Conditional Modulation of Extreme Internal Solitary Waves in the Lombok Strait

Abstract. Using 13 months of continuous mooring observations at the Lombok Strait (November 2023–December 2024), we identify 302 internal solitary wave (ISW) packets and 618 individual solitons with amplitudes up to 104 m. ISW occurrence peaks in boreal winter–spring (March: 45 packets/month) and drops to near-zero in summer (July: 3 packets/month). The observations reveal an amplitude-dependent dynamical structure. ISW occurrence for both amplitude classes is primarily modulated by the ITF: normal-amplitude ISWs (25–65 m) are seasonally suppressed during enhanced ITF periods—when thermocline stratification is concurrently elevated—indicating that the apparent negative N²–ISW correlation is a seasonal covariance with ITF strength rather than a direct stratification effect. Extreme ISWs (>65 m) show negligible stratification dependence and instead tend to coincide with transient ITF weakening as a precondition for nonlinear amplification. Low-pass filtered acoustic Doppler current profiler records show that extreme events consistently coincide with northward velocity pulses in the 50–200 m layer that substantially reduce Doppler retardation, consistent with the existence of episodic dynamic windows favorable for nonlinear wave amplification.