The vertical structure of tropospheric winds on the gas giant planets

While the zonal mean zonal velocities in the upper tropospheres ofJupiter and Saturn have been well-determined from cloud-trackingobservations for several decades, the wind structure below the clouddeck remains unknown. Constraints on the deeper structure of theatmosphere may be obtained, however, by consideration of themarginally stable latitudinal distribution of potential vorticity andthe inferred latitudinal variations of potential temperature. Thermalwind balance yields the associated vertical shears of midlatitude jetsin an altitude range bounded above by the cloud-tops and bounded belowby the level of a putative inflection point in the vertical profile ofzonal wind, where the latitudinal gradient of static stability changessign as required by thermal wind balance. The inferred vertical shearbelow the cloud tops is consistent with existing thermal profiling ofthe upper troposphere. The sense of the associated mean meridionalcirculation in the upper troposphere is discussed and expectedmagnitudes are given based on existing estimates of the radiativetimescale on each planet.