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Seasonal and latitudinal variations of the HD0/H20 ratio in the martian atmosphere

机译：Martian氛围中HD0 / H20比率的季节性和纬度变化

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We observed latitudinal variations of the HDO/H2O ratio in the martian northern midsummer at L-S = 128 degrees using CSHELL at NASA IRTF. This is the last observation in our decadal monitoring of HDO/H2O on Mars (Krasnopolsky, 2015, Icarus 257, 377-386). The observed latitudinal variations agree with those predicted for that season by the GCM model for HDO/H2O by Montmessin et al. (2005, J. Geophys. Res. 110, E03006).The observation shows very high correlation between HDO/H2O and the mean temperature in the lowest scale height with correlation coefficient of 0.955. The Arrhenius plot for this function is well fitted by activation energy of 1072 +/- 90 K. However, similar plots for our observations at L-S = 42 degrees and 70 degrees with correlation coefficients of 0.89 and 0.72 gave activation energies of 2123 +/- 350 K and 819 +/- 300 K, respectively.The observed correlation between HDO/H2O and the mean temperature is caused by the temperature-dependent isotope fractionation. However, the quantitative assessment of the correlation and its variations remain uncertain, and activation energy is not a proper tool to explain latitudinal variations of HDO/H2O. Fractionation of HDO/H2O along the martian globe is too complicated to be described by unique activation energy.The observational data for seven seasonal points are collected into a map of the seasonal-latitudinal variations of HDO/H2O. The map makes it possible to predict HDO/H2O at given season and latitude. A similar map in the GCM by Montmessin et al. (2005) is the only analog of our map. HDO/H2O is more variable in our map than in the GCM map, and this is partly caused by the observational uncertainties in our map and zonal averaging in the GCM map. However, some features in our map look real. For example, the GCM predicts for L-S = 60 degrees to 150 degrees rather constant HDO/H2O approximate to 4.5 from 60N to 40S, while our map shows 5 +/- 1 from 80N to the equator and then the decrease to approximate to 2 at 40S. The GCM for HDO/H2O by Montmessin et al. (2005) neglects the isotope fractionation by photolysis of water vapor. Here we compare times of vertical and global mixing with those of condensation and photolysis and conclude that this neglect is valid up to approximate to 50 km.
机译：在NASA IRTF使用CShell，观察到L-S = 128度的火星北中仲瘤中HDO / H2O比率的纬度变化。这是我们在火星的HDO / H2O的Dodadal监测中的最后一个观察（Krasnopolsky，2015年，Icarus 257,377-386）。观察到的纬度变化与Montmessin等人的GDO / H2O的GCM模型预测的那些。 （2005，J.Geophys。Res.110，E03006）。观察结果在HDO / H 2 O和最低尺度高度的平均温度之间具有非常高的相关性，其相关系数为0.955。该功能的Arrhenius图是通过1072 +/- 90 K的激活能量良好装配。然而，在LS = 42度和0.89和0.72的相关系数下，我们在LS = 42度和70度下观察的类似地块给激活能量为2123 +/- 350 k和819 +/- 300 k分别。观察到的HDO / H 2 O与平均温度之间的相关性由温度依赖性同位素分馏引起。然而，对相关性的定量评估及其变化仍然不确定，激活能量不是解释HDO / H2O纬度变化的适当工具。沿着火星地球仪的HDO / H2O的分馏太复杂，无法通过独特的激活能量来描述。七个季节点的观察数据被收集到HDO / H2O的季节延迟变化的地图中。该地图可以在给定季节和纬度来预测HDO / H2O。 Montmessin等人的GCM中的类似地图。 （2005）是我们地图的唯一模拟。 HDO / H2O在我们的地图中比在GCM地图中更具变量，这部分是由我们地图中的观测性不确定性和GCM地图中的Zonal平均来源的部分引起的。但是，我们地图中的一些功能看起来真实。例如，GCM预测LS = 60度至150度，而是相当恒定的HDO / H2O近似于4.5到40s，而我们的地图从80N到赤道显示5 +/- 1，然后减少到2 40s。 Montmessin等人的HDO / H2O的GCM。 （2005）通过对水蒸气的光解忽略同位素分级。在这里，我们将垂直和全球混合的时间与冷凝和光解的时期进行比较，并得出结论，这种忽视是有效的，达到50公里。

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