Titan's temporal evolution in stratospheric trace gases near the poles
Titan's temporal evolution in stratospheric trace gases near the poles
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DOI：
10.1016/j.icarus.2015.08.027
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发表时间：
2016-05-15
期刊：
影响因子：
3.2
通讯作者：
Flasar, F. Michael
中科院分区：
文献类型：
--
作者：
Coustenis, Athena;Jennings, Donald E.;Flasar, F. Michael
我们分析了卡西尼/复合红外光谱仪（CIRS）从2010年10月到2014年9月在最低点模式下获得的高分辨率光谱。直到2012年中期，土卫六的北方大气层显示出自旅行者日（1980年11月）以来发现的丰富的化学成分，在2009年北方春分（NSE）左右达到峰值。从那时起，我们首次在土卫六南极观测到了几种痕量物质的出现，如HC 3 N和C 6 H 6，这些物质只在春分前的北方高纬度地区观测到。我们在这里调查纬度50度S和50度N从2010年（南方秋分后）到2014年。对于一些最丰富和寿命最长的碳氢化合物（C2 H2，C2 H6和C3 H8）和二氧化碳，在过去4年中，特定纬度的变化在误差条内并不非常显著，特别是直到2013年年中。在最近的日期，这些分子显示出在南方增加的趋势。对于其他痕量物种，这种趋势更为明显，特别是在2013-2014年，并且相对于50 ° S，70 ° S。这两个区域表明，它们受到不同的动力学过程的极涡区内外。对于大多数物种，我们发现50度N比50度S的丰度更高，除了C3 H8，CO2，C6 H6和HC 3 N，它们在2013年年中之后达到类似的混合比例。北纬70度的数据显示，2014年大多数物种总体上没有变化，而是有小幅下降的趋势，而南纬70度的结果表明，2012年之后平流层痕量气体的含量大幅增加。663 cm（-1）的HC 3 N和674 cm（-1）的C6 H6发射带于2011年底/2012年初出现在南极地区，此后其丰度急剧增加。在70 ° S，HC 3 N、HCN和C6 H6在过去3-4年中增加了3个数量级，而其他分子，包括C2 H4、C3 H4和C4 H2，增加得不那么急剧（增加了1-2个数量级）。这是一个强烈的迹象，表明2013-2014年期间南部平流层的气体存量迅速而突然地增加，正如人们所预期的那样，随着极点深入冬季阴影。自2012年以来，在没有紫外线阳光的情况下积累的沉降气体明显迅速增加，其中一些可能也是报告的北部雾霾减少和南部雾霾出现的原因。(C)2015 Elsevier Inc. All rights reserved.
We analyze spectra acquired by the Cassini/Composite Infrared Spectrometer (CIRS) at high resolution from October 2010 until September 2014 in nadir mode. Up until mid 2012, Titan's Northern atmosphere exhibited the enriched chemical content found since the Voyager days (November 1980), with a peak around the Northern Spring Equinox (NSE) in 2009. Since then, we have observed the appearance at Titan's south pole of several trace species for the first time, such as HC3N and C6H6, observed only at high northern latitudes before equinox. We investigate here latitudes poleward of 50 degrees S and 50 degrees N from 2010 (after the Southern Autumnal Equinox) until 2014. For some of the most abundant and longest-lived hydrocarbons (C2H2, C2H6 and C3H8) and CO2, the evolution in the past 4 years at a given latitude is not very significant within error bars especially until mid-2013. In more recent dates, these molecules show a trend for increase in the south. This trend is dramatically more pronounced for the other trace species, especially in 2013-2014, and at 70 degrees S relative to 50 degrees S. These two regions then demonstrate that they are subject to different dynamical processes in and out of the polar vortex region. For most species, we find higher abundances at 50 degrees N compared to 50 degrees S, with the exception of C3H8, CO2, C6H6 and HC3N, which arrive at similar mixing ratios after mid-2013. While the 70 degrees N data show generally no change with a trend rather to a small decrease for most species within 2014, the 70 degrees S results indicate a strong enhancement in trace stratospheric gases after 2012. The 663 cm(-1) HC3N and the C6H6 674 cm(-1) emission bands appeared in late 2011/early 2012 in the south polar regions and have since then exhibited a dramatic increase in their abundances. At 70 degrees S HC3N, HCN and C6H6 have increased by 3 orders of magnitude over the past 3-4 years while other molecules, including C2H4, C3H4 and C4H2, have increased less sharply (by 1-2 orders of magnitude). This is a strong indication of the rapid and sudden buildup of the gaseous inventory in the southern stratosphere during 2013-2014, as expected as the pole moves deeper into winter shadow. Subsidence gases that accumulate in the absence of ultraviolet sunlight, evidently increased quickly since 2012 and some of them may be responsible also for the reported haze decrease in the north and its appearance in the south at the same time. (C) 2015 Elsevier Inc. All rights reserved.