摘要 :
We use a general circulation model (Urata, R.A., Toon, O.B. [2013]. Icarus, submitted for publication) to simulate the martian hydrologic cycle, including the radiative effects of water-ice clouds. We find that the current observe...
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We use a general circulation model (Urata, R.A., Toon, O.B. [2013]. Icarus, submitted for publication) to simulate the martian hydrologic cycle, including the radiative effects of water-ice clouds. We find that the current observed hydrologic cycle can be duplicated by tuning the polar cap albedo. The hydrologic cycle is very sensitive to the size and albedo of the North Polar water-ice cap. The radiative effects of ice clouds on atmospheric temperatures can be significant. Simulations of an ancient climate were performed with a 500mb CO_2 atmosphere and a reduced solar constant. The results show that the climate is highly sensitive to the hydrologic cycle, and can range from cold and dry, to warm and wet depending on initial conditions, cloud particle size, precipitation rates, and cloud cover fraction. A warm climate is obtained by assuming cloud ice particles greater than or equal to 10μm, and by reducing the efficiency of precipitation to maximize the cloud optical thicknesses. The warm, wet climates have precipitation rates that are 10% of the present day Earth. While carbon dioxide plays only a minor role in creating warm temperatures, it is necessary to have more than 250mb of carbon dioxide in order to obtain these high temperatures for the conditions assumed in our simulations due to the need for heat transport to the poles.
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摘要 :
We introduce a new general circulation model for Mars.?Results are consistent with temperature, pressure, and boundary layer observations.?The model is freely available to interested users. We introduce and present results from a ...
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We introduce a new general circulation model for Mars.?Results are consistent with temperature, pressure, and boundary layer observations.?The model is freely available to interested users. We introduce and present results from a new general circulation model for Mars adapted from the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) version 3.1 terrestrial model. The radiative transfer has been replaced with a two-stream correlated-k scheme with carbon dioxide gas absorption coefficients suited for Mars. A time-invariant dust field is assumed with a Conrath (Conrath, B.J. [1975]. Icarus 24, 34-46) vertical distribution. Carbon dioxide is allowed to sublimate and condense at the surface, and the mass is removed from the atmosphere. The topography is averaged from MOLA data. The surface albedos and thermal inertias are derived from TES observations. The model is freely distributed to interested users.Comparisons between model temperatures, and spacecraft and Lander observations show agreement within ±10. K, depending on dust concentration. The annual pressure cycle is typically within 20. Pa of Viking Lander observations, however the model underestimates the surface pressure during southern summer, possibly due to increased dust activity that is not reflected in the model. Predicted model boundary layer depths are typically within a few hundred meters of observations, and tend to depend inversely on surface pressure, agreeing with observations.
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