The dependence of convection‐related parameters on surface and boundary‐layer conditions over complex terrain

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, H 0 /Q 0 and E 0 /Q 0 respectively, reveal a weak dependence on soil moisture. H 0 /Q 0 was lower and E 0 /Q 0 was higher at higher soil moisture. The correlation of the diurnal increase of the equivalent potential temperature, e , with the energy supplied by H 0 and E 0 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 e 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.

The Convective and Orographically‐induced Precipitation Study (COPS): the scientific strategy, the field phase, and research highlights

“…The process chain of soil moisture, surface fluxes, CBL conditions, and convection-related parameters over complex terrain are analysed by Hauck et al (2011) and Kalthoff et al (2011). The results were different for valley and mountain sites.…”

“…The frequency of low CIN was higher in the Black Forest than in the Rhine valley, which facilitates convection initiation over the mountain sites (e.g. Kalthoff et al, 2011;Behrendt et al, 2011).…”

Assessing the uncertainty of soil-moisture impact on convective precipitation by an ensemble approach

“…The influences on simulated precipitation is more complex and depends strongly on the chosen case and domain. A dependency of all convective indices on the equivalent potential temperature was found by Kalthoff et al (2011) over different orographic terrains. However, convection was predominantly initiated over mountain, independent of the instability indices, but with smaller 20 convective inhibition.…”

“…Significant differences between planetary boundary driven and synoptic forced conditions could not be detected. Further studies by Kalthoff et al (2011) and Hauck et al 15 (2011) over orographic complex terrain investigate the role of orographic effects in the synergy of soil moisture-precipitation feedbacks. Hauck et al (2011) determines large systematic differences between modelled and observed soil moisture.…”

Processes driving deep convection over complex terrain: a multi‐scale analysis of observations from COPS IOP 9c

“…Detailed studies by Kalthoff et al (2009) and Behrendt et al (2011) on COPS-IOP 8b investigate the initiation of convection by superposition of a synopticscale convergence and a regional-scale mountain range and thermally induced convergence. The dependence of convection-related parameters on surface and boundarylayer conditions over complex terrain during the COPS period was investigated by Kalthoff et al (2011).…”