B. A Summary of One-Dimensional Radiative-Convective Equilibrium Modeling

The dependency of the structure of the three-dimensional gray atmosphere on the solar constant and the runaway greenhouse states A. Chronology of Studies on the Runaway Greenhouse State B.b. Characteristics of One-Dimensional Radiative-Convective Equilibrium Solutions

a. Characteristics of Radiative Equilibrium Solutions: Results of Stratospheric Model

The Stratospheric Model

A stratospheric model similar to those of Komabayashi (1967) and Ingersoll (1969) is considered. Since the solution for the stratosphere is the radiative equilibrium solution, the structure of the stratosphere can be determined by the following three equations:

eqnarray76

Here, tex2html_wrap_inline5910 and tex2html_wrap_inline5912 represent upward and downward radiative fluxes, respectively, and tex2html_wrap_inline5916, where τ is the vertical coordinate. F^{\uparrow}_{top}corresponds to the OLR. Refer to Basic Equations for the definitions of other variables and parameters.

Furthermore, determining equilibrium solution, the lower boundary of the stratosphere is assumed to be saturated. This requirement comes from the assumption that the lower boundary of the stratosphere is equivalent to the tropopause and is situated on the moist adiabatic line. Because q is constant in the stratosphere in the case under consideration, the following relationship holds:

displaymath5904

Thus, in this model, the water vapor content is uniquely determined by the value of τ.

Based on the water vapor profile determined by the above equation, the dew point temperature profile is evaluated. This profile is expressed as a function of τ as in the case for the radiative flux formulations. With the use of the definition of, the equation for the saturated water vapor pressure curve

displaymath5905

can be rearranged as

displaymath5906

Conditions for the Existence of Equilibrium Solutions

If the position of the tropopause is determined, so are the equilibrium solutions in the above model. The tropopause is located at the crossing point of the graphed lines for \sigma T^{4*}(\tau) and the radiation equilibrium solution, tex2html_wrap_inline5932. In the figure, the profiles of the radiative fluxes for three representative values for F^{\uparrow}_{top} and the dew point profile, \sigma T^{4*}(\tau) are illustrated.

An examination of this figure leads to the following conclusions:

  • For tex2html_wrap_inline5952 W/m2:
    Two equilibrium solutions exist. Of the two solutions, the one associated with the higher tropopause does not have a physical meaning since this solution has supersaturated layers within the stratosphere.
  • For tex2html_wrap_inline5970 W/m2:
    One equilibrium solution exists.
  • For tex2html_wrap_inline5974 W/m2:
    No equilibrium solutions exist.

figure1
Figure 1: The vertical structures of radiative-equilibrium solutions and the dew point temperature. Red: the values of tex2html_wrap_inline5982 determined from the dew point temperature, \sigma T^{4*}(\tau). Aqua: upward radiative flux, tex2html_wrap_inline5910. Blue: radiation source function, tex2html_wrap_inline5980. Green: downward radiative flux, tex2html_wrap_inline5912. The results presented in the figure were obtained for the gravitational acceleration of g = 9.8 m s-2 and the water vapor absorption coefficient κ of 0.01 m2kg-1.

According to the above discussions, the following condition needs to be fulfilled for equilibrium solutions to exist in the stratospheric model: There needs to be a crossing point of the graphed lines of \pi B(\tau) and \sigma T^{\ast 4}(\tau). For the case with the values of the parameters used above, this condition corresponds to
F^{\uparrow}_{top} ≤ 385.2 W/m2.

This condition was identified by Komabayashi (1967) and Ingersoll (1969) and will be referred to as the tropopause flux passage condition in the present paper. In addition, the upper limit of the radiation emitted by the atmosphere prescribed by this condition will be referred to as the Komabayashi-Ingersoll limit, as in Nakajima et al. (1992).


B.a. Characteristics of Radiative Equilibrium Solutions: Results of Stratospheric Model The dependency of the structure of the three-dimensional gray atmosphere on the solar constant and the runaway greenhouse states A. Chronology of Studies on the Runaway Greenhouse State B.b. Characteristics of One-Dimensional Radiative-Convective Equilibrium Solutions