Diurnal variations of different types of cloud over the Baiu-Meiyu frontal zone using retrieved cloud properties: Implication for the rainfall process

The diurnal variations of clouds and their relationships with the rainfall associated with the Baiu-Meiyu front in Eastern China and over the ocean in the south of Japan in June 2016-2019 are investigated with the cloud product retrieved from the infrared brightness temperature of the Himawari-8 satellite. Clouds are classified into three types: low (<3 km), middle (3-10 km), and high clouds (>10 km); high clouds are further divided into thin (0.1-1), moderately-thick (1-6), and thick (>6) clouds based on their cloud optical thickness. Prominent diurnal variations of high clouds were observed to have an evening-to-midnight maximum in Eastern China, an early afternoon-to-evening maximum around the Ryukyu Islands, and an evening maximum around the Izu Islands. In Eastern China and around the Ryukyu Islands, there was a clear diurnal amplitude maximum of the thick cloud and the moderately-thick cloud. And the diurnal peak time of the thick cloud was 1-2 h later than the peak time of rainfall. Around the Izu Islands, a diurnal amplitude maximum of moderately-thick cloud was found. While for the thick cloud, its peak occurrence was found to be 4-6 h later than that of the rainfall. Our results suggest that the convective activity is highly related to the primary mode of the diurnal variation of rainfall and cloud in Eastern China and around the Ryukyu Islands. Meanwhile, it is less related to the diurnal variation of rainfall and cloud around the Izu Islands.