On the Potential Role of the Kalahari Thermal Low on Southern Africa Precipitation Variability

Abstract

Large body of works has studied the impacts of different drivers on southern Africa precipitation. But the influence of the Kalahari thermal low (KTL) on the southern Africa precipitation variability is overlooked to date and deserve more attention. Here, we reconcile two most important features of the southern Africa climate – the Angola low and the Botswana high through the Kalahari thermal low. Results show that the relationship between the KTL and the Angola low has two distinct behaviors at different timescales: (i) at seasonal timescale (annual cycle), the Angola low, driven by the KTL, is also a thermal low; (ii) but at interannual timescale, the reversal of the relationship suggests that the Angola low behaves as a tropical low in summer and forms as a Gill-like response to the diabatic heating related to KTL. Secondly, the KTL shows a strong negative correlation with southern Africa rainfall, implying that a strong KTL reduces the rainfall intensity. This teleconnection can be explained by the leading mode of variability of KTL. However, the composite analysis highlights two physical mechanisms responsible of this teleconnection: the heat dome mechanism during the warm phase of KTL, conducive to below normal rainfall conditions over southern Africa. In the cold phase of KTL, the Angola low plays a crucial role in modulating the regional precipitation and leads to above normal rainfall conditions. Furthermore, our findings found that current climate models from CMIP6 are unable to reproduce the observed mechanisms.