3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds
3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds
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DOI：
10.1016/j.icarus.2012.10.019
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发表时间：
2013-01-01
期刊：
影响因子：
3.2
通讯作者：
Haberle, R. M.
中科院分区：
文献类型：
--
作者：
Forget, F.;Wordsworth, R.;Haberle, R. M.
根据地质证据，人们经常说，由于厚厚的大气层的温室效应，火星早期的气候足够温暖，液态水可以在表面流动。我们提出了早期火星气候的三维全球气候模拟，假设一个微弱的年轻太阳和表面压力在0.1到7巴之间的二氧化碳大气。该模型包括一个详细的辐射传输模型，使用修正的CO2气体碰撞诱导吸收特性，以及CO2冰云微物理和辐射特性的参数化。利用倾角、轨道参数、云微物理参数、大气粉尘载荷和表面特性的各种值，探索了各种可能的气候。不像今天的火星，火星上的气压高于一个大气压的几分之一，由于大气垂直移动时的绝热冷却和升温，火星表面温度随海拔高度而变化。在大多数模拟中，二氧化碳冰云覆盖了地球的大部分。先前的研究表明，由于它们的散射温室效应，它们可能使地球变暖。然而，即使假设参数最大化这种效果，它也不会超过+15 K。结合修正后的CO2光谱和表面CO2冰对行星反照率的影响，我们发现CO2大气不可能使地球上任何地方的年平均气温升高到0摄氏度以上。据预测，当压力高于3巴时，大气将坍塌成永久的二氧化碳冰帽，反之，如果倾角足够低，压力低于1巴。据预测，在高纬度地区，夏季日平均地表温度高于0摄氏度（这一条件可能导致河流和湖泊的形成），倾角大于40度，但在观察到大多数山谷网或层状沉积单元的地区则不然。在缺乏其他变暖机制的情况下，我们的气候模型结果因此与火星早期寒冷的情景相一致，在这种情况下，必须出现非气候机制来解释液态水的证据。在华兹华斯等人的一篇论文中，我们模拟了这样一个星球上的水文循环，并更详细地讨论了这是如何发生的。(C) 2012爱思唯尔公司版权所有。
On the basis of geological evidence, it is often stated that the early martian climate was warm enough for liquid water to flow on the surface thanks to the greenhouse effect of a thick atmosphere. We present 3D global climate simulations of the early martian climate performed assuming a faint young Sun and a CO2 atmosphere with surface pressure between 0.1 and 7 bars. The model includes a detailed radiative transfer model using revised CO2 gas collision induced absorption properties, and a parameterisation of the CO2 ice cloud microphysical and radiative properties. A wide range of possible climates is explored using various values of obliquities, orbital parameters, cloud microphysic parameters, atmospheric dust loading, and surface properties.Unlike on present day Mars, for pressures higher than a fraction of a bar, surface temperatures vary with altitude because of the adiabatic cooling and warming of the atmosphere when it moves vertically. In most simulations, CO2 ice clouds cover a major part of the planet. Previous studies had suggested that they could have warmed the planet thanks to their scattering greenhouse effect. However, even assuming parameters that maximize this effect, it does not exceed +15 K. Combined with the revised CO2 spectroscopy and the impact of surface CO2 ice on the planetary albedo, we find that a CO2 atmosphere could not have raised the annual mean temperature above 0 degrees C anywhere on the planet. The collapse of the atmosphere into permanent CO2 ice caps is predicted for pressures higher than 3 bar, or conversely at pressure lower than I bar if the obliquity is low enough. Summertime diurnal mean surface temperatures above 0 degrees C (a condition which could have allowed rivers and lakes to form) are predicted for obliquity larger than 40 degrees at high latitudes but not in locations where most valley networks or layered sedimentary units are observed. In the absence of other warming mechanisms, our climate model results are thus consistent with a cold early Mars scenario in which nonclimatic mechanisms must occur to explain the evidence for liquid water. In a companion paper by Wordsworth et al. we simulate the hydrological cycle on such a planet and discuss how this could have happened in more detail. (C) 2012 Elsevier Inc. All rights reserved.