The Jovian sodium nebula: Two years of ground-based observations

The 1000-R(sub J)-wide neutral sodium nebula of Jupiter has now been observed on four separate occasions from late 1989 to early 1992. The observations have consisted of both low-dispersion spectroscopy and direct imaging. These observations have allowed us to establish some of the general features of the nebula, such as the largely equatorial confinement of emission, the r(exp -1) intensity behavior in the equatorial plane, and flaring of the emission with respect to the equator. Some additional evidence exists for more subtle morphology, such as a possible variable east-west intensity asymmetry. In this paper, we present a summary of observational evidence of variability in overall intensity, as well as in some of the morphological features of the nebula, over timescales of days, months, and years.