Kl. Chan et al., A SPECTRAL APPROACH FOR STUDYING MIDDLE AND UPPER ATMOSPHERIC PHENOMENA, Journal of atmospheric and terrestrial physics, 56(10), 1994, pp. 1399-1419
We report on the application of a newly developed spectral code to the
study of the middle upper atmosphere. The spectral approach offers co
nceptual and practical convenience for analyzing the generation and in
teraction of different components of atmospheric activity through the
decomposition of the dynamical fields into components with different z
onal wave numbers (m). As examples and tests. we obtain solutions for
the m = 0 (the mean circulation) and 1 (the diurnal tides) components
separately (no mutual interactions), as well as the m = 1 component un
der the influence of the mean circulation. By simulating gravity wave
effects with Rayleigh friction and eddy diffusion peaking near 90 km a
ltitude, the mean circulation thus generated can reproduce the observe
d mesospheric temperature anomaly under solstice conditions. The compu
ted diurnal tides are in good agreement with results obtained earlier
by other authors. The large temperature gradient (associated with the
m = 0 component) set up by the mesospheric temperature anomaly under s
olstice conditions creates a condition favorable for the development o
f baroclinic instabilities in the mesopause layer, especially near the
summer pole. In our time dependent calculation, waves with approximat
ely 4-day period are generated in the m = 1 component, superimposing w
ith the 1-day period tides.