Jupiter's ammonia distribution derived from VLA maps at 3–37 GHz

Imke de Pater, R. J. Sault, Michael H. Wong, Leigh N. Fletcher, David DeBoer, Bryan Butler

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Abstract

We observed Jupiter four times over a full rotation (10 h) with the upgraded Karl G. Jansky Very Large Array (VLA) between December 2013 and December 2014. Preliminary results at 4–17 GHz were presented in de Pater et al. (2016); in the present paper we present the full data set at frequencies between 3 and 37 GHz. Major findings are: i) The radio-hot belt at 8.5–11° N latitude, near the interface between the North Equatorial Belt (NEB) and the Equatorial Zone (EZ) is prominent at all frequencies (3–37 GHz). Its location coincides with the southern latitudes of the NEB (7–17° N). ii) Longitude-smeared maps reveal belts and zones at all frequencies at latitudes ≲ |20°|. At higher latitudes numerous fainter bands are visible at frequencies ≳ 7 GHz. The lowest brightness temperature is in the EZ near a latitude of 4° N, and the NEB has the highest brightness temperature near 11° N. The bright part of the NEB increases in latitudinal extent (spreads towards the north) with deceasing frequency, i.e., with depth into the atmosphere. In longitude-resolved maps, several belts, in particular in the southern hemisphere, are not continuous along the latitude line, but broken into small segments as if caused by an underlying wave. iii) Model fits to longitude-smeared spectra are obtained at each latitude. These show a high NH3 abundance (volume mixing ratio ∼4×10−4) in the deep (P > 8–10 bar) atmosphere, decreasing at higher altitudes due to cloud formation (e.g., in zones), or dynamics in combination with cloud condensation (belts). In the NEB ammonia gas is depleted down to at least the 20 bar level with an abundance of 1.75×10−4. The NH3 abundance at latitudes > |50|° is characterized by a relatively low value (∼1.75×10−4) between ∼ 1 and 10 bar. iv) Using the entire VLA dataset, we confirm that the planet is extremely dynamic in the upper layers of the atmosphere, at P < 2–3 bar, i.e., at the altitudes where clouds form. At most latitudes the relative humidity within and above the NH3 cloud is considerably sub-saturated. v) The radiative transfer models that best fit the longitude-smeared VLA data at 4–25 GHz match the Juno PeriJove 1 microwave data extremely well, i.e., the NH3 abundance is high in the deep atmosphere, and either remains constant or decreases with altitude. vi) Hot spots have a very low, sub-saturated NH3 abundance at the altitudes of the NH3-ice cloud, gradually increasing from an abundance of ∼10−5 at 0.6 bar to the deep atmosphere value (∼4×10−4) at 8 bar. vii) We previously showed the presence of large ammonia plumes, which together with the 5-µm hot spots constitute the equatorially trapped Rossby wave. Observations of these plumes at 12–25 GHz reveal them to be supersaturated at ∼ 0.8–0.5 bar, which implies plumes rise ∼ 10 km above the main clouddeck. Numerous small ammonia plumes are detected at other locations (e.g., at 19° S and interspersed with hot spots). viii) The Great Red Spot (GRS) and Oval BA show relatively low NH3 abundances throughout the troposphere (∼ 1.5–1.8 × 10−4), and the GRS is considerably sub-saturated at higher altitudes.
Original languageEnglish
Pages (from-to)168-191
Number of pages24
JournalIcarus
Volume322
DOIs
Publication statusPublished - 2019

Keywords

  • Atmosphere
  • Jupiter
  • Radiative transfer
  • Radio observations

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