Teanby Nicholas A, Irwin Patrick G J, de Kok Remco, Nixon Conor A
Atmospheric, Oceanic & Planetary Physics, Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK.
Philos Trans A Math Phys Eng Sci. 2009 Feb 28;367(1889):697-711. doi: 10.1098/rsta.2008.0164.
Titan's diverse inventory of photochemically produced gases can be used as tracers to probe atmospheric circulation. Since the arrival of the Cassini-Huygens mission in July 2004 it has been possible to map the seasonal and spatial variations of these compounds in great detail. Here, we use 3.5 years of data measured by the Cassini Composite InfraRed Spectrometer instrument to determine spatial and seasonal composition trends, thus providing clues to underlying atmospheric motions. Titan's North Pole (currently in winter) displays enrichment of trace species, implying subsidence is occurring there. This is consistent with the descending branch of a single south-to-north stratospheric circulation cell and a polar vortex. Lack of enrichment in the south over most of the observed time period argues against the presence of any secondary circulation cell in the Southern Polar stratosphere. However, a residual cap of enriched gas was observed over the South Pole early in the mission, which has since completely dissipated. This cap was most probably due to residual build-up from southern winter. These observations provide new and important constraints for models of atmospheric photochemistry and circulation.
土卫六上由光化学反应产生的各种气体可作为示踪剂，用于探测大气环流。自2004年7月卡西尼-惠更斯任务抵达以来，已能够非常详细地绘制这些化合物的季节和空间变化图。在此，我们使用卡西尼综合红外光谱仪仪器测量的3.5年数据来确定空间和季节组成趋势，从而为潜在的大气运动提供线索。土卫六的北极（目前处于冬季）显示出痕量物种的富集，这意味着那里正在发生下沉。这与单一的从南到北的平流层环流单元和极地涡旋的下沉分支一致。在大部分观测时间段内，南极缺乏富集现象，这表明南极平流层不存在任何次级环流单元。然而，在任务早期，南极上空观测到一个富集气体的残留帽状物，此后它已完全消散。这个帽状物很可能是由于南方冬季的残留积累造成的。这些观测结果为大气光化学和环流模型提供了新的重要限制条件。
