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T. Temma, K.H. Baines, L. Brown, R. Butler (Jet Propulsion Laboratory)
The visible infrared mapping spectrometer(VIMS) onboard the Cassini spacecraft has observed latitudinal variations in the PH3 absorption strength over Saturn's southern hemisphere (Baines et al. 2005, Earth, Moon, and Planets, submitted) in the near-infrared region. While CH4, NH3, and H2 absorption features over the spectral range of 1-5 micron are much weaker at the equatorial region - indicating a higher tropospheric cloud top - than in mid-latitude regions, PH3 absorption is nearly unchanged. This suggests that the upper troposphere of the equatorial region contains more PH3 than that of the mid-latitudes on Saturn. Since the horizontal PH3 abundance variation likely indicates commensurate variability of convective activity from deep interior of Saturn, we are combining CH4 band cloud modeling and PH3 band analysis to quantitatively examine the PH3 increase associated with increased dynamical activities in Saturn's equatorial region.
As the first step of our analysis, PH3 absorption spectrum is synthesized from the spectroscopic data obtained in the Jet Propulsion Laboratory (Butler et al. 2005, J. Mol. Spectrosc, submitted). The line-by-line spectral features are summed up to create synthetic transmission spectra at different pressures. Following Baines et al. 1993 (J. Geophys. Res., 98, E3, 5517-5529), the transmission spectra are binned to derive effective absorption coefficients over the passband width that matches the spectral resolution of VIMS. We present our preliminary results of the PH3 band transmissions and effective absorption coefficients.
The first author of this presentation is supported by the Research Associateship Award of the National Research Council at the Jet Propulsion Laboratory.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.