Understanding Jupiter's polar vortex crystals, Mathematics

在包括地球在内的大多数太阳系行星的大气中，极地涡旋是孤立的单一气旋，其中心位于两极或两极附近。相比之下，木星的极地涡旋有着前所未有的结构，正如美国宇航局朱诺号探测器最近发现的那样，每个极点上都有一个气旋，周围环绕着几个水晶图案的气旋。这些晶体结构，以及它们如何随时间变化，在被观察到之前是无法预测的，解释它们形成和演化的机制仍然未知。一种可能的机制是，潮湿对流（由于水凝结释放的潜热）在极地地区产生小漩涡，然后气旋通过“β漂移”机制向极地迁移并合并[3]。但是，包括这些过程的模型在木星极地发现了无序运动漩涡的随机场，而不是观察到的有序漩涡晶体[4,5]。该项目的目的是确定不同的过程是如何将木星的两极从混沌漩涡的海洋转变为观察到的极地漩涡的结晶秩序的。我们建议使用几个数值模型来研究大气流体动力学和其他物理过程的有序相互作用如何给木星的极地地区带来秩序。使用的模型范围从简单的浅水模型到为木星配置的最先进的大气环流模型（GCM）。这些模型中的每一个都是使用埃克塞特大学开发的“Isca”建模框架构建的。在这个项目中使用Isca的优点是可以打开和关闭不同的过程（例如潮湿对流）来测试每个过程所起的作用。在成功的学生的兴趣指导下，将对每个模型进行实验，以了解这种漩涡的晶体排列是如何形成的，它们是如何维持的，以及它们在朱诺号任务的剩余时间内是如何变化的Adriani等，Nature, 555, 2018， [2] Agle等，https://go.nasa.gov/2sgvwCc, 2019， [3] Thomson和McIntyre， JAS 73, 2016, [3] O’neill等，Nature Geoscience 8, 2015， [5] Brueshaber等，Icarus 323, 2019， [6] Thomson和Vallis， Atmosphere, 10(12), 803, 2019。

Project DescriptionIn the atmospheres of most solar-system planets, including Earth, polar vortices are isolated single cyclones centred over or near the poles. By contrast, Jupiter's polar vortices have an unprecedented structure, as recently discovered by NASA's Juno probe, having a single cyclone over each pole surrounded by several other cyclones in crystalline patterns [1]. These crystalline structures, and how they change in time [2], were not predicted prior to being observed, and the mechanisms explaining their formation and evolution remain unknown. One possible mechanism is that moist convection (due to latent heat release from water condensation) produces small vortices in the polar regions, with the cyclones then migrating polewards via the 'beta-drift' mechanism and merging [3]. But models including these processes find random fields of chaotically-moving vortices in Jupiter's polar regions, rather than the orderly vortex crystals that are observed [4, 5]. This project's aim is to determine how different processes contribute to transforming Jupiter's poles from a sea of chaotic vortices to the crystalline order of the observed polar vortices.We propose to use several numerical models to study how order the interaction of atmospheric fluid dynamics and other physical processes can bring order to Jupiter's polar regions. The models to be used range from a simple shallow-water model through to a state-of-the-art General Circulation Model (GCM) configured for Jupiter. Each of these models has been built using the 'Isca' modelling framework, developed at Exeter [6]. The advantage of using Isca for this project is that different processes can be turned on and off (e.g. moist convection) to test the role each process plays. Guided by the interests of the successful student, experiments will be conducted with each of the models to understand how such crystalline arrangements of vortices can be formed, how they are sustained, and how they may change over the remaining length of the Juno mission.[1] Adriani et al, Nature, 555, 2018, [2] Agle et al, https://go.nasa.gov/2sgvwCc, 2019, [3] Thomson and McIntyre, JAS 73, 2016, [4] O'Neill et al, Nature Geoscience 8, 2015, [5] Brueshaber et al, Icarus 323, 2019, [6] Thomson and Vallis, Atmosphere, 10(12), 803, 2019.