A new value of Jupiter’s deep isentrope - implications for Jupiter’s deep thermal and compositional structure

We analyze the Juno microwave observations of Jupiter’s atmosphere and find a warmer interior temperature than previously assumed based on the Voyager’s radio occultation measurement (Lindal et al., 1981, JGR-Space Physics, 86.A10, 8721-8727) and the Galileo Probe (Seiff et al., 1998, JGR-Planets, 103.E10, 22857-22889). By analyzing globally averaged observations from 1.4 – 50 cm wavelength, we find that the deep isentrope of Jupiter is at  169 +/- 1 K referenced at 1 bar pressure level. The globally averaged kinetic temperature at 1-bar is closer to 175 K and Jupiter’s weather layer is stably stratified. On the other hand, the 1-bar temperature inverted from Juno microwave observations at the Equatorial Zone between 0 and 5 ^oN remains low at 166 K, consistent with the previous remote sensing measurements made at the equator from the infrared (Fletcher et al., 2016, Icarus 278, 128-161). This also implies a vertical temperature gradient at the equator which is super-adiabatic. Our results suggest that the potential temperature difference between 1-bar and the deep isentrope is approximately  2.8 +/- 1.4 K. To avoid dynamic instability, the super-adiabatic temperature gradient must be stabilized by a change of mean molecular weight within the 5 – 10 bars pressure levels which only water can provide. The result implies that an abundance of water at the equator is constrained to a value between 2.2 and 6.2 times solar.