The Meteorology of Giant Planets Revealed Through Automated Cloud Feature Tracking

Abstract

We examine the meteorology of the giant planets using our automated cloud feature tracker. Through pattern recognition and correlation optimization, our software returns a dense, regular grid of wind vectors ideal for further analysis, in contrast with an irregular grid of relatively sparse vectors returned using manual (hand-eye) cloud tracking. We measure the winds in and around Jupiter's Great Red Spot (GRS) to reveal its distinctive "hollow" structure, its counter-rotating interior, and a newly-discovered cyclonic ring around its periphery. This cyclonic ring suggests the presence of a thermally indirect, downwelling secondary circulation at the periphery of the GRS. We also analyze a time-series of images of Jupiter's White Ovals. Over a decade, the system has evolved from three discrete, white anticyclones to one reddish vortex (Oval BA). Our measurements reveal non-uniform acceleration of the flow within Oval BA coincident with the coloration event, and areas of organized cyclonic circulation in apparent turbulent regions in the vicinity of the White Ovals and Oval BA. The proximity and apparent longevity of these cyclonic circulations implies a connection with the anticyclonic systems, perhaps through energy transfer and long-term maintenance of the systems. We have also directly measured the power spectrum of the turbulent kinetic energy present in Jupiter's atmosphere. Our measurements provide evidence consistent with an inverse cascade of energy from small to large scales that may fuel Jupiter's impressive jet streams and vortices. Finally, our analysis of near-infrared images of silhouetted clouds in Saturn's atmosphere demonstrates that the measured latitudinal zonal wind profile is largely similar to previous measurements using visible-wavelength images. This result, accompanied by a statistical analysis of the cloud features imaged in the near-infrared, implies that both visible and near-infrared images are observing a single cloud deck at different altitudes, though this implication does not necessarily extend to Saturn's jet streams. Furthermore, our measurements indicate that the equatorial jet stream at depth flows at relatively high speeds, suggesting that reports of significantly slower speeds within the equatorial jet are confined to the upper troposphere.