Interannual variations of tropical cyclone activity over the north Indian Ocean

Abstract

An examination of the interannual variations of tropical cyclone (TC) activity over the North Indian Ocean during 1983-2008 has been carried out. The results suggest that instead of local sea surface temperatures, such variations, at least over the Bay of Bengal (BB) during October-November-December (OND), can be attributed to similar variations in the atmospheric flow patterns and moist static energy that are apparently forced largely by the El Niño/Southern Oscillation (ENSO). In an El Niño year, conditions for TC genesis and development, including 850-hPa relative vorticity, 200-850-hPa vertical shear of zonal wind, moist static energy, 500-hPa zonal wind, 500-hPa and 850-hPa geopotential height and 200-hPa divergence, are generally less favourable in BB and fewer intense cyclones are observed during OND. The reverse occurs during a La Niña event. However, causes of the variability of TC activity over BB during April-May-June and that over Arabian Sea have yet to be found, which may be due to the small sample size.

Association of the pre-monsoon thermal field over north India and the western Tibetan Plateau with summer monsoon rainfall over India

“…Hence the cooling over R2 may be due to frequent formation of pre-monsoon thunderstorm/squall activities over the region and favors abovenormal ISMR. It is also observed through earlier studies that when the number of cyclones forming over the Bay of Bengal region in pre-monsoon season is increased (Fadnavis et al, 2011(Fadnavis et al, , 2014, the subsequent ISMR is found to be above normal (Krishna, 2009;Ng and Chan, 2012). During premonsoon months, most of the cyclones, formed in Bay of Bengal region, show north-east movement and hit the land in the north of the Bay of Bengal region (Fadnavis et al, 2014).…”

The Interannual and Interdecadal Variability in Hurricane Activity

“…This ENSO and PDO related variability is similar to that occurring in the Atlantic (LJ00). While the most extensive studies have been performed in the Atlantic Region, there have been studies demonstrating ENSO variability in West Pacific and Northern Indian Ocean region TC occurrence as well (e.g., Chan, 1985;Wu and Lau, 1992;Ng and Chan, 2010). These studies showed similar results for the Pacific Ocean basin as a whole.…”

“…Lastly, the JTWC also monitors TC activity over the Northern Indian Ocean and the Southern Hemisphere as well. The data are also available via the International Best Track archive for Climate Stewardship Project (http:/ / www.ncdc.noaa.gov/ oa/ ibtracs/ ) (e.g., Ng and Chan, 2010). In this study, we use the term TC to include both hurricanes and tropical storms (TS) following Lupo et al (2008), and here tropical storms refer only to those entities that obtained maximum wind speeds between 35 -64 kt.…”

“…Table 7 shows that the ENSO variability results in maybe one more TC per year in LN years, however, this basin has less activity than the other NH basins. In this basin, it has been recognized that TC activity maximizes at two particular times, late spring and fall with a summer minimum in TC activity (e.g., Ng and Chan, 2010). October and November are the most active months with 76 total TC's occurring over the 33 year climatology (about 1 TC in each month per year).…”

Seasonal Environmental Characteristics for the Tropical Cyclone Genesis in the Indian Ocean during the CINDY2011/DYNAMO Field Experiment

“…Previous studies have shown that El Niño/La Niña and Southern Oscillation (ENSO) significantly controls the inter-annual variability of TCG in the Pacific [11,12] and in the Indian Ocean [13][14][15][16][17][18]. Furthermore, the Indian Ocean Dipole (IOD) mode [19] is one of the pronounced phenomena in the tropical coupled atmosphere-ocean system in the Indian Ocean, and is considered to influence the TC activity in the Indian Ocean and in the southern Pacific [16,20,21].…”