Measuring vorticity in and around the polar cyclones of Jupiter using the Juno JIRAM instrument

Abstract:

From its pole-to-pole orbit, the Juno spacecraft discovered arrays of cyclonic vortices in polygonal patterns around the poles of Jupiter. In the north, there are eight vortices around a central vortex, and in the south there are five. The patterns and the individual vortices that define them have been stable since August 2016. The azimuthal velocity profile vs radius has been measured, but vertical structure is unknown. Work by Cheng Li, Andrew Ingersoll, Alexandra Klipfel, and Harriet Brettle, which is under review, tests the stability of these patterns using the shallow water equations. Instability means disruption of the pattern and loss of vortices by merging. An important parameter that leads to stability involves the spatial distribution and magnitude of the vorticity between the large cyclones. Here we present measurements of the vorticity between the vortices using cloud-tracked wind analysis. Because of its high spatial resolution, we use observations by the Jovian Infrared Auroral Mapper (JIRAM), one the instruments on the Juno spacecraft. The measurements require overcoming the uncertainties associated with camera pointing in sequences of images. Besides testing the theory of Cheng Li and colleagues, the measurements reveal related conditions for stability and also point the way toward how the vortices are created and how they are maintained against dissipation and modes of instability.