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Keywords:

  • soil moisture;
  • energy balance;
  • pre-convective environment;
  • COPS;
  • convective boundary layer

Abstract

The field campaign ‘Convective and Orographically-induced Precipitation Study’ (COPS) was performed in south-western Germany and eastern France in summer 2007. Within the COPS context this study focused on the process chain of soil moisture, surface fluxes, conditions of the convective boundary layer (CBL), and convection-related parameters.

The results were different for valley and mountain sites. Only in the Rhine valley did the ratios of sensible and latent heat to the net radiation at the surface, H0/Q0 and E0/Q0 respectively, reveal a weak dependence on soil moisture. H0/Q0 was lower and E0/Q0 was higher at higher soil moisture. The correlation of the diurnal increase of the equivalent potential temperature, Θe, with the energy supplied by H0 and E0 was found to be lower for higher surface inhomogeneity. Furthermore, only a weak dependence of the CBL depth on the sensible surface heat flux was found for valley sites and was non-existent for the mountain crest.

The convective indices in the whole COPS domain were found to depend on Θe in the CBL. The absolute values of conditional and potential instability are not necessarily the decisive parameters for convection to occur, because highest instability was observed in the Rhine valley while convection was preferably initiated over the mountains. Convective inhibition (CIN) was positively correlated with the capping strength and negatively with the CBL height: the higher the CBL, the lower the upper threshold of CIN. The frequency of low CIN was higher in the Black Forest mountains than in the Rhine valley, which facilitates convection initiation over the mountain sites. Copyright © 2011 Royal Meteorological Society