The stability of Jupiter’s circumpolar cyclones


  Nimrod Gavriel  ,  Yohai Kaspi  
Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel

 

The poles of Jupiter were recently observed to posses polar cyclones that are encompassed by a ring of circumpolar cyclones. The enduring presence of those cyclones has been an open question since their discovery by the Juno mission in 2016. The North Pole holds 8 such circumpolar vortices, while the South Pole has 5, with both circumpolar rings positioned along latitude ∼ 84 degrees (N/S). Here we explain the location, stability and number of the Jovian circumpolar cyclones by establishing the primary forces that act on them, which develop due to vorticity changes in the background of a vortex. In the meridional direction, the background vorticity varies due to the planetary sphericity and the presence of the polar vortex. In the zonal direction the vorticity varies due to the presence of adjacent cyclones in the ring. This analysis successfully predicts the latitudinal location and the number of circumpolar cyclones for both the North and the South poles, according to the respective polar vortex size and spin. Moreover, this criterion successfully predicts that Jupiter can hold circumpolar vortices while Saturn cannot