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Ann. Geophys., 25, 929-940, 2007
www.ann-geophys.net/25/929/2007/
© European Geosciences Union 2007
Changes of dayside auroral distribution caused by a solar wind pressure pulse and associated interplanetary magnetic field disturbances
A. Kozlovsky1, M. Meurant2,3, and T. Turunen1
1Sodankylä Geophysical Observatory, Sodankylä, Finland
2Institute for Space Research, University of Calgary, Calgary, Canada
3Institut d'Astrophysique et de Géophysique, Université de Liège, Liège, Belgium
Abstract. Global auroral images from the IMAGE satellite were used to study
statistically changes of the dayside aurora spatial distribution after an
abrupt solar wind pressure increase, or so-called "Sudden Impulse" (SI).
Contributions from IMF changes associated with a SI were also investigated.
The effects of the IMF and pressure variations were separated using a
multi-factor correlation analysis. The first prominent effect due to
pressure increase is the auroral intensification equatorward of the middle
dayside oval within 6 min after a SI occurred. This is consistent with the
midday sub-auroral patches. The second effect due to pressure increase is
the auroral intensification at high latitudes in the vicinity of the polar
cap boundary. For the first 6 min the auroral intensification is most
prominent in the postnoon sector. Later on (6–20 min) the intensification
occurs in the prenoon sector. The most obvious effect of IMF changes is the
"IMF By" effect, an intensification (fading) of the most poleward auroral
forms when IMF By becomes negative (positive). This effect occurs 6–20 min
after changes in the interplanetary medium. Such an effect is consistent
with the IMF By-related system of field-aligned currents. No significant
motion of the dayside auroral oval was observed associated with IMF Bz
variations. This can be explained by a response time to IMF Bz changes
larger than 20 min.
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