GPS-derived ionospheric total electron content response to a solar flare that occurred on 14 July 2000

This paper studies the ionospheric response to an X5.7/3B solar flare that occurred at 10:03 UT on 14 July 2000. With Global Positioning System (GPS) observations, temporal evolution of the ionospheric total electron content (TEC) values was obtained within the latitude range of 30°N ∼ 45°N and the longitude range of 15°E ∼ 45°E. It was found that dayside TEC values were enhanced during the flare event, which could be as large as 5 TECU (1 TECU =10¹⁶ /m²) in regions with small solar zenith angles. The enhancement tended to depend on latitude, longitude and the solar zenith angle of the subionospheric point. However, the TEC enhancement derived from the latitude belt between 30°N and 45°N was not symmetrical about either the longitude or the local hour; it was smaller in the local morning than in the afternoon. The TEC enhancement in the Southern Hemisphere seems to be larger than that in the Northern Hemisphere for the same solar zenith angle. This implies that the background levels of the ionosphere and thermosphere had some influence on the TEC enhancement. The temporal variation of TEC shows minor correlative disturbances from 10:15 UT to 10:27 UT when the solar flare was in the maximum phase. It is likely that the minor disturbances resulted from the evolution of flare emission in the EUV domain.