Abstract
AbstractJupiter's tropospheric ammonia (NH3) abundance is studied using spatially resolved 5 μm observations from the cryogenic high‐resolution infrared spectrograph (CRIRES) at the European Southern Observatory's Very Large Telescope. The high‐resolving power (R = 96,000) allows the line shapes of three NH3 absorption features to be resolved. We find that within the 1–4 bar pressure range, the NH3 abundance decreases with altitude. The instrument slit was aligned north‐south along Jupiter's central meridian, allowing us to search for latitudinal variability. There is considerable uncertainty in the large‐scale latitudinal variability, as the increase in cloud opacity in zones compared to belts can mask absorption features. However, we do find evidence for a strong NH3 enhancement at 4–6°N, consistent with a localized “ammonia plume” on the southern edge of Jupiter's North Equatorial Belt.
Highlights
As a condensible species in Jupiter’s atmosphere, ammonia (NH3) plays an important role in understanding the planet’s meteorology
We find that within the 1–4 bar pressure range, the NH3 abundance decreases with altitude
NH3 is a significant contributor to the microwave radiation from the planet; from the ground, this spectral region has been used to probe down to the 10 bar level in Jupiter’s atmosphere, and the microwave radiometer (MWR) on the Juno mission is sensitive to the NH3 abundance at pressures of up to 100 bar (Li et al, 2017)
Summary
As a condensible species in Jupiter’s atmosphere, ammonia (NH3) plays an important role in understanding the planet’s meteorology. Different spectral regions are sensitive to different altitudes in Jupiter’s atmosphere and can be combined to constrain the vertical profile of NH3. NH3 is a significant contributor to the microwave radiation from the planet; from the ground, this spectral region has been used to probe down to the 10 bar level in Jupiter’s atmosphere (de Pater et al, 2001), and the microwave radiometer (MWR) on the Juno mission is sensitive to the NH3 abundance at pressures of up to 100 bar (Li et al, 2017). While the previous microwave and long-wavelength infrared analyses of Jupiter’s NH3 abundance have explored spatial variability, these 5 μm studies have typically either used disc-averaged spectra or focused on a specific area of interest, such as the 5 μm hot spots (e.g., Grassi et al, 2017).
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