木星平流层中乙炔和乙烷的长期变化的评估
Assessing the long-term variability of acetylene and ethane in the stratosphere of Jupiter
摘要：
乙炔（C $_2$ H $_2$）和乙烷（C $_2$ H $_6$）都是在木星的平流层中通过甲烷（CH $_4$）的光解产生的。尽管有共同的来源，但这两种物质的纬度分布是完全不同的，乙炔的丰度向两极减少，乙烷向两极增加。我们提出了六年的NASA IRTF TEXES中红外观测的带状平均排放的甲烷，乙炔和乙烷。我们确认，乙烷和乙炔的纬度分布是去耦的，这是一个持续多年的功能。乙炔分布朝向极点下降，在$\sim$ 30 $^{\circ}$ N处达到峰值，在1毫巴下$\sim$的体积混合比（VMR）为百万分之0.8（ppm），并且在$\pm70^\circ$处仍然下降，VMR为$\sim$ 0.3 ppm。乙炔分布平均是不对称的，但随着我们从2013年到2017年的移动，赤道附近的区域平均丰度变得更加对称。我们认为，乙炔的短期变化及其纬度不对称性是由垂直平流层混合的变化驱动的，可能与传播波现象有关。与乙炔不同的是，乙烷在赤道附近呈对称分布，向极地方向增加，在大约$\pm50^{\circ}$纬度处$\sim$的摩尔分数峰值为18 ppm，在1毫巴下赤道处的最小值为$\sim$ 10 ppm。[...]乙炔和乙烷的赤道到极点的分布是一致的，乙炔具有较短的寿命比乙烷，是不敏感的较长的平流时间尺度，但增加了短期的动态，如垂直混合。相反，乙烷的长寿命使其能够以比化学消耗更快的速度被运输到更高的纬度。
英文摘要：
Acetylene (C$_2$H$_2$) and ethane (C$_2$H$_6$) are both produced in the stratosphere of Jupiter via photolysis of methane (CH$_4$). Despite this common source, the latitudinal distribution of the two species is radically different, with acetylene decreasing in abundance towards the pole, and ethane increasing towards the pole. We present six years of NASA IRTF TEXES mid-infrared observations of the zonally-averaged emission of methane, acetylene and ethane. We confirm that the latitudinal distributions of ethane and acetylene are decoupled, and that this is a persistent feature over multiple years. The acetylene distribution falls off towards the pole, peaking at $\sim$30$^{\circ}$N with a volume mixing ratio (VMR) of $\sim$0.8 parts per million (ppm) at 1 mbar and still falling off at $\pm70^\circ$ with a VMR of $\sim$0.3 ppm. The acetylene distributions are asymmetric on average, but as we move from 2013 to 2017, the zonally-averaged abundance becomes more symmetric about the equator. We suggest that both the short term changes in acetylene and its latitudinal asymmetry is driven by changes to the vertical stratospheric mixing, potentially related to propagating wave phenomena. Unlike acetylene, ethane has a symmetric distribution about the equator that increases toward the pole, with a peak mole fraction of $\sim$18 ppm at about $\pm50^{\circ}$ latitude, with a minimum at the equator of $\sim$10 ppm at 1 mbar. [...] The equator-to-pole distributions of acetylene and ethane are consistent with acetylene having a shorter lifetime than ethane that is not sensitive to longer advective timescales, but is augmented by short-term dynamics, such as vertical mixing. Conversely, the long lifetime of ethane allows it to be transported to higher latitudes faster than it can be chemically depleted.
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