Mapping the zonal structure of Titan's northern polar vortex
Mapping the zonal structure of Titan's northern polar vortex
复制标题
绘制土卫六北极涡旋的地带结构图
DOI：
10.1016/j.icarus.2019.113441
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发表时间：
2020
期刊：
影响因子：
3.2
通讯作者：
Sharkey J
中科院分区：
文献类型：
--
作者：
Sharkey J
土星的赤道度为26.7°，最大的卫星土卫六会经历季节性变化，包括在冬季半球形成极涡。土卫六的极地涡旋的特点是由于冬季极地缺乏日照而导致平流层温度较低，以及由于高层大气中复杂的有机化学与极地沉降相结合而导致微量气体丰度增加。以前已经研究过整个涡旋的温度和气体丰度的经向变化，但是还没有对北方涡旋的温度或成分的纬向变化进行任何深入的研究。在这里，我们提出了第一个全面的二维季节性映射土卫六的北方冬季涡旋。使用卡西尼号上的复合红外光谱仪（CIRS）观测到的18个最低点映射序列，我们研究了从冬末到仲夏（Ls= 326 − 86°，2007-2017）近半个泰坦年的涡旋演变。我们发现平流层对称轴从固体旋转轴倾斜约3.5°，尽管我们对倾斜方位角的结果是不确定的。我们发现，北方涡旋似乎保持纬向均匀的温度和成分在任何时候。与在地球、火星和金星上观察到的涡旋相比，在其他类地行星上重要的大尺度波动机制在土卫六的大气中并不重要。这使得北方涡旋更加对称，并且与其他类地行星相比，在整个年度周期中持续时间更长。
Saturn exhibits an obliquity of 26.7° such that the largest moon, Titan, experiences seasonal variations including the formation of a polar vortex in the winter hemisphere. Titan's polar vortex is characterised by cold stratospheric temperatures due to the lack of insolation over the winter pole, and an increase in trace gas abundance as a result of complex organic chemistry in the upper atmosphere combined with polar subsidence. Meridional variations in temperature and gas abundance across the vortex have previously been investigated, but there has not yet been any in-depth study of the zonal variations in the temperature or composition of the northern vortex. Here we present the first comprehensive two-dimensional seasonal mapping of Titan's northern winter vortex. Using 18 nadir mapping sequences observed by the Composite InfraRed Spectrometer (CIRS) instrument on-board Cassini, we investigate the evolution of the vortex over almost half a Titan year, from late winter through to mid summer (Ls= 326 − 86°, 2007–2017). We find the stratospheric symmetry axis to be tilted from the solid body rotation axis by around 3.5°, although our results for the azimuthal orientation of the tilt are inconclusive. We find that the northern vortex appears to remain zonally uniform in both temperature and composition at all times. A comparison with vortices observed on Earth, Mars, and Venus shows that large-scale wave mechanisms that are important on other terrestrial planets are not as significant in Titan's atmosphere. This allows the northern vortex to be more symmetrical and persist longer throughout the annual cycle compared to other terrestrial planets.
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期刊：
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