MOSE: Operational forecast of the optical turbulence and atmospheric parameters at european southern observatory ground-based sites - II.atmospheric parameters in the surface layer 0-30m

Abstract

This paper is the second of a series in which we aim to prove the feasibility of forecasting all the most relevant classical atmospheric parameters for astronomical applications (wind speed, wind direction, temperature, relative humidity) and the optical turbulence (C2N and the derived astroclimatic parameters, such as seeing e, isoplanatic angle θ0, wavefront coherence time τ0, etc.). This study is carried out in the framework of the MOSE (MOdelling ESO Sites) project, and is focused above the two European Southern Observatory ground-based sites of Cerro Paranal and Cerro Armazones. In this paper, we present the results related to the MESO-NH model ability in reconstructing the surface layer atmospheric parameters (wind-speed intensity, wind direction and absolute temperature, 0-30m above ground level). The model reconstruction of all the atmospheric parameters in the surface layer is very satisfactory. For the temperature, at all levels, the root mean square error (RMSE) is inferior to 1°C. For the wind speed, it is ~2ms-1, and for the wind direction, it is in the range 38°-46°, at all levels, which corresponds to a RMSErelative in the range 21-26 per cent. If a filter is applied for the wind direction (winds inferior to 3ms-1 are discarded from the computations), the wind direction RMSE is in the range 30°-41° (i.e. RMSErelative in the range 17-23 per cent). The model operational forecast of the surface layer atmospheric parameters is suitable for different applications, as follows. It can be used for thermalization of the dome using the reconstructed temperature, hours in advance, of the beginning the night. It can provide knowledge in advance of the main direction from which strong winds will come during the night, which could allow an astronomer to anticipate the occurrence of a good/bad seeing night, and to plan observations accordingly. It can also prevent adaptive secondary mirror shake generated by the wind speed. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.