Publications by Jane Hurley

Latitudinal variation of upper tropospheric NH<inf>3</inf>on Saturn derived from Cassini/CIRS far-infrared measurements

Planetary and Space Science 73 (2012) 347-363

J Hurley, LN Fletcher, PGJ Irwin, SB Calcutt, JA Sinclair, C Merlet

Ammonia (NH3) has been detected both on Saturn and Jupiter, and although its concentration and distribution has been well-studied on Jupiter, it has proven more difficult to do so on Saturn due to higher sensitivity requirements resulting from Saturn's lower atmospheric temperatures and the dominance of Saturn's phosphine which masks the ammonia signal. Using far-infrared measurements of Saturn taken by Cassini/CIRS between February 2005 and December 2010, the latitudinal variations of upper tropospheric ammonia on Saturn are studied. Sensitivity to NH3in the far-infrared is explored to provide estimates of temperature, para-H2and PH3, from 2.5 cm-1spectral resolution measurements alone, 0.5 cm-1spectral-resolution measurements alone, and 0.5 cm-1measurements degraded to 2.5 cm-1spectral resolution. The estimates of NH3from these three different datasets largely agree, although there are notable differences using the high emission angle 0.5 cm-1data, which are asserted to result from a reduction in sensitivity at higher emission angles. For low emission angles, the 0.5 cm-1-retrieved values of NH3can be used to reproduce the 2.5 cm-1spectra with similar efficacy as those derived directly from the 2.5 cm-1resolution data itself, and vice versa. Using low emission angle data, NH3is observed to have broad peak abundances at ±25°latitude, attributed to result from condensation and/or photolytic processes. Lack of data coverage at equatorial latitudes precludes analysis of NH3abundance at less than about 10°latitude. Noise levels are not sufficient to distinguish fine zonal features, although it seems that NH3cannot trace the zonal belt/zone structure in the upper troposphere of Saturn. © 2012 Elsevier Ltd. All rights reserved.

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