Meridional transport of HCN from SL9 impacts on Jupiter

In July 1994, the Shoemaker-Levy 9 (SL9) impacts introduced hydrogen cyanide (HCN) to Jupiter at a well confined latitude band around -44degrees, over a range of specific longitudes corresponding to each of the 21 fragments (Bezard et al. 1997, Icarus 125, 94-120). This newcomer to Jupiter's stratosphere traces jovian dynamics. HCN rapidly mixed with longitude, so that observations recorded later than several months after impact witnessed primarily the meridional transport of HCN north and south of the impact. latitude band. We report spatially resolved spectroscopy of HCN emission 10 months and 6 years following the impacts. We detect a total mass of HCN in Jupiter's stratosphere of 1.5 +/- 0.7 x 10(13) g in 1995 and 1.7 +/- 0.4 x 10(13) g in 2000, comparable to that observed several days following the impacts (Bezard et al. 1997, Icarus 125, 94-120). In 1995, 10 months after impact, HCN spread to -30degrees and -65degrees latitude (half column masses), consistent with a horizontal eddy diffusion coefficient of K-yy = 2-3 x 10(10) cm(2) s(-1). Six years following impact HCN is observed in the northern hemisphere, while still being concentrated at 44degrees south latitude. Our meridional distribution of HCN suggests that mixing occurred rapidly north of the equator, with K-yy = 2-5 x 10(11) cm(2) s(-1), consistent with the findings of Moreno et al. (2003, Planet. Space Sci. 51, 591-611) and Lellouch et al. (2002, Icarus 159, 112-131). These inferred eddy diffusion coefficients for Jupiter's stratosphere at 0.1-0.5 mbar generally exceed those that characterize transport on Earth. The low abundance of HCN detected at high latitudes suggests that, like on Earth, polar regions are dynamically isolated from lower latitudes. (C) 2004 Elsevier Inc. All rights reserved.