LExEn: Extraordinary Climates of Earth-Like Planets: GCM Simulations at High Obliquity

p.i.: Williams， Darren提案号：ast -9977980地球的倾角由于月球的大小和距离而稳定。通过巨大的撞击形成月球可能是行星吸积的一个相对不太可能的结果。因此，许多围绕其他恒星的类地行星可能没有很好地配置自转轴稳定性，这可能使它们的倾角变化很大，有时接近90度。一个自然的问题是，具有高倾角的类地行星是否仍然适合生命生存。过去使用能量平衡气候模式的工作表明，中纬度和高纬度地区接收到的日照的大规模季节性变化将使高倾角的气候在区域内变得严重。由此产生的反常的季节性温度波动可能会损害许多依赖液态水的生命形式。其他类地行星的反应将主要取决于它们的陆海部分和大陆地理位置，这将影响季节性加热和冷却的速度，以及水和二氧化碳等温室气体的水平。威廉姆斯博士及其同事将使用三维大气环流模型（GCM）来模拟高倾角的极端气候。这些模型更适合于研究高倾角引起的气候变化，因为它们比简单的一维模型更真实地模拟了风和其他过程的热输送。将采用的GMC包括一个耦合的冰盖模型，用于监测冰川的生长和消融。这将有助于调查高倾角是否可能是地球历史上前寒武纪低纬度冰川作用的原因。将对不同的大陆布局、二氧化碳水平和倾角进行一系列实验，以限制早期地球的可能气候和其他恒星周围行星的可居住性。

P.I.: Williams, Darren Proposal Number: AST-9977980The obliquity of Earth is stabilized by the size and proximity of the Moon. The formation of the Moon through a giant impact may be a relatively improbable outcome of planetary accretion. Thus, many Earth-like planets around other stars may not be well configured for spin-axis stability, which could allow their obliquities to vary wildly and to episodically approach 90 degrees. A natural question is whether Earth-like planets with high obliquities might still be climatically suitable for life. Past work using an energy-balance climate model has revealed that climate at high obliquity would be made regionally severe by large-scale seasonal changes to insolation received in the middle and upper latitudes. The extraordinary seasonal temperature fluctuations that would result might be damaging to many forms of life that depend on liquid water. The response of other Earth-like planets will depend primarily on their land-sea fractions and continental geographies, which affect the rate of seasonal heating and cooling, as well as levels of greenhouse gases such as H2O and CO2. Dr. Williams and colleagues will use a three-dimensional general circulation model (GCM) to simulate extreme climates at high obliquity. These models are better suited to examining changes to climate caused by high obliquity because they simulate heat transport by winds and other processes more realistically than do simpler one-dimensional models. The GMC that will be employed includes a coupled ice-sheet model equipped to monitor the growth and ablation of glaciers. This will enable an investigation of whether high obliquity could have been the cause for low-latitude glaciation in the Precambrian Era of Earth's history. A suite of experiments will be performed for different continental arrangements, CO2 levels, and obliquities to place constraints on possible climates of early Earth and on the habitability of planets around other stars.