Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival

TL;DR

This study documents the expansion of Jupiter's North Equatorial Belt in 2015, revealing thermal wave activity and atmospheric changes, and compares these phenomena to previous similar events.

Contribution

It identifies new thermal waves and atmospheric dynamics associated with NEB expansion, providing insights into Jupiter's atmospheric variability and wave activity.

Findings

Expansion of NEB observed in 2015 with associated thermal and aerosol changes.

Discovery of two new thermal waves in the troposphere and stratosphere.

Waves are stationary, linked to eastward zonal flow, and resemble previous events.

Abstract

The dark colors of Jupiter's North Equatorial Belt (NEB, $7-17^\circ$N) appeared to expand northward into the neighboring zone in 2015, consistent with a 3-5 year cycle of activity in the NEB. Inversions of thermal-IR imaging from the Very Large Telescope revealed a moderate warming and reduction of aerosol opacity at the cloud tops at $17-20^\circ$N, suggesting subsidence and drying in the expanded sector. Two new thermal waves were identified during this period: (i) an upper tropospheric thermal wave (wavenumber 16-17, amplitude 2.5 K at 170 mbar) in the mid-NEB that was anti-correlated with haze reflectivity; and (ii) a stratospheric wave (wavenumber 13-14, amplitude 7.3 K at 5 mbar) at $20-30^\circ$N. Both were quasi-stationary, confined to regions of eastward zonal flow, and are morphologically similar to waves observed during previous expansion events.