Multi-Instrument Observations of a Jovian Thunderstorm from Juno and Ground-Based Telescopes

Multi-Instrument Observations of a Jovian Thunderstorm from Juno and Ground-Based Telescopes

 

• Brueshaber¹, G. Orton¹, S. Brown¹, S. Levin¹, A. Ingersoll², C. Hansen³, D. Grassi⁴, A. Mura⁴, L. N. Fletcher⁵, S. Bolton⁶

 

On November 29^th, 2021, the Juno Spacecraft completed its 38^th perijove as part of its Extended Mission. Three of the spacecraft’s instruments, JunoCam, JIRAM, and MWR, imaged a thunderstorm in the NEB at approximately 9^oN planetocentric latitude.  JunoCam and the MWR captured data from an altitude of a few thousand kilometers, following JIRAM’s images of the storm four hours before. Ground-based observers tracked this storm over a period of a few days, providing a planetary-scale perspective to Juno’s observations.

 

The morphology of the storm as shown in JunoCam’s RGB filters (observations with the methane filter were not conducted), and from ground-based observers, is highly suggestive of a moist-convective thunderstorm complex with clouds reaching the upper troposphere. Furthermore, JunoCam images suggest that the storm is shaped by vertical shear as the presumed anvil is offset from a thicker region of white clouds. On Earth, vertical shear is necessary for non-tropical cyclone thunderstorm systems to persist for prolonged periods.  JunoCam imaging also suggests a previous anvil top located to the west of the optically thick clouds, which may indicate a temporarily-varying nature to the convection, which is consistent with ground-based observations showing upwelling at this location for several days before the Juno images. JIRAM’s observations show a cold spot at 4.78 µm near the region of the thickest white clouds, which would be expected from optically thick clouds blocking heat transport to space. Spectroscopic retrievals show a slight enhancement of H₂0 and PH₃ compared to the surrounding region, which is expected from upwelling from the interior. The MWR instrument detected numerous lightning flashes at 0.6 GHz (Channel 1) and several flashes at 1.2 and 2.4 GHz (Channels 2 and 3, respectively), which are correlated with JunoCam and JIRAM’s observations of optically thick clouds.

 

Given the close approach of the Juno spacecraft with three instruments observing the storm, this feature may be the most highly instrumented observation of a Jovian thunderstorm to date. The cloud morphology, size, optical thickness of its clouds, and lightning detection in this feature suggest that the storm is probably the equivalent of a terrestrial mesoscale convective complex, possibly composed of multiple individual thunderstorms as is the case on Earth.  However, differences between jovian and terrestrial thunderstorms exist, most notably the lack of a surface to help focus convection and the composition of the atmosphere.  Nevertheless, the observations that we detail here may ultimately shed light on the mechanisms that form, sustain, and characterize moist convective storms in hydrogen-dominated atmospheres.  Here we summarize our observations to date and perform a preliminary comparison to terrestrial and Saturnian thunderstorms.

 

¹ Jet Propulsion Laboratory and California Institute of Technology

² California Institute of Technology

³ Planetary Science Institute

⁴ Institute for Space Astrophysics and Planetology INAF-IAPS

⁵ School of Physics and Astronomy, University of Leicester

⁶ Southwest Research Institute