Long-term ground-based microwave radiometric measurements of atmospheric brightness temperature in SKYNET Hefei (31.90N, 117.17E) site

A dual-frequency, ground-based microwave radiometer (WVR-1100) is used to investigate the behavior of the atmosphere in terms of zenith brightness temperature (T_B) at 23.8 and 31.4 GHz respectively. Some experimental findings in SKYNET Hefei site from September 2002 to August 2012 are presented. The cumulative distributions of T_B at both frequencies for all sky conditions show four different regions, while only two regions can be identified for clear, lightly cloudy and cloudy condition. Annual cycle of T_B at 23.8 GHz is apparently remarkable, indicating the large annual cycle of atmospheric water vapor. Regular seasonal variations of T_B are observed with the strongest value in summer and the weakest in winter. - Highlights: • Long-term observations of atmospheric brightness temperature are studied in SKYNET Hefei using the radiometer (model WVR-1100). • Results of cumulative distributions of zenith T_B from Hefei site are different from other regions with seasonal variations. • Long-term observations of T_B are useful for investigating water vapor and cloud of regional climate.