Variation of the Hemispheric Asymmetry of the Equatorial Ionization Anomaly with Solar Cycle

• Published in: Journal of astronomy and space sciences Vol. 36; no. 3; pp. 159 - 168
• Main Authors: Kwak, Young-Sil, Kil, Hyosub, Lee, Woo Kyoung, Yang, Tae-Yong
• Format: Journal Article
• Language: English
• Published: The Korean Space Science Society 01-09-2019; 한국우주과학회
• Subjects: equatorial ionization anomaly; hemispheric asymmetry; solar cycle; 천문학
• ISSN: 2093-5587; 2093-1409
• DOI: 10.5140/JASS.2019.36.3.159

In solstices during the solar minimum, the hemispheric difference of the
equatorial ionization anomaly (EIA) intensity (hereafter hemispheric asymmetry) is
understood as being opposite in the morning and afternoon. This phenomenon is explained
by the temporal variation of the combined effects of the fountain process and
interhemispheric wind. However, the mechanism applied to the observations during the
solar minimum has not yet been validated with observations made during other periods of
the solar cycle. We investigate the variability of the hemispheric asymmetry with local
time (LT), altitude, season, and solar cycle using the electron density taken by the
CHAllenging Minisatellite Payload satellite and the global total electron content (TEC)
maps acquired during 2001–2008. The electron density profiles provided by the
Constellation Observing System for Meteorology, Ionosphere, and Climate satellites
during 2007–2008 are also used to investigate the variation of the hemispheric asymmetry
with altitude during the solar minimum. During the solar minimum, the location of a
stronger EIA moves from the winter hemisphere to the summer hemisphere around 1200–1400
LT. The reversal of the hemispheric asymmetry is more clearly visible in the F-peak
density than in TEC or in topside plasma density. During the solar maximum, the EIA in
the winter hemisphere is stronger than that in the summer hemisphere in both the morning
and afternoon. When the location of a stronger EIA in the afternoon is viewed as a
function of the year, the transition from the winter hemisphere to the summer hemisphere
occurs near 2004 (yearly average F10.7 index = 106). We discuss the mechanisms that
cause the variation of the hemispheric asymmetry with LT and solar cycle.