Analysis on atmospheric profiles retrieved from microwave radiometer observation at Ganzi in the eastern Qinghai-Tibet Plateau

Microwave radiometer (MWR) can retrieve atmospheric profiles with a temporal resolution of several minutes, which compensates for the low temporal resolution of the meteorological radiosonde data. In this study, we use the data of MWR and radiosonde observed from August to October in 2017 at Ganzi, a station on the eastern side of the Qinghai-Tibet Plateau (QTP), to analyze the accuracy of atmospheric profiles retrieved from the MWR observation and investigate the properties of atmospheric thermal profiles and cloud liquid water content profiles over Ganzi. The results show that the correlation coefficient between the MWR and radiosonde observations is high. The general deviations of MWR-retrieved temperature, relative humidity and vapour density against the data of radiosonde were 1.3℃, -2%, and 0.71 g/m³, with the corresponding root mean square errors of 2.9℃, 20%, and 1.08 g·m^-3, respectively. The impact of precipitation weather on the accuracy of observed data by the MWR was weak except for heavy rainfall weather conditions. The deviation of temperature profile between the MWR and radiosonde was less than 2℃ in most height layers, which can meet the deviation requirement of meteorological operations. The relative humidity deviation between the MWR and radiosonde under non-precipitation condition was about 10% in most height layers, while it was less than 5% below 3.5 km under precipitation conditions. Based on the statistical analysis of the MWR data in Ganzi, it was found that the atmosphere was dry and hot in daytime while wet and cold at nighttime during the observation period. At the same time, the cloud liquid water content was lower in daytime and larger at nighttime, and the development of low-level clouds was weaker during the daytime with higher cloud base heights and stronger during the nighttime with lower cloud base heights. Moreover, the cloud liquid water content showed a similar vertical structure under cloudy and rainy conditions, in which the cloud liquid water content rapidly increased with height and significantly decreased after a fluctuation within a certain height. This variation well indicated the characteristics of entering and leaving clouds. In addition, the cloud body of low-level clouds under cloudy conditions mainly located at the height of 0.1-2.5 km, while the cloud body of low-level clouds under rainy condition widely spread from the surface to 3.5 km. These analysis results showed that the atmospheric profiles retrieved from the MWR observation were credible at the Ganzi station, and the MWR can provide actual data for quantitative study of cloud characteristics.