Internal Waves in Celebes Sea

Internal Waves in Celebes Sea

The Celebes Sea is one of the regions where high-frequency internal waves occur. Located in the western Pacific Ocean, it lies north of the Indonesian island of Sulawesi (also known as Celebes), south of the Sulu Sea and the Philippines, and covers an area of approximately 435,000 km². It is a deep-sea basin with a maximum depth of over 4,000 meters, but it is bordered by shallow shelves along the surrounding islands. The bathymetry changes sharply from the coastal areas and narrow straits-that connect it to the Sulu Sea in the north, the Philippine Sea and the Molucca Sea in the east, and the Makassar Strait in the south – toward the deep central basin of the Celebes Sea. This configuration appears to be the source of the semidiurnal internal waves, which are generated by barotropic tidal forces interacting with the highly variable seabed topography.
Internal waves are a widespread phenomenon in the world’s oceans, occurring under conditions of stable density stratification. They can modulate small-scale surface roughness patterns on the ocean surface as they propagate. These changes affect the slope angles of the sea surface facets, resulting in local variations in reflectivity and altering the position of the reflective (or nearly reflective) zone in optical remote sensing images. Consequently, internal waves can become visible as alternating dark and light stripes with a defined gradient in optical satellite data, -most clearly within the region of sun glint.
These internal waves pose potential hazards to navigation safety due to the strong associated vertical and horizontal currents associated with them. They also influence several oceanographic processes, such as the upward transport of nutrients for photosynthesis, the redistribution of sediments and pollutants, and the propagation of underwater acoustics. Therefore, researching internal waves in the ocean is important for science and technology.
Tide-generated internal waves in the Celebes Sea have large spatial scales and spread with high phase velocities, primarily south-eastward into the Sulu Sea and towards the Indonesian coastline.
Relatively few dedicated investigations of internal waves in the Celebes Sea have been conducted to date. Here, we present Sentinel-2 satellite images of internal wave convergence patterns in the Celebes Sea, acquired on October 25 and on November 6 within the sun glint region (Figures 1 and 3). The image from October reveals three prominent internal wave packets extending up to 310 km in length, with individual wave crests reaching up to 2 km in width (Figure 2).

Further reading

Internal waves in the Celebes and Banda Seas (NASA visible earth)
Sunglint-enabled views of internal waves in the Celebes Sea (CIMSS Satellite Blog)
Oceanic Internal Waves in the Sulu–Celebes Sea Under Sunglint and Moonglint (IEEE Xplore)
Satellite image of internal wave convergences in the Sulu Sea (ResearchGate)

Fig. 1

Fig. 2

Fig. 3