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

Traveling ionospheric disturbances observed at South African midlatitudes during the 29--31 October 2003 geomagnetically disturbed period

This paper presents traveling ionospheric disturbances (TIDs) observations from GPS measurements over the South African region during the geomagnetically disturbed period of 29\textendash31 October 2003. Two receiver arrays, which were along two distinct longitudinal sectors of about 18\textdegree-20\textdegree and 27\textdegree-28\textdegree were used in order to investigate the amplitude, periods and virtual propagation characteristics of the storm induced ionospheric disturbances. The study revealed a large sudden TEC increase on 28 October 2003, the day before the first of the two major storms studied here, that was recorded simultaneously by all the receivers used. This pre-storm enhancement was linked to an X-class solar flare, auroral/magnetospheric activities and vertical plasma drift, based on the behaviour of the geomagnetic storm and auroral indices as well as strong equatorial electrojet. Diurnal trends of the TEC and foF2 measurements revealed that the geomagnetic storm caused a negative ionospheric storm; these parameters were depleted between 29 and 31 October 2003. Large scale traveling ionospheric disturbances were observed on the days of the geomagnetic storms (29 and 31 October 2003), using line-of-sight vertical TEC (vTEC) measurements from individual satellites. Amplitude and dominant periods of these structures varied between 0.08\textendash2.16 TECU, and 1.07\textendash2.13\ h respectively. The wave structures were observed to propagate towards the equator with velocities between 587.04 and 1635.09\ m/s.

Katamzi, Zama; Habarulema, John;

Published by: Advances in Space Research      Published on: 01/2014

YEAR: 2014     DOI: 10.1016/j.asr.2013.10.019

geomagnetic storm; Substorm; Total electron content (TEC); Traveling ionospheric disturbances (TIDs)