Analysis of the Water Vapor Characteristics of Short-Time Heavy Rainfall in July and August Based on Microwave Radiometer Data

Based on the observational data from RPG HATPRO-G4 microwave radiometer and automatic meteorological stations, the evolution characteristics of vapor density (VD), relative humidity (RH), and integrated water vapor (IWV) of July-August short-time heavy rain in Chengdu are studied. Applications of microwave radiometer data in short-time heavy rain are also discussed. Results showed that moisture conditions in both the shower and short-time heavy rainfall are good in July-August in Chengdu. Moisture conditions includes,near surface VD reach 19±3g·m^-3, IWV is more than 53kg·m^-2 and RH is greater than or equal to 90% at the height between 1km to 3km. Sum of the near surface VD and the 500-hPa VD 1 hour before the precipitation begins can be used as the indicator of occurrence of short-time heavy rain. When it greater than or equal to 26.3g·m^-3, the distinguish rate reaches 75%. 3 hours before the short-time heavy rain begins, continuous convergence of water vapor form a wet layer(98%≤RH≤100%) at the height of 3km. Thickness of this wet layer increases as the rainfall approaches, and then stethches down to the boundary layer. At the beginning of the rainfall, RH drops sharply above 4km and RH increases slightly below 4km. IWV after the rainfall reduces to a value close to that before the rainfall.