Investigation of multimodal wave climate using spectral partitioning and wave system tracking algorithms

Typically, ocean waves comprise both wind sea and swell systems, each exhibiting different characteristics in terms of decay, propagation, and their impact on engineering. Distinguishing between wind sea and short/long swell systems is critical for both scientific research and engineering applications, such as climate assessment, harbor agitation, and structural design, which has led to a growing interest in studies of multimodal wave climate.

This study investigates the origin and characteristics of multimodal waves based on spectral partitioning and wave system tracking, taking Sri Lanka in the North Indian Ocean as a case study. The data is generated from the spectral wave model WAVEWATCH III. Results show that the wave systems mainly originate from the southwest monsoon, northeast monsoon, southeast trade winds, and southern storm belt. Tropical cyclones can occasionally contribute to multimodal waves. Subsequently, four spectral zones of wave origins are defined according to the joint probability density distribution of partitioned mean wave directions and peak periods estimated by a kernel function. Storm belt waves are responsible for over 36 % of the total wave systems. Finally, two ways of describing wave climate based on the partitioned bulk wave parameters are compared. One offers a thorough understanding of the wave climate from the perspective of wave origin; however, it loses the combined information of wave systems. The other method, while lacking a guaranteed coherence between the wave systems over time, preserves the crucial combined information of wave systems, which is useful in generating a reduced dataset comprising representative cases.