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2021 |
The Dynamics of the Alfvénic Oval The auroral oval is a well-established concept, introduced more than five decades ago. The Alfvénic oval, on the other hand, is a very recent concept, which has been revealed in both observational and numerical studies. This is the first review of the global Alfvénic oval, while also defining primary, secondary and tertiary layers of the Alfvénic oval. The focus lies on the large-scale dynamic properties of the global Alfvénic oval in relation to the AE index, substorm phases, storm phases and solar wind/IMF conditions. Statistical data recorded above and below the nominal auroral acceleration region are reviewed, together with results from global simulation studies. The Alfvénic oval s relation to the auroral oval is also reviewed. This review demonstrates that the Alfvénic oval is well enough defined and investigated to give it its name, and it demonstrates that our understanding allows for the prediction of the Alfvénic oval under various conditions. Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: aug YEAR: 2021   DOI: 10.1016/j.jastp.2021.105616 AURORA; Alfven wave; Energy transport; geomagnetic activity; magnetosphere-ionosphere coupling; Wave-particle interaction |
2020 |
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 |
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