物理組演講公告 6月2日(五) 10：30 Characteristics, Arrival Patterns, and Generation of Nonlinear Internal Waves Impinging on Dongsha Reef, Northeastern South China Sea. Dr. Steve Ramp
講者：Dr. Steve Ramp
題目：Characteristics, Arrival Patterns, and Generation of Nonlinear Internal Waves Impinging on Dongsha Reef, Northeastern South China Sea.
時間：6月2日(五) 10:30 – 11:30
A series of field experiments performed since 2000 have observed the world’s largest nonlinear internal waves (also called solitary waves or solitons) as they propagate WNW from the Luzon Straits to the Chinese continental shelf and slope. Their life cycle could briefly be described as generation, somewhere around the rough topography in the straits; propagation and nonlinear steepening in the deep basins; transformation under shoaling over the continental slope and shelf; and ultimately dissipation in shallow water. Due to the intense vertical velocities and buoyancy fluctuations they induce, the waves are of high biological interest since they potentially provide the nutrient pump that fuels entire ecosystems, including the region surrounding Dongsha.
Several investigators have reported an intriguing pattern of wave arrivals in which weaker, usually solitary waves arrive six to eight hours before larger waves with several waves per packet. The timing makes the wave arrivals appear to be almost, but significantly, not quite semidiurnal. Numerical models producing the phenomenon have improved steadily over the last fifteen years, but the exact mechanisms and locations for wave generation have remained elusive. The wave energy has been clearly linked to the fortnightly cycle of the barotropic tide in the Luzon Strait, but several different hypotheses regarding the generation mechanism have been published and are still being evaluated against the data.
Recently, two additional data analyses have been done which help illuminate the problem. The first, using four moorings from the 2014 ONR Sand Dunes experiment over the continental slope northeast of Dongsha, shows how the wave properties change while shoaling up a gradual (dynamically weak) bottom slope.
Some waves form remotely and others locally. The second, called the IWISE Synthesis Program, is a joint analysis of moorings near generation, inverted echo sounders in the deep basins, and moorings in the far field deployed by several different investigators. This is the first fully three-dimensional data set in the SCS that was able to observe the longitudinal as well as latitudinal variation of the wave energy. These data, in concert with the SUNTANS numerical model, show different generation locations for the weaker (type-b) vs. the stronger (type-a) waves. The details, including arrival timing and why the a-waves are stronger, will be presented in the talk.