Nighttime enhancements in ionospheric electron content: seasonal and solar cycle variation

Abstract

Abstract. Various characteristics of anomalous nighttime enhancement in ionospheric electron content (IEC) at Lunping (14.08°N geomagnetic), a station near the crest of the equatorial anomaly, have been presented by considering the IEC data for the 21st solar cycle. Out of a total of 1053 enhancements, 354 occur in pre-midnight and 699 occur in post-midnight hours, which indicates an overall dominance of post-midnight events at Lunping. The occurrence is more frequent during summer, less during the equinox and least during winter months. All the characteristics of the enhancements have seasonal dependencies and they reach their maximum values during summer months. The occurrence of the pre-midnight events show positive and post-midnight events show negative correlation with solar activity. The results have been discussed and compared with those at low-latitude stations in India and Hawaii and at the mid-latitude station, Tokyo.

Nighttime enhancements in TEC near the crest of northern equatorial ionization anomaly during low solar activity period

“…The characteristics of the TEC enhancements are in general agreement with those reported by Chen et al [11] at the crest of the northern equatorial anomaly region in China except for occurrence of TEC enhancement in summer season. Our result of solar activity effect on percentage occurrence and peak amplitude are similar to the results of Jain et al [4,6]. Our result shows that the percentage occurrence of nighttime TEC enhancement decreases as the magnetic activity increases, similar to the results of Watanabe and Oya [19].…”

“…Peak amplitude shows strong dependence on solar activity and observed maximum during summer months (r = 0.91) whereas the percentage occurrence does not show any significant dependence on solar activity. Our result of solar activity effect on percentage occurrence and peak amplitude supported with the result of Jain et al [4,6].…”

“…Occurrence and other characteristics of the nighttime TEC enhancements in equatorial and low latitude have been also studied by several authors [3][4][5][6][7][8][9][10][11]. Near the crest of Equatorial Ionization Anomaly (EIA) region the nighttime enhancement occurs during both pre-midnight and post-midnight hours [4,11] and different mechanisms have been given for different latitude regions.…”

“…Occurrence and other characteristics of the nighttime TEC enhancements in equatorial and low latitude have been also studied by several authors [3][4][5][6][7][8][9][10][11]. Near the crest of Equatorial Ionization Anomaly (EIA) region the nighttime enhancement occurs during both pre-midnight and post-midnight hours [4,11] and different mechanisms have been given for different latitude regions. The strong pre-midnight enhancements are caused mainly by the prereversal increase of the equatorial fountain at low latitudes [12]; the downward flow of plasma from the protonosphere to the ionosphere for mid latitudes [13], corpuscular ionization and movement of the mid-latitude trough for high latitude [14,15].…”

“…Nighttime enhancement in ionospheric total electron content (TEC) is a well known equatorial, low and middle latitude phenomenon and has been studied by many groups under the wide range of geophysical conditions [1][2][3][4][5][6]. Occurrence and other characteristics of the nighttime TEC enhancements in equatorial and low latitude have been also studied by several authors [3][4][5][6][7][8][9][10][11].…”