A numerical study of gravity waves induced by convection associated with Typhoon Rusa

Typhoon Rusa (2002) is simulated using a three-dimensional mesoscale model (MM5), and the characteristics of gravity waves generated by convection associated with the typhoon are investigated. The gravity waves in the stratosphere propagate in two directions, northwestward and southeastward according to the convective bands propagating in the same directions, although the typhoon itself moves north-northeastward. Spectral analyses show that the inertio-gravity waves (IGWs) in the stratosphere generated by Rusa have a dominant horizontal wavelength of 300-600 km, a vertical wavelength of 3-11 km, and a period of 6-11 hrs. A large fraction of the IGWs is filtered out in the upper troposphere and stratosphere mainly due to the critical-level filtering process. The decreased magnitude of the momentum flux with height in a non-filtered region is likely due to the damping process, with a minor contribution by the wave breaking process that can occur exclusively near the critical-level phase speeds.