Laboratory measurements of the 15–46 cm wavelength opacity of water vapor under temperature conditions characteristic of the deep atmosphere of Jupiter

Abstract

The Juno Microwave Radiometer (MWR) has six channels ranging from 600 MHz (50 cm) to 22 GHz (1.3 cm) and has the ability to peer deep into the Jovian atmosphere. Previous laboratory measurements determined the microwave opacity of ammonia and water vapor at pressures and temperatures corresponding to regions sensed by MWR channels 2–6 which function between 1.25 GHz and 22 GHz (Hanley et al., 2009, Devaraj et al., 2014, Bellotti et al., 2016/2017, Karpowicz and Steffes, 2011a, b). The discovery of significant ammonia and water variability at pressures >30 bars (Bolton et al., 2021) indicated the need to provide laboratory opacity measurements at the higher temperatures characteristic of the conditions at higher pressures. Of specific interest is the region sensed by MWR's lowest frequency which senses regions where the physical temperatures reach well above 750 K. Laboratory measurements of the microwave opacity of water vapor at 760 K have been conducted in the frequency range from 649 to 2001 MHz (wavelengths from 15 to 46 cm). These are the first such laboratory measurements known to be conducted at such high temperatures and long wavelengths, and can resolve the inconsistency between the water vapor self-continuum opacity components of the existing models. The results from these laboratory measurements provide better insight into the effects of water vapor on Jupiter's 50 cm wavelength emission and will provide more reliable retrievals of atmospheric composition in the deep atmosphere of Jupiter.Print.