Comparing Electron Energetics and UV Brightness in Jupiter's Northern Polar Region During Juno Perijove 5
R. W. EbertT. K. GreathouseG. ClarkF. AllegriniF. BagenalS. J. BoltonJ. E. P. ConnerneyG. R. GladstoneMasafumi ImaiVincent HueW. S. KŭrthS. LevinP. LouarnB. H. MaukD. J. McComasC. ParanicasJ. R. SzalayM. F. ThomsenP. W. ValekR. J. Wilson
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Abstract:
We compare electron and UV observations mapping to the same location in Jupiter's northern polar region, poleward of the main aurora, during Juno perijove 5. Simultaneous peaks in UV brightness and electron energy flux are identified when observations map to the same location at the same time. The downward energy flux during these simultaneous observations was not sufficient to generate the observed UV brightness; the upward energy flux was. We propose that the primary acceleration region is below Juno's altitude, from which the more intense upward electrons originate. For the complete interval, the UV brightness peaked at ~240 kilorayleigh (kR); the downward and upward energy fluxes peaked at 60 and 700 mW/m2, respectively. Increased downward energy fluxes are associated with increased contributions from tens of keV electrons. These observations provide evidence that bidirectional electron beams with broad energy distributions can produce tens to hundreds of kilorayleigh polar UV emissions.Keywords:
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Jupiter (rocket family)
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This paper presents the first observations of simultaneous polar cap patches and polar cap arcs in a single common 1000‐km field of view, and identifies a model that explains the interplanetary magnetic field (IMF) dependencies of the observed phenomenology. To study the characteristics of the polar cap optical emissions in the 630.0 nm line during transitions of the IMF B z , we have scanned images taken at Qaanaaq, Greeland, between 1989 and 1994. We found that on a few occasions, when B z changed from a south to a north orientation, a particular pattern of polar cap patches and Sun‐aligned arcs coexisted. No similar pattern of coexisting arcs and patches was found during north‐to‐south IMF transitions. The detailed analyses of three of these events are presented here in which patches and polar cap arcs are clearly identified to reside simultaneously within the Qaanaaq imager field of view. The digisonde located also at Qaanaaq is used to confirm that the optical patches correspond to enhancements in the number density and a simultaneous decrease of the h m F 2 value. These two factors increase the capability of the imager to differentiate between patches and the background airglow. Data collected by the DMSP F8 satellite during one of the events reaffirm the appearance of polar cap precipitation during the B z positive period. The J4 sensor on board DMSP F8 detected typical electron fluxes commonly associated with polar cap arcs. The coexistence of patches and arcs is due to a slower response of the patches in exiting the polar cap, and then the relatively sudden appearance of polar cap arcs presumably driven by dayside reconnection between the IMF and open flux drawn initially equatorward toward the cusp. This model, of dayside reconnection switching from equatorward of the cusp for B z south to poleward of the cusp for B z north, likewise explains why arcs and patches are seen by the imager to coexist for rapid B z reversals only from south to north and not from north to south.
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X‐ray images of auroral arcs for consecutive north and south polar crossings of the DMSP‐F6 satellite are presented. On January 18, 1983, the north polar region was in the earth's shadow and the south polar region was in complete sunlight. The X‐ray images of both polar cap regions show features of the dawn and dusk auroral oval that are quite similar. However a strong polar cap structure appears only in the north pole image. Near simultaneous measurements of precipitating electrons obtained by instruments aboard the NOAA‐6 and NOAA‐7 satellites crossing the south pole, show no indication of polar auroral structures. These examples illustrate the utility of X‐ray imaging in both sunlight and in darkness for studying auroral boundaries and morphology.
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Coronal hole
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