Dipolarization Fronts With Associated Energized Electrons in Saturn's Magnetotail

Smith, Andy, Jackman, C. M., Thomsen, M. F., Sergis, N., Mitchell, D. G. and Roussos, E. (2018) Dipolarization Fronts With Associated Energized Electrons in Saturn's Magnetotail. Journal of Geophysical Research: Space Physics, 123 (4). pp. 2714-2735. ISSN 2169-9380

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Official URL: https://doi.org/10.1002/2017JA024904


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.

Item Type: Article
Additional Information: Funding Information: Part of this work was discussed within the ISSI team on How does the Solar Wind Influence the Giant Planet Magnetospheres? A. W. S. thanks M. K. Dougherty for access to Cassini Magnetometer data, and S. Kellock and L. Alconcel at Imperial College London for MAG data processing. Cassini MAG data processing activities are supported in the United Kingdom by STFC. A. W. S. thanks A. J. Coates and G. R. Lewis for CAPS/ELS moments processing. A. W. S. is funded by a SEPnet PhD studentship. C. M. J. is supported by a Science and Technology Facilities Council Ernest Rutherford FellowshipST/L004399/1. M. F. T. is supported by the NASA Cassini program through JPL contract 1243218 with Southwest Research Institute. The magnetic field, CAPS (including moments), and LEMMS data shown in this analysis are available from the Planetary Data System (http://pds.nasa.gov/). A. W. S. would like to thank A. Masters, C. S. Arridge. and P. A. Delamere for helpful discussions. Data analysis and plotting were conducted in Python. Specifically, the libraries used were NumPy, SciPy, Matplotlib, and Pandas.
Uncontrolled Keywords: Cassini, dipolarization, magnetotail, reconnection, Saturn
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 07 Nov 2022 11:29
Last Modified: 07 Nov 2022 11:30
URI: https://nrl.northumbria.ac.uk/id/eprint/50563

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