A numerical study of generation and propagation of type-a and type-b internal solitary waves in the northern South China Sea

Numerical simulations based on a high-resolution three-dimensional MIT general circulation model (MITgcm) using realistic topography and tidal forcing are conducted to investigate the generation and propagation of the so-called type-a waves (large-amplitude rank-ordered wave packets) and type-b waves (isolated wave packets) in the northern South China Sea. At first, we summarized and analyzed the generation and propagation characteristics of these waves. Then, energy budget at the Luzon Strait is calculated. Energy generation has three local maxima every day, of which the largest one corresponds to the emergence of the type-a wave. Energy flux at the west boundary of the Luzon Strait shows two local maxima each day. The larger one is consistent with the generation of the type-a wave and the smaller one is in correspondence with the generation of the type-b wave. Sensitivity experiments are designed to explore the role of the east and west ridge of the Luzon Strait on the generation and propagation of the type-a and type-b waves. It is found that the east ridge is indispensable on the generation of the type-a wave while the west ridge has little contribution. The west ridge diminishes the type-a waves’ amplitude but hardly changes their propagation speed. The type-b waves also come from perturbation signals which originate from the east ridge and are enhanced in amplitude and reduced in propagation speed by the west ridge.