Prof. Peter Read

Abstract:

Maps of Ertel potential vorticity on isentropic surfaces (IPV) and quasi-geostrophic potential vorticity (QGPV) on isobaric surfaces in the vicinity of Jupiter's Great Red Spot (GRS) are derived by making use of a combination of velocity measurements, derived from the tracking of cloud features in Voyager 1 and 2 images, and thermal measurements from the Voyager 1 IRIS instrument. The thermal data were obtained during Voyager 1's closest approach to Jupiter. IPV and QGPV in the vicinity of the GRS show a clearly isolated anticyclonic patch in the troposphere, with a suggestion of some spiral structure. The relationship of IPV and QGPV q with the corresponding isentropic or isobaric stream function Ψ near the GRS is not compatible with marginal stability with respect to Arnol'd's second stability theorem, and does not indicate a relaxed, maximum entropy structure except perhaps close to the tropopause. q(Ψ) in the upper troposphere and lower stratosphere for both Ertel and QGPV is reasonably well defined within the GRS and on a different branch to the ambient zonal flow, though is less well defined close to the cloud tops where local thermodynamic forcing may be significant. The profile in the upper troposphere is consistent with an isolated 'free mode' structure for which the air inside the GRS has a different dynamical origin to the atmosphere outside. © Royal Meteorological Society, 2006.