The relationship between cloud distribution characteristics and meteorological elements over China.

The meteorological elements in the cloud background field influence and change with the cloud macro and micro characteristics, so it is of great significance to study the relationship between them. Using CALIOP Level 2 VFM products and ERA5 reanalysis data, this paper studies and analyzes the relationship between the distribution characteristics of different types and phases clouds and meteorological elements over China through statistical methods. The results show that: In the two-dimensional probability density function distribution of cloud occurrence probability and relative humidity-temperature, there are two significant high value regions, which can be divided into tropical clouds and temperate clouds. Further linear fitting of cloud and relative humidity-temperature two-dimensional probability density function shows that transparent altocumulus and altostratus show a similar linear trend, which indicates that the relationship between temperature and relative humidity is consistent in the background field with high frequency of mixed-phase clouds. Tropical and temperate cirrus may correspond to in-situ origin cirrus and liquid origin cirrus, respectively. Further analysis of the relationship between specific humidity and temperature in the cloud background field shows that with a high cloud occurrence probability, water vapor content was exponentially correlated with temperature. The ratio between the actual fitted water vapor and the saturated water vapor calculated by Tetens formula is defined as the water vapor content saturability in the cloud background field. It is found that the water vapor content saturability in the cloud background field increases with the decrease of temperature, and this trend is more obvious in cirrus.