Bibliography

Temporal evolution of substorm-driven global Alfv\ en wave power above the auroral acceleration region

The onset of substorms is associated with bursty enhancements of Alfv\ en wave power throughout the magnetotail. While impossible to assess the total Alfv\ en wave power in the entire magnetotail, we have instead monitored waves that are funneled into the auroral acceleration region, in order to assess the temporal evolution of Alfv\ en wave power above the nightside auroral zone in relation to substorm phases. The substorms were grouped by three conditions: nonstorm periods, storm periods, and all (unconditioned) periods. Using superposed epoch analysis, we found that the global magnetohydrodynamic Alfv\ en wave power increased significantly at onset for all three conditions, while a power decrease to pre-onset values occurred within 2 h. Specifically, the peak inflowing power during the expansion phase was 5.7 GW for unconditioned substorms, 5.6 GW for nonstorm-time substorms, and 7.8 GW for storm-time substorms. These results correspond to power increases with respect to pre-onset values of 138\%, 366\%, and 200\%, respectively. Additional analysis in relation to the aurora was performed for nonstorm-time substorms only. During the expansion phase, about 50\% of the Alfv\ en wave power over the entire nightside auroral zone is collocated with the auroral bulge region. Furthermore, the total inflowing Alfv\ en wave power over the entire nightside auroral zone is 17\% of the conjugate auroral power, while the inflowing power over the auroral bulge region is 32\% of the conjugate aurora. However, allowing for a finite absorption efficiency inside the auroral acceleration region, the likely average Alfv\ enic contributions to the aurora are approximately 10\% and 18\%,respectively.

Keiling, Andreas; Thaller, Scott; Dombeck, John; Wygant, John;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2020

YEAR: 2020     DOI: 10.1029/2019JA027444

Alfven wave; Alfvenic electron; AURORA; auroral acceleration; magnetotail; Substorm

Link between pre-midnight second harmonic poloidal waves and auroral undulations: Conjugate observations with a Van Allen Probes spacecraft and a THEMIS all-sky imager

We report, for the first time, an auroral undulation event on 1 May 2013 observed by an all-sky imager (ASI) at Athabasca (L = 4.6), Canada, for which in situ field and particle measurements in the conjugate magnetosphere were available from a Van Allen Probes spacecraft. The ASI observed a train of auroral undulation structures emerging spontaneously in the pre-midnight subauroral ionosphere, during the growth phase of a substorm. The undulations had an azimuthal wavelength of ~180 km and propagated westward at a speed of 3\textendash4 km s^-1. The successive passage over an observing point yielded quasi-periodic oscillations in diffuse auroral emissions with a period of ~40 s. The azimuthal wave number m of the auroral luminosity oscillations was found to be m ~ -103. During the event the spacecraft \textendash being on tailward stretched field lines ~0.5 R_E outside the plasmapause that mapped into the ionosphere conjugate to the auroral undulations \textendash encountered intense poloidal ULF oscillations in the magnetic and electric fields. We identify the field oscillations to be the second harmonic mode along the magnetic field line through comparisons of the observed wave properties with theoretical predictions. The field oscillations were accompanied by oscillations in proton and electron fluxes. Most interestingly, both field and particle oscillations at the spacecraft had one-to-one association with the auroral luminosity oscillations around its footprint. Our findings strongly suggest that this auroral undulation event is closely linked to the generation of second harmonic poloidal waves

Motoba, T.; Takahashi, K.; Ukhorskiy, A.; Gkioulidou, M.; Mitchell, D.; Lanzerotti, L.; Korotova, G.; Donovan, E.; Wygant, J.; Kletzing, C.; Kurth, W.; Blake, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2015

YEAR: 2015     DOI: 10.1002/2014JA020863

Direct measurements of the Poynting flux associated with convection electric fields in the magnetosphere

Nishimura, Y.; Kikuchi, T.; Shinbori, A.; Wygant, J.; Tsuji, Y.; Hori, T.; Ono, T.; Fujita, S.; Tanaka, T.;

Published by: Journal of Geophysical Research      Published on: Jan-01-2010

YEAR: 2010     DOI: 10.1029/2010JA015491