TRMM derived sea surface temperature in the wake of a cyclonic storm over the central Bay of Bengal

Abstract

Sea surface cooling associated with a cyclone in the Bay of Bengal was investigated using the data derived from TRMM Microwave Imager (TMI) onboard Tropical Rainfall Measuring Mission (TRMM) spacecraft. Though the TRMM/TMI sensor has all weather capabilities, sea surface temperature (SSTs) can not be obtained during heavy rain conditions. Hence, to overcome the problem of having no observations during the cyclone day, weekly analysis was carried out during the cyclone week (27 March–2 April 2000) and pre‐cyclone week (20–26 March 2000). To compute the magnitude of SST cooling in the cyclone track, weekly SSTs of the cyclone period were subtracted from the pre‐cyclone period. Similar analysis was carried out during non‐cyclonic periods of 20–26 March and 27 March–2 April of 2001, 2002. The analysis indicated that the TMI SST was reduced by maximum of 1.57°C along the cyclone track during the passage of cyclonic storm. Such an activity was not observed during 27 March–2 April 2001 and 2002, indicating that the cooling observed in 27 March–2 April 2000 was due to the cyclonic storm. On the other hand, SST anomalies are positive during 27 March–2 April of 2001, 2002 over these regions. TRMM observations shows higher wind speed and precipitation rate associated with the storm and are responsible for decrease in SST. Analysis of Pathfinder Advanced Very High Resolution Radiometer (AVHRR) SST showed the cyclone induced cooling but the SSTs measurement was blocked by clouds during the cyclone period (27 March–2 April 2000). In the same time, Reynolds SSTs was unable to detect the cooled sea surface. In these circumstances, the cyclone induced sea surface cooling was well captured by TRMM/TMI and had distinct advantage of providing SSTs in presence of cloud as compared to infrared SSTs measurement like those from pathfinder SSTs.

Acknowledgements

We are thankful to Director, NRSA, Deputy Director (RS&GIS) and Group Director (Water Resources & Oceanography), Head, Oceanography Division for their support to prepare the article. We also acknowledge Dr T. Sesha Rao (ERDAS Inc.), Dr E. V. R. Parthasaradhi and Mr B. V. Ramana Kumar of Remote Sensing Instruments (RSI), Hyderabad. We are also thankful to Remote Sensing Systems, Santa Rosa and NASA's Earth Science Enterprise (ESE) for providing TMI data. We acknowledge, EOSDIS, Distributed Active Archive Centre at Goddard Space Flight Centre for providing AVHRR pathfinder SSTs.