Trumpet-Shaped Topography Modulation of the Frequency, Vertical Structures, and Water Path of Cloud Systems in the Summertime Over the Southeastern Tibetan Plateau: A Perspective of Daytime-Nighttime Differences

摘要

The warm and humid summer monsoon frequently reaches the steep southern slope of the Himalayas, which is conducive to the formation of unique cloud systems. However, few studies have comprehensively evaluated the characteristics and mechanisms of cloud systems over the trumpet-shaped topography (TST) region in the southeastern Tibetan Plateau. Therefore, we investigated the occurrence frequency, vertical structures, and water path of clouds over the TST regions and their daytime-nighttime differences using the combined measurements of the CloudSat and CALIPSO satellites from 2007 to 2010 during June-August. Results show a marginal difference in occurrence frequency of total clouds between the daytime (95.4%) and nighttime (97%) over the TST region, while different-typed clouds exhibit various daytime-nighttime differences in frequency, vertical structures, and water path. In particular, deep convection, cirrus, altocumulus, and nimbostratus clouds tend to occur more frequently at nighttime, while stratocumulus and cumulus clouds occur more in the daytime. Multilayered clouds form more easily at nighttime, especially triple-layered clouds. The cloud top/bottom heights and liquid/ice water paths of clouds are higher at nighttime than in the daytime over the TST region, which is associated with the increase in deep convection, cirrus, and altocumulus clouds at nighttime. In general, the differences in cloud properties are mainly related to the combined effects of the TST-induced unique mountain-valley circulation, the large-scale monsoonal circulation, and the thermal difference between the day and night. These findings provide valuable observational evidence for the further understanding and accurate simulation of cloud systems over the southeastern Tibetan Plateau region.