East Asia and Western Pacific METEOROLOGY AND CLIMATE

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clouds.
These clouds trap the IR radiation emitted from the warm surface and
reradiate it at the cloud top with a much colder temperature in the upper
troposphere.
Thus the transient patterns of the OLR are directly related to
the transient patterns of the clouds and their associated radiative heating
field.
In the recent theoretical studies of the 30-50 day oscillation presented
by Lau and Peng (1987) and Chang and Lira (1988), the direct consequence of
these OLR patterns, which is related to the cloud field and cloud radiative
heating, was not considered.
the convective condensation.
Rather, these patterns were used as indices of
Lau and Peng (1987) proposed a wave-CISK
hypothesis to produce a condensation heating that is associated with the lowlevel
convergence circulation.
In their model, they generated a Kelvin wave
that propagates eastward at a speed of about 20 m/s if the vertical profile
has a maximum in the upper troposphere, and a speed of about 10 m/s if the
heating has a maximum in the lower troposphere. However, most budget studies
(Reed and Recker, 1971; Yanai et al., 1973; Kuo and Anthes, 1984) show that
the vertical profile of latent heat for deep convection has a maximum in the
upper half of the troposphere.
In this case, the wave speed simulated by Lau
and Peng (1987) is faster than the observed value.
From the observed clouds studies during winter monsoons, Webster and
Stephen (1980) found that the most common species over the equatorial South
China Sea and Indonesian region are thick (optically black) middle and upper
tropospheric extended clouds with the top in the vicinity of the 200 mb level.
The cover area of the extended upper and middle cloud decks is perhaps an
order of magnitude larger than the convective region itself.
Based on the
cloud and atmospheric state from the MONEX data, they computed the radiative