b. Implications of the Present Study
The above conclusions suggest that the 1D radiative-convective
equilibrium model is an extremely effective for describing the
runaway greenhouse state. Therefore, it is considered that the
results in Nakajima et al. (1992), as related to cases in which the
dry air amount was changed, or where the absorption coefficient was
varied, can be directly extended to the 3D system. Furthermore, the
conclusions reached in Kasting (1988) and Abe and Matsui (1988) on
the evolution of primitive atmosphere can be expected to be
generally consistent with the results of similar studies in
3D. However, as they pointed out in their studies, the upper limit
of outgoing infrared radiation at the top of the atmosphere would
most likely be higher than the values they calculated if relative
humidity were to be considered. Therefore, a slight increase in the
value of the accumulation energy flux for forming the primitive
ocean calculated in Abe and Matsui (1988) can be expected.
Nakajima et al. (1992) found solutions which give same values of
outgoing radiation flux at different surface temperatures, which
implies that multiple equilibrium solutions exist depending on the
incident solar radiation flux. However, the stability of such
equilibrium solutions has not been fully studied. The results of the
present study favor the equilibrium solution for the lower surface
temperature in Nakajima et al. (1992) as the stable
solution. However, the stability of the equilibrium solution for the
higher surface temperature has not been confirmed, even though it is
predicted to be unstable. The time evolution problem must be solved
in order to reach a conclusion, because various time scales, such as
the radiation relaxation time and the time scale of water vapor
distribution variation, must be known for it to be calculated. One
method for resolving this problem is to use the results of S1600 in
the experiment as the initial values, and to give a lower value for
incident solar radiation flux to confirm whether an equilibrium
state is reached. These will be themes for future studies.
