Abstract:

This study investigated the characteristics of polar E-Layer Dominated Ionosphere (ELDI) events under various solar activities, based on field-aligned measurements from the EISCAT (EISCAT Tromsø UHF) and ESR (EISCAT Svalbard Radar) instruments during 1999–2011. It was found that ELDI occurrences exhibit clear reliance on solar activity. During solar maximum, ELDI events appear more frequently at the EISCAT site (at the auroral latitude) than at the ESR site (at cusp latitude), and vice versa during solar minimum. ELDI events are rarely observed by both radars in summer, which illustrates few effects of solar activity. Seasonal variations of ELDI occurrences at both sites during solar maximum are in accordance with those during solar minimum., i.e., ELDI occurrences are higher in winter and early spring than in other seasons, especially summer. On the occurrence of ELDI events, the duration of the event and the thickness of the ionospheric E-layer show remarkable variations under different solar activity conditions: the duration is shorter and the thickness is greater during solar maximum, while N_mE/N_mF₂ and H_mE appear less variable.

Key words: polar region, E-Layer Dominated Ionosphere, solar activity, incoherent scatter radar