Understanding the Effects of Land Hydrology, Water Volatility, and Rotation Rate on Clouds, Climate, and Circulation in a Hierarchy of Models

任何地球气候动力学的第一性原理理论都应该适用于比地球上更广泛的条件。例如，这样的理论应该预测，如果行星旋转速度更快或更慢，喷射流将如何变化，或者如果水多或少丰富，云和降水将如何变化。但是，这样的地球类似物并不容易得到，无法检验我们的理论，也无法帮助我们获得对地球理解的信心。在这个奖项下进行的工作探索了土卫六的想法，尽管它是土星的卫星，表面温度为零下290华氏度，但它可以作为一个有用的地球模拟物。这个类比是基于卡西尼号任务的观测结果，该观测表明土卫六具有类似地球的水文循环的所有特征：云、雨（通常是大风暴带来的暴雨）、湖泊和海洋的表面蒸发，只是甲烷代替了水。该奖项的首席研究员（PI）开发了一个“水挥发性”参数，该参数允许在类似泰坦的温度下将甲烷作为一种水当量来模拟地球大气。通过这种处理，地球和土卫六可以被视为沿连续体下降的气候系统，因此，通过将挥发性参数的值从1增加到约3，可以从地球的水文循环中产生类似土卫六的水文循环。要产生类似土卫六的气候状态，还必须改变另外两个参数，一个是行星自转速度，因为土卫六上的一天持续16个地球日；另一个是陆地面积的数量和分布，因为土卫六的热带纬度完全被陆地覆盖。该项目测试了这三个参数在多大程度上足以解释类地和类泰坦气候之间的本质差异。这里讨论的一个问题是低云和高云在变化的水挥发性下的行为，正如PI以前的工作（见AGS-1912673）表明，在增加的挥发性下，低云倾向于下降，而高云倾向于上升。两层在低波动时合并，在高波动时突然被一个非常厚的层所取代。这种行为是在单柱大气模式中产生的，使用一般环流模式和全球风暴分解模式（马克斯普朗克气象研究所的ICON模式）进一步探讨了这种行为。额外的工作考虑了大气环流的变化，因为参数从地球到泰坦的变化。一种考虑是，土卫六上的热带陆地覆盖导致大部分表面蒸发发生在比地球更高的纬度，另一种考虑是，较慢的自转速度导致土卫六上发生不同类型和大小的大气波动。该项目的更广泛影响包括一些教育活动，其中之一是在圣莫尼卡湾进行研究巡航，期间学生收集有关海湾温度和环流的数据。另一个是开发和建造一个实验室装置，以演示与海洋和行星大气有关的密度驱动的倾覆环流。该奖项还为研究生提供支持和培训，从而促进该研究领域的劳动力发展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Any first-principles theory of the climate dynamics of the Earth should apply across a broader range of conditions than those found on Earth. Such a theory should predict, for example, how the jet streams would change if the planetary rotation rate were faster or slower, or how clouds and precipitation would change if water were more or less abundant. But such Earth analogs are not readily available to test our theories and help us gain confidence in our understanding of the Earth. Work performed under this award explores the idea that Titan, despite being a moon of Saturn with a surface temperature of -290F, can serve as a useful Earth analog. The analogy is based on observations from the Cassini mission showing that Titan has all the features of an Earth-like hydrological cycle: clouds, rain (often torrential rain from large storms), and surface evaporation from lakes and seas, only with methane instead of water. The Principal Investigator (PI) of this award has developed a "water volatility" parameter that allows methane at Titan-like temperatures to be treated as a kind of water equivalent in simulations of Earth's atmosphere. With this treatment Earth and Titan can be treated as climate systems that fall along a continuum, so that a Titan-like hydrological cycle can be produced from Earth's hydrological cycle by increasing the value of the volatility parameter from one to about three. Two other parameters that must also be changed to produce a Titan-like climate state are the planetary rotation rate, as a day on Titan lasts 16 Earth days, and the amount and distribution of land area, as the tropical latitudes of Titan are entirely land covered. The project tests the extent to which these three parameters suffice to account for the essential differences between Earth-like and Titan-like climates.One issue addressed here is the behavior of low and high clouds under changing water volatility, as previous work by the PI (see AGS-1912673) shows that low clouds tend to descend while high clouds ascend under increasing volatility. The two layers merged at low volatility and are abruptly replaced by a single very thick layer at high volatility. This behavior, which was produced in a single-column atmospheric model, is further explored using a general circulation model and a global storm-resolving model (the ICON model from the Max Planck Institute for Meteorology). Additional work considers changes in atmospheric circulation as parameters are varied from Earth-like to Titan-like. One consideration is that the tropical land cover on Titan causes the bulk of surface evaporation to occur at higher latitudes than on Earth and another is that the slower rotation rate causes different types and sizes of atmospheric wave motions to occur on Titan.Broader impacts of the project include a number of educational activities, one of which is a research cruise on Santa Monica Bay during which students collect data related to the temperature and circulation of the bay. Another is the development and construction of a laboratory device to demonstrate density-driven overturning circulations relevant to oceans and planetary atmospheres. The award also provides support and training for a graduate student, thereby promoting workforce development in this research area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.