Abstract
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)
Highlights
Ionization enhancements in the ionospheric F-region responding to magnetic storms are usually called positive ionospheric storms
Ma positive ionospheric storms at mid- and low-latitudes have been investigated extensively in recent decades (e.g. Rishbeth et al, 1987; Fuller-Rowell et al, 1990, 1994; Danilov & Berlik, 1992; Prolss, 1995; Mikhailov et al, 1995; Namgaladze et al, 2000; and references therein). The physics for this phenomenon involves F-region uplifting towards lower recombination loss regions by an enhanced equatorward neutral wind excited in the heated auroral region, the thermospheric composition changes of O/N2, and the electric field caused by the disturbance dynamo effect, etc
It is evident that enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow play an important role in the formation of polar-cap patches (e.g. Valladares et al, 1994; Walker et al, 1999; Smith, et al, 2000)
Summary
It is evident that enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow play an important role in the formation of polar-cap patches (e.g. Valladares et al, 1994; Walker et al, 1999; Smith, et al, 2000). Valladares et al, 1994; Walker et al, 1999; Smith, et al, 2000). It is evident that enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow play an important role in the formation of polar-cap patches Most of these observations, are not related to magnetic storms. During the magnetic storm of 15 May 1997, both the EISCAT radar 16.0◦ E) were in operation and caught the storm simultaneously during its main phase at the dayside sector. Ma et al: Positive storm effects in the dayside polar ionospheric F-region
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