Water column observations and imaging: Revealing internal solitary waves and implications for sand wave dynamics in the Alor Strait

This study presents the first comprehensive characterization of internal solitary waves (ISWs) in the Alor Strait, Indonesia, utilizing multi-modal observations from the Jala Citra Expedition 3-2023 “Flores.” High-resolution water column imaging via echosounder, coupled with satellite synthetic aperture radar (SAR) imagery, revealed exceptional ISWs with amplitudes frequently exceeding 100 m, with scattering volume (SV) value ranges from −73 to −60 dB. The Korteweg-de Vries (KdV) equation was employed to analyze the subsurface wave structure, correlating with SAR-derived bright-dark patterns. In situ measurements confirmed bi-directional wave propagation towards the Flores and Sawu Seas. This research demonstrates that the Alor Strait, not just the Ombai Strait, is a significant generator of internal waves in the southern Indonesian archipelago. Time-series analysis indicated that intra-seasonal events (ENSO) significantly modulate ISW characteristics. Notably, the study uncovered a potential link between ISWs, bolus activity, and sand wave evolution, with observations suggesting ISW-induced formation of sand wave crests up to 20 m high, ∼4 km long, and SV value ranges from −18.38 to −17.96 dB. These findings expand our understanding of internal wave generation in narrow Indonesian straits bordering the Indian Ocean and highlight the critical role of ISWs in shaping benthic morphodynamics, with implications for sediment transport and marine geohazards.