Morphological Differences of the Northern Equatorial Ionization Anomaly Between the Eastern Asian and American Sectors

Abstract

The morphological difference of the northern equatorial ionization anomaly between the eastern Asian and American sectors is statistically studied with ground-based total electron content data from 2000 to 2011. The intensity (Ic), latitudinal location (Lc), and occurrence time (Tc) of the daytime equatorial ionization anomaly crest are derived from daytime peak total electron content in time-latitude plots. The main results are as follows. Lc in the two sectors exhibits an apparent difference, especially in solar minimum, during which Lc in the American sector shows an annual variation that is more poleward in northern summer and more equatorward in northern winter, while Lc in the eastern Asian sector shows a semiannual variation that is more poleward around equinoxes and more equatorward around solstices. Ic tends to be stronger in the eastern Asian sector than that in the American sector in all seasons, and this difference increases with the increase of the solar flux index. Tc tends to be earlier in northern winter and later in northern summer in both sectors and shows dependence on solar activity. We demonstrate that the seasonal variation of Lc in the American sector is not dominated by the ionospheric equatorial zonal electric field, and suggest that the difference of Lc between the two sectors is probably related to different meridional wind effects due to the displacement of geographic and magnetic equators. The Ic difference is probably related to the longitudinal wave number-3 and -4 structures driven by tidal forcing from the 5lower atmosphere.

The Latitudinal Variation and Hemispheric Asymmetry of the Ionospheric Lunitidal Signatures in the American Sector During Major Sudden Stratospheric Warming Events

“…These modeling results were supported by the statistical study by Liu, Zhang, Mo, et al. (2020), which revealed that the northern EIA crest in the American sector tends to approach (deviate from) the geomagnetic equator in the Northern Hemispheric winter (summer). The hemispheric asymmetry of the PSSD perturbations in the low latitude in our result is consistent with the hemispheric asymmetry in the EIA crest location evolution.…”

“…Simulation studies provided evidence that such a northward transequatorial wind tends to induce a dual-crest structure of EIA whose northern crest is closer to the geomagnetic equator than the southern one (Abdu, 2005;Nanan et al, 2012). These modeling results were supported by the statistical study by Liu, Zhang, Mo, et al (2020), which revealed that the northern EIA crest in the American sector tends to approach (deviate from) the geomagnetic equator in the Northern Hemispheric winter (summer). The hemispheric asymmetry of the PSSD perturbations in the low latitude in our result is consistent with the hemispheric asymmetry in the EIA crest location evolution.…”

Latitudinal and interhemispheric differences of the ionospheric semi-diurnal lunitidal perturbations during the 2009 Arctic sudden stratospheric warming event in the eastern Asia–Australia sector

“…The eastern Asia-Australia sector also has groundbased ionospheric observation network across both hemispheres with relatively good resolutions. The geomagnetic field configuration, atmospheric waves activities, and the background ionospheric features in the eastern Asia-Australia sector significantly differs from those in the American sector (Liu et al, 2020). The 2009 SSW is one of the strongest SSW events in record with quiet solar and geomagnetic activities (Manney et al, 2009;Yamazaki et al, 2020, and reference therein), which benefits the analysis of the lower-atmosphere influence to the ionosphere during the SSW.…”

Six‐Day Periodic Variation in Equatorial Ionization Anomaly Region

“…Moreover, the EIA crests derived from CHAMP measurement (the electron density data obtained from the CHAMP Planar Langmuir Probe observation) are used for comparison with that from GPS observation. Since the CHAMP satellite has the nearly circular and polar orbit at approximately 400-km altitude with inclination of 87° (Reigber et al, 2002), its trajectory will meridionally pass through the EIA crest region, and the latitude corresponding to maximum electron density value can be used to locate EIA crest (Liu et al, 2020). There are distinct difference of EIA crest between the eastern Asian and American longitudinal sectors due to the difference in the displacement between the geographical equator and dip equator (Liu et al, 2020), so the daily average EIA crest at 0-180°E every day is used to describe the variation in northern and southern EIA region.…”

“…Since the CHAMP satellite has the nearly circular and polar orbit at approximately 400-km altitude with inclination of 87° (Reigber et al, 2002), its trajectory will meridionally pass through the EIA crest region, and the latitude corresponding to maximum electron density value can be used to locate EIA crest (Liu et al, 2020). There are distinct difference of EIA crest between the eastern Asian and American longitudinal sectors due to the difference in the displacement between the geographical equator and dip equator (Liu et al, 2020), so the daily average EIA crest at 0-180°E every day is used to describe the variation in northern and southern EIA region. It should be noted that the local time of each satellite trajectory passing through the EIA crest changes day by day; the EIA crests measured by CHAMP are not the daily most developed EIA crest.…”