Nowcasting severe convective activity over south-east India using ground-based microwave radiometer observations

Abstract

In the present study, the feasibility of nowcasting convective activity is examined by using thermodynamic indices derived from the ground based Microwave Radiometer (MWR) observations located at a tropical station, Gadanki (13.5º N, 79.2º E). There is a good comparison between thermodynamic parameters derived from MWR and co-located GPS radiosonde observations, indicating that MWR observations can be used for developing techniques for nowcasting severe convective activity. Using MWR observations, a nowcasting technique was developed with the data of 26 thunderstorm cases observed at Gadanki. The analysis showed that there are sharp changes in some thermodynamic indices like KI, HI, Precipitable water content, stability index and equivalent potential temperature lapse rates, about 2-4 hours before the occurrence of thunderstorm. A super-epoch analysis was made to examine the composite temporal variations of the thermodynamic indices associated with the occurrence of thunderstorms. The super-epoch analysis revealed that 2-4 hours prior to the storm occurrence, appreciable variations in many parameters are observed suggesting thermodynamic evolution of the boundary layer convective instability. It is further demonstrated that by monitoring these variations it is possible to predict the ensuing thunderstorm activity over the region at least 2 hours in advance. The association between the temporal evolution of thermodynamic indices and convective activity has been tested for the independent case of 9 thunderstorms. The present results suggest that ground based MWR observations can be used effectively to predict the occurrence of thunderstorms at least 2 hours in advance.