Insights Into Internal Solitary Waves East of Dongsha Atoll From Integrating Geostationary Satellite and Mooring Observations

Abstract

Understanding of internal solitary wave (ISW) behavior has been limited due to sparse observations. We used high-resolution Himawari-8 satellite imagery and mooring observations to reveal the two-dimensional (x-y) propagation process of ISWs in the South China Sea as they westward propagate onto the Dongsha plateau and encounter Dongsha Atoll. The 2D depiction of wave speed distribution, derived from detected wave crest positions every 10 min, shows the wave speeds range from 3 m s(-1) to 1 m s(-1) and have a tight correspondence to the local water depth. The correlation coefficient between the wave speeds and the Dubreil-Jacotin-Long (DJL) solutions is around 0.7, with a root mean squared value of 0.26 m s(-1), and the representative available potential energy for this region is considered to be 130 MJ m(-1). However, diffusions of wave speed in the ISW's lateral direction, particularly around abrupt topography, contribute to occurrences of outliers. Pairs of incident and reflected waves are well recognized east of Dongsha Atoll. The incident wave packet is known to be classified into a-type and b-type waves. The reflected waves associated with the b-wave, identifiable as mode-1 depression ISWs, are traced back to their generation site at depths of 100-200 m. In contrast, the reflected waves of the a-wave remain elusive in shallower waters (<300 m), likely due to interference from their longer incident counterparts. The reflected wave, however, is slower and decelerates toward deeper water, deviating from the DJL prediction. These comprehensive observations can help refine models for improved accuracy.