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An analysis of near-simultaneous visible, infrared and microwave observations of Saturn’s clouds

Presentation #325.01 in the session Origin and Evolution of Giant Planet Systems I (Poster + Lightning Talk)

Published onOct 23, 2023
An analysis of near-simultaneous visible, infrared and microwave observations of Saturn’s clouds

We present an analysis of near-simultaneous visible, infrared and microwave observations of Saturn recorded by the Cassini spacecraft in order to understand the interplay of cloud and atmospheric properties on Saturn. Between 2005 and 2011, there were 5 epochs where Cassini’s CIRS (Composite Infrared Spectrometer), VIMS (Visible and Infrared Mapping Spectrometer) and RR (Radar/Radiometer) instruments recorded observations near-contemporaneously of Saturn’s low-to-mid latitudes. Our ultimate goal is to globally characterize cloud structures on Saturn between late southern summer and southern fall. In this work, we present preliminary results analyzing VIMS, CIRS and RR observations in March 2011 of regions with high-altitude clouds (which appear dark in VIMS data near 5 µm) and regions without such clouds (appearing bright at 5 µm). First, CIRS spectra were inverted to constrain the zonal-mean temperature profile at the latitude of the clouds. Second, the Clausius-Clapeyron equation was used to calculate the base pressure/altitude of the NH4SH and NH3 clouds. Third, the relative humidity of NH3 is constrained from inverting the RR observations of the clouds. Finally, we invert VIMS spectra of our test regions in order to derive the physical properties of clouds and abundances of PH3, NH3 and AsH3. As noted in previous studies, we find a range of solutions can provide reasonable fits to the VIMS spectra. In an attempt to minimize the degeneracy and better constrain the retrieved properties, we fix the base pressures of the NH4SH and NH3 clouds and the gaseous NH3 ‘knee pressure’ (the pressure below which NH3 is vertically well mixed) to the Clausius-Clapeyron values and fix the NH3 relative humidity to the values retrieved from RR measurements. At the meeting, we will report on the effectiveness of using the Clausius-Clapeyron predictions and RR data to reduce the uncertainty in retrieved atmospheric properties. We will also present results that demonstrate the variability of Saturn’s clouds in a single epoch.

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