Mid-infrared mapping of Jupiter’s temperatures, aerosol opacity and chemical distributions with IRTF/TEXES

Abstract

International audienceGlobal maps of Jupiter’s atmospheric temperatures, gaseous composition and aerosol opacity are derived from a programme of 5–20 µm mid-infrared spectroscopic observations using the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA’s Infrared Telescope Facility (IRTF). Image cubes from December 2014 in eight spectral channels, with spectral resolutions of R ∼2000−12,000−12,000 and spatial resolutions of 2–4° latitude, are inverted to generate 3D maps of tropospheric and stratospheric temperatures, 2D maps of upper tropospheric aerosols, phosphine and ammonia, and 2D maps of stratospheric ethane and acetylene. The results are compared to a re-analysis of Cassini Composite Infrared Spectrometer (CIRS) observations acquired during Cassini’s closest approach to Jupiter in December 2000, demonstrating that this new archive of ground-based mapping spectroscopy can match and surpass the quality of previous investigations, and will permit future studies of Jupiter’s evolving atmosphere. The visibility of cool zones and warm belts varies from channel to channel, suggesting complex vertical variations from the radiatively-controlled upper troposphere to the convective mid-troposphere. We identify mid-infrared signatures of Jupiter’s 5-µm hotspots via simultaneous M, N and Q-band observations, which are interpreted as temperature and ammonia variations in the northern Equatorial Zone and on the edge of the North Equatorial Belt (NEB). Equatorial plumes enriched in NH3 gas are located south-east of NH3-desiccated ‘hotspots’ on the edge of the NEB. Comparison of the hotspot locations in several channels across the 5–20 µm range indicate that these anomalous regions tilt westward with altitude. Aerosols and PH3 are both enriched at the equator but are not co-located with the NH3 plumes. The equatorial temperature minimum and PH3/aerosol maxima have varied in amplitude over time, possibly as a result of periodic equatorial brightenings and the fresh updrafts of disequilibrium material. Temperate mid-latitudes display a correlation between mid-IR aerosol opacity and the white albedo features in visible light (i.e., zones). We find hemispheric asymmetries in the distribution of tropospheric PH3, stratospheric hydrocarbons and the 2D wind field (estimated via the thermal-wind equation) that suggest a differing efficiency of mechanical forcing (e.g., vertical mixing and wave propagation) between the two hemispheres that we argue is driven by dynamics rather than Jupiter’s small seasonal cycle. Jupiter’s stratosphere is notably warmer at northern mid-latitudes than in the south in both 2000 and 2014, although the latter can be largely attributed to strong thermal wave activity near 30°N that dominates the 2014 stratospheric maps and may be responsible for elevated C2H2 in the northern hemisphere. A vertically-variable pattern of temperature and windshear minima and maxima associated with Jupiter’s Quasi Quadrennial Oscillation (QQO) is observed at the equator in both datasets, although the contrasts wer...

Multiple‐wavelength sensing of Jupiter during the Juno mission's first perijove passage

“…The correlation of regions with high 5‐µm radiance and blue‐gray appearance has been well established [ Owen and Terrile , ]. These regions are characterized as the driest and clearest in Jupiter [ Terrile and Westphal , ; Ortiz et al , ; Fletcher et al , ] and are of specific interest because the Galileo Probe descended into one of them [ Orton et al , , ]. A correlation between Juno measurements of the physical properties of the atmosphere in 5‐µm hot spots and the Galileo Probe results is considered an important element of closure in the study of Jupiter's atmosphere, linking independent spacecraft results.…”

The distribution of ammonia on Jupiter from a preliminary inversion of Juno microwave radiometer data

“…Both the medium‐high water case and the low water case show a column of concentrated ammonia gas at the EZ and a global depletion of ammonia down to 50–60 bars. Although the overall structure of the distribution of ammonia is similar to what was shown by Voyager Infrared Interferometer Spectrometer [ Gierasch et al , ], Cassini Composite Infrared Spectrometer [ Achterberg et al , ], and ground‐based Infrared Telescope Facility Texas Echelon Cross Echelle Spectrograph observations [ Fletcher et al , ] at the cloud level, the remarkable penetration depth of the depleted ammonia and the cascade of its concentration within the NEB are new discoveries. The choice of the bottom boundary is not consequential as long as it is sufficiently deep because the contribution function of channel 1 is very flat from 100 bars to 1000 bars.…”

“…The positive brightness temperature anomaly in the North Equatorial Belt (NEB) at 10–20°N is the other prominent feature in the spectra; it can be interpreted as a significantly low concentration of ammonia. The high brightness temperature in the NEB in channels 5 and 6 is consistent with ground‐based observations [ Bjoraker et al , ; Fletcher et al , ]. The largest temperature anomaly is on the southern side of the NEB at shallow depth, and then it gradually shifts to the northern side of the NEB at greater depth.…”

Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival

“…The main article covers two newly-identified wave patterns in the 0-30 • N domain, but the data presented throughout the article also shows thermal contrasts associated with a third wave on the prograde NEBs jet between 6-9 • N. This pattern of visibly-dark, longitudinallyelongated 'hotspots' and adjacent bright fans of material (referred to as plumes, although these are not always associated with convection) that can be seen near 8 • N in reflected sunlight [Allison, 1990;Baines et al, 2002;Arregi et al, 2006;Choi et al, 2013], infrared [Or- Fletcher et al, 2016], and radio-wave observations [de Pater et al, 2016;Cosentino et al, 2017]. This chain moves slowly westward with respect to the rapid eastward flow of the NEBs, and has been interpreted as an equatorial Rossby wave pattern [Showman and Ingersoll, 1998;Showman and Dowling, 2000;Friedson, 2005], with rising air and condensation in the plumes and descent and aerosol-clearing in the hotspots.…”

“…The interior of the NEB is characterized by upper-tropospheric thermal wave activity [e.g., Magalhaes et al, 1990;Orton et al, 1994;Rogers et al, 2004;Li et al, 2006;Fisher et al, 2016]. Stratospheric waves in the 20−30 • N region were also reported [Orton et al, 1991;Fletcher et al, 2016]. A chronology of these previous wave detections is presented in Supplemental Text S2.…”