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An Application of Brightness Temperature Received from a Ground-based Microwave Radiometer to Estimation of Precipitation Occurrences and Rainfall Intensity

Ground-based microwave radiometers (MWR) provide continuous thermodynamic (temperature, water vapor, and cloud liquid) soundings in the clear and cloudy weather conditions. These profiles can be determined by observing the intensity of the atmospheric radiation at selected frequencies. The MWR used in this study is TP/WVP-3000A, which measures the intensity of radiation at 8 water vapor channels (22-30 ㎓) and 14 oxygen channels (51-59 ㎓) to obtain thermodynamic profiles at National Center for Intensive Observation of severe weather (NCIO) located at Haenam, Korea. In this study, the predictability of precipitation occurrences and the estimation of rainfall intensity were investigated by using the brightness temperature (TB) of the MWR. The averaged differences of TBs in 2 hours before raining were calculated and compared with those of period unrelated with rain. In 2 hours before raining, the pronounced increase of TB was observed in water vapor channels (22-30 ㎓), while TBs in 54-59 ㎓ as oxygen channels were almost remaining constant except for the great increase of TB at 51-52 ㎓ related to cloud liquid water. Performance for forecasts of precipitation occurrences using the preceding increases of TBs at 22.2 ㎓, 30.0 ㎓, and 51.2 ㎓ was improved and better than the 3-hour operational (routine) forecasts. The estimation of rainfall intensity was examined by two simple estimative methods using the linear and the nonlinear regression analyses between rainfall intensity and TBs. Rainfall intensity was estimated by the calculated regression curves of TBs from MWR and compared with observed one by an Optical Rain Gauge (ORG) at the Haenam NCIO. As a result of the verification on forecasting performances, both the linear and the logarithmic regression methods between the observed and the estimated rainfall intensity showed substantially high in Equitable Threat Scores (ETSs) and correlation coefficients.