A comparison of the structure of the aerosol layers in the great red spot of Jupiter and its surroundings before and after the 1993 SEB disturbance

The structure of the aerosol layers in the Great Red Spot (GRS) of Jupiter is investigated from high-quality CCD ground-based observations. The observation of the feature was made at a variety of wavelengths at UV through the near-infrared and at different observational geometries as the large oval rotated from the central meridian to the limb, and at different times, specifically before and after the 1993 major South Equatorial Belt Disturbance (SEBD) on the planet. The particle size distribution as a function of height at tropospheric to lower stratospheric levels was retrieved at the different times observed, as well as the variation of the particle index of refraction as a function of wavelength. The total column abundance of particles above the 500 mbar level was found to be 2.3×108 cm−2, with particle sizes ranging from 0.18 to 0.60 μm, depending on pressure level. A comparison with the ambient atmosphere that surrounds the GRS indicates that the difference in colour between the feature and its neighborhood could be due to a different particle size rather than to a different refractive index of the particles. The average size of the particles above 500 mbar was different just before the SEBD as compared with their average size after the disturbance. The largest differences in size were found near the 120 mbar level (50% smaller after the SEBD). The analysis of the observations made just after the disturbance on June 1993 and a year after the disturbance on July 1994 reveals that the particle size and their optical properties remained constant throughout this period.