Transition of Interhemispheric Asymmetry of Equatorial Ionization Anomaly During Solstices

Abstract

The magnitudes of the two crests of equatorial ionization anomaly (EIA) vary with local time. During the solstices, EIA crest in the winter hemisphere is larger than that in the summer hemisphere before noon/early afternoon. Whereafter, the crest in the summer hemisphere becomes intensified, and the stronger EIA crest transits to the summer hemisphere. Using Constellation Observing System for Meteorology, Ionosphere, and Climate ionospheric radio occultation data, we examine the longitudinal and altitudinal variations of this interhemispheric transition in four longitudinal sectors and at seven heights under low/high solar activity conditions. The results show that during the June solstice the transition of the stronger EIA peak from the winter to the summer hemisphere is earlier in the sectors where the geomagnetic equator is further away from the subsolar point and the geomagnetic field declination is larger, while during the December solstice the longitudinal variations generally show the opposite compared with that in the June solstice. The distance between the geomagnetic equator and subsolar point and the geomagnetic field configuration control the upward/downward plasma movements in the summer/winter hemisphere, leading to the different transition times in different longitudinal sectors. For both solstices, transition times emerge earlier as height increases, which is mainly caused by the larger effective scale height in the summer hemisphere than in the winter hemisphere, resulting in a smaller electron density difference at higher altitudes with a fast transition. Solar activity alters the transition time below 320 km, whereas it has no evident effect at higher altitudes.

Observation of Postsunset OI 135.6 nm Radiance Enhancement Over South America by the GOLD Mission

“…The asymmetry of EIA structures has been studied for decades by using data from multiple ionosondes (Thomas, 1968), TEC maps (Khadka et al, 2018;Rama Rao et al, 2006;M. L. Zhang et al, 2009;Zhao et al, 2009) and LEO satellites (Balan et al, 2013;Basu et al, 2009;Henderson et al, 2005;Huang et al, 2018;Kil et al, 2006;Lin et al, 2007;Luan et al, 2015;McDonald et al, 2008;Tallat et al, 2013;Tulasi Ram et al, 2009;Zeng et al, 2008). Zeng et al (2008) found that the hemispherically asymmetric magnetic field was the most important factor to generate the EIA annual asymmetry.…”

Conjugate Ionospheric Perturbation During the 2017 Solar Eclipse

“…The southern EIA crest is usually weaker in the afternoon and is asymmetric to the northern one in this season (Huang et al., 2018; Luan et al., 2015). This asymmetric behavior was visible also during the eclipse as described earlier, and therefore the eclipse observation agrees with some of the expected EIA climatology for this season.…”

A Global Empirical Model of Electron Density Profile in the F Region Ionosphere Basing on COSMIC Measurements

“…A stronger crest first presents in the winter hemisphere and would transit to the summer hemisphere at noon/afternoon local times during solstices. Huang et al (2018) reported that the transition time of EIA displays evident seasonal and longitudinal dependences. They found that the transition time is earlier in December than the June solstice, and it performs opposite longitudinal variation during two solstices based on COSMIC observation.…”