Preliminary JIRAM results from Juno polar observations: 1. Methodology and analysis applied to the Jovian northern polar region

Abstract

During the first orbit around Jupiter of the NASA/Juno mission, the Jovian Auroral Infrared Mapper (JIRAM) instrument observed the auroral regions with a large number of measurements. The measured spectra show both the emission of the H3+ ion and of methane in the 3–4 μm spectral region. In this paper we describe the analysis method developed to retrieve temperature and column density (CD) of the H3+ ion from JIRAM spectra in the northern auroral region. The high spatial resolution of JIRAM shows an asymmetric aurora, with CD and temperature ovals not superimposed and not exactly located where models and previous observations suggested. On the main oval averaged H3+ CDs span between 1.8 × 1012 cm−2 and 2.8 × 1012 cm−2, while the retrieved temperatures show values between 800 and 950 K. JIRAM indicates a complex relationship among H3+ CDs and temperatures on the Jupiter northern aurora.

The first close‐up images of Jupiter's polar regions: Results from the Juno mission JunoCam instrument

“…One possibility is that the HAC is directly related to local auroral processes, similar to the “south dark patch” reported previously within the south auroral oval [ Vincent et al ., ; Porco et al ., ]. We believe this is unlikely because the feature is physically distant from the auroral oval, which is centered closer to 180°W longitude [ Bonfond et al ., , ; Connerney et al ., ; Dinelli et al ., ], illustrated in Figures S1 and S3 in the supporting information. Alternatively, the HAC could be related to the haze of complex hydrocarbons expected to form in the stratosphere [ Atreya et al ., ], either directly or indirectly by the hydrocarbon haze particles facilitating the formation of a thin ammonia cloud/haze layer in the lower stratosphere.…”

Preliminary JIRAM results from Juno polar observations: 2. Analysis of the Jupiter southern H3+ emissions and comparison with the north aurora

“…All the observations of the southern aurora have been made on the Jovian dayside, and no measurements are available for the nightside during PJ1. The absolute and relative intensities of the H 3 + emission bands are directly related respectively to the number of emitting ions and their effective temperatures, so the H 3 + column densities and temperatures have been computed using the method described by Dinelli et al [] and applied to the analysis the northern hemisphere auroral data. According to this method, the intensity of each transition k of any molecule M can be computed using the expression reported by Altieri et al [] taken from Stallard et al [, and references therein].…”

“…H 3 + effective temperatures and column densities have been obtained only for the measurements where the infrared auroral emissions are present. Only spectra with an emission angle smaller than 75° have been retained in the analysis, and the results of the analysis were further filtered by retaining the retrievals for which the final χ 2 test was smaller than 20 and the obtained temperatures had a random error (the error due to the mapping of the measurement noise onto the retrieved parameters) lower than 100°K [ Dinelli et al , ]. No filter was applied to the size of the error on the H 3 + column densities.…”

Infrared observations of Jovian aurora from Juno's first orbits: Main oval and satellite footprints

“…The image intensity is adjusted (multiplied by the cosine of the emission angle), assuming that radiance is constant along such column, to normalize the measured radiance to that coming from a vertical column. This also implies that there is no methane absorption above the H 3 + emission region; in fact, the spectrometer measurements of the auroral region (made with the same viewing geometry of the imager) show that even where the methane emission is large, it is always superimposed to the H 3 + spectrum, this indicates that the two molecules either coexist at the same altitudes or the methane layer is below the H 3 + layer [ Dinelli et al ., ; Adriani et al ., ; Moriconi et al ., ]. The image intensity is not the total H 3 + emission, but only the segment in the filter passband.…”

“…The southern aurora appears significantly brighter at the time of observation (~50% higher intensity), as found in the spectrometer measurements [ Adriani et al ., ; Dinelli et al ., ]. Three or four diffuse emission spots, placed at 0° System III west longitude and outside the main oval in the south, are visible in the spectrometer data as well and can be linked with similar features in the north aurora at 0° longitude; these may be signatures of plasma injections [ Mauk et al ., ; Dumont et al ., ].…”