Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999dps....31.5403s&link_type=abstract
American Astronomical Society, DPS meeting #31, #54.03
Astronomy and Astrophysics
Astronomy
Scientific paper
\newcommand{\hhhplus}{H_3(+) } As well as the intense polar {\hhhplus} aurorae, spectroscopic observations detected weak emission of this ion covering Jupiter's disk (Ballester et al., Icarus 107, 189, 1994; Marten et al., Planet. Space Sci. 42, 391, 1994). We have analyzed intensity distribution of the {\hhhplus} emission across Jupiter's disk in 3.4-{\micron} images acquired using ProtoCAM at NASA's Infrared Telescope Facility (IRTF) in 1992. The apparent disk emission is approximated using a mathematical function of the form, D(mu , mu_0 , theta ) = D_0 mu (a) mu_0 (b) x f(theta ) , where mu_0 and mu are the direction cosines of incident (solar illumination) and emergent (towards the observer) angles relative to the local zenith, and theta is the planetocentric latitude. The formulation is similar to the Minnaert's function which is a popular tool to characterize the limb-to-limb intensity variations in visible wavelengths. Three parameters of the above function characterize the dependence on the solar illumination angle (b), limb brightening due to increasing path length near the planetary limb (a), and the latitudinal variation (f(theta )). We have found that the apparent limb brightening is consistent with the line-of-sight effect (a = -1.0), evidencing that the layer of {\hhhplus} emission is indeed optically thin. We then adopt a simple atmospheric model to obtain the vertical distribution of the {\hhhplus} ion. The true disk emission (corrected for the line-of-sight effect) can be well reproduced with {\hhhplus} peak density 9.6 x 10(3) {cm(-3) } at an altitude 700--750 km (7--5 nb pressure) above P = 600 mb level. For the first time, the observation of Jupiter's {\hhhplus} disk emission is proven useful to study the vertical distribution of this ion, although the assumptions in our model may be too simple. Images of higher signal-to-noise ratio should be obtained and compared with more sophisticated atmospheric models such as JIM (Achilleos et al., JGR 103, 20089, 1998).
Connerney Jack E. P.
Satoh Takao
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