Warming early Mars with carbon dioxide clouds that scatter infrared radiation

Science

Volumn 278, Issue 5341, 1997, Pages 1273-1276

  Forget, François ^a   Pierrehumbert, Raymond T ^b  

^a LABORATOIRE DE MÉTÉOROLOGIE DYNAMIQUE   (France)

^b UNIVERSITY OF CHICAGO   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CARBON DIOXIDE;

CARBON DIOXIDE; IR RADIATION; PALAEOCLIMATE;

ARTICLE; CLOUD; GREENHOUSE EFFECT; INFRARED RADIATION; MATHEMATICAL MODEL; PRIORITY JOURNAL; RADIATION SCATTERING; THERMAL ANALYSIS; WARMING;

ATMOSPHERE; CARBON DIOXIDE; EXTRATERRESTRIAL ENVIRONMENT; GREENHOUSE EFFECT; ICE; INFRARED RAYS; MARS; SCATTERING, RADIATION; TEMPERATURE; WATER;

MARS;

EID: 0030657714     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.278.5341.1273     Document Type: Article

References (28)

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21. 2 condensation. Rather than adopting the isothermal-stratosphere approach used in (2), we used a time-stepping scheme similar to that in S. Manabe and R. T. Wetherald, [J. Atmos. Sci. 24, 241 (1967)], in which the model is integrated as an initial value problem until it reaches equilibrium. Convergence to equilibrium was reliable but typically required several hundred time steps even when adaptively adjusted time-stepping was used to accelerate convergence. In contrast, the Newton's method iteration, when it works, converges in a dozen or fewer iterations.
22. Moisture affects both IR opacity and lapse rate. In our "dry" calculation, we zeroed out the radiative effects of water vapor but still used the moist adiabat for the tropospheric temperature profile. This corresponds to the typical practice in radiative-convective modeling of using the moist adiabat even in highly subsaturated conditions, as in (2). On Earth, it is known that a moist adiabat can be maintained even if the relative humidity is low almost everywhere in the atmosphere [K. A. Emanuel, J. D. Neelin, C. S. Bretherton, Q. J. R. Meteorol. Soc. 120, 1111 (1994); K. M. Xu and K. A. Emanuel, Mon. Weather Rev. 117,1471 (1989)]. Our use of the moist adiabat is a conservative choice from the standpoint of surface warming. A totally dry planet would likely adjust to the dry adiabat, which is steeper and would yield slightly greater surface temperatures than the "dry" case we show.
23. Moisture affects both IR opacity and lapse rate. In our "dry" calculation, we zeroed out the radiative effects of water vapor but still used the moist adiabat for the tropospheric temperature profile. This corresponds to the typical practice in radiative-convective modeling of using the moist adiabat even in highly subsaturated conditions, as in (2). On Earth, it is known that a moist adiabat can be maintained even if the relative humidity is low almost everywhere in the atmosphere [K. A. Emanuel, J. D. Neelin, C. S. Bretherton, Q. J. R. Meteorol. Soc. 120, 1111 (1994); K. M. Xu and K. A. Emanuel, Mon. Weather Rev. 117,1471 (1989)]. Our use of the moist adiabat is a conservative choice from the standpoint of surface warming. A totally dry planet would likely adjust to the dry adiabat, which is steeper and would yield slightly greater surface temperatures than the "dry" case we show.
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28. We thank J. Kasting for lending us his model and for helpful comments and suggestions; and J.-L. Dufresne, R. Fournier, C. McKay, and B. Weare for their advice. R.T.P. gratefully acknowledges the support of the John Simon Guggenheim Foundation and of NSF (grant ATM-9505190).