卡西尼号约束的木星平流层中的光化学、混合和传输
Photochemistry, mixing and transport in Jupiter's stratosphere constrained by Cassini
摘要：
我们的目标是约束在木星的平流层的扩散和平流输送过程。卡西尼/CIRS在飞越木星期间记录的红外光谱包含几种大气化合物的指纹，并允许探测其大气成分。C2 H2和C2 H6，甲烷光化学产生的主要化合物，检索作为纬度在一定的压力水平的函数。CIRS观测表明，这两个物种有不同的纬向分布，很难与它们的光化学历史相一致，这被认为是与甲烷光解相耦合的。虽然C2 H2的丰度随纬度而降低，但C2 H6在高纬度变得更丰富。建立了一个新的二维（纬度-高度）季节性光化学模式，研究平流层扩散和平流等平流层输送过程的加入是否能解释C2 H2和C2 H6的纬向行为。C2 H2的观测结果在没有扩散的情况下得到了很好的再现。通过使C2 H6的扩散扩散分布平坦化，将扩散添加到模型中，可以改善与C2 H6观测的一致性，但会降低与C2 H2分布的拟合。单独的经向扩散不能产生所观察到的C2 H6随纬度的增加。当加入30毫巴和0.01毫巴之间的平流输送，在赤道和高纬度地区的下沉风上升风，我们可以重现C2 H6丰度随纬度的增加。然而，与C2 H2分布的拟合度下降。对流风的强度需要重现C2 H6丰度是非常敏感的纬向涡动扩散系数的值。C2 H2和C2 H6的耦合命运表明模型中缺少额外的过程。离子中性化学在这项工作中没有考虑，可能是解决这个问题的一个很好的候选者。
英文摘要：
We aim at constraining the diffusive and advective transport processes in Jupiter's stratosphere. The IR spectrum recorded by Cassini/CIRS during the Jupiter flyby contains the fingerprints of several atmospheric compounds and allows probing its atmospheric composition. C2H2 and C2H6, the main compounds produced by methane photochemistry, were retrieved as a function of latitude at certain pressure levels. CIRS observations suggest a different meridional distribution for these two species, difficult to reconcile with their photochemical histories, which are thought to be coupled to the methane photolysis. While the C2H2 abundance decreases with latitude, C2H6 becomes more abundant at high latitudes. A new 2D (latitude-altitude) seasonal photochemical model is developed to study whether the addition of stratospheric transport processes, such as meridional diffusion and advection, can explain the latitudinal behavior of C2H2 and C2H6. C2H2 observations are fairly well reproduced without meridional diffusion. Adding meridional diffusion to the model provides an improved agreement with the C2H6 observations by flattening its meridional distribution, but degrades the fit to the C2H2 distribution. Meridional diffusion alone cannot produce the observed increase with latitude of C2H6. When adding advective transport between 30 mbar and 0.01 mbar, with upwelling winds at the equator and downwelling winds at high latitudes, we can reproduce the C2H6 abundance increase with latitude. However, the fit to the C2H2 distribution is degraded. The strength of the advective winds needed to reproduce the C2H6 abundances is very sensitive to the value of the meridional eddy diffusion coefficient. The coupled fate of C2H2 and C2H6 suggests that an additional process is missing in the model. Ion-neutral chemistry was not accounted for in this work and might be a good candidate to solve this issue.
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