Impacts of the Central Pacific El Niño on Tropical Cyclone Activity in the North Indian Ocean

Tropical cyclone (TC) activity in the North Indian Ocean (NIO) is unique as compared with other basins due to its bimodal annual distribution, which consists of the pre-monsoon (April – June) and the post-monsoon (October – December) season. The geographic distribution of TCs over the NIO is also asymmetric: with climatologically more TCs over the Bay of Bengal (BoB) than those over the Arabian Sea (AS). Previous studies indicated that the pre-monsoon activity is largely associated with the summer monsoon trough development, while the post-monsoon activity is due to the winter monsoon circulation creating appropriate dynamical conditions for TC development. Although not well studied as TCs in the Atlantic and western North Pacific, it is known that climate variability such as El Niño South Oscillation and Indian Ocean Dipole (IOD) in sea surface temperature (SST) pattern has influences to TC activity over the NIO. Namely, it has been found in recent studies that the La Niña phase is able to generate more conductive environment in NIO for TC development. As a regional SST pattern, the IOD would enhance/suppress TC development over the AS/BoB depending on its phase. Recently a new kind of ENSO has been identified, which is termed central-Pacific El Niño (or El Niño Modoki/warm-pool El Niño in various studies). The central-Pacific El Niño has the significant SST changes occurring over the central part of the Ocean rather than the eastern part. Because of this distinct spatial SST pattern, it is known to possess different remote atmospheric responses in the Indian Ocean as compared with the canonical ENSO. In this study we investigate the impacts of central-Pacific El Niño on NIO TC activity through two pathways: (1) directly due to the changes in atmospheric and oceanic conditions in the NIO and (2) indirectly due to the potential modulation of IOD events by the central-Pacific El Niño.