Comparing FY-2F/CTA products to ground-based manual total cloud cover observations in Xinjiang under complex underlying surfaces and different Weather Conditions
Authors: Li Shuai , Zhang Hua , Chen Yonghang , Wang Zhili , Li Xiangyu , Li Yuan , Xue Yuanyuan 
Published: June 2023

Abstract. Clouds are an important parameter of artificial water augmentation, which are of substantial significance to judge the precipitation capacity. Xinjiang is an arid region in Northwest China, where weather stations are sparsely distributed, the types of underlying surface are complex and the climate difference between southern and northern Xinjiang varies greatly. However, the retrieval of the total cloud cover (TCC) from satellite in arid areas is a challenging task. Based on the hourly data of TCC observed by ground observation stations from June 2015 to May 2016, considered the complex underlying surfaces and different weather conditions, the precision, consistency and error between the cloud total amount products of FengYun-2F stationary satellite (FY-2F/CTA) and manually observed TCC are compared and evaluated in Xinjiang region. The findings of this study are as follows: (1) The precision rate (PR) of FY-2F/CTA in Xinjiang region is 74.6 %, which gradually decreases from north to south, demonstrating a high false rate (FR) and a low missing rate (MR); The consistency rate (CR) is 51.5 %, with little difference among three sub-regions of Xinjiang, all showing high weak rate (WR) and low strong rate (SR), which means that the TCC inverted from FY-2 satellite data are generally lower than that observed by ground observation stations, especially in Southern Xinjiang; The Bias is -20 %, and all the error indexes (EIs) including Bias, AE and RMSE increase from central to the north and south of Xinjiang, that means the EIs are the lowest in Tianshan Mountains, and the highest in Southern Xinjiang. The PR and CR of FY-2F/CTA in the vegetation underlying surface are better than those of non-vegetation, that is to say, FY-2F/CTA have the best identification effect on the forest and plowland underlying surfaces, and the worst effect on the snow and ice underlying surface. (2) With the increase of temperature, the PR and CR of FY-2F/CTA increase, while the EIs decrease; Under various temperature conditions, FY-2F/CTA have always been exhibiting high MR, low FR (on the contrary in January), high WR and low SR. From low elevation to high elevation, the PR and CR of FY-2F/CTA decrease, but the PR increases significantly when the altitude is higher than 2000 m. (3) Dust reduces the CR of FY-2F/CTA, increases the SR, but it has little effect on the identification of cloud and non-cloud. (4) Under different cloud cover levels, the PR and EIs of FY-2F/CTA are proportional to the amount of TCC, while the CR is inversely proportional to it, that is, the CR is higher, the PR and EIs are lower under clear sky and partly cloudy conditions, and the CR is lower, the PR and EIs are higher under cloudy and overcast conditions. This study is the first to evaluate the FY-2F/CTA on the scales of complex underlying surface, various temperature and altitude, dust effects and different cloud cover levels in arid areas of Xinjiang. Thus, the results would provide an important reference for satellite retrieval and application of TCC in arid areas.