Temporal and spatial variations of convection and precipitation over the Tibetan Plateau based on recent satellite observations. Part I: Cloud climatology derived from CloudSat and CALIPSO

Abstract

This sequence of papers, consisting of two parts, examines temporal and spatial variations of convection and precipitation over the Tibetan Plateau (TP) based on recent satellite observations. Here in Part 1, seasonal and diurnal variations of cloud vertical structure and cloud properties have been derived from four combined CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite data sets and compared between three subregions in the TP which are marked by different dominating large-scale atmospheric circulations and moisture sources. The results show that the plateau is generally dominated by low-level single-layer clouds and stratiform cloud types. Cloud occurrence frequencies peak during the summer monsoon season between May and September and are generally higher during daytime compared with nighttime in all the three subregions. The fraction of detected ice cloud layers in the TP domain exceeds 50% during all months and 80% between January and April. While ice cloud layers occur as altostratus clouds in the westerly dominated north and transition zone, high-level cirrus cloud occurs frequently accompanied by lower level cumulus clouds in the monsoon-dominated south, especially during nighttime. This study complements previous satellite observations of clouds over the TP and reveals firstly the high contribution of stratiform ice cloud layers in the westerly dominated north, secondly the importance of the monsoon season which outweighs day-night differences and affects the examined cloud parameters in all regions and finally the significant regional differences of cloud characteristics within the plateau. It is therefore suggested to focus on the relative importance of stratification, mesoscale convective systems and advection in future studies on hydro-climatic changes in the TP region.