Near‐pure vapor condensation in the Martian atmosphere: CO2 ice crystal growth
Near‐pure vapor condensation in the Martian atmosphere: CO2 ice crystal growth
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火星大气中近乎纯净的蒸气凝结：二氧化碳冰晶的生长
DOI：
10.1002/jgre.20149
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
F. Lefévre
中科院分区：
文献类型：
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作者：
C. Listowski;A. Määttänen;I. Riipinen;F. Montmessin;F. Lefévre
提出了一种新的方法来模拟火星上二氧化碳（CO2）冰晶的凝聚生长。这些凝析物在非常特殊的条件下形成。首先，约95%的大气是由二氧化碳组成的，因此发生了接近纯的蒸汽冷凝。其次，大气稀薄，对晶体生长有显著影响。实际上，随后降低的热传递效率有助于维持晶体表面和环境之间的高温差异，从而抑制生长。此外，由于近纯蒸汽的凝结，预期会增加晶体生长速率的斯特芬流可以忽略不计。我们表明，在火星中间层中常见的高饱和比的近纯蒸汽冷凝情况下，必须重新考虑用于地球云的方便和明确的线性化晶体生长速率公式的遗产，该公式最初是为微量气体导出的。然而，通过将我们的方法与更复杂的冷凝模型（适用于所有大气条件和所有蒸汽丰度）进行比较，我们表明，一组非常简单的方程仍然可以用来有效地再现CO2冰晶生长速率。我们的模型（这里称为CLASSIC模型）在低过饱和度下提供了与传统线性化生长速率模型相似的晶体生长速率，但在高过饱和度下预测的晶体生长速率较低。因此，它可以用来模拟观测到高过饱和度的中间层中CO2冰晶的凝聚生长。
A new approach is presented to model the condensational growth of carbon dioxide (CO2) ice crystals on Mars. These condensates form in very particular conditions. First, ∼95% of the atmosphere is composed of CO2 so that near‐pure vapor condensation takes place. Second, the atmosphere is rarefied, having dramatic consequences on the crystal growth. Indeed, the subsequently reduced efficiency of heat transport helps maintain a high temperature difference between the crystal surface and the environment, inhibiting the growth. Besides, the Stefan flow which would have been expected to increase the growth rate of the crystal, because of the near‐pure vapor condensation, is negligible. We show that the heritage of the convenient and explicit linearized crystal growth rate formula used for Earth clouds, initially derived for a trace gas, has to be reconsidered in the case of near‐pure vapor condensation for high saturation ratios that appear to be common in the Martian mesosphere. Nevertheless, by comparing our approach with a more complex condensation model, valid for all atmospheric conditions and all vapor abundances, we show that a very simple set of equations can still be used to efficiently reproduce the CO2 ice crystal growth rate. Our model, referred to as the CLASSIC model here, provides similar crystal growth rates than the traditionally used linearized growth rate models at low supersaturations but predicts lower crystal growth rates at high supersaturations. It can thus be used to model the condensational growth of CO2 ice crystals in the mesosphere where high supersaturations are observed.