Hayashi, Y., and D. G. Golder, 1994: 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. Journal of the Meteorological Society of Japan,
72(6), 901-935.
Abstract: 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.