Abstract
The region 1 (R1) and region 2 current systems typically form concentric rings of field‐aligned currents in the polar ionospheres; we term the inner ring the R1 oval. We apply an automated fitting scheme to field‐aligned current densities provided by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) and identify the latitude of maximum R1 current at all magnetic local times to yield the size of the R1 oval. We investigate the dynamics of the R1 oval size in response to geomagnetic activity for two cases corresponding to: repeated substorm activations with a minimally enhanced ring current; a significant ring current enhancement with multiple substorms. During the first event the dynamics of the R1 oval size reflected an expanding‐contracting polar cap: during substorm growth phase dayside reconnection added open magnetic flux to the polar cap, expanding the R1 oval equatorward. Tail reconnection during the substorm expansion phase converted open into closed magnetic flux and the polar cap contracts as reflected by the poleward retreat of the R1 oval. During the period of enhanced ring current intensity the R1 oval grew to larger sizes during each substorm growth phase than it did during the other event, consistent with the suggestion that a stronger ring current stabilizes the magnetospheric tail to the onset of magnetic reconnection. The presented methodology allows AMPERE data to be condensed into a single parameter, the R1 oval size, which reflects magnetospheric dynamics and provides a convenient measure of the instantaneous magnetospheric system state in both hemispheres.
Highlights
[2] At the dawn of the space age, using data from the early polar-orbiting Satellite 1963 38C, Zmuda et al [1966] reported transverse magnetic disturbances in the auroral regions and interpreted these disturbances - fashionable in those days - as signatures of hydromagnetic waves
The cycle begins with closed terrestrial magnetic field lines located on the dayside which reconnect with solar wind magnetic field lines during periods of southward interplanetary magnetic field (IMF)
The fitting scheme described above identifies the location of both the region 1 (R1) and region 2 (R2) current system, here we focus on the R1 location, hereinafter called the R1 oval, because the R1 currents are believed to locate closer to the ionospheric projection of the open-closed field line boundary [e.g., Cowley, 2000]
Summary
[2] At the dawn of the space age, using data from the early polar-orbiting Satellite 1963 38C, Zmuda et al [1966] reported transverse magnetic disturbances in the auroral regions and interpreted these disturbances - fashionable in those days - as signatures of hydromagnetic waves. Other authors have used this dataset to characterize the average FAC distribution during various IMF conditions [Anderson et al, 2008;Green et al, 2009], to relate FACs to auroral phenomena [Korth et al, 2004], and to estimate the global Poynting flux into the polar regions by combining the magnetic perturbation data with electric field data from the SuperDARN radars [Waters et al, 2004] All of these studies used the engineering magnetometer data which was telemetered to the ground with coarse time resolution (200 s per sample) such that the data had to be accumulated over long periods of time, about two hours, to acquire a composite sample of the magnetic signatures in the polar regions. The fitted data used in this study are publicly available from the project website at http:// ampere.jhuapl.edu
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