Implications of the altitude of transient 630-nm dayside auroral emissions

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JA00811· OSTI ID:86368

Lockwood, M ^[1]; Carlson, Jr, H C ^[2]; Sandholt, P E ^[3]

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1. Rutherford Appleton Lab., Chilton (United Kingdom)
2. Phillips Lab., Bedford, MA (United States)
3. Univ. of Oslo (Norway)

The altitude from which transient 630-nm ({open_quotes}red line{close_quotes}) light is emitted in transient dayside auroral breakup events is discussed. Theoretically, the emissions should normally originate from approximately 250 to 550 km. Because the luminosity in dayside breakup events moves in a way that is consistent with newly opened field lines, they have been interpreted as the ionospheric signatures of transient reconnection at the dayside magnetopause. For this model the importance of these events for convection can be assessed from the rate of change of their area. From field line mapping, it is shown for both a westward and an eastward moving event, that the main 557.7-nm emission comes from the edge of a the 630 nm transient, where a flux transfer event model would place the upward field-aligned current (on the poleward and equatorward edge, respectively). The observing geometry for the two cases presented is such that this is true. From comparisons with the European incoherent scatter radar data for the westward (interplanetary magnetic field B{sub y} > 0) event on January 12, 1988, the 630-nm emission appears to emanate from an altitude of 250 km, and to be accompanied by some 557.7-nm `green-line` emission. However, for a large, eastward moving event observed on January 9, 1989, there is evidence that the emission altitude is considerably greater and, in this case, the only 557.7-nm emission is that on the equatorward edge of the event; consistent with a higher altitude 630-nm excitation source. The higher-emission altitude has a highly significant implication, namely that the reconnection bursts which cause the dayside breakup events could explain most of the voltage placed across the magnetosphere and polar cap by the solar wind flow. Analysis of the plasma density and temperatures during the event on January 9, 1989, predicts the required thermal excitation of significant 630-nm intensities at altitudes of 400-500 km. 49 refs., 9 figs., 3 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 86368
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A9 Vol. 98; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ALTITUDE
AURORAE
EARTH MAGNETOSPHERE
ELECTRIC FIELDS
EMISSION
MAGNETIC RECONNECTION
MAGNETOPAUSE
TRANSIENTS