Abstract
Abstract This study utilizes total electron content (TEC) observed by a network of ground-based GPS receivers located in the Western Pacific region (∼120°E) to study the responses of the low-latitude equatorial ionization anomaly (EIA) to the two major magnetic storms that occurred during April 4–10 and July 12–18, 2000. The latitude, time, and TEC (LTT) maps in the northern and southern EIA regions show that both EIA peaks move equatorward along with a pronounced reduction of the TEC values 10–12 h after the storm onset. The variations in the EIA peak TEC values and locations in the northern EIA are highly correlated with those in the southern EIA. The correlation coefficients of the day-to-day variations of peaked TEC between the northern and southern EIA regions are 0.75 in the April storm and 0.83 in the July storm. The correlation coefficients of the day-to-day EIA peak movements between the two hemispheres are 0.98 in the April storm event and 0.88 in the July storm event. The highly correlated peaked TEC and movements between the northern and the southern hemisphere suggest that the storm-produced electrodynamics played a dominant role in affecting the low-latitude ionosphere during the two major storms.
Highlights
During magnetic storms, the ionospheric electric field, neutral wind, and neutral composition have often been observed to deviate from their quiet time patterns (e.g. Fesen et al, 1989; Fejer and Scherliess, 1995; Prolss, 1995; Fuller-Rowell et al, 1997; Buonsanto, 1999; Kil et al, 2003; Lin et al, 2005a)
According to the empirical stormtime electric field model at the equatorial region built by Fejer and Scherliess (1995) and the recent theoretical model studied by Fuller-Rowell et al (2002), the storm-generated disturbance neutral winds can reach lower latitudes, producing the disturbance dynamo effects about 4–5 h or even shorter after the storm onset, depending on the amount of the energy deposition to the high latitude region
Both the background and storm-produced neutral wind and composition effects may both contribute to modify the morphology of the equatorial ionization anomaly (EIA), the strong correlations in peaked total electron content (TEC) variations and peak movements of the two hemispheres (Figs. 4 and 5) suggest that the electric field effect may be the major driver in producing the simultaneous EIA variations during the two storm events
Summary
The ionospheric electric field, neutral wind, and neutral composition have often been observed to deviate from their quiet time patterns (e.g. Fesen et al, 1989; Fejer and Scherliess, 1995; Prolss, 1995; Fuller-Rowell et al, 1997; Buonsanto, 1999; Kil et al, 2003; Lin et al, 2005a). These storm-generated disturbances in electric field, neutral wind, and neutral composition significantly affect the low-latitude ionosphere. Disturbances in the neutral composition a produce positive (increase in plasma density) or negative (decrease in plasma density)
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