Kelvin and Mixed Rossby-Gravity Waves Appearing in the GFDL "SKYHI" General Circulation Model and the FGGE Dataset : Implications for Their Generation Mechanism and Role in the QBO

摘要

To evaluate simulations and theories of equatorial Kelvin and mixed Rossby-gravity (MRG) waves, and to gain insight into their generation mechanism and role in the quasi-biennial oscillation, a space-time spectral analysis is performed on output data from the 40-level, three-degree latitude GFDL "SKYHI" general circulation model and on the GFDL FGGE dataset. The SKYHI and FGGE stratospheric Kelvin waves are dominated by an eastward-moving, wavenumber-one, 10-20-day period component in the lower stratosphere. These waves are accompanied by higher wavenumber-frequency components, which can be detected more clearly in the upper stratosphere than in the lower stratosphere. On the other hand, the SKYHI and FGGE MRG waves are dominated by a westward-moving, wavenumber 3-5, 4-6-day component in the lower stratosphere. These waves are dominated by lower-wavenumbers (1-2) and shorter periods (2-4 days) in the upper stratosphere. The amplitudes of the SKYHI/FGGE Kelvin and MRG waves are comparable to those estimated from observed (non-FGGE) station data, whereas the SKYHI model produces only a very weak quasi-biennial oscillation. The SKYHI precipitation data intermittently exhibit grid-size pulses of precipitation, but do not clearly exhibit spectral peaks which correspond to Kelvin and MRG waves. On the basis of the present analysis, it is proposed that Kelvin, MRG, and gravity waves result from wave-convection interactions and are intermittently triggered by random pulses of convective heating. It is speculated that the quasi-biennial oscillation is produced primarily by gravity waves and will increase in amplitude with horizontal resolution, as grid-size pulses of convective heating and small-scale gravity waves are more adequately produced in the model.