Dynamical regimes of polar vortices on terrestrial planets with a seasonal cycle

TL;DR

This study uses an idealized model to explore how planetary parameters influence polar vortex dynamics, revealing multiple regimes with some resembling observed vortices on Earth, Mars, and Titan, and highlighting potential variability on exoplanets.

Contribution

The paper identifies distinct dynamical regimes of polar vortices across planetary parameters, linking model results to observed phenomena and suggesting diverse vortex behaviors on exoplanets.

Findings

Identified regimes similar to observed polar vortices on Earth, Mars, and Titan.

Discovered vortex structures with potential vorticity annularity in certain parameter regimes.

Observed suppression of storm activity during midwinter at high jet speeds.

Abstract

Polar vortices are common planetary flows that encircle the pole in the middle or high latitudes, and are observed on most of the solar systems' planetary atmospheres. The polar vortices on Earth, Mars, and Titan are dynamically related to the mean meridional circulation and exhibits a significant seasonal cycle. However, the polar vortex's characteristics vary between the three planets. To understand the mechanisms that influence the polar vortex's dynamics and dependence on planetary parameters, we use an idealized general circulation model with a seasonal cycle in which we varied the obliquity, rotation rate, and orbital period. We find that there are distinct regimes for the polar vortex seasonal cycle across the parameter space. Some regimes have similarities to the observed polar vortices, including a weakening of the polar vortex during midwinter at slow rotation rates, similar to Titan's polar vortex. However, other regimes found within the parameter space have no counterpart in the solar system. In addition, we show that for a significant fraction of the parameter space, the vortex's potential vorticity latitudinal structure is annular, similar to the observed structure of the polar vortex on Mars and Titan. We also find a suppression of storm activity during midwinter that resembles the suppression observed on Mars and Earth, which occurs in simulations where the jet speed is greater than ~60 ms$^{-1}$. This wide variety of polar vortex dynamical regimes that shares similarities to observed polar vortices suggests that among exoplanets, there can be a wide variability of polar vortices.