Solar activity variations of thermospheric temperatures on Mars and a problem of CO in the lower atmosphere
Solar activity variations of thermospheric temperatures on Mars and a problem of CO in the lower atmosphere
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DOI：
10.1016/j.icarus.2009.12.036
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发表时间：
2010-06
期刊：
影响因子：
3.2
通讯作者：
V. Krasnopolsky
中科院分区：
文献类型：
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作者：
V. Krasnopolsky
390km 处的长期 MGS 阻力密度观测揭示了密度随季节 LS（2 倍）和太阳活动指数 F10.7（F10.7=40–100 时 3 倍）的变化。据《福布斯》等人报道。 (Forbes, J.M., Lemoine, F.G., Bruinsma, S.L., Smith, M.D., Zhuang, X. [2008]. Geophys. Res. Lett. 35, L01201, doi:10.1029/2007GL031904)，F10.7 的变化反映了外层温度从 192 到284K。然而，导出的温度范围对应于 390km 处的密度变化 8 倍，远高于观测到的 3 倍。最近的热层 GCM 与导出的温度一致，但没有证明它们足以满足 390km 处的 MGS 密度。福布斯等人使用的模型。忽略了涡流扩散、化学和逃逸对 138 公里以上物种密度的影响。我们制作了 80-400km 处的中性和离子组成的一维模型，该模型使用 F10.7、T∞ 和 [CO2]80kmas 输入参数来处理自洽化学和物质输运。将此模型应用于 390km 处的 MGS 密度，我们发现当 F10.7=40 和 100 时，T∞ 分别从 240 变化到 280K。将结果与其他观察结果和模型进行比较。一些观测结果和最新模型的温度与低太阳活动和平均太阳活动时的 MGS 密度不一致。观测数据的外层温度线性拟合为 T∞=122+2.17F10.7，最新模型的 T∞=131+1.46F10.7，390km 处 MGS 密度的线性拟合为 T∞=233+0.54F10.7。也许观测到的 MGS 密度在太阳极小期附近被高估，因为它们很低并且难以测量。根据日心距离的变化校正的火星热层的季节变化主要是由于中低层大气的密度变化造成的，对热层温度的影响微弱。 H、D、H2、HD 和 He 的非热逃逸过程是根据太阳最小和最大条件计算的。这里考虑的另一个问题涉及火星中低层大气中的全球光化学。模型给出的二氧化碳丰度太低，比观察到的要小一个数量级。我们目前的工作表明，Zahnle 等人提出的边界条件修改。 (Zahnle, K., Haberle, R.M., Catling, D.C., Kasting, J.F. [2008]. J. Geophys. Res. 113, E11004, doi:10.1029/2008JE003160) 是合理的，但无助于解决问题。
Long-term MGS drag density observations at 390km reveal variations of the density with season LS(by a factor of 2) and solar activity index F10.7(by a factor of 3 for F10.7=40–100). According to Forbes et al. (Forbes, J.M., Lemoine, F.G., Bruinsma, S.L., Smith, M.D., Zhang, X. [2008]. Geophys. Res. Lett. 35, L01201, doi:10.1029/2007GL031904), the variation with F10.7reflects variations of the exospheric temperature from 192 to 284K. However, the derived temperature range corresponds to variation of the density at 390km by a factor of 8, far above the observed factor of 3. The recent thermospheric GCMs agree with the derived temperatures but do not prove their adequacy to the MGS densities at 390km. A model used by Forbes et al. neglects effects of eddy diffusion, chemistry and escape on species densities above 138km. We have made a 1D-model of neutral and ion composition at 80–400km that treats selfconsistently chemistry and transport of species with F10.7, T∞, and [CO2]80kmas input parameters. Applying this model to the MGS densities at 390km, we find variation of T∞from 240 to 280K for F10.7=40 and 100, respectively. The results are compared with other observations and models. Temperatures from some observations and the latest models disagree with the MGS densities at low and mean solar activity. Linear fits to the exospheric temperatures are T∞=122+2.17F10.7for the observations, T∞=131+1.46F10.7for the latest models, and T∞=233+0.54F10.7for the MGS densities at 390km. Maybe the observed MGS densities are overestimated near solar minimum when they are low and difficult to measure. Seasonal variations of Mars’ thermosphere corrected for the varying heliocentric distance are mostly due to the density variations in the lower and middle atmosphere and weakly affect thermospheric temperature. Nonthermal escape processes for H, D, H2, HD, and He are calculated for the solar minimum and maximum conditions. Another problem considered here refers to Mars global photochemistry in the lower and middle atmosphere. The models gave too low abundances of CO, smaller by an order of magnitude than those observed. Our current work shows that modifications in the boundary conditions proposed by Zahnle et al. (Zahnle, K., Haberle, R.M., Catling, D.C., Kasting, J.F. [2008]. J. Geophys. Res. 113, E11004, doi:10.1029/2008JE003160) are reasonable but do not help to solve the problem.