J/ApJ/771/L45 3D global climate models for exoplanet around M-star (Yang+, 2013)
Stabilizing cloud feedback dramatically expands the habitable zone of tidally
locked planets.
Yang J., Cowan N.B., Abbot D.S.
<Astrophys. J., 771, L45 (2013)>
=2013ApJ...771L..45Y 2013ApJ...771L..45Y
ADC_Keywords: Models ; Planets ; Stars, M-type ; Effective temperatures
Keywords: astrobiology; planets and satellites: atmospheres; stars: low-mass
Abstract:
The habitable zone (HZ) is the circumstellar region where a planet can
sustain surface liquid water. Searching for terrestrial planets in the
HZ of nearby stars is the stated goal of ongoing and planned
extrasolar planet surveys. Previous estimates of the inner edge of the
HZ were based on one-dimensional radiative-convective models. The most
serious limitation of these models is the inability to predict cloud
behavior. Here we use global climate models with sophisticated cloud
schemes to show that due to a stabilizing cloud feedback, tidally
locked planets can be habitable at twice the stellar flux found by
previous studies. This dramatically expands the HZ and roughly doubles
the frequency of habitable planets orbiting red dwarf stars. At high
stellar flux, strong convection produces thick water clouds near the
substellar location that greatly increase the planetary albedo and
reduce surface temperatures. Higher insolation produces stronger
substellar convection and therefore higher albedo, making this
phenomenon a stabilizing climate feedback. Substellar clouds also
effectively block outgoing radiation from the surface, reducing or
even completely reversing the thermal emission contrast between
dayside and nightside. The presence of substellar water clouds and the
resulting clement surface conditions will therefore be detectable with
the James Webb Space Telescope.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 75 58 Climate characteristics of terrestrial planets
around an M-star
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See also:
J/A+A/567/A133 : Habitable zone code (Valle+, 2014)
J/A+A/556/A110 : HARPS radial velocities of GJ 163 (Bonfils+, 2013)
J/ApJ/770/90 : Candidate planets in the habitable zones (Gaidos, 2013)
J/ApJ/767/95 : Improved parameters of smallest KIC stars (Dressing+, 2013)
J/ApJ/736/L25 : Habitability of Kepler planet candidates (Kaltenegger+, 2011)
J/A+A/534/A58 : HD20794, HD85512, HD192310 HARPS RVs (Pepe+, 2011)
J/ApJ/716/1336 : Stability analysis of single-planet (Kopparapu+, 2010)
J/ApJ/649/1010 : Habitability of known exoplanetary systems (Jones+, 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 I1 --- Group [1/6] Group number (1)
3 A1 --- n_Group [d-i] Flag on Group (1)
5- 9 A5 --- Model Model type (2)
11- 57 A47 --- Design Experimental design description (5)
59 A1 --- n_Design [jk] Additional design description (3)
61- 65 F5.1 K TS [219/304] Global-mean surface temperature TS
67- 70 F4.2 --- Albedo [0.2/0.6] Planetary albedo (4)
72- 75 F4.1 K G [3/33] Global-mean greenhouse effect
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Note (1): Groups are:
1(d) = Group 1, tidally locked cases, simulated by CAM3, CAM4 and CAM5. For
these simulations, the sea-ice modules are switched off because there
are significant differences in sea-ice simulation among these models.
CAM3 has a resolution of 3.75○*3.75○ and 26 vertical
levels from the surface to ∼30km. CAM4 and CAM5 have a horizontal
resolution of 1.9○*2.5○ and 26 and 30 vertical levels,
respectively.
2(e) = Group 2, tidally locked cases, simulated by CCSM3 without or with
meridional barriers. The atmosphere component of CCSM3 is the same as
CAM3. The ocean component has a variable latitudinal resolution
starting at ∼0.9○ near the equator, a constant longitudinal
resolution of 3.6○, and 25 vertical levels. The CCSM3
simulations have stronger greenhouse effect, this is due to that ocean
heat transports from the dayside to the nightside and from the tropics
to the extra-tropics of the dayside weaken or eliminate the temperature
inversion.
3(f) = Group 3, tidally locked cases with different stellar fluxes in CAM3.
The default time step is 1800∼s; for high stellar flux, it is reduced
to 100 or 50s to avoid numerical instability.
4(g) = Group 4, non-tidally locked cases (2:1 spin-orbit resonance) in CAM3
5(h) = Group 5, non-tidally locked cases (6:1 spin-orbit resonance) in CAM3
6(i) = Group 6, sensitivity tests for the tidally locked case in CAM3
Note (2): Atmospheric global climate model types as follows (see section 2):
CAM3 = Community Atmosphere Model version 3.1 (Collins, W. D., Basch, P. J.,
& Boville, B. A. et al. 2004, Description of the NCAR Community
Atmosphere Model (CAM) 3.0, NCAR-TN-464+STR, NCAR)
CAM4 = version 4.0 (Neale, R. B., Richter, J. H., & Conley, A. J. et al.
2010b, Description of the NCAR Community Atmosphere Model (CAM) 4.0,
NCAR-TN-485+STR, NCAR)
CAM5 = version 5.0 (Neale, R. B., Chen, C. C., & Gettlelman, A. et al. 2010a,
Description of the NCAR Community Atmosphere Model (CAM) 5.0,
NCAR-TN-486+STR, NCAR) coupled with a mixed layer (immobile) ocean
with a uniform depth of 50m.
CCSM3 = Community Climate System Model version 3.0 (Collins+,
2006JCli...19.2122C 2006JCli...19.2122C) with a uniform ocean depth of 4000m.
Note (3): Flag as follows:
j = The substellar point is set to 180°E over the Pacific Ocean.
k = The substellar point is set to 20°E over Africa.
Note (4): Primary contributed from clouds.
Note (5): keys to some abbreviations:
E-day = Earth-day (24h)
OHT = Ocean Heat Transport
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 23-Jan-2015