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Ann. Geophys., 20, 1377-1384, 2002
www.ann-geophys.net/20/1377/2002/
© European Geosciences Union 2002
Positive storm effects in the dayside polar ionospheric F-region observed by EISCAT and ESR during the magnetic storm of 15 May 1997
S. Y. Ma1, H. T. Cai1, H. X. Liu2, K. Schlegel3, and G. Lu2
1Dept. of Space Physics, College of Electronic Information, Wuhan University, Wuhan 430072, P. R. China
2High Altitude Observatory, National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301, USA
3Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany
Correspondence to: S. Y. Ma (syma@whu.edu.cn)
Abstract. EISCAT/ESR radar data and
in situ FAST and POLAR satellite observations are coordinately analyzed to
investigate positive ionospheric storm effects in the dayside upper F-region in
both the polar cap and the auroral oval during the magnetic storm of 15 May
1997. An ionization enhancement, lasting for about 2.5 h, appeared first over
the EISCAT site around magnetic noon; about one hour later, a similar
ionization enhancement was also seen over ESR. During the concerned time period
ion energy spectra measured on board FAST show clearly continuous
energy-latitude dispersion when the satellite passed by over the EISCAT
latitude. This implies that EISCAT was located under the polar cusp region
which was highly active, and expanded greatly equatorwards due to magnetopause
reconnections during long-lasting southward IMF. Simultaneously, soft particles
of the magnetosheath precipitated into the F-region ionosphere and caused the
positive storm effects over EISCAT. The coincident increase in electron
temperature at EISCAT gives additional evidence for soft particle
precipitation. Consistently, POLAR UV images show strong dayside aurora
extending to as low as 62° N magnetic latitude. The ionization enhancement
over ESR, however, seems not to be caused by local particle precipitation,
evidenced by a lack of enhanced electron temperature. The observed plasma
convection velocity and data-fitted convection patterns by AMIE suggested that
it is likely to be a polar patch originating from the cusp region and traveling
to the ESR site.
Key words. Ionosphere (auroral
ionosphere; particle percipitation) Magnetospheric physics (storms and
substorms)
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