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[PPS21-27] Tropopause of steam atmosphere and inner edge of habitable zone
Keywords:steam atmosphere, radiative property, habitable zone, water loss limit
Kasting 1988, Kopparapu et al., 2013 estimate two boundaries of inner edge of habitable zone for our solar system. The model pressure-temperature profiles consist of a moist pseudoadiabat extending from the surface up to an isothermal stratosphere. The stratosphere temperature is 200 K. Kasting et al., 1993 notes that this assumption (200 K stratosphere) has negligible effect on the runaway greenhouse limit, but may have a significant effect on the water loss limit. In this study, we calculate radiative transfer for the profiles consist of a moist pseudoadiabat extending from the surface up to top of atmosphere, and estimate tropopause temperature.
Our model pressure-temperature profiles consist of a moist pseudoadiabat (Nakajima et al., 1992) extending from the surface up to top of atmosphere. We assumed an Earh-mass planet with H2O dominated atmosphere (H2O and non-absorbed gas). Relative humidity is assumed to be unity. The surface temperature is varied from 250 to 400 K. The amount of non-absorbed gas is varied from 1e+3 to 1e+7 Pa. We use line data for water from the HITRAN2008 spectral database (Rothman et al., 2009), the continuum absorption from MT_CKD 2.5 continuum model (Mlawer et al., 2012) and ultraviolet absorption (Chan et al., 1993). Solar radiation is assumed as a black body radiation of 5800 K. A surface albedo is 0.2 in the wavenumer range from 3000 to 100000 cm-1. A two-stream approximation (Toon et al., 1989) is used to calculate radiative transfer by line-by-line treatment with resolution of 0.01 cm?1 wavelength in the range of 0 - 25000 cm-1 and resolution of 10 cm-1 in the range of 25000 - 100000 cm-1. We estimate tropopause temperature from the heating rate profiles.
We estimate tropopause temperatures of around 150 K. The values are lower than that of previous studies are assumed. The lower temperature indicates that tropapause works stronger cold trap and the water loss limits locate nearer from the sum than that previously reported.