Nowcasting of rain events using multi-frequency radiometric observations

•Microwave radiometric observations are used to nowcast heavy rain events.•Brightness temperatures of 22.24 GHz and 58 GHz show concurrent change before rain.•Brightness temperature derivatives indicate favorable conditions for imminent rain.•The prediction technique generates alarm 25 min before rain for 90% of cases.

SummaryNowcasting of heavy rain events using microwave radiometer has been carried out at Kolkata (22.65°N, 88.45°E), a tropical location. Microwave radiometer can produce the temperature and humidity profiles of the atmosphere with fairly good accuracy. Definite changes are observed in temperature and humidity profiles before and at the onset of heavy rain events. Concurrent changes in the brightness temperatures (BT) at 22 GHz and 58 GHz are found to be suitable to nowcast rain. The time derivatives of brightness temperatures at 22 GHz and 58 GHz are used as inputs to the proposed nowcasting model. In addition, the standard deviation of the product of these time derivatives is also considered. The model has been developed using the data of 2011 and validated for rain events of 2012-2013 showing a prediction efficiency of about 90% with alarm generated about 25 min in advance.