On the interaction of Jupiter’s Great Red Spot and zonal jet streams

Jupiter’s Great Red Spot (GRS) has been observed in sufficient detail that we can use it to determine properties of the jovian atmosphere that cannot otherwise be found. These properties include: the potential vorticity of the GRS and its neighboring zonal jet streams, the shear imposed on the GRS by the jet streams, and the vertical entropy gradient (i.e., Rossby deformation radius). We show that the cloud cover of the GRS, which is often used to define the GRS’s area and aspect ratio, differs significantly from the region of the GRS’s potential vorticity anomaly. The westward-going jet stream to the north of the GRS and the eastward-going jet stream to its south both have large potential vorticity “jumps”, with the jump at the former larger than at the latter. The two jumps have opposite sign, and as a consequence of these “reverse” jumps, the shear at the GRS is reduced. The east-west to north-south aspect ratio of the GRS (based on its potential vorticity anomaly) depends on the ratio of the shear at the location of the GRS to the strength of the GRS’s potential vorticity anomaly. The aspect ratio is ≈2:1, but without the reverse jumps it would be much greater. The GRS has a high-speed collar and quiescent interior, which requires that the potential vorticity in the interior be approximately half that in the collar. No other persistent geophysical vortex has a significant local minimum of potential vorticity in its interior, and laboratory vortices with such a minimum are unstable.