Ground-based observations of an onset of localized field-aligned currents during auroral breakup around magnetic midnight

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H.J. Opgenoorth
R.J. Pellinen
H. Maurer
F. Kuppers
W.J. Heikkila
K.U. Kaila
P. Tanskanen


The substorm on 2 March 1978 was selected for study as a relatively weak substorm, starting at about local magnetic midnight, that could be observed with instruments in Northern Scandinavia. The analysis is based on a comparative study of data from the IMS magnetometer network, all-sky cameras, pulsation magnetometers, and riometers in the Scandinavian area. In addition other data are used to support the results, e.g., a photograph from the DMSP-F2 satellite, showing the auroral situation over Scandinavia, and further west, immediately after the substorm onset. The substorm was preceded by a weak activation of aurora and magnetic disturbance about 3 min before the onset. After a fading that lasted for 20 s and could be observed only in optical aurora, the substorm onset led to a strong brightening of the aurora, an enhancement of the westward electrojet, a sudden rise in the ionospheric D-layer absorption, and Pi B type pulsations. Immediately after the onset, the ground magnetic data suggest the appearence of a pair of oppositely directed, localized, field-aligned currents (FACs). The main development of the signatures of the downward FAC was clearly delayed by about 3 min. There were significant correlations between the magnetic signatures of the two FACs and different features and spectra of the optical aurora, both in time and location. The observed Pi B type pulsations lasted as long as a growth in the local onset-connected FACs could be inferred. Within the first three minutes the localized three dimensional current system developed into a more sheet-like configuration. An expansion to the west, possibly accompanied by a westward travelling surge, was traced with riometers and magnetometers on Iceland and Greenland.

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Opgenoorth, H., Pellinen, R., Maurer, H., Kuppers, F., Heikkila, W., Kaila, K., & Tanskanen, P. (1980). Ground-based observations of an onset of localized field-aligned currents during auroral breakup around magnetic midnight. Journal of Geophysics, 48(1), 101-115. Retrieved from


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