Time–frequency variability of internal solitary waves in relation to oceanographic conditions in the Lombok Strait, Indonesia: a wavelet analysis approach

Internal Solitary Waves (ISWs) play a crucial role in vertical mixing and energy redistribution, influencing regional circulation in the Indonesian seas and water mass exchange with the Indian Ocean. The Lombok Strait, the principal southern exit passage of the Indonesian Throughflow (ITF), is a key hotspot of ISW activity, yet the mechanisms governing its variability remain poorly understood. This study integrates five years (2015–2020) of Sentinel-1 Synthetic Aperture Radar (SAR) detections with Copernicus Marine Environment Monitoring Service (CMEMS) reanalysis data to examine the temporal – frequency characteristics of ISWs using continuous and cross-wavelet analyses. Pearson’s correlation analysis (p < 0.005) reveals a strong negative relationship between ISW occurrence and thermocline depth, indicating enhanced wave generation under shallow thermocline conditions. ISW propagation speed (1.2–2.8 m s−1) shows a significant negative correlation with halocline depth and a positive correlation with the depth of maximum buoyancy frequency (N2), demonstrating that both the structure and strength of stratification modulate wave kinematics. Wavelet and cross-wavelet results identify dominant semi-annual (~6-month), annual (~12-month), and interannual (16–32-month) periodicities associated with monsoon-driven stratification and climate anomalies, particularly during the 2015–2016 El Niño and 2019 positive IOD. Compared with other tropical regions, such as the South China and Andaman Seas, the Lombok Strait exhibits stronger and more coherent interannual signals due to its topographic focusing and ITF-controlled stratification. These findings establish stratification as the primary control on ISW variability, providing a time – frequency framework for understanding internal wave – climate interactions and energy transport in the ITF system.