Meteorological profiles and optical turbulence in the free atmosphere with NCEP/NCAR data at Oukaimeden - I. Meteorological parameters analysis and tropospheric wind regimes

In this paper, we have used the National Centers for Environmental Prediction (NCEP)/National Centers for Atmospheric Research (NCAR) Reanalysis data base to study, first, a comparison between balloon sounding made at different stations with coinciding model-based meteorological analysis. The comparison allows the assessment of reliability of the analysis in the studied period and to highlight NCEP/NCAR Reanalysis as an interesting data base for site characterization. Using the same system of Reanalysis, we present, secondly, the first complete characterization of main meteorological parameters at Oukaimeden Observatory: wind speed, its direction, temperature and pressure. The statistical treatment of data will cover the years between 1990 and 2009. Monthly, seasonal and annual results are analysed. The comprehensive and reliable statistics of tropospheric wind speeds at Oukaimeden are presented. We found a clear annual periodicity of 200 mbar wind speed. This periodicity could be related to the seasonal dependence of seeing that is affected by the existence of cloud sea during the period around autumn-winter and by high wind speed regimes during spring. The connection of high-to low-altitude tropospheric winds has been explored. We found a high correlation comparable to the ones found at La Silla and La Palma sites. The local parameters in particular topography and stratocumulus formations might affect 700 mbar wind roses. Richardson numbers R-i calculated for each month at Oukaimeden and La Palma are presented. By analysing the 1/R-i values, we found out that the periods and the regions of development of turbulence in relative terms of stability for the two locations are very similar. In addition, we present the first example of a C-n(2) profile estimated from NCEP/NCAR Reanalysis. We found that this profile presents a tendency very similar to the same averaged profile measured by the balloon-born radiosondes.