From storms to planetary-scale disturbances in the atmospheres of Jupiter and Saturn

Abstract

<p>The deep atmospheres of the giant planets Jupiter and Saturn are covered by different layers of clouds and hazes where a rich variety of dynamical phenomena take place. At the cloud tops, the winds blow along latitude circles forming a system of jet streams that alternate in East-West direction with latitude. The upper clouds are organised in parallel bands (the low reflectivity belts and the white zones) whose structure follows the winds and correlate with the temperature field over a range of altitudes.</p><p>In this zonal system of jets and bands, meteorological formations grow and evolve over a wide range of spatial and temporal scales, among others, vortices, waves, storms and chaotic and turbulent features. The most spectacular of all of them are those in which the outbreak of a small bright spot that growths and expands rapidly up to a size in the range of 5,000 - 10,000 km, produces a strong interaction with the winds generating a planetary scale disturbance that propagates zonally according to prevailing winds. Jupiter events begin at localized latitudes in the South Equatorial Belt at 16º South, where wind speeds are close to zero, and in the North Temperate Belt at 23º North where the winds have the velocity record on the planet with a jet peak reaching about 180 m/s. The disturbance produces cyclically a change in the albedo of the band, from a zone to a belt, with periods in the range 5-10 years. On Saturn, the phenomenon is known as the Great White Spot (GWS) and has been observed at different latitudes, from the Equator to near the pole, but always in the northern hemisphere. The GWS has been recorded only six times in the history of observations of the planet with a periodicity close to 30 years (about one Saturn year). The proposed models to explain these phenomena involve the trigger of an initial storm produced by moist convection at the water clouds located below the visible clouds. The associated vigorous upward motions generate massive cumulus-like clouds and their non-linear interaction with the wind system forms the series of vortices and waves that make-up the disturbance that propagates away from the active source until fully encircling the planet.</p>