报告题目：Hazes and Clouds in Cold and Hot Planetary Atmospheres（云雾缭绕的行星大气）
报告人：Xi Zhang（张曦）University of California Santa Cruz
张曦，2007年北京大学空间物理系本科，2012年加州理工学院行星科学系博士，师从翁玉林（Yuk L. Yung）教授，研究行星大气物理和化学，2013到2015年在亚利桑那大学做Bisgrove Fellow博士后，与Adam Showman教授合作发展行星大学动力学理论，2015年夏天开始在加州大学圣克鲁兹分校（UCSC）做Assistant Professor助理教授。研究方向为行星气候学，主要研究太阳系内行星的大气，但对系外行星也多有涉猎，论文曾在自然（nature）杂志及其子刊（nature geoscience，nature communication）等发表。
报告摘要：Hazes and clouds are ubiquitous in all substantial atmospheres in the outer solar system. Abundant condensed particles are also inferred from the transmission observations in the warm and hot (500-2200 K) atmospheres of exoplanets which are hundreds to thousands of degrees warmer than the solar system planets. These exotic clouds could result from condensation of salts, silicates and metals, and/or hydrocarbons produced by atmospheric chemistry upon UV radiation. In this presentation, I will first talk about the thin, cold and hazy atmospheres in the outer solar system such as on Saturn’s moon Titan, Neptune’s moon Triton, and Pluto. I will present how these atmospheres regulate themselves such that the chemical-produced hydrocarbon haze particles significantly dominate the radiative energy balance over the gas volatiles. In particular, the haze particles could explain the colder-than-expected temperature on Pluto observed by the New Horizons mission. Then I will talk about the thick, hot and cloudy atmospheres of hot Jupiters and brown dwarfs. I will show how to form clouds of salts, silicates and metals in this regime, highlighting the important physical processes such as seed formation, nucleation, condensation, gravitational settling as well as atmospheric particle transport. I will also emphasize the importance of particle size distribution on interpreting the transmission spectra of exoplanets and how to predict it from first principles in a self-consistent microphysical cloud formation model.
报告时间：2018年6月15日，星期五，下午2:00
报告地点：紫金山天文台仙林园区3号楼302会议室
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紫金山天文台学术委员会
