Abstract:

With EISCAT-Svalbard Radar observations from March,1999 to February,2003,a statistical analysis is made on the electron density variations in different seasons around solar maximum to in- vestigate the characteristics of background ionosphere at polar cusp latitudes.It is found that the so- called “winter anomaly”does not exist in the concerned area and for the first time,a major maxi- mum of electron density is found before local magnetic midnight in winter over ESR site.Besides, there always exists a maximum of electron density around local magnetic noon during daytime in all three seasons.The ESR observation results are compared with the IRI-2001 model,showing signifi- cant distinctions,especially in topside ionosphere above 500 km altitude and winter season.The importance of soft particle precipitation on the formation of the electron density maximum at local magnetic noon is discussed briefly,along with the mechanism of the pre-magnetic-midnight major peak in the winter.