Tropical cyclones (TCs) are amongst the most devastating natural hazards worldwide. They have led to considerable economic and personal damages in densely populated coastal areas, including the degradation of industrial and fishery infrastructures (ports, desalination plants, petrochemical facility and etc.) and destructive winds and flashfloods on coastal plains (Wang and Oey 2008; Han et al. 2012; Sun et al. 2013; Mei et al., 2015; Zhang et al. 2016). According to the World Meteorological Organization, the world’s deadliest tropical cyclone during last 50 years was Cyclone Bhola, formed in the south center of the Bay of Bengal and hit East Pakistan on the 12th -13th November 1970. Nearly half a million people were killed due to the large storm surge, overwhelmed tidal flats and low-lying islands in the Bay of Bengal. The Orissa super cyclone in 1999 and Cyclone Nargis in 2008 caused around 238,000 deaths in Bangladesh and Myanmar (Singh et al., 2001).
TC genesis is controlled by four physical processes: atmospheric conditions (low-level cyclonic vorticity, less vertical wind shear, moisture at mid-tropospheric level), internal TC dynamics, Coriolis forces and underlying boundary conditions (Chen and Ding, 1979; Gray, 1979; Emanuel et al., 2004). The underlying boundary conditions, such as sea surface temperature (SST) and sufficiently mixed deep water are the most important factors to TC intensification (Jaimes et al., 2011; Yablonsky and Ginis, 2012; Yan et al., 2017; Lavender et al., 2018; Sun et al., 2019). The TC’s energy source is heat transfer from the ocean surface; this heat is used to strengthen a cyclonic disturbance into an intense vortex. TC intensification is correlated with the 26.5°C isotherm depth and upper ocean heat content (Palmen, 1948; Williams, 2013; Shay and Brewster, 2010; Ackerman and Knox 2015).
TCs occur in the southwest Pacific, the northeast and northwest Pacific, the North Atlantic, the northern and southern Indian Ocean and Australian Sea basins (Gray, 1979). A recent study on the global distribution pattern of TCs for 1980–2018 demonstrated that the frequency of TCs has decreased over the southern Indian Ocean, the northeast of the Australian Sea and the northwest Pacific. Meanwhile, an increasing trend is observed in the Arabian Sea (AS), the northern Atlantic and central Pacific basins (Murakami et al., 2020). TCs are rare phenomena in the northern Indian Ocean (NIO). On average, just 7% of global TCs form in this basin (Neumann, 1993). The NIO basin is divided into the Bay of Bengal (BoB) and Arabian Sea (AS) basins. The number of TC events in the Bay of Bengal is four times greater than the Arabian Sea. Average TC frequency (Bay of Bengal/Arabian Sea) for the period 1982–2000 was 2.7 events/year and 1.6 events/year between 2001 and 2019. For the recent period, TC duration has significantly increased in the Arabian Sea. The increase in TC frequency and duration in the Arabian Sea has been concurrent with accelerating accumulated cyclone energy during the pre-monsoon (March–April–May) and post-monsoon (October-November) seasons. By contrast, no significant changes in TCs were observed in the Bay of Bengal (Deshpande et al., 2021; Bandyopadhyay et al., 2021).
The ocean mesoscale eddy is a significant ocean phenomenon that covers 20–30% of the ocean area (Cheng et al., 2014; Lumpkin, 2016). The mesoscale eddy (ME) circulation system has important effects on surface ocean water temperatures and also on subsurface layers, general circulation and regional climate (Macdonald & Wunsch, 1996; Dong et al., 2014; Zhang, et al., 2014; Yang et al., 2015). Mesoscale eddy energy transfer could have positive impacts on TC intensity (Sun et al., 2020). Strong eddy activity exists in the western basin of the Arabian Sea that is similar to eddy-rich regions in the global ocean (Scharffenberg & Stammer, 2010; Roullet et al., 2014). Eddy activities in the Arabian Sea exhibit strong seasonality that peaks during the summer monsoon season (Trott et al., 2018). Wind stress, the Somali current, the westerly propagating Rossby wave and background currents are all parameters that can further reinforce eddies in the region (Brandt et al., 2002; Trott et al., 2017).
Studies of global warming impacts on TC intensity, duration and tracks are important in the Gulf of Oman and the Arabian Sea because of their local and global economic importance. For instance, the Gulf of Oman is the only maritime entrance into the Persian Gulf (Fig. 1), a region which exports approximately 18.2 million barrels of oil per day. Several important cargo and fishery ports also exist on the Omani and Iranian coasts that are vital for the regional economy. The increasing number, intensity and duration of TC events in the Arabian Sea and the Gulf of Oman could accentuate maritime risks and economic damages.
The aim of this study is to evaluate the impacts of global warming on ocean-atmospheric parameters leading to the creation and migration of the most deadly and destructive TCs (Gonu, Phet and Shaheen) in the Arabian Sea and the Gulf of Oman, using satellite SST data and model reanalysis.