The Influence of Soil and Vegetation Parameters on Atmospheric Variables Relevant for Convection in the Sahel

Abstract

A key issue in modeling the Sahelian climate is to correctly predict the energy fluxes between the land surface and the atmosphere. A problem faced by land surface models in the Sahel is the horizontal heterogeneity of soil and vegetation properties in the region, where measured data are scarce. Experiments have been designed to evaluate a land surface model both in offline mode and coupled to the Advanced Regional Prediction System (ARPS), a mesoscale atmospheric model. For the evaluation in offline mode, an observational dataset of 58 days from the Hydrological and Atmospheric Pilot Experiment in the Sahel (HAPEX-Sahel) is gathered to interpret the results. For the evaluation in the coupled mode, boundary layer development is simulated for 4 individual days. The model is able to reproduce the observations close to measurement errors. Sensitivity experiments are conducted to identify the most important parameters that affect the simulation of the convective available potential energy (CAPE) and the equivalent potential temperature (?e), two variables closely linked to convection and rainfall in the Sahel. During the selected cases, model results depend significantly on the soil moisture conditions. When bare soil evaporation is dominant, the soil parameters have the most impact on CAPE and ?e, whereas in dry soil conditions, the vegetation parameters gain in importance. Differences due to the change of one parameter can reach 400 J kg?1 for CAPE and 4 K for ?e, which is large enough to affect local convection.