Abstract
Abstract. Using 8-year global ionosphere maps (GIMs) of TEC products from the Jet Propulsion Laboratory (JPL), we make a statistical study on the morphology of the global ionospheric behaviors with respect to the geomagnetic disturbances. Results show that the behaviors of TEC during geomagnetic storm present clear seasonal and local time variations under geomagnetic control in a similar way as those of NmF2 (Field and Rishbeth, 1997). A negative phase of TEC occurs with high probability in the summer hemisphere and most prominent near the geomagnetic poles, while a positive phase is obvious in the winter hemisphere and in the far pole region. A negative storm effect toward lower latitudes tends to occur from post-midnight to the morning sector and recedes to high latitude in the afternoon. A positive storm effect is separated by geomagnetic latitudes and magnetic local time. Furthermore, ionospheric responses at different local time sectors with respect to the storm commencement shows very different developing processes corresponding to the evolution of the geomagnetic storm. A daytime positive storm effect is shown to be more prominent in the American region than those in the Asian and European regions, which may suggest a longitudinal effect of the ionospheric storm.
Highlights
Geomagnetic storm can induce strong disturbances in the Fregion of the ionosphere
Seasonal variations of an F-region storm have long been accepted to be caused by the change in [O/N2] that is associated with large-scale storm wind surges superimposed on the normal summer-to-winter thermospheric circulation (Duncan, 1969)
The total electron content (TEC) storm resembles the seasonal feature of NmF2, which shows that a negative phase occurs with high probability in the summer hemisphere and a positive phase is shown to be more prominent in the winter hemisphere
Summary
Geomagnetic storm can induce strong disturbances in the Fregion of the ionosphere. These perturbations involve large enhancements and depletions of the electron density at the F2 region during periods termed as positive and negative ionospheric storm phases, respectively. Field and Rishbeth (1997) applied the AC/DC analysis technique of Rodger et al (1989), which separates the NmF2 storm changes ln(NmF2storm/NmF2quiet) into a mean (DC) component and a local time component (AC), to over 20 years worth of data from each of the 53 stations between 70◦ N and 80◦ S. GIMs have increasingly become a powerful ionospheric diagnostic tool in studies of ionospheric behavior, under disturbed conditions (Ho et al, 1996; Pi et al, 1997; Buonsanto et al, 1999; Aponte et al, 2000; Afraimovich et al, 2002; Vlasov et al, 2003; Kil et al, 2003) These studies show numerous positive and negative storm features which have been observed in NmF2, including auroral/subauroral enhancements, dayside mid-latitude enhancements, TID/TAD, latitudinal structures, negative phase depletions, and intensified equatorial “fountain” effects, and so on. Results show that the ionospheric response in the different local time sectors and different longitudes displays a very different developing process, corresponding to the evolution of the magnetic storm
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