Nagare Multimedia 98 |
Japanese |

Masaki Ishiwatari (Graduate School of Environmental Earth Science, Hokkaido University)

Kensuke Nakajima (Faculty of Science, Kyushu University)

Shin-ichi Takehiro (Faculty of Science, Kyushu University)

Yoshi-Yuki Hayashi (Graduate School of Mathematical Science, University of Tokyo)

## Abstract :

We determined the value of the solar constant at which the runaway greenhouse state realizes in the three-dimensional gray atmosphere, and performed the numerical integration of the runaway greenhouse state using the simplified general circulation model (GCM). The radiative active gas is assumed to be only water vapor. The vapor is transparent to solar radiation and has a gray infrared absorption coefficient. This model is equivalent to the system of Nakajima

et al.(1992) which defined the runaway greenhouse state, except for the effect of atmospheric dynamics taken into account.

Under various values of the solar constant, integrations of about 1000 day were performed. The atmospheric thermal structure reaches the statistical equilibrium state in about 500 days when the value of solar constant is smaller than 1600 W/m

^{2}. However, the atmosphere does not reach the equilibrium state, and instead thermally "runaways" when the solar constant value is larger than 1600 W/m^{2}. Outgoing longwave radiation (OLR) cannot balance out the incident energy flux. The vapor content and the amount of the atmosphere continue to increase as well as the atmospheric temperature and ground temperature.The pole-equator contrast of distributions of vapor and temperature decreases with increasing solar constant value. As a result of homogenization of the radiation structure, the solar constant value when the "thermally runaway" state realizes corresponds to the upper limit of the outgoing radiation of the model of Nakajima

et al.(1992) with the constant value of relative humidity of 60 %. This value of relative humidity is the mean value in the troposphere of three-dimensional calculation. The "thermally runaway" states realized when the value of the solar constant is larger than 1600 W/m^{2}correspond to the state in which one-dimensional model has no equilibrium solution, that is, the runaway greenhouse state.