Saturn's magnetospheric planetary period oscillations, neutral atmosphere circulation, and thunderstorm activity: Implications, or otherwise, for physical links
journal contributionposted on 16.12.2016, 11:25 by S. W. H. Cowley, G. Provan
Suggestions that the planetary period oscillations (PPOs) observed in Saturn’s magnetosphere may be driven or influenced by neutral atmospheric perturbations motivate an exploratory comparison of PPO rotation periods with available tropospheric and stratospheric determinations. Nonpolar atmospheric rotation periods occupy the range ~10.2–10.7 h associated with the latitudinal jet structure, are similar north and south, and are independent of season, while PPO periods lie in a narrower partly overlapping range ~10.6–10.8 h, are persistently shorter north than south, and undergo a seasonal cycle. In this cycle, widely separated north-south PPO periods during southern summer converge across equinox to values lying within the atmospheric west jet band, remaining well-separated from east jet periods. Closest convergence occurred 1 year post equinox, contemporaneously with the switch in seasonal thunderstorm activity from Southern to Northern Hemispheres. Since most large-scale atmospheric phenomena are related to the west jets, rotating with closely similar periods, they also rotate with periods close to the PPOs under post equinoctial conditions but not otherwise. Specifically, post equinox northern PPOs rotate with a period close to the southern thunderstorms, as well as the north polar spot and hexagon features, while the post equinox southern PPOs rotate with a period close to the pre-equinox northern “string of pearls” and the first colocated post equinox northern thunderstorm, the Great White Spot event. However, even under these conditions, no consistent correspondences in period are found at a detailed level, which taken together with the lack of correspondence at other times does not suggest a direct physical link exists between these phenomena.