On the Spatial Distribution of Minor Species in Jupiter's Troposphere as Inferred From Juno JIRAM Data

Abstract

The spatial distribution of water, ammonia, phosphine, germane, and arsine in the Jupiter's troposphere has been inferred from the Jovian Infrared Auroral Mapper (JIRAM) Juno data. Measurements allow us to retrieve the vertically averaged concentration of gases between~3 and 5 bars from infrared-bright spectra. Results were used to create latitudinal profiles. The water vapor relative humidity varies with latitude from <1% to over 15%. At intermediate latitudes (30-70°) the water vapor maxima are associated with the location of cyclonic belts, as inferred from mean zonal wind profiles (Porco et al., 2003). The high-latitude regions (beyond 60°) are drier in the north (mean relative humidity around 2-3%) than the south, where humidity reaches 15% around the pole. The ammonia volume mixing ratio varies from 1 × 10 −4 to 4 × 10 −4 . A marked minimum exists around 10°N, while data suggest an increase over the equator. The high-latitude regions are different in the two hemispheres, with a gradual increase in the south and more constant values with latitude in the north. The phosphine volume mixing ratio varies from 4 × 10 −7 to 10 × 10 −7 . A marked minimum exists in the North Equatorial Belt. For latitudes poleward 30°S and 30°N, the northern hemisphere appears richer in phosphine, with a decrease toward the pole, while the opposite is observed in the south. JIRAM data indicate an increase of germane volume mixing ratio from 2 × 10 −10 to 8 × 10 −10 from both poles to 15°S, with a depletion centered around the equator. Arsine presents the opposite trend, with maximum values of 6 × 10 −10 at the two poles and minima below 1 × 10 −10 around 20°S.

Storms and the Depletion of Ammonia in Jupiter: II. Explaining the Juno Observations

“…Yet, to this day, Jupiter's atmospheric water and ammonia abundances calculated by cloud models and global circulation models (del Genio & McGrattan, 1990;Palotai & Dowling, 2008) remain incompatible with retrievals from spectroscopic observations: The analysis of Galileo/NIMS and Juno/JIRAM spectroscopic observations (Grassi et al, 2017(Grassi et al, , 2020Roos-Serote et al, 2004) essentially confirms the previous observations by Bjoraker et al (1986). In order to reproduce the 5-μm spectra in the North Equatorial Belt, one generally requires a very low water abundance to great depths (8 bar or so), or at least a low relative humidity ( ∼ 10%) until a cloud deck with a high opacity is reached.…”

Mapping Jupiter's Mischief

“…The major scientific products of these encounters are now coming to light. New results by Grassi et al (2020) map the distribution of key atmospheric gases in Jupiter's atmosphere using data collected by the Jovian Infrared Auroral Mapper (JIRAM) over the first 2 years of Juno's orbit (August 2016 to September 2018). The JIRAM observations at 4-5 μm are sensitive to thermal emission from the cloud-forming region near ∼3-5 bar (with clouds in silhouette against a bright background), along with spectral features from several tropospheric gases.…”

“…The JIRAM observations at 4-5 μm are sensitive to thermal emission from the cloud-forming region near ∼3-5 bar (with clouds in silhouette against a bright background), along with spectral features from several tropospheric gases. Grassi et al (2020) performed retrieval analysis on a subset of available JIRAM data, using spectra selected for relatively high radiance, low emission angle, and high resolution. The Juno spacecraft measurements provide two key advantages over previous observations: very high resolution (courtesy of its close proximity to Jupiter) and coverage at high latitudes using similar viewing geometries as for low latitudes (courtesy of its polar orbit).…”

“…No new data were generated in the preparation of this manuscript. Data used for the abundance profiles in Figure 2 are included in Grassi et al (2020), and the full JIRAM data sets can be found in Grassi (2019).…”

“…Gaps in the abundance profiles occur at latitudes with high aerosol opacity (corresponding with cloud-thick zones), where measurements of the gas composition are difficult to obtain. SeeGrassi et al (2020) for details.…”