Morphological Changes in Jupiter’s Northern Circumpolar Cyclones as Revealed by JunoCam and JIRAM.

Juno has observed the circumpolar cyclones (CPCs) on Jupiter with the visible-light camera, JunoCam, and the 2-5 µm infrared JIRAM camera, since orbit insertion.  The CPCs have distinctive cloud features, and unique characteristics that broadly classify into two morphological forms, chaotic and filled.  As revealed by JunoCam, the filled CPCs typically appear with large bright cloud features on the periphery, similar in appearance to a circular saw blade.  Just inward of those, nearly uniform darker regions appear---probably stratiform clouds---occasionally displaying small hole-like openings, which appear bright at 5 μm. The overall appearance of the periphery and just inward is reminiscent of shear-like instability in the flow. Anticyclonic circulation has been witnessed in the center of several filled CPCs. Lightning has also been observed by JunoCam in one of the blade-like cloud features at perijove 31, and we occasionally observe thin, bright curvilinear cloud features and clusters of bright clouds with shadows indicating vertical structure. The chaotic CPCs, including the central cyclone, have a different morphology, however, appearing as a flocculent and tightly wrapped series of alternatively bright and dark spirals. Interestingly, CPC #2 has partially transformed from a chaotic morphology into a filled morphology, similar perhaps to how oval cyclones and barges in the low latitudes can sometimes transform into folded-filamentary cyclones (e.g., Clyde’s Spot).

Here, we discuss each CPC and the central cyclone throughout the course of the mission thus far. We primarily use images captured by JunoCam and JIRAM, but we note that the MWR is now resolving the CPCs (see separate abstract), providing additional clues on their vertical structure. This work is an attempt to document the morphology of the CPCs and their changes for future modeling attempts to replicate them in detail, which, in turn, may provide additional insight into their formation, evolution, and stability.