The dynamics of polar vortices and jets on Mars and beyond

: investigating large-scale atmospheric circulation on terrestrial planets

Abstract

In recent years, there has been a growing appreciation for the value of modelling planetary atmospheres at varying levels of complexity. This ‘hierarchical modelling’ bridges the gap between theory and fully-comprehensive simulations, and builds physical understanding in a way that is not possible with either one of these alone. Improving understanding of planetary atmospheric dynamics through hierarchical modelling places the circulation patterns seen in Earth’s atmosphere in a broader context, and allows deeper insight into which planetary parameters play a key role in driving circulation. This thesis uses
an idealised modelling framework to study how both physical processes and planetary parameters impact large-scale atmospheric circulation, with a focus on polar vortices.
First, the modelling framework and reanalysis datasets are employed to study Mars’s present-day northern polar vortex. The annularity of this vortex is surprising: such a morphology is expected to be unstable, so its persistence indicates the presence of a restoring mechanism. Here, a process-attribution study investigates the relative roles of possible such mechanisms and compares results to reanalyses.
The modelling framework is subsequently utilised to investigate both northern and southern Martian polar vortices across a range of possible orbital configurations. Mars’s orbital parameters have varied substantially across its history; these changes may be linked to the formation of the polar layered deposits. Effective diffusivity, a geometric method used to quantify mixing, is calculated for the first time in Mars’s atmosphere in order to quantify the extent to which the polar vortices may act as transport barriers.
Finally, motivated by exoplanetary atmospheres, the range of planetary parameters studied is broadened further still to investigate the relationships between dynamical metrics for tropical width. Given the uncertainty concerning relationships between these metrics in models, reanalyses, and observations in Earth’s atmosphere, this study helps to contextualise their coupling in a broader parameter space.

Date of Award	3 Oct 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Dann M Mitchell (Supervisor) & William Seviour (Supervisor)