Early Stage Soliton Observations in the Sulu Sea*

Abstract

Abstract Observations of early stage, large-amplitude, nonlinear internal waves in the Sulu Sea are presented. Water column displacement and velocity profile time series show the passage of two solitary-like waves close to their generation site. Additional observations of the same waves are made as they propagate through the Sulu Sea basin. These waves of depression have an estimated maximum amplitude of 44 m. Observed wave amplitude and background stratification are used to estimate parameters for both a Korteweg–de Vries (K-dV) and a Joseph wave solution. These analytic model solutions are compared with a fully nonlinear model as well. Model wave half-widths bracket the observed wave, with the Joseph model narrower than the K-dV model. The modal structure of the waves change as they transit northward though the Sulu Sea, with higher mode features present in the southern Sulu Sea, which dissipate by the time the waves reach the north. Observed and modeled energies are roughly comparable, with observed potential energy estimated at 6.5 × 107 J m−1, whereas observed kinetic energy is between 4.6 × 107 J m−1 and 1.5 × 108 J m−1, depending on the integration limits. If this energy remains in the Sulu Sea, an average dissipation rate of 10−9 W kg−1 is required over its volume, helping to maintain elevated mixing rates.