Prediction of convective events using multi-frequency radiometric observations at Kolkata

• Microwave radiometric observations are used to nowcast convective rain events.
• Brightness temperatures of 22.24 GHz and LI show definite change before convection.
• These two parameters indicate impending convective growth much before rain.
• The prediction technique generates alarm 75 min before rain for 80% of cases.

In the present study, the effectiveness of nowcasting convective activities using a microwave radiometer has been examined for Kolkata (22.65° N, 88.45° E), a tropical location. It has been found that the standard deviation of brightness temperature (BT) at 22 GHz and instability indices like Lifting Index (LI), K Index (KI) and Humidity Index (HI) has shown definite changes before convective events. It is also seen that combination of standard deviation of BT at 22 GHz and LI can be most effective in predicting convection. A nowcasting algorithm is prepared using 18 isolated convective events of 2011 and in all cases, a marked variation of these parameters has been seen an hour before the event. Accordingly, a prediction model is developed and tested on convective events of 2012 and 2013. It is seen that the model gives reasonable success in predicting convective rain about 7075 min in advance with a prediction efficiency of 80%.