Characterization of internal solitary waves in the Andaman Sea and Arabian Sea using EOS-04 and sentinel observations

ABSTRACT

In this study, we synergistically used Synthetic Aperture Radar (SAR) and optical observations to characterize the Internal Solitary Waves (ISW) in the Andaman Sea and Arabian Sea region. Total 25 scenes combined from EOS-04, Sentinel-1&2 satellites are considered for the year 2022. Various approaches, including Fast Fourier Transform (FFT), Multiple Image Comparison (MIC), Tidal Time Period (TTP) and Korteweg-de Vries (KdV) equations, were employed to characterize the ISW, and its spatial and seasonal variations are also analysed. The dominant wavelength of ISW over the Andaman Sea in June 2022 is found to be 6500 m travelling towards the Andaman coast. The overall phase speed of ISW in the Andaman Sea lies in the range of 1.87–2.60 ms⁻¹. It shows a seasonal variation of around 16% between winter and summer months, where a significant variation in the seasonal mixed layer depth was noticed. The phase speed also decreased as the ISW travelled from deep water to shallower regions. In contrast, the dominant wavelength of ISW in the continental shelf region of the west coast of India (near Goa) was much smaller (~400 m) compared to the Andaman Sea. Here, the ISW phase speed estimated using MIC and TTP methods was ~ 0.56 ms⁻¹ in February 2022. The KdV equation yielded lower estimates of phase speed compared to the other two methods. The use of multiple satellite images and various approaches possess an advantage in comprehending the spatial and temporal variations in the characteristic features of ISW.

KEYWORDS:

• Internal solitary waves
• phase speed
• synthetic aperture radar
• EOS-04

Acknowledgements

Authors wish to acknowledge the Director, SAC; Deputy Director, EPSA; Group Director, AOSG; Head, OSD for their continual support and encouragement.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data Availability statement

All Sentinel-1/2 datasets are publicly available. The sentinel datasets are obtained from Copernicus open access hub (scihub.copernicus.eu/dhus) provided by European Space Agency (ESA). The EOS-04 datasets are available upon request through proper channel from ISRO’s earth observation data hub (bhoonidhi.nrsc.gov.in) provided by National Remote Sensing Center (NRSC). The HYCOM data is publicly available and can be obtained from https://www.hycom.org. The Gebco-2022 bathymetry and NCMRWF wind fields are also publicly available and are obtained from download.gebco.net and https://ftp.ncmrwf.gov.in/pub/outgoing/respectively.