The role of the Kuroshio Current on the diurnal cycle of Meiyu-Baiu rainband in mid-June

Abstract

This study investigated the mechanism of the strong diurnal cycle of precipitation over the Kuroshio Current (KC) in mid-June when the climatological location of the Meiyu-Baiu (MB) front is aligned with the KC. The diurnal cycle of precipitation exhibits double peaks, with the primary peak in the morning (03–12 LST) and the secondary peak in the afternoon (12–15 LST). It was revealed that the morning peak is induced by convective instability associated with the large temperature difference between the sea surface and the surface air (TDiff), whereas the cross-frontal circulation is responsible for the afternoon peak. In the morning, heating from the KC intensifies as the TDiff maximizes. Intensified convective instability due to the enhanced heating from the KC increases the mean amount of convective precipitation (CP) as well as the probability of stronger CP. The surface wind convergence and the confluence sustaining the convection intensify the frontogenesis, which leads to the maximization of the frontal intensity in the afternoon. The afternoon peak of precipitation is in accordance with the intensified MB front and the associated cross-frontal circulation. However, direct contribution of diabatic heating to the frontogenesis is relatively weak. This study provides a physical understanding of the intensified diurnal cycle of MB rainfall in terms of the interaction between oceanic and atmospheric fronts, the KC and MB, respectively.