Laboratory Measurements of the Microwave Opacity of Water Vapor under Temperature Conditions Characteristic of Deep Atmospheres of Jupiter

The Juno Microwave Radiometer (MWR) has six channels ranging from 1.36 50 cm (600 MHz 22 GHz) 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 corresponding to regions sensed by MWR frequencies between 1.2 GHz to 22 GHz (Bellotti et al., 2016, Karpowicz et al.,2011). The discovery of significant ammonia and water variability at pressures greater than 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 2000 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. 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.