Characteristics of orographic clouds and associated mechanisms in the Qilian Mountains, northeastern Tibetan Plateau based on FengYun-4A satellite TBB product

Abstract

The Qilian Mountains (QM) in northwest China is a key source of orographic cloud formation, significantly influencing regional weather, climate, and hydrological balance. However, due to the sparse distribution of ground-based observational stations, the characteristics of orographic clouds and their associated precipitation remain insufficiently understood. Utilizing FengYun-4A black body temperature (TBB) data from 2018 to 2021 in boral summer, this study investigated the spatial and diurnal characteristics of orographic clouds and associated mechanisms over the QM. Results indicate that orographic clouds primarily form over the mountainous terrain, with deep convective clouds concentrated in the central and eastern QM. A distinct diurnal cycle is observed, with peak cloud activity occurring in the afternoon to early evening (15:00–19:00 local solar time), minimal activity late at night, and the weakest development in the morning. These variations are more pronounced in the central and eastern QM, where cloud formation persists for longer durations, compared to the western region. Three dominant diurnal cloud cycles are identified in the southeast, northeast, and eastern fringes of the western, central, and eastern QM, respectively, along with smaller-scale cycles along mountain ridges. Orographic cloud formation is driven by the convergence of low-level westerlies and the Asian monsoon, with moisture contributions from the westerlies, the Tibetan Plateau, and the monsoon system. Additionally, interactions between solar heating and complex terrain shape the spatial and diurnal distribution of these clouds. These findings enhance our understanding of regional water cycles and provide valuable insights for weather and climate research.