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Atmospheric Structure of Jupiter from Radiometric Observations of the Galileo Photopolarimeter-Radiometer (PPR) and Ancillary Earth-Based Observations

G. Orton, T. Martin. L.Tamppari, O. Liepack, B. Fisher, J. Friedson, M. Ressler, P. Yanamandra-Fisher, K. Baines, R. West (JPL), L. Travis (NASA/GISS), S. Stewart (Caltech), H. Peiris (Cambridge U.), E. Noe Dobrea (Cornell U.), S. Hinkley (Reed Coll.), W. Golisch, D. Griep, C. Kaminski (U. Hawaii)

Temperature fields for Jupiter's upper troposphere were derived from thermal radiometric observations of discrete regions by the Galileo Photopolarimeter-Radiometer (PPR), on orbits Ganymede-1, Europa-6, and Ganymede-7, often in concert with other Galileo remote sensing instruments. A large set of synoptic earth-based observations of both reflected sunlight and thermal emission enabled more global comparisons. The coldest region of the planet was at the center of the Great Red Spot (GRS), whose bright southern region detected in the June, 1996, Ganymede-1 orbit encounter (Orton et al., 1996, Science 274, 388) continued through the April, 1997, Ganymede-7 orbit encounter. These spatially denser G7 GRS observations show that much of the warm ring at the GRS exterior edge is surrounded by a narrow, cool band near the 2000-km resolution limit of the PPR, suggesting a region of upwelling, expanding gas. Smaller anticyclonic vortices, such as the classical white ovals in the southern hemisphere, are also colder than their surroundings, and the nearby cyclonic regions are warmer, suggesting a series of upwelling, divergent areas interspaced with downwelling, convergent ones. The relatively warm North Equatorial Belt (NEB) contains considerable thermal heterogeneity, often with variability unrelated to the cloud field. On the other hand, 5- m hot spots, among the clearest and driest regions of the planet and considered to be the best examples of strong downdrafts, are not characterized by relatively warm temperatures. While this might imply that the main convergence is deeper in the troposphere, it might also imply much of the surrounding region near this latitude is already downwelling under fully adiabatic conditions.

Caltech Summer Undergraduate Research Fellow