AI 中文总结
研究土卫六南极苯云，通过在模拟土卫六托林上进行苯冰临界饱和比实验测量，将结果纳入模型计算成核接触参数，探讨其对云粒子的影响，发现新测量使模拟苯云高度降低，或因多种挥发性气体共凝结所致。
AI 中文摘要
2009年8月北半球春分之后，卡西尼复合红外光谱仪（CIRS）揭示出土卫六秋季南极平流层存在苯（C6H6）冰云。这一事件提高了苯的混合比并提升了云顶高度。本文给出了纯C6H6冰在低温（从138K时的13.8到157K时的3.3）下临界饱和度（Scrit）的新实验测量结果，该温度代表土卫六大气温度，实验是将其沉积在美国国家航空航天局艾姆斯宇宙模拟室（COSmIC）产生的土卫六气溶胶类似物（托林）上进行的。对比在空白基底和土卫六托林上苯蒸汽沉积的Scrit值，揭示出气溶胶作为凝结核所起的非常有利的作用。我们将这些新的Scrit测量值纳入大气社区气溶胶和辐射模型（CARMA）中m = 2.6e-4 T + 0.9494来计算成核接触参数，以研究土卫六南极87S处大气中C6H6云粒子的大小和数密度随高度的变化。我们讨论了这些新的与温度相关的测量结果如何影响微物理模型，并导致模拟的苯云形成高度比先前观测低约20千米。这种差异的一个可能解释是云系统可能受到不止一种挥发性气体物种共凝结的影响。
英文摘要
The Cassini Composite Infrared Spectrometer (CIRS) revealed the presence of a benzene (C6H6) ice cloud in Titan's autumn south polar stratosphere, following the northern spring equinox in August 2009. This event increased the mixing ratio of benzene and raised the cloud top altitude. We present here new experimental measurements of the critical saturation (Scrit) of pure C6H6 ice at low temperature (from 13.8 at 138 K to 3.3 at 157 K), representative of Titan's atmospheric temperatures, when deposited onto Titan aerosol analogs (tholins) produced in the NASA Ames COsmic SImulation Chamber (COSmIC). Comparisons of Scrit values of benzene vapor deposition obtained on blank substrates versus on Titan tholins reveals the highly favorable role aerosols play as condensation nuclei. We have included these new Scrit measurements to calculate the nucleation contact parameter from m = 2.6e-4 T + 0.9494 in the Community Aerosol and Radiation Model for Atmospheres (CARMA) to investigate the variation in size and number density of C6H6 cloud particles as a function of altitude in Titan's southern polar atmosphere at 87 S. We discuss how these new temperature-dependent measurements impact the microphysical modeling and result in simulated benzene clouds forming about 20 km lower than seen in previous observations. A possible explanation for this discrepancy is that the cloud system was likely influenced by the co-condensation of more than one volatile gas species.
Comments33 pages, 7 figures, 3 tables, accepted for publication in the Planetary Science Journal
