Diagnostics and energetics of the topographic Rossby waves generated by a typhoon propagating over the ocean with a continental shelf slope

Abstract

The dynamics of the subinertial response when a typhoon propagates over the ocean with a sloping bottom topography is investigated by carrying out a set of idealized numerical experiments. At least two different topographic Rossby waves (TRWs) are identified at the same along-slope wavenumber and two different subinertial frequencies in the wavenumber–frequency spectra. The diagnostics of vorticity balance demonstrates that the bottom pressure torque plays an important role in both the generation and propagation of TRWs. Two sets of sensitivity experiments show that the spatial structure of the typhoon is a “decisive” parameter in determining the along-slope wavenumber as well as the corresponding frequencies; the along-slope wavenumber of a TRW is first determined as a response to the typhoon-induced perturbation, and the corresponding frequencies are then determined so as to satisfy the theoretical TRW dispersion relationship. The amplitude of TRWs, in contrast, are controlled by both the typhoon radius as well as the typhoon traveling speed. For typhoons with a large radius or slow traveling speed, the resulting TRWs can be comparable to or more energetic than the near-inertial waves. This indicates that the TRWs might play an important role in inducing the near-bottom mixing along the shelf slope by using energy supplied from typhoon winds.