A Wideband Self-Consistent Disk-Averaged Spectrum of Jupiter Near 30 GHz and Its Implications for NH$_{3}$ Saturation in the Upper Troposphere

Abstract

We present a new set of measurements obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) of Jupiter's microwave thermal emission near the 1.3 cm ammonia (NH$_{3}$) absorption band. We use these observations to investigate the ammonia mole fraction in the upper troposphere, near $0.3 < P < 2$ bar, based on radiative transfer modeling. We find that the ammonia mole fraction must be $\sim2.4\times 10^{-4}$ below the NH$_{3}$ ice cloud, i.e., at $0.8 < P < 8$ bar, in agreement with results by de Pater et al. (2001, 2016a). We find the NH$_{3}$ cloud-forming region between $0.3 < P < 0.8$ bar to be globally sub-saturated by 55% on average, in accordance with the result in Gibson et al. (2005). Although our data are not very sensitive to the region above the cloud layer, we are able to set an upper limit of $2.4\times 10^{-7}$ on the mole fraction here, a factor of $\sim$10 above the saturated vapor curve.