a. Utilized System and Assumptions
The system utilized is basically the same as that of the 1D model developed by Nakajima et al. (1992), except for the inclusion of atmospheric motion. In our study, the following assumptions are made:
- Atmospheric component:
The atmosphere consists of dry air and water vapor. Both behave as ideal gases with constant specific heat. The molecular weight of water vapor is the same as dry air.
- Radiative Properties:
There is no absorption of incident solar radiation flux (shortwave radiation) by the atmosphere. Only water vapor is assumed to absorb and emit longwave radiation. The absorption coefficient is constant and independent of wavelength. Together, these conditions make up a so-called gray atmosphere.
- Cloud Effect:
The cloud effect is ignored and condensation of water vapor has no effect on radiation. Additionally, the evaporation of rain droplets and the processes of cloud physics are not considered.
- Surface Condition:
The surface is assumed to be always in a heat balanced ocean. The specific heat of the surface is set to 0 (swamp condition). Oceanic motion, heat transport, and material transport are completely ignored. The surface albedo is constant and set to 0.
- Planetary Condition:
The radius of the planet and the rotation rate are constant.
As can be seen from the above, the system setup used in the present study is extremely simple. The reason for this is that we are attempting a 3D version of the study by Nakajima et al. (1992). By applying the results of Komabayashi (1967) and Ingersoll (1969) to a reproducible stratosphere/troposphere model, Nakajima et al. (1992) succeeded in constructing a theoretical framework for a runaway greenhouse state. The goal of the present study is to move on to the further step by the use of their framework.