[A-OS18] 海洋物理学一般

[AOS18-15] Interannual Variability of Semidiurnal Internal Tides in the Eastern Arabian Sea: Influence of the Indian Ocean Dipole and ENSO

*Pragnya Makar¹、Ambarukhana Devendra Rao¹、B. Yadidya²、Vimlesh Pant¹ (1.Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, New Delhi, India. 、2.Department of Earth & Environmental Sciences, University of Michigan, Ann Arbor, MI, USA)

キーワード：Internal waves, Indian Ocean Dipole, El Niño-Southern Oscillation , Baroclinic tides

The Arabian Sea (AS), located in the northern Indian Ocean to the west of the Indian subcontinent, experiences strong seasonal and interannual variations in its physical and biogeochemical processes. The amount of energy converted from barotropic tides to internal tides (ITs) is directly influenced by density stratification. There are three main IT generation sites in the eastern AS: (1) the shelf-slope break off Mumbai, (2) the Lakshadweep, and (3) the Maldives Islands. Numerical model simulations are carried out for the 15-year period from 2009 to 2023 to observe the interannual variability in the generation and propagation of ITs in this region. The months of January, April, July, and October are considered to represent winter, pre-monsoon, monsoon, and post-monsoon seasons, respectively. In the region off Mumbai, the highest semidiurnal IT generation is observed during the pre-monsoon season, with a 15-year mean of 1.34 GW and the highest interannual variability of 0.32 GW. In contrast, IT generation in the Lakshadweep and Maldives regions is higher during the monsoon season, with mean values of 0.64 GW and 3.47 GW, respectively, along with variability of 0.12 GW and 0.54 GW. The study reveals that the combined effects of the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) influence the circulation in the AS, which in turn affects the region's density stratification on interannual timescales. Increased IT generation at key generation sites, along with enhanced propagation, is observed during positive IOD and El Niño years, particularly its peak phases during the fall and winter seasons. In contrast, negative IOD and La Niña years exhibit reduced IT generation and propagation in the region. We observed that during positive IOD and El Niño years, energy conversion from barotropic to baroclinic can increase by as much as 61% at the generating sites compared to the previous years. In contrast, during negative IOD and La Niña years, energy conversion can decrease by as much as 30% compared to the previous years, based on data from the last 15 years. The increasing strength and frequency of IOD and ENSO events can significantly influence IT activity in the AS. This study provides an insight into the interannual variability of semidiurnal IT activity and highlights the potential impact of IOD and ENSO on IT generation and propagation in the eastern AS.