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

The dark colors of Jupiter's North Equatorial Belt (NEB, 7 − 17∘N) appeared to expand northward into the neighboring zone in 2015, consistent with a 3-5 year cycle. 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∘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∘N. Both were quasi-stationary, confined to regions of eastward zonal flow, and are morphologically similar to waves observed during previous expansion events.