DPS 34th Meeting, October 2002
Session 18. Outer Planet Atmospheres
Poster, Chair(s): , Tuesday, October 8, 2002, 3:30-6:00pm, Exhibit Hall

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[18.06] Evidence for water clouds on Jupiter from 5-micron spectra

G. L. Bjoraker, T. Hewagama (NASA/GSFC), G. S. Orton (JPL)

In August 1999, we observed Jupiter at 5 microns using the CSHELL spectrometer and the NSFCAM camera on the IRTF at about the same time as Galileo NIMS. We have modeled 3 regions of interest: the Great Red Spot, a Dark Spot at 33 degrees South targeted by Galileo NIMS, and a zone region. CSHELL resolved spectrally the line shapes of an NH3 and a CH4 absorption line at 5.18 microns. NSFCAM images were used to reconstruct the pointing. In the Great Red Spot and in low-flux zone regions solar absorption lines are evident. Solar line ratios permit the separation of the reflected solar component from thermal radiation transmitted from the deep atmosphere. The NH3 and CH4 lines vary enormously in strength and width as a function of spatial position on Jupiter. Hot Spots, such as the targeted Dark Spot, exhibit strong pressure-broadened features due to sounding the 3-8 bar level. In the Great Red Spot and in the zones weak and fairly narrow NH3 and CH4 features indicate the transmission of a small amount of flux from the 3 to 4 bar level but essentially nothing from deeper levels. We interpret this as evidence for thick water clouds in addition to the well-known presence of thick ammonia clouds. We cannot distinguish between NH4SH and NH3 cloud opacity, as both clouds are above the line formation region. In the center of the GRS there is a double-peaked core of water cloud opacity. However, east and west of the core, the continuum flux remains low, but the CH4 line is strong. This indicates thick ammonia and/or NH4SH clouds, but a thin water cloud. The combination of continuum flux, which indicates the total opacity above 8 bars, plus CH4 and NH3 line shapes, sensitive to the 3-6 bar level, and solar lines, sensitive to NH3 cloud opacity, provides a powerful technique to disentangle Jupiterís deep cloud structure.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.