Sounding Jupiter's Thunderstorms and Environs: Results from JIRAM, JunoCam, MWR and Earth-Based Observations

The Juno spacecraft's polar orbit with periapses (perijove; PJ) within a few thousand kilometers of the 1-bar level has allowed for detailed observations of Jupiter's atmosphere from multiple instruments at unprecedented resolution. Here, we detail the observations of a 2,500-km wide thunderstorm feature located in the North Equatorial Belt (at planetocentric latitude 9°N) from the six channels of the Microwave Radiometer Instrument (MWR), from JunoCam's RGB filters, from the Jovian Infrared Auroral Mapper's (JIRAM) 5-micron band, and from supporting Earth-Based images taken during near the time of the 38^th perijove. Juno flew over one such thunderstorm complex at close range (~5,000 km) on 29 Nov. 2021 for the first time with a favorable alignment to observe such a feature at low emission angles. JunoCam and MWR observations were taken nearly simultaneously while JIRAM's data was collected approximately 4.5 hours prior. This storm feature was also tracked by amateur astronomers over its ~2-week lifespan observing its motion, its morphological changes, and its changing reflectivity at different wavelengths, all of which provide valuable constraints and insight to Juno's detailed observations.

JIRAM's M-band filter images clearly show the structure of the cloud tops, matching observations from JunoCam once the zonally-averaged motion over the 4.5-hour time separation is accounted for. Preliminary spectral analysis from JIRAM shows a slightly enhanced signal of H₂O and PH₃ near the anvil top but NH₃ ice is undetectable in these night-time JIRAM observations.

Lightning is a defining characteristic thunderstorms and the MWR instrument detected numerous flashes in and around the bright white feature with a storm-like morphology clearly observed by JunoCam. This thunderstorm complex is visible from the cloud tops (~0.7 bar) down to approximately the level of the water cloud. Below this level, the thunderstorm signal is no longer apparent, which indicates that any dry convective updraft carrying MWR opacity-inducing vapor is either not present, or its air temperature and humidity are combined in such a way to mask its presence perfectly. If this thunderstorm is a result of dry convection from below the base of the water cloud lifting moist air to the level of free convection (LFC) then the effect of the dry convection is to lift vapor already located around the base of the water-cloud level rather than bringing up significantly moist air from deep below the base of the water cloud, or otherwise a signal would be detected in the short wavelength channels of MWR.