Talk, Joint 8th COPS Workshop and CSIP Meeting 2009, Madingley Hall, Cambridge, UK: 2009-10-26 - 2009-10-28
Abstract:
Within the framework of the „Convective and Orographically-induced Precipitation Study‟ (COPS) a field campaign was performed in summer 2007 to investigate convective precipitation over complex terrain. In this study data from the COPS network were used to analyse the process chain between soil moisture, energy transformation at the Earth's surface, near-surface and boundary layer conditions and convection-related parameter like conditional instability and convective inhibition. At the investigated sites in the Rhine valley the soil moisture is lower than in the Black Forest. No dependence of the albedo on the soil moisture could be detected. Only in the Rhine valley the surface temperature, Ts, and the ratios of sensible and latent heat to the net radiation, Ho/Qo and Eo/Qo, respectively, reveal a dependence on soil moisture. Ts and Ho/Qo are lower and Eo/Qo is higher for higher soil moisture. In the Rhine valley the mean diurnal increase of the equivalent potential temperature, Θe, correlates with the energy supplied by the surface fluxes of heat and moisture. However, the correlation coefficient is low indicating that the near-surface and boundary layer conditions are influenced to a great extent by advective processes, too. At the mountain top of the northern Black Forest (Hornisgrinde) the evolution of Θe is nearly independent on the energy supply from the surface. The same findings as for Θe are valid for the dependence of the boundary layer growth on the surface heat flux. The conditional and potential instability depend on the moist static energy in the boundary layer and the diurnal evolution of the convective indices is highly related to the development of the boundary layer characteristics. Indices indicating convective inhibition, like CIN and CAP, are highly correlated and the boundary layer height can be used to denote an upper threshold for CIN. The frequency of low CIN values is higher in the Black Forest than in the Rhine valley, which favours convection initiation over the mountain sites.