Statistical characteristics of the polar ionospheric scale height around the peak height of F2 layer with observations of the ESR radar: Disturbed days

In this paper, based on observations of the European Incoherent Scatter Svalbard Radar (ESR) between 1997 and 2008, we analyzed variations of HmF2, the ionospheric scale height around the peak height of F2 layer (hmF2) at high latitude with geomagnetic activities, as well as variations of the HmF2 with the local time (LT), season and solar activity under disturbed conditions (2 < Kp ≤ 5). We found that the HmF2 shows a significant increment with enhancements of geomagnetic activities. In addition, based on a linear regression, the correlation and fitting coefficients are shown, which quantitatively describe the correlations between polar HmF2 and geomagnetic activity index Kp. The HmF2 shows a diurnal variation with a maximum early in the morning and a minimum around noon in disturbed days (2 < Kp ≤ 5), which is more complex in comparison with that in quiet days. However, in summer and autumn, the HmF2 in disturbed days shows a bulge during 06:00-11:00 LT instead of the continuous decline under quiet condition. We consider that the ESR was under the cusp region during the period so that the bulge might be related to the high-energy particles precipitating into the ionosphere resulting in changes of the electron density profile. The HmF2 has the highest seasonal magnitude in summer and the lowest seasonal magnitude in winter generally. The seasonal magnitude of the HmF2 in autumn is lower than that in spring and larger than that in winter under low solar activity, while the HmF2 shows the same seasonal variations in spring and autumn under moderate and high solar activities.