.3 arcsec at Dome C. Site-testing campaigns are however extremely expensive; instruments provide only local measurements and atmospheric modelling might represent a step ahead in the search and selection of astronomical sites, thanks to the possibility of reconstructing three-dimensional (3D) C 2 N maps over a surface of several km. The Antarctic Plateau therefore represents an important benchmark test to evaluate the possibility of discriminating between sites on the same plateau. Our group has proven that the analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) global model do not describe the Antarctic boundary and surface layers in the plateau with the required accuracy. A better description could be obtained with a mesoscale meteorological model. The mesoscale model Meso-NH has proven to be reliable in reproducing 3D maps of optical turbulence above mid-latitude astronomical sites. In this paper we study the ability of the Meso-NH model to reconstruct the meteorological parameters as well as the optical turbulence above Dome C with different model configurations (monomodel and grid-nesting). We concentrate our attention on the abilities of the model in reproducing the optical turbulence surface-layer thickness (h sl ) and the integral of C 2 N in the free atmosphere and in the surface layer. It is worth highlighting that these are the first estimates ever made with a mesoscale model of the optical turbulence above the internal Antarctic Plateau.