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Temporal and Spatial Development of Global Birkeland Currents
Author(s) -
Anderson Brian J.,
Olson Cameron N.,
Korth Haje,
Barnes Robin J.,
Waters Colin L.,
Vines Sarah K.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja025254
Subject(s) - magnetosphere , physics , interplanetary magnetic field , magnetopause , electrojet , solar wind , ionosphere , interplanetary spaceflight , geophysics , local time , current (fluid) , magnetic field , earth's magnetic field , statistics , mathematics , quantum mechanics , thermodynamics
The development of large‐scale Birkeland currents is examined using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), which measures global Birkeland currents continuously on 10‐min time scales. The integrated current was used to identify onsets of at least 1 MA preceded by periods of quiescence lasting at least 3 hr. The Region 1 currents do not fully form without Region 2. Rather, they develop together, first on the dayside, then on the nightside, and lastly, they fill in and intensify at all local times to form the nominal statistical pattern. The onsets are closely correlated with enhancements of magnetospheric forcing as indicated by the solar wind electric field and the orientation of the interplanetary magnetic field. Nightside onsets correspond to intensifications of the auroral electrojet as reflected in the AE index; they are delayed by ~40 min relative to the increase of the dayside current and are 2.8 times more rapid than the dayside current increase. After nightside onset, Birkeland currents expand toward dawn and dusk and merge with the dayside currents while also intensifying at all local times. The dayside current pattern depends on the sign of the interplanetary magnetic field B Y . The nightside current distributions are the same for positive and negative B Y and display a Harang discontinuity independent of the sign of B Y . The predominant development and intensification of Birkeland currents occur after nightside onset at all local times with roughly 75% of the total current, both Regions 1 and 2, appearing after nightside onset.