Internal solitary waves (ISWs) have considerable energy to drive the
mixing of water masses in the Sulu Sea. The propagation speed is a
critical parameter in demonstrating the dynamic characteristics of ISWs.
We collected 1354 groups of ISWs’ speeds from tandem satellite remote
sensing images with short temporal intervals and analyzed their spatial
and multi-scale temporal variations in the Sulu Sea. The wave speeds
increase exponentially with water depth with a power of 0.26. The
fortnightly spring/neap tidal currents cause daily variations of wave
speeds up to 30%. In addition to the well-recognized stratification
that leads to monthly variations of wave speed, the seasonal
circulations lead to a maximum decrease of wave speeds by 0.27 m/s. With
respect to interannual variations, the wave speeds increase in La Niña
years and decrease in El Niño years, caused by the climatic modulation
of ocean stratification.