High‐resolution infrared spectroscopy of ethane in Titan's stratosphere in the Huygens epoch
High‐resolution infrared spectroscopy of ethane in Titan's stratosphere in the Huygens epoch
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惠更斯时代土卫六平流层乙烷的高分辨率红外光谱
DOI：
10.1029/2005je002669
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发表时间：
2006
影响因子：
--
通讯作者：
R. Schieder
中科院分区：
文献类型：
--
作者：
T. Livengood;T. Kostiuk;G. Sonnabend;J. Annen;K. Fast;A. Tokunaga;K. Murakawa;T. Hewagama;F. Schmülling;R. Schieder
[1]2005年1月15日，在土卫六的平流层中形成的乙烷（C2 H6）发射特征的高分辨率红外光谱在11.74 μm波长（851 cm−1）的圆盘中心收集。这些观测是在位于夏威夷莫纳克亚山的日本国家天文台的斯巴鲁8.2米望远镜上利用美国航天局戈达德空间飞行中心的行星风和成分外差仪获得的。用红外外差光谱（IRHS）测量了C_2H_6分子的全分辨转动-振动跃迁，分辨本领λ/Δλ ≥ 106。最有效地复制的频谱是垂直分布的乙烷丰度是均匀的，通过平流层和中间层内增强。平流层内有明显梯度的廓线不受欢迎。检索平流层乙烷摩尔分数弱依赖于中间层增强调用的形式。发现两种形式的乙烷摩尔分数廓线能有效地再现观测到的光谱：最佳拟合结果是中间层乙烷浓度随压力降低而增加的廓线，得到平流层乙烷浓度为8.2 ± 2.1 × 10−6（1σ），从平流层顶到中间层（p为压力）与p−1.2成比例增加。第二种形式的剖面图，中层乙烷浓度均匀增强9.5倍，得到的平流层浓度为9.7 ± 4.9 × 10−6（1σ），增强不连续性在平流层顶上方约一个尺度高度处。检索同温层摩尔分数是一致的，从IRHS早期检索，并略低于同期检索红外光谱在较低的分辨率由卡西尼号航天器。检索到的中间层浓度与土卫六飞越期间卡西尼离子中性质谱仪仪器在土卫六热层中进行的原位测量一致（Waite等人，2005年）。
[1] High-resolution infrared spectroscopy of ethane (C2H6) emission features formed in the stratosphere of Titan was collected on disc center at 11.74 μm wavelength (851 cm−1) on 15 January 2005 UT. The observations were obtained at the Subaru 8.2 m telescope of the National Astronomical Observatory of Japan on Mauna Kea, Hawaii, using the NASA Goddard Space Flight Center Heterodyne Instrument for Planetary Winds and Composition (HIPWAC). Fully resolved rotational-vibrational transitions of C2H6 were measured with resolving power λ/Δλ ≥ 106 by infrared heterodyne spectroscopy (IRHS). The spectrum is reproduced most effectively by vertical profiles of ethane abundance that are uniform through the stratosphere and enhanced within the mesosphere. Profiles in which there is a significant gradient within the stratosphere are not favored. The retrieved stratospheric ethane mole fraction depends weakly on the form invoked for the mesospheric enhancement. Two forms of the ethane mole fraction profile are found to reproduce the observed spectrum effectively: the best fitting results are obtained with a profile in which the mesospheric ethane concentration increases logarithmically versus decreasing pressure, retrieving a stratospheric ethane concentration of 8.2 ± 2.1 × 10−6 (1σ), increasing proportional to p−1.2 from the stratopause through the mesosphere (p is pressure). A second form of profile, in which the mesospheric ethane concentration is enhanced uniformly by a factor of 9.5, retrieves a stratospheric concentration of 9.7 ± 4.9 × 10−6 (1σ), with the enhancement discontinuity at about one scale height above the stratopause. The retrieved stratospheric mole fraction is consistent with earlier retrievals from IRHS and is somewhat less than contemporaneous retrievals from infrared spectroscopy at lower resolution by the Cassini spacecraft. The retrieved mesospheric concentration is consistent with in situ measurements in Titan's thermosphere made by the Cassini Ion Neutral Mass Spectrometer instrument during the Titan flyby (Waite et al., 2005).