Oxygen compounds in Titan's stratosphere as observed by Cassini CIRS
Oxygen compounds in Titan's stratosphere as observed by Cassini CIRS
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DOI：
10.1016/j.icarus.2006.09.016
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发表时间：
2007-02-01
期刊：
影响因子：
3.2
通讯作者：
Taylor, F. W.
中科院分区：
文献类型：
--
作者：
de Kok, R.;Irwin, P. G. J.;Taylor, F. W.
我们利用卡西尼号轨道飞行器上的复合红外光谱仪的0.5厘米(-1)分辨率光谱研究了土卫六平流层氧化合物的丰度。利用在卡西尼号到达土星之前尚未分析的旋转线，在一定纬度(S-35度)和发射角度(0-60度)范围内进行的几次远红外最低点光谱观测，得出了CO丰度。无论纬度如何，不同观测数据的体积混合比是相互一致的。假设CO随纬度均匀分布，加权平均CO体积混合比为47+/-8ppm。未能检测到H2O，并确定上限为0.9 ppb。从中红外最低点光谱得到的二氧化碳丰度没有明显的纬度变化，典型的值为16+/-2 ppb。S首次利用55度的中红外肢体光谱来约束二氧化碳的垂直分布。在体积混合比为15 ppb时，在凝结水平以上保持恒定的垂直二氧化碳廓线在200公里以下很好地再现了边缘光谱。这与土卫六平流层中二氧化碳的长化学寿命是一致的。在200公里以上，二氧化碳体积混合比没有受到很好的约束，不能排除随着高度的增加而增加的可能性。(C)2006 Elsevier Inc.保留所有权利。
We have investigated the abundances of Titan's stratospheric oxygen compounds using 0.5 cm(-1) resolution spectra from the Composite Infrared Spectrometer on the Cassini orbiter. The CO abundance was derived for several observations of far-infrared nadir spectra, taken at a range of latitudes (75 degrees S-35 degrees N) and emission angles (0 degrees-60 degrees), using rotational lines that have not been analysed before the arrival of Cassini at Saturn. The derived volume mixing ratios for the different observations are mutually consistent regardless of latitude. The weighted mean CO volume mixing ratio is 47 +/- 8ppm if CO is assumed to be uniform with latitude. H2O could not be detected and an upper limit of 0.9 ppb was determined. CO2 abundances derived from mid-infrared nadir spectra show no significant latitudinal variations, with typical values of 16 +/- 2 ppb. Mid-infrared limb spectra at 55 degrees S were used to constrain the vertical profile Of CO2 for the first time. A vertical CO2 profile that is constant above the condensation level at a volume mixing ratio of 15 ppb reproduces the limb spectra very well below 200 km. This is consistent with the long chemical lifetime Of CO2 in Titan's stratosphere. Above 200 km the CO2 volume mixing ratio is not well constrained and an increase with altitude cannot be ruled out there. (c) 2006 Elsevier Inc. All rights reserved.