Jupiter's Cloud Structure as Constrained by Galileo Probe and HST Observations

Details Jupiter's Cloud Structure as Constrained by Galileo Probe and HST Observations Jupiter's Cloud Structure as Constrained by Galileo Probe and HST Observations

Jun 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002icar..157..373s&link_type=abstract

Icarus, Volume 157, Issue 2, p. 373-400.

Physics

17

Scientific paper

The Galileo Probe sampled Jupiter's atmosphere at the edge of a 5-μm hot spot, where it found very little cloud opacity above the 700 mb level. Only τ=1-2 at λ=0.5 μm was inferred from Net Flux Radiometer observations (Sromovsky et al. 1998, J. Geophys. Res.103, 22,929-22,977), in seeming conflict with Chanover et al. (1997, Icarus128, 294-305) who inferred τ=6-8 above the 700 mb level (at λ~0.9 μm) from 893-nm and 953-nm WFPC2 observations of a group of hot spots. Postulating a heterogeneous cloud structure is one way to resolve the conflict. We obtained a more satisfying resolution by reinterpretation of the HST observations with Probe-compatible assumptions about the vertical distribution of cloud particles. Assuming a physically thin upper (putative NH3) cloud with adjustable optical depth and effective pressure (peff<440 mb) and a physically thin midlevel (putative NH4SH) cloud with adjustable optical depth but a fixed pressure of 1.2 bars, we are able to fit WPFC2 observations with probe-consistent opacities in hot spot regions. With the same cloud pressures, but higher middle cloud opacities, we are even able to fit the visibly bright regions. Little variability is seen in the upper cloud. Best fits to October 1995 WFPC2 observations in dark regions (5-μm hot spots) yielded τupper=1.3-1.9 at 0.9 μm and peff=240 mb-270 mb, while in visibly bright regions between hot spots we obtained τupper=1.6-2.2 and peff=250 mb-290 mb. May 1996 observations yielded slightly higher values of τupper (1.8-2.3 and 2.0-2.8) and peff (250 mb-310 mb and 265 mb-320 mb). We found that the most important variable parameter is the opacity of the middle cloud, which ra nged from τ=1, 2 in dark regions, to τ=8-30 in bright regions. >From limb darkening characteristics, we inferred a wavelength-dependent haze opacity ranging from 0.2+/-0.05 at 660 nm to 0.35+/-0.05 at 953 nm, and an effective haze pressure near 120 mb. We did not find it necessary to use low single scattering albedos that require effective imaginary indices, that are several orders of magnitude larger than the values of the main putative cloud components.

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