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

The ionospheric scale height around the peak height of F2 layer （HmF2） is a very important parameter defining the profile of topside ionosphere. Based on observations of the EISCAT ESR radar, we statistically study the HmF2 at high latitudes. In order to derive the HmF2, a least square method is adopted to fit the electron density profile above the peak height of F2 layer （hmF2） from observations of the ESR radar. The result shows that it is in well agreement between the topside profiles deduced from the fitted HmF2 and the actual measuring topside profile with a height range from hmF2 to 300 km above the hmF2. Therefore, HmF2 can be considered as a constant in this range. With observations of the ESR between 1997 and 2008, we analyze the statistical characteristics of polar HmF2 with local time, season, and solar activity under quiet geomagnetic conditions （Kp≤2）, respectively. Variations of HmF2 in quiet days show a diurnal trend with a maximum in the morning and a minimum in the afternoon. The HmF2 always has the highest seasonal amplitude in summer under three kinds of solar activities. The seasonal magnitude of the HmF2 in winter remains between that in spring and that in autumn under low solar activity, while it is the lowest under moderate and high solar activities. We also compare measured HmF2 with those derived by IRI2007, which indicates that IRI2007 model can only approximately provide the average values of polar HmF2 in quiet days but is limited in presenting diurnal and solar activity variations of HmF2.