Seasonal and Semi-Diurnal Variations in Cloud-Phase Characteristics Over the Southern Himalayas and Adjacent Regions as Observed by the Himawari-8 Satellite

Investigated in this study are the seasonal and semi-diurnal variations of the cloud-phase climatology over the southern Himalayas and adjacent regions by using 5 years of Himawari-8 cloud-product data (2016-2020). The four selected regions from south to north are the Gangetic Plains (I), Himalayan foothills (II), southern slope of the Himalayas (III), and the Himalayan-Tibetan Plateau region (IV), respectively. Results showed that the cloud frequency of cloud gradually increases from region I via II to III, then sharply decreases as the altitude increases up to IV. Ice-phase clouds occurs more frequently over regions I/II (III/IV) during boreal summer (winter), while water-phase cloud has a higher frequency over region III/IV (I/II) in summer (winter), respectively. All of the different cloud phases have a clear seasonal cycle. Furthermore, the semi-diurnal variation shows that water-phase clouds tends to have an occurrence frequency peak around noon (in the later afternoon) over regions I/II/III in summer (winter), whereas over region IV it only occurs more in the morning in both seasons. Ice-phase cloud generally occurs more in the late afternoon in both boreal summer and winter, especially over region IV. Further analysis showed that the differences in the cloud-phase characteristics over the southern Himalayas and adjacent regions are likely related to the interactions of the synoptic-scale circulation, the topography, and the water vapor transport.