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L. A. Sromovsky, P. M. Fry (University of Wisconsin - Madison)
The 1995 Galileo Probe sampled Jupiter's atmosphere at the edge of a 5-\mum hot spot, where it found little cloud opacity above the 700-mb level. Only \tau = 1-2 at \lambda = 0.5 \mum was inferred from Net Flux Radiometer observations (Sromovsky et al. 1998, JGR \bf 103), in seeming conflict with Chanover et al. (1997, Icarus \bf 128, 294-305) who inferred \tau = 6-8 above the 700-mb level (at \lambda ~0.9 \mum) from 893-nm and 953-nm WFPC2 observations of a group of hot spots. We found a possible resolution to this conflict by reinterpretation of the HST observations with Probe-consistent assumptions about the vertical distribution of cloud particles. For two physically thin cloud layers, an upper (putative NH3) cloud with adjustable optical depth and effective pressure (p\mathrm{eff}<440 mb) and a mid-level (putative NH4SH) cloud with adjustable optical depth but a fixed pressure of 1.2 bars chosen to match Galileo Probe Nephelometer observations (Ragent et et al. 1998. JGR \bf 103), we find excellent fits to October 1995 WFPC2 observations when the upper cloud in dark regions (5-\mum hot spots) has \tau = 1.3-1.9 at 0.9 \mum and an effective pressure of 240 mb - 270 mb, and excellent fits to visibly bright regions between hot spots for \tau = 1.6-2.2 and p\mathrm{eff} = 250 mb - 290 mb. For May 1996 HST observations we found slightly higher values for both parameters. We find that the main variable parameter in the cloud structure is the opacity of the middle cloud, which ranges from \tau = 1-2 in dark regions, to \tau = 8-30 in bright regions. This work is based on NASA/ESA HST observations, obtained at STScI, operated by AURA under NASA contract No. NAS5-26555. Support was provided by NASA through STScI grant HST-AR-09220.01 and JSDAP grant NAG5-6788.