Physics
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999icar..142..116s&link_type=abstract
Icarus, Volume 142, Issue Icarus, pp. 116-124.
Physics
23
Scientific paper
During the 1998 Jupiter-Sun conjunction, the 60-year-old white ovals BC and DE at 33 deg south latitude merged into a larger oval ``BE'' at the same latitude (J. Lecacheux, P. Drossart, F. Colas, G. S. Orton, B. Fisher, A. Sanchez-Lavega, R. Hueso, J. F. Rojas, and I. Miyazaki, IAU Circular No. 6942). Here we report our study of the motions, morphology, and reflectivity changes pre and postmerger of the ovals based on extensive and continuous Earth-based CCD imaging (April 1997-September 1998) in the visual range (400-800 nm) and in the methane band at 890 nm. In late August 1997, BC and DE started their mutual approach with a relative zonal velocity of 1 m/s. The longitude drift curves of BC, DE, and new BE suggest that a merger of BC and DE took place in February 1998 in the position of BC. A smaller apparently cyclonic oval called O1 was seen in the northwest side of BE at latitude -31 deg. BE is about 12% larger than BC or DE as measured in the blue, red, and 890-nm methane band filters. However, if O1 is assumed to be a by-product of the merger, the sum of the areas of BC and DE is about that of BE and O1. The motion of BE is similar to that of the classic white oval spots. No significant center-to-limb reflectivity changes in the white oval spots at the 890-nm wavelength (sensitive to upper hazes and clouds) were noted before and after the merger. However the area-integrated blue-red color index changed slightly, with BE being bluer than BC or DE probably because the particles in BE have a higher single-scattering blue albedo. Using a radiative transfer model, the 890-nm data suggest that the upper cloud and haze (above 600 mbar) in BE are similar to those of BC and DE. In the limit, the upper cloud in BE could be higher (cloudtop at 110 mbar instead of 150 mbar) or have slightly larger optical depths (3.5 instead of 2.85) than that of BC or DE.
Acarreta Juan Ramon
Colas Francois
Hueso Ricardo
Lecacheux J.J.
Miyazaki Isao
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