Horizontal variations of typhoon-forced near-inertial oscillations in the south China sea simulated by a numerical model

Abstract Horizontal variations of near-inertial oscillations (NIOs) in the northeastern South China Sea after the passage of typhoon Kalmaegi were investigated by using a three-dimensional Price-Weller-Pinkel (3DPWP) model. The 3DPWP model was modified by considering simple viscosity terms and the real topography to better simulate the typhoon-forced NIOs. The model results can generally match the observations. According to the model results, the horizontal structure of typhoon-forced NIOs is somewhat like a series of ellipses propagating northwestward with their centers parallel to the track of typhoon. The order of near-inertial wavelength is about 500 km. On the left side of the track, the near-inertial kinetic energy (NIKE) is weak and decreases quickly with distance. However, on the right side, NIKE increases from center of typhoon, gets the maximum at about one and a half radius of maximum wind speed ( R max ) , and then decreases quickly. Several sensitivity experiments were designed to investigate the effect of R max , the maximum wind speed ( V max ) and the moving velocity of typhoon ( U m ) on NIOs. As R max increases, the influence scope of NIOs narrows, whilst increases of V max and U m tend to enlarge the influence scope. When three parameters increase by 10%, the corresponding NIKE increases by 18%, 38% and 19%, respectively, revealing that V max has the most effect. The moving of typhoon is a major reason for horizontal propagation of NIOs. When typhoon is stationary, the time-averaged and depth-integrated NIKE is about only 3.5% of the total kinetic energy input by typhoon, and the induced NICs are much less than those induced by a moving typhoon.