East Asia and Western Pacific METEOROLOGY AND CLIMATE

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reach the top of model atmosphere to show its percentage contribution in the total
budget. The corresponding observed climatology from NRC (1975) is shown in
Fig. 2. From Fig. 1 for the shortwave radiation (SW) part, the planetary albedo
simulated by the model is 37.1%, the absorption within the atmosphere is 13%,
and the surface absorption is 49.9%. In contrast to the observed climatology, the
simulated planetary albedo is stronger than the observed (37% vs 30%), while
the atmospheric absorption is consequently reduced (13% vs 19%). The simulated
surface absorption is quite comparable to the observed (49.9% vs 51%). Simulated
surface latent and sensible heat fluxes contribute 30% of the heat transfer from
surface to the atmosphere, which are the same as those from observed climatology.
For the longwave radiation (LW), the net upward outgoing LW from earth's
surface is 20.8%, quite close to the observed estimate (21%). The simulated net
longwave radiative cooling (sum over the radiative cooling in the atmosphere to
the space and the absorption of longwave fluxes from surface to the atmosphere)
in the model is 41.4%, and the observed value is 49%.
The very recent ERBE estimate for the global radiative balance from Ramanathan
et al. (1989) are reconstructed and shown in Fig. 3. The ERBE results
differ with the NRC (1975) estimate slightly. The ERBE data shows a smaller
earth absorption of SW (49.4% vs 51%), with a larger atmospheric absorption
of SW (19.9% vs 19%). For the LW part, the ERBE estimate smaller net upward
outgoing LW (18.4% vs 21%), while the surface fluxes and planetary albedo
estimation are larger (31% vs 30%), (30.7% vs 30%), respectively.
The main discrepancy in the model simulation is related to the overestimation
of the planetary albedo and the underestimation of the atmospheric absorption in
the SW. For the net longwave radiative cooling, it is underestimated by about 7%,
which can clearly be attributed to the discrepancy in the shortwave simulation.
This net atmospheric longwave cooling, in a global mean sense, has to be balanced
by the atmospheric absorption of shortwave radiation and the heat fluxes from
the earth's surface to the atmosphere. Fig. 2 identifies that value from observed
climatology is 49% vs 19%+30% for NRC (1975) and 50.9% vs 19.9%+31% from
ERBE, an exact balance. While the simulated balance is 41.4% vs 13%-f 30%.
There is a small imbalance. This leaves the atmosphere with a small fraction of
heating contribution. The sampling problem may be the cause of this imbalance.
If more months can be included in the estimation of the annual mean, the balance
should be achieved.
As summarized in Ramanathan et al. (1989), clouds in general are shown
to trap longwave radiation and reduce the emission of longwave radiation to the