E layer dominated ionosphere observed by EISCAT/ESR radars during solar minimum

Abstract

Abstract. According to the study by Mayer and Jakowski (2009), periods of E layer dominated ionosphere (ELDI) are defined as being characterized by vertical electron density profiles having a maximum density at E layer altitudes. In this paper, characteristics of ELDI intervals have been investigated, focusing on their temporal variations, using field-aligned measurements from the EIS-CAT and ESR radars during the interval 2009-2011. ELDI events were identified using simple but reasonable criteria, in which a minimal duration was required to exclude possible "fake" events induced by random errors in measurements. It was found that ELDIs were observed more often in winter and earlier spring than other seasons, especially in the auroral zone. The occurrence of ELDI intervals peaks around geomagnetic midnight at auroral latitudes, while it reaches a maximum around geomagnetic local noon at the latitude of the ESR. Our results imply that ELDI intervals appear to be a sporadic rather than a regular phenomenon, in disagreement with previous results inferred from radio occultation measurements. The discrepancy between the typical durations of ELDI events observed by the two radars is remarkable, being 30 min on average at Tromsø but about a half of this at Svalbard. During intervals of ELDI, the mean thicknesses of the E layer are quite close at the two sites, as are the values of H m E and the ratio of N m E / N m F 2 . Case studies confirm that either extra E layer ionization or F layer density depletion alone could lead to the presence of ELDIs. Based on a careful check on ELDI intervals of various types, however, we suggest that both of them play a critical role in ELDI formation.

Evaluation of E Layer Dominated Ionosphere Events Using COSMIC/FORMOSAT-3 and CHAMP Ionospheric Radio Occultation Data

“…The plots show a maximum of %ELDI in local winter and a minimum in local summer. This result fits the findings of Cai et al [6], who have found out from the analysis of incoherent scatter radar data that more ELDI events emerged in winter and early spring for both the EISCAT and the ESR site.…”

“…The plots reveal that in all cases %ELDI reaches its maximum around local night and its minimum around local noon. This result confirms the findings of Mayer and Jakowski [4], who have also observed an increase in ELDI occurrence during nighttime for the entire northern high latitude region, while Cai et al [6] have found a similar trend for the EISCAT site. Especially for the COSMIC mission, due to the large amount of profiles, our plots are smoothed out and show a clearly sinusoidal trend over the course of a day.…”

“…The influence of the 11 year solar cycle on the occurrence of ELDI events, which was selectively examined by Mayer and Jakowski [4] for four winter seasons, is suitable for such a continuous analysis. The investigations of Mayer and Jakowski [4] and Cai et al [6] have shown a diurnal variation of the number of ELDI events. Furthermore, Cai et al [6] have found a seasonal variation of ELDI occurrence, with more events emerging in winter and early spring.…”

“…The investigations of Mayer and Jakowski [4] and Cai et al [6] have shown a diurnal variation of the number of ELDI events. Furthermore, Cai et al [6] have found a seasonal variation of ELDI occurrence, with more events emerging in winter and early spring. By evaluating IRO data for the entire high latitude regions of both hemispheres, we would like to confirm the diurnal and the seasonal variation of ELDI events and put their analysis on a broader basis.…”

“…Cai et al [6] studied the diurnal and seasonal variations of ELDI occurrences and their durations. For this purpose, they evaluated electron density profiles which were generated from incoherent scatter radar observations.…”