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arXiv 1310.4286astro-ph.EP
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用三维GCM探测暗淡的年轻太阳问题和太古代地球的可能气候

Exploring the faint young Sun problem and the possible climates of the Archean Earth with a 3-D GCM

Benjamin Charnay, François Forget, Robin Wordsworth, Jérémy Leconte, Ehouarn Millour, Francis Codron, Aymeric Spiga

摘要:

人们提出了不同的解决方案来解决“暗淡的年轻太阳问题”,这一问题的定义是,尽管太阳较暗,但地球在太古代并没有完全冻结。以前的研究大多是用简单的一维辐射对流模式进行的,没有很好地考虑云和冰的反馈或大气和海洋的能量传输。我们应用一个全球气候模式(GCM)来测试不同的解决方案的微弱的年轻太阳的问题。我们探索温室气体(CO2和CH 4),大气压力,云滴大小,陆地分布和地球自转速率的影响。我们表明,忽略有机烟雾,100毫巴的CO2与2毫巴的CH 4在3.8 Ga和10毫巴的CO2与2毫巴的CH 4在2.5 Ga允许温带气候(平均地面温度之间10°C和20°C)。这些温室气体的数量与地质数据保持一致。移除大陆会产生低于+4 ° C的变暖。旋转速率的影响甚至更有限。较大的液滴(半径为17微米对12微米)和大气压力的两倍会产生类似的+7 ° C左右的变暖。在我们的模型中,无冰水带可以保持高达25°N/S,CO2小于1 mbar,没有甲烷。一个有趣的云反馈出现在寒冷的海洋上方,停止了冰川作用。这种对完全冰川作用的抵抗力往往会大大减轻年轻太阳微弱的问题。

英文摘要:

Different solutions have been proposed to solve the "faint young Sun problem", defined by the fact that the Earth was not fully frozen during the Archean despite the fainter Sun. Most previous studies were performed with simple 1-D radiative convective models and did not account well for the clouds and ice-albedo feedback or the atmospheric and oceanic transport of energy. We apply a global climate model (GCM) to test the different solutions to the faint young Sun problem. We explore the effect of greenhouse gases (CO2 and CH4), atmospheric pressure, cloud droplet size, land distribution, and Earth's rotation rate. We show that neglecting organic haze, 100 mbar of CO2 with 2 mbar of CH4 at 3.8 Ga and 10 mbar of CO2 with 2 mbar of CH4 at 2.5 Ga allow a temperate climate (mean surface temperature between 10°C and 20°C). Such amounts of greenhouse gases remain consistent with the geological data. Removing continents produces a warming lower than +4°C. The effect of rotation rate is even more limited. Larger droplets (radii of 17 microns versus 12 microns) and a doubling of the atmospheric pressure produce a similar warming of around +7°C. In our model, ice-free water belts can be maintained up to 25°N/S with less than 1 mbar of CO2 and no methane. An interesting cloud feedback appears above cold oceans, stopping the glaciation. Such a resistance against full glaciation tends to strongly mitigate the faint young Sun problem.

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