Diurnal variation of total cloud cover and cloud type in summer in Xinjiang, China based on FY4A and ERA5

Xinjiang, China (XJ). This study compared the diurnal variations of ground observation- (OBS-), FY4A- and ERA5-based total cloud cover (TCC) and revealed the diurnal variation of FY4A-based cloud type (CLT) in XJ. The relationship between diurnal variation in TCC and various meteorological factors was investigated. The OBS-based TCC ranged from 30 % to 50 % (20 % to 40 %) at most stations in southern (northern) XJ, exhibiting a diurnal variation characterized by slight increases during the day and slight decreases at night. The diurnal variation of the ERA5- and FY4A-based TCC at most stations is similar to that based on OBS, but with larger variations and systematic biases. The ERA5-based TCC tends to be overestimated (underestimated) by 0 %-20 % (0 %-10 %) at most stations in northern (southern) XJ, while the FY4A-based TCC is found to be overestimated by 0 %-30 % (20 %-40 %) at most stations in northern (southern) XJ. The ERA5- and FY4A-based gridded TCC reveals more spatially complete and refined diurnal variation characteristics, with differences evident between basins and mountains. The diurnal variation curve of TCC from ERA5 lags behind FY4A by approximately 3 h in phase, with average values of 48.3 % and 58.5 %, respectively. The diurnal variations of the frequencies of water type, supercooled type, mixed type, ice type, cirrus type and overlap type were in the ranges of 12.4 %-35.6 %, 12.3 %-17.9 %, 9.1 %-13.1 %, 4.0 %-7.6 %, 3.8 %-4.7 %, and 3.3 %-5.1 %, respectively, with the corresponding means of 25.2 %, 15.4 %, 11.6 %, 5.5 %, 4.3 % and 4.1 %, respectively. The diurnal variation in TCC at most stations demonstrates a significant positive (negative) correlation with surface wind speed and relative humidity (temperature). These findings provide precise targets for the optimization of artificial rain (snow) enhancement operations. Moreover, they offer novel insights into a comprehensive understanding of the coupled relationships among mountain precipitation replenishment, ecological water demand in river basins, and atmospheric water resources. Furthermore, the findings of this study provide a scientific basis for the development of integrated air-land water resource regulation strategies, which are of urgent practical significance for the safeguarding of regional water security and ecological security. • First OBS-based assessment of diurnal variations in ERA5- and FY4A-based TCC in XJ. • ERA5- and FY4A-based TCC diurnal variations resemble OBS but show larger variability. • FY4A’s spatial pattern is more optimal, while values of ERA5 are closer to OBS in XJ. • The diurnal variations of TCC and CLT both exhibit spatial heterogeneity across XJ. • Diurnal variation of TCC shows a significant positive correlation with SI10 and RH.