Observed and modeled diurnal variations around Lake Malawi
Abstract. We investigate how the intensity and spatial distribution of precipitation varies around Lake Malawi on a diurnal time scale, which can be valuable information for water resource management in tropical southeastern African nations. Using a state-of-the-art satellite product and regional atmospheric model, the well-defined diurnal cycle is detected around Lake Malawi with harmonic and principle component analyses: the precipitation is intense during midnight to morning over Lake Malawi and the precipitation peaks in the daytime over the surrounding area. This diurnal cycle in the precipitation around the lake is associated with the lake-land breeze circulation. Comparisons between the benchmark simulation and an idealized simulation in which Lake Malawi is removed, reveals that the diurnal variations in the precipitation are substantially amplified by the presence of Lake Malawi. This is most evident over the lake and relatively surrounding coastal regions. Lake Malawi also enhances the lake-land breeze circulation; the nocturnal lakeward land breeze generates the surface convergence effectively and the precipitation intensifies over the lake. Conversely, the daytime landward lake breeze generates the intense divergence over the lake and the precipitation is strongly depressed over the lake. The lake surface helps to create the thermal contrast between the lake and land and consequently the local lake-land breeze system is maintained via sensible heat flux. The lake-land breeze and the background water vapour enriched by Lake Malawi drives dominantly a diurnal variation in the surface moisture flux divergence/convergence over the lake and surrounding area and consequently, contributes to the diurnal cycle of the precipitation.