Zonal Jets as Transport Barriers in Planetary Atmospheres

TL;DR

This paper investigates how zonal jets in planetary atmospheres act as transport barriers, revealing that both eastward and westward jets can serve as effective barriers even when PV gradients are weak, supported by simulations and theory.

Contribution

It demonstrates that westward jets, despite having vanishing PV gradients, can serve as robust transport barriers, expanding understanding of atmospheric jet dynamics.

Findings

Both eastward and westward jets act as transport barriers.

Westward jets serve as barriers despite minimal PV gradients.

Simulations and theory explain the barrier mechanisms.

Abstract

The connection between transport barriers and potential vorticity (PV) barriers in PV-conserving flows is investigated with a focus on zonal jets in planetary atmospheres. A perturbed PV-staircase model is used to illustrate important concepts. This flow consists of a sequence of narrow eastward and broad westward zonal jets with a staircase PV structure; the PV-steps are at the latitudes of the cores of the eastward jets. Numerically simulated solutions to the quasigeostrophic PV conservation equation in a perturbed PV-staircase flow are presented. These simulations reveal that both eastward and westward zonal jets serve as robust meridional transport barriers. The surprise is that westward jets, across which the background PV gradient vanishes, serve as robust transport barriers. A theoretical explanation of the underlying barrier mechanism is provided. It is argued that transport barriers near the cores of westward zonal jets, across which the background PV gradient is small, are found in Jupiter's midlatitude weather layer and in the Earth's summer hemisphere subtropical stratosphere.