Understanding the Differences in Tropical Cyclone Activity in the Arabian Sea and the Bay of Bengal

Understanding the Differences in Tropical Cyclone Activity in the Arabian Sea and the Bay of Bengal

Iris Liu¹, Adam H. Sobel² and Suzana J. Camargo³

1 Department of Physics, Barnard College, New York, NY

2 Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY

3 Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY

The North Indian Ocean (NIO) is the basin with the least tropical cyclone (TC) activity globally, among those which have any regular TC activity at all. Nonetheless, some NIO TCs have historically been among the deadliest in history worldwide, due to large vulnerable populations in low-lying coastal areas. Within the basin, TC activity in the Bay of Bengal (BOB) sub-basin is substantially greater than that in the Arabian Sea (AS) sub-basin, but the reasons for this difference have not been well explained in the literature. Prior studies suggested that differences in sub-basin geography and wind circulation could contribute to this discrepancy..

Here, we attempt to quantify the roles of specific environmental factors in order to understand the reasons of the difference between the two basins. We consider environmental variables in the basin as a whole, and in the immediate vicinity of storms reaching at least 35 knots in each sub-basin, in particular at the times of cyclogenesis and the storm Lifetime Maximum Intensity (LMI). The results for the two sub-basins are then compared to determine which environmental variables differed significantly between the sub-basins. Our analysis revealed that humidity (CRH and RHUM600), potential intensity, and vertical wind shear differ significantly between the sub-basins, suggesting that these contribute to the discrepancy in TC activity between BOB and AS. More specifically, higher humidity and lower vertical shear values near cyclogenesis in BOB, on average, are associated with greater frequency of cyclogenesis in the BOB. Similarly, higher humidities and higher potential intensities near storm LMI are associated with higher rates of TC intensification in BOB than in AS.