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Michael J. Wolff (SSI), R. Todd Clancy (SSI), U. J. Sofia (Whitman College), Barbara A. Whitney (Prism Computational Sciences)
An interesting discussion has developed in the community regarding the state of the Martian atmosphere since Viking. That is to say, to what degree can the Viking period observations -- as synthesized in the Mars global circulation models (e.g., Zurek et al. 1992, in "Mars", U. of Ariz. Press) -- be used to represent the current state of the atmosphere? One of the driving forces in the debate has been the extended (1988-1998) earth-based millimeter retrievals of disk-averaged temperature profiles which produce temperatures near aphelion that are much colder than those reported for the same season in the Viking era (Clancy et al. 1996, Icarus, 122, 36). A natural consequence of such lower temperatures would be a reduction in the altitude of water vapor saturation: 5-10 km vs. the 20-25 km for Viking era. Clancy and Nair (1996, JGR, 101, 12,785) have argued that the lower hygropause (near aphelion) will drive order-of-magnitude orbital variations in Ox, HOx, and NOx densities above 10 km. Such a photochemical effect has been initially identified using low-latitude ozone abundances retrieved from Faint Object Spectrograph observations taken in Feb. 1995, Sep. 1996, and Jan 1997. However, these three epochs represent only the early-to-mid northern spring. Consequently, the use of a more comprehensive dataset, in terms of seasonal and diurnal coverage, will provide a more extensive examination of the Clancy and Nair predictions. We will present the additional ozone abundaces retrieved from three additional sets of FOS and two sequences of Space Telescope Imaging Spectrograph observations. With these data, the seasonal coverage now extends from late winter (LS=310\arcdeg) through early fall (190\arcdeg). Furthermore, the substantially higher quality and two-dimensional nature of the STIS spectra allow us to betterquantify diurnal changes in the ozone columns.
This research was supported by NASA through the Space Telescope Science Institute with GO program 7276. MJW was also supported through the STScI Archival program 6390.
The author(s) of this abstract have provided an email address for comments about the abstract: wolff@colorado.edu