Cumulus over the Tibetan Plateau in the Summer Based on CloudSat–CALIPSO Data

Abstract

Cumulus (Cu) can transport heat and water vapor from the boundary layer to the free atmosphere, leading to the redistribution of heat and moist energy in the lower atmosphere. This paper uses the fine-resolution CloudSat–CALIPSO product to characterize Cu over the Tibetan Plateau (TP). It is found that Cu is one of the dominant cloud types over the TP in the northern summer. The Cu event frequency, defined as Cu occurring within 50-km segments, is 54% over the TP in the summer, which is much larger over the TP than in its surrounding regions. The surface wind vector converging at the central TP and the topographic forcing provide the necessary moisture and dynamical lifting of convection over the TP. The structure of the atmospheric moist static energy shows that the thermodynamical environment over the northern TP can be characterized as having weak instability, a shallow layer of instability, and lower altitudes for the level of free convection. The diurnal variation of Cu with frequency peaks during the daytime confirms the surface thermodynamic control on Cu formation over the TP. This study offers insights into how surface heat is transported to the free troposphere over the TP and provides an observational test of climate models in simulating shallow convection over the TP.

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

“…Grid cell values vary between a few and 1,400. According to Li and Zhang (), the optimal compromise between profile sample amount per grid and an equal distribution over the grid cells is achieved in the 1° × 1° resolution grid…”

“…Grid cell values vary between a few and 1,400. According to Li and Zhang (2016), the optimal compromise between profile sample amount per grid and an equal distribution over the grid cells is achieved in the 1 × 1 resolution grid F I G U R E 2 Topography of the TP and illustration of the three subregions based on impact of large-scale moisture transport according to Yao et al (2013). Locations within the domain 27 -40 N, 70 -105 E and above 3,000 m a.s.l.…”

“…Several previous studies have used active remote sensing techniques to examine convection over the TP (Ruethrich et al, 2013;Li and Zhang, 2016;Yan et al, 2016;Pan et al, 2017;Yan et al, 2017;Hu et al, 2017;Shang et al, 2018). Li and Zhang (2016) have found that cumulus clouds from shallow convection are among the most common cloud types over the TP, especially between June and August, when the summer monsoon dominates the moisture transport to the region. Climate model simulations suggest that these cumulus clouds hamper the development of stratiform cloud layers over large areas (Li and Zhang, 2017).…”

Why is there a tilted cloud vertical structure associated with the northward advance of the East Asian summer monsoon

“…Associated with the northward advance of the EASM, the convective instability layer is thinner on the northern side of the convective center (Figure c). The relatively dry environment, with a smaller CAPE of 350 J, is not conducive to the formation of DC clouds, but it is conducive to the formation of shallow clouds, such as Cu and Ac clouds (Li and Zhang, ). In the convective center, the convective instability layer extends from near the surface up to 14 km, and the CAPE increases to 1824 J.…”

Modification of the convective adjustment time‐scale in the Kain–Fritsch eta scheme for the case of weakly forced deep convection over the Tibetan Plateau region

“…The TP also prominently affects the global climate system (Xu et al, 2008;Dong et al, 2016), and the many unique characteristics of weather events over the TP have proven challenging to simulate (Boos and Kuang, 2010;Huang et al, 2010;Xu et al, 2012;Wang et al, 2014;Yan et al, 2016). In summer, many convective events are frequently initiated by strongly enhanced surface diabatic heating and dynamic lifting by topographic forcing (Fu et al, 2006a;Li and Zhang, 2016;Wang and Wang, 2016). Meanwhile, since the water vapour amounts over the TP are relatively low in summer, the convective available potential energy (CAPE) is lower than in most other continental regions during this season (Fu and Liu, 2007).…”