Japanese-French model studies of planetary atmospheres@ CPS, Kobe University
May 15, 2015

Radiation model development andits use for exoplanets

Masanori Onishi1, George L. Hashimoto2, Kiyoshi Kuramoto3,Yoshiyuki O. Takahashi1, Masaki Ishiwatari3, Yasuto Takahashi3,Yoshi-Yuki Hayashi1
1. Kobe University, 2. Okayama University, 3. Hokkaido University

1. Introduction

Radiative transfer model is a fundamental tool toclarify planetary environment
Spectral analyses of radiation from a planet
which give us information about temperature andcomposition of its atmosphere
Estimate composition: e.g. Kreidberg et al., 2014a high resolution
spectral calculationis required
fluxWavenumber

Energy budget calculations
with which we can proceed to discuss such as circulationof an atmosphere and evolution of a planet
Habitable zone: e.g. Kopparapu et al., 2013
Planetary evolution: e.g. Hamano et al., 2013a high speed
calculation covering awide spectral range isrequired2. Model Overview
1. Line-by-line model
Vertical profile
Pressure

Opacity calculation

Pressure(P, T, C)

Optical Depth

Single scattering Albedo

Optical data・Line absorption:
HITRAN, HITEMP・Continuum absorption:
MT_CKD 2.5, UV absorption

・Scattering:Temperature Composition

Wavenumber

Wavenumber

Rayleigh scattering(T, OD, SA) Boundary condition
Upward & Downward Flux
・Solar flux
・Surface albedo

Flux calculation

2. k-distribution model for GCM
Line-by-line opacity data
Optical Depth

Single scattering Albedo

Wavenumber

Wavenumber

Wavenumber

Absorption Coefficient
Absorption CoefficientBand number

GCM

3. Application to exoplanets

Tropopause of steam atmosphere and inner edge of
habitable zone
Inner edge of habitable zone:
1. Runaway greenhouse limit:
net solar irradiance = radiation limit
2. Water loss limit:
a planet has ocean as long as 4.6 billion yr.

・Kasting+1993: 0.95AU・Kopparapu+2013: 0.99AU

Habitable zone

: Kasting et al., 1993

The model stratosphere was taken to be isothermal at 200K;
this assumption has negligible effect on the runaway
greenhouse limit but may have a significant effect on the“water loss” limit. (Kasting+1993)

We are trying to estimate tropopause temperature by 1-D lime-by-line model.

3. Application to exoplanets

Model & Setup

Estimate of tropopause
Pressure
heatingAtmosphere(H2O + non absorption gas)

Heating rate change point:coolingHeating rate

Temperature profile
H2O mixing ratio profile
・H2O + non-absorption gas (105 [Pa])・Convective atmosphere up to TOA・Moist pseudoadiabatic lapse rate
・Surface temperature:
280, 300, 320, 340, 350, 360 [K]

Optical depthSingle scattering albedo

Radiation budget
Heating rate・Line absorption:
・Solar irradiance:
HITRAN 2008
5800[K] black body・Continuum absorption:
・Surface albedo:
MT_CKD 2.5, Chan et al., 1993
0 – 3000cm-1: 0.0> 3000cm-1: 0.2
・Rayleigh scattering cross section:
Goldblatt et al., 2013
・Wavenumber range:
0 – 100000cm-1

3. Application to exoplanets

Results: Estimate of tropopause temperature & mixing ratio
Temperature profile

1.E+00Tropopausetemperature

1.E+01

1.E+02
1.E+03

1.E+03
1.E+04

1.E+05

1.E+05

Tropopause temperature:
Kasting+1993, Kopparapu+2013 (=200K)
100

150

200250temperature [K]300

H2O volume mixing ratio:
3×10-3

1.E+02

1.E+04

1.E+06

H2O volume mixing ratio profile

1.E+01

pressure [Pa]pressure [Pa]1.E+00This study
200 K tropopause

1.E+06350
1.E-12 1.E-10 1.E-08 1.E-06 1.E-04 1.E-02 1.E+00
H2O volume mixing ratio

Water loss limit is estimated near the previous studies.

We have been developing k-distribution model and trying tocalculate 1-D radiative convective profiles.

3. Application to exoplanets

Comparison of Earth atmosphere
Heating rate (tropical atmosphere of Earth)

1.E+01

Heating rate (this study)

Earth’s atmosphere has lower
tropopuase than this study.

1.E+03

1.E+04

pressure [Pa]pressure [Pa]1.E+02 Surface temperature:
1.E+02 300KDifferent points between both:・this study is lack of O3
・1-d model and 3-d Earth・ ・・

1.E+03

1.E+04

Heating rate (solar+planetary)
Heating rate (planetary)
Heating rate (solar)

1.E+05
1.E+05-1.E-04 0.E+00 1.E-04-2.E-04 0.E+00 2.E-04 4.E-04 6.E-04
heating ratio [K s-1]
heating rate [K s-1]

3. Application to exoplanets

Atmospheric evolution and tropopause level
Atmospheric evolution
Solar irradiance

H2O, CO2, N2

H2O, CO2, N2
O2, O3

Absorption cross section

1. General circulation is modified?

Solar radiation: NREL, 2000 ASTM Standard Extraterrestrial Spectrum Reference E-490-00
H2O: HITRAN2008, MT_CKD2.5, Chan+1993
CO2: HITRAN2008, MT_CKD2.5, Cairns&Samson 1966, Cook&Metzger 1964, Edward et al.,1953, Thompson et al., 1963
O3: HITRAN2008, MT_CKD2.5
O2: Hudson 1971, Cook&Metzger 1964, Watanabe&Marmo 1956, Nagata&Todomatsu 1973
N2: Hudson 1971, Cook&Metzger 1964, Watanabe&Marmo 1956

2. Chemical radical is well mixed?
OHOH

OHOH-4. Summary・We have been developing a radiative transfer model for exoplanets.
・Line-by-line model and k-distribution model for GCM (under development)

・The model is applied to exoplanet atmosphere.
・We estimate tropopause temperature of convective atmosphereby 1-D line-by-line model.
・Tropopause temperatures are lower than 200K as in surface temperature islower than 340 K.
・Water loss limit is estimated near the previous studies.