Dipolarization fronts with associated energized electrons in Saturn’s magnetotail

Abstract

We present a statistical study of dipolarization fronts within Saturn’s magnetotail. Automated methods were used to identify 28 significant southward rotations of the field coupled with enhancements in the electron energy. The observed dipolarizations cover the majority of the magnetotail, though possess a strong dawn-dusk asymmetry (79% occur postmidnight). Almost half (43%) of dipolarizations occur within 3 hr of another event, though these chains are solely observed postmidnight. Most pitch angle distributions of the heated electron populations show increased relative fluxes parallel or perpendicular to the field, likely due to nonlocal heating effects. The electron temperature and density following the passage of a front are anticorrelated; the temperature increases are accompanied by a decrease in their density. The temperature increases by factors of 4–12, while the density drops by factors of 3–10. Premidnight events consistently show the smallest relative heating and density depletion, suggesting they are observed closer to their generation. In contrast, the location of the postmidnight x-line is inferred to be more variable, with a large variety of heating factors observed. Forty percent of the events show a strong reduction in water (W+) group fraction, likely related to either the preferential loss
of equatorial heavy ions in departing plasmoids or the closure of open field. Two of these events show significant compositional changes suggesting the addition of plasma of external origin; we suggest that these events involved the closure of open field.

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Identifiers

ORCID for A.W. Smith: orcid.org/0000-0001-7321-4331

ORCID for C.M. Jackman: orcid.org/0000-0003-0635-7361

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