Meteorology of Jupiter's Equatorial Hot Spots and Plumes from Cassini

TL;DR

This study analyzes Jupiter's equatorial hot spots and plumes using Cassini data, revealing their dynamics, interactions with vortex systems, and implications for understanding jet stream speeds.

Contribution

It provides new insights into the morphology and dynamics of Jupiter's equatorial hot spots and plumes, and discusses how Rossby waves influence observed drift speeds.

Findings

Hot spots are quasi-stable, rectangular dark areas with variable size and shape.

Bright white plumes and fast-moving scooter clouds are observed between hot spots.

Rossby wave phase velocity may cause underestimation of true jet stream speeds.

Abstract

We present an updated analysis of Jupiter's equatorial meteorology from Cassini observations. For two months preceding the spacecraft's closest approach, the Imaging Science Subsystem (ISS) onboard regularly imaged the atmosphere. We created time-lapse movies from this period in order to analyze the dynamics of equatorial hot spots and their interactions with adjacent latitudes. Hot spots are quasi-stable, rectangular dark areas on visible-wavelength images, with defined eastern edges that sharply contrast with surrounding clouds, but diffuse western edges serving as nebulous boundaries with adjacent equatorial plumes. Hot spots exhibit significant variations in size and shape over timescales of days and weeks. Some of these changes correspond with passing vortex systems from adjacent latitudes interacting with hot spots. Strong anticyclonic gyres present to the south and southeast of the dark areas appear to circulate into hot spots. Impressive, bright white plumes occupy spaces in between hot spots. Compact cirrus-like 'scooter' clouds flow rapidly through the plumes before disappearing within the dark areas. These clouds travel at 150-200 m/s, much faster than the 100 m/s hot spot and plume drift speed. This raises the possibility that the scooter clouds may be more illustrative of the actual jet stream speed at these latitudes. Most previously published zonal wind profiles represent the drift speed of the hot spots at their latitude from pattern matching of the entire longitudinal image strip. If a downward branch of an equatorially-trapped Rossby waves controls the overall appearance of hot spots, however, the westward phase velocity of the wave leads to underestimates of the true jet stream speed.