标题： 土星2010-2011年大风暴后平流层的时间演化观测 I. 2011-2013年土星热涡旋中水含量的时间演化 显示英文标题

标题： Observations of the temporal evolution of Saturn's stratosphere following the Great Storm of 2010-2011 I. Temporal evolution of the water abundance in Saturn's hot vortex of 2011-2013

摘要： 水蒸气通过土卫二的喷发羽流和随后在行星系统中的扩散被输送到土星平流层。 预计它会在中层平流层冷凝成烟雾。 2010年土星大风暴后形成的热平流层涡旋（“灯塔”）显著改变了土星北半球平流层的温度、成分和环流。 先前的光化学模型建议，烟雾升华和垂直风可能是增加灯塔地区水蒸气柱密度的过程。 我们旨在量化风暴期间灯塔地区平流层水蒸气的时间演变。 我们使用赫歇尔空间天文台的PACS仪器，在2011年7月至2013年2月间七次测量了土星在66.44和67.09 $\mu$米的情况。 观测探查到毫巴级别，这是水冷凝区域因灯塔地区的温暖温度而改变的地方。 利用辐射传输建模，我们测试了几种经验性和基于物理的模型来限制在灯塔地区发现的增强水排放的原因。 观测显示，灯塔地区出现了增强的排放，这不能仅通过考虑更温暖的温度来再现。 因此需要额外的水蒸气来源。 使用经验模型，我们发现与风暴前条件相比，灯塔地区的水柱增加了(7.5$\pm$1.6)倍。 结合我们2011年7月的云形成模型的结果，我们评估升华贡献占灯塔地区水排放增加所推导出的额外柱数的45-85%。 观测证实，由于灯塔地区的烟雾升华和垂直风，风暴条件增强了毫巴级别的水丰度。 未来关于风暴期间烟雾时间演变的研究将有助于更好地约束随时间变化的升华贡献。 显示英文摘要

摘要： Water vapour is delivered to Saturn's stratosphere by Enceladus' plumes and subsequent diffusion in the planet system. It is expected to condense into a haze in the middle stratosphere. The hot stratospheric vortex (the `beacon') that formed as an aftermath of Saturn's Great Storm of 2010 significantly altered the temperature, composition, and circulation in Saturn's northern stratosphere. Previous photochemical models suggested haze sublimation and vertical winds as processes likely to increase the water vapour column density in the beacon. We aim to quantify the temporal evolution of stratospheric water vapour in the beacon during the storm. We mapped Saturn at 66.44 and 67.09 $\mu$m on seven occasions from July 2011 to February 2013 with the PACS instrument of the Herschel Space Observatory. The observations probe the millibar levels, at which the water condensation region was altered by the warmer temperatures in the beacon. Using radiative transfer modelling, we tested several empirical and physically based models to constrain the cause of the enhanced water emission found in the beacon. The observations show an increased emission in the beacon that cannot be reproduced only accounting for the warmer temperatures. An additional source of water vapour is thus needed. We find a factor (7.5$\pm$1.6) increase in the water column in the beacon compared to pre-storm conditions using empirical models. Combining our results with a cloud formation model for July 2011, we evaluate the sublimation contribution to 45-85% of the extra column derived from the water emission increase in the beacon. The observations confirm that the storm conditions enhanced the water abundance at the millibar levels because of haze sublimation and vertical winds in the beacon. Future work on the haze temporal evolution during the storm will help to better constrain the sublimation contribution over time.