Nonlinear processes of energy transfer from traveling hurricanes to the deep ocean internal wave field

Abstract

Generation of large‐scale internal waves by a hurricane traveling over the ocean with a uniform velocity is investigated by using a three‐dimensional, multilevel numerical model. It is found that two distinctive kinds of internal waves are excited in the wake of the hurricane, namely, near‐inertial waves, which can be explained based on the linear theory, and superinertial waves with frequencies 2ƒ0 and 3ƒ0(ƒ0 is the inertial frequency at the latitude of the hurricane track), which are generated through nonlinear effects. Our special attention is directed to the superinertial waves with frequencies 2ƒ0 and 3ƒ0 because these internal waves are considered to be efficient energy sources for small‐scale mixing in the deep ocean. These superinertial waves predominantly have low‐vertical‐mode structures and satisfy the dispersion relation for lee waves. In areas away from the hurricane track, in particular, the double‐inertial frequency waves become larger than the near‐inertial waves. The nonlinear resonant triads causing the generation of such superinertial waves are examined by calculating the bispectrum, which clearly shows that the lowest‐vertical‐mode double‐inertial frequency wave is generated efficiently through the nonlinear interaction between the high‐vertical‐mode near‐inertial waves.