[1] On the basis of ionospheric total electron content (TEC) enhancement over the subsolar region during flares, and combined with data of the peak X-ray flux in the 0.1-0.8 nm region, EUV increase in the 0.1-50 and 26-34 nm regions observed by the SOHO Solar EUV Monitor EUV detector, also with the flare location on the solar disc, the relationship among these parameters is analyzed statistically. Results show that the correlation between ionospheric TEC enhancement and the soft X-ray peak flux in the 0.1-0.8 nm region is poor, and the flare location on the solar disc is one noticeable factor for the impact strength of the ionospheric TEC during solar flares. Statistics indicate clearly that, at the same X-ray class, the flares near the solar disc center have much larger effects on the ionospheric TEC than those near the solar limb region. For the EUV band, although TEC enhancements and EUV flux increases in both the 0.1-50 and 26-34 nm regions have a positive relation, the flux increase in the 26-34 nm region during flares is more correlative with TEC enhancements. Considering the possible connection between the flare location on the solar disc and the solar atmospheric absorption to the EUV irradiation, an Earth zenith angle is introduced, and an empirical formula describing the relationship of TEC enhancement and traditional flare parameters, including flare X-ray peak and flare location information, is given. In addition, the X-ray class of the flare occurring on 4 November 2003, which led the saturation of the X-ray detector on GOES 12, is estimated using this empirical formula, and the estimated class is X44.

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.

Using the ionospheric total electron content (TEC) and the location of the equatorial ionization anomaly (EIA) crest derived from GPS data observed at Nanning (22.84°N, 108.33°E, dip latitude ~ 12.14°N), China, a GPS station situated near the daytime EIA crest region, the local time, seasonal, and solar cycle variations of EIA crests from 2006 to 2015 was investigated. The TEC and the magnetic latitude (MLAT) location of EIA crest experience an ascendant and descendant process with the daytime evolution of EIA crest. Also, this diurnal variation of EIA crest depends on season and solar cycle. The TEC and MLAT location of EIA crest is stronger and higher in equinoctial months than that in solistial months showing a semiannual variation. The TEC and MLAT location of EIA crest increase with the solar activity. The local time, seasonal, and solar cycle variations of EIA crest is consistent with that of the strength of equatorial electrojet (EEJ). Comparatively, the correlation of the EEJ strength with the EIA location is better than that with the TEC of EIA crest.

Abstract. Based on the daytime location of the equatorial ionization anomaly (EIA) crest derived from GPS observations at low latitude over China during the 2005-2006 stratospheric sudden warming (SSW), a quasi-16-day periodic meridional movement of EIA crest with the maximum amplitude of about 2 degrees relative to the average location of EIA crest has been revealed. In addition, periodic variations that are in phase with the meridional EIA movement are also revealed in the equatorial electrojet (EEJ) and F2 layer peak height (hmF2) over Chinese ionosonde stations Haikou and Chongqing. The quasi-16-day periodic component in Dst index is weak, and the 16-day periodic component does not exist in F10.7 index. Such large-scale periodic meridional movement of EIA crest is likely related to the globally enhanced stratospheric planetary waves coupled with anomalous stratospheric zonal wind connected with SSW. In addition, such large-scale periodic movement of EIA should be global, and can affect the ionospheric morphology around the low-latitude belt near the EIA region. Further case analysis, simulation and theoretical studies must proceed in order to understand the periodic movements of EIA connected with the different periodic atmospheric variations.