Vertical structure of non-precipitation cloud obtained from cloud radar observation at Ganzi in the eastern Qinghai-Tibet Plateau

Based on the observation data of Ka-band cloud radar at Ganzi site in the eastern Qinghai-Tibet Plateau (QTP) from June to August 2019, the vertical structure of non-precipitation cloud in this area is analyzed. The results show that: (1) The cloud occurrence frequency (COF) of single-layer cloud is 78.3%, which is higher than 18.3% of two-layer cloud and 3.4% of multi-layer cloud under the cloudy condition. For clouds with different height, the COF of low cloud is 46%, while middle and high clouds account for 27% each. When the number of cloud layers increases, the COFs of middle and high clouds increase. (2) The COF presents a diurnal variation, in which it is low in daytime and high in nighttime. However, the COF diurnal variation of upper layer clouds weakens, when the number of cloud layers increases. Additionally, terrain has a certain impact on the COF diurnal variation. (3) The vertical distributions of cloud base height (CBH) and cloud top height (CTH) are mostly bimodal. When three-layer cloud happens, the vertical distributions of CBH and CTH are unimodal for the lower layer cloud. (4) The cloud thickness shows the phenomenon of cloud compression. Namely, for single-layer cloud, the average cloud thickness is about 3.8 km. For two-layer cloud, the average cloud thickness of lower layer cloud is about 2.5 km, and that of upper layer cloud is about 1.5 km. For three-layer cloud, the average cloud thickness of lower and upper layer clouds decrease to about 1.8 and 1.2 km, respectively, and the average cloud thickness of middle layer cloud is the smallest, with a value about 1 km. The phenomenon of cloud compression becomes more obvious with the increase of cloud layers. These results indicate that ground-based cloud radar shows the advantages of local cloud detection, which is beneficial to cloud detection and research over the QTP.