Stratospheric wind speeds from an IR image analysis of the SL-9 impact regions on Jupiter

Abstract

The effects of comet Shoemaker-Levy-9's impacts on Jupiter were imaged from 16 July to 26 July 1994 through 1500 nm, 1580 nm, 1700 nm and 2300 nm filters with the 3.5 m telescope+MAGIC camera at the Calar Alto Observatory, Spain. The pixel resolution of 0.32″ corresponds to about 1200 km at the sub-Earth-point on Jupiter. Good weather conditions enabled excellent time coverage of the event. An unsharp masking image technique was applied to the images as a high-pass filter in order to enhance the impact spot structures. For the analysis of the actual spot geometry two kinds of maps were calculated from enhanced images: (1) for overview purposes a projection of the southern hemisphere to a cone and (2) for the study of details projections to a tangential plane for each visible spot. From these maps we determined the sizes of the core and of the ejecta regions and their temporal changes during the first 10 days after impact. In that way we derived wind speeds and wind directions in the planet's stratosphere for the spots of fragments A, C, D, E, G, H, K, L, R and Q1. The stratospheric winds varied from 20 to 170 km h −1 and are thus of the order of those in the visual cloud deck. The wind directions varied strongly from region to region. We have seen material of the core region being influenced by structures of the visual cloud deck, but a similar interrelation for the ejecta material was not evident. We neither found impact spots from the fragments Q2, B, N (as seen by other observers) nor of F, P2, T, U, V.