Abstract
Using a new technology for global GPS detection of ionospheric disturbances, GLOBDET, it has been established that a drastic increase in the time derivative of the magnetic field strength during magnetic storms is accompanied by an almost simultaneous decrease in mid-latitude total electron content on the entire dayside. The corresponding correlation coefficient is not below -0.8; the delay with respect to the time of a magnetic storm sudden commencement is about 3-10 min. This is most pronounced for magnetic storms with a well-marked sudden storm commencement. The sudden storm commencements presented in the paper were observed during the initial storm phase. The analysis reported here was made for a set of from 90 to 300 GPS stations for 10 days in 1998-2001 with a different level of geomagnetic activity (Dst from -6 nT to -295 nT, and K p from 0 to 9). The «simultaneous» total electron content response for the events under consideration was 0.1-0.4 TECU, and the travel velocity of the disturbance from the dayside to the nightside was in the order of 10-20 km/s. Results obtained are consistent with earlier ionospheric parameter measurements obtained using high temporal resolution methods.
Highlights
The ionospheric response to a Sudden Storm Commencement (SSC) should be set off from the large number of phenomena observed during different phases of magnetospheric stormDistinctive decreases in maximum ionization (Nm) and in ionization at fixed levels (Nh) after SSC were observed for a strong magnetic storm of July 11-19, 1959 (Potapova and Shapiro, 1961)
Using the new technology for global GPS detection of ionospheric disturbances, GLOBDET, it has been ascertained that a drastic increase in the time derivative of the magnetic field strength at the time of magnetic storms is accompanied by an almost simultaneous decrease of the mid-latitude Total Electron Content (TEC) throughout the dayside
The corresponding correlation coefficient is not below – 0.8; the delay with respect to the time of the sudden magnetic storm commencement is about 3-10 min
Summary
The ionospheric response to a Sudden Storm Commencement (SSC) should be set off from the large number of phenomena observed during different phases of magnetospheric storm. Some publications (Huang and Cheng, 1991; Buonsanto, 1995) contain estimates of variations of ionospheric parameters after SSC made on the basis of data from Incoherent Scatter Stations (ISS) and by determining the value of the Total Electron Content (TEC) from Faraday effect measurements of the signal from geostationary satellites (GOES2, GOES7). A global spatial averaging of TEC variation, obtained using data from the international GPS network, seems to have been used for the first time by Afraimovich et al (2000a) in investigating the global ionospheric response to SSC. An «instantaneous» ionospheric response to a sudden commencement, SSC, of a strong magnetic storm of April 6, 2000 was detected; it appeared as a single negative TEC disturbance with a duration of about 20 min, with about 200s delay with respect to the SSC at mid-latitudes, almost simultaneously on the entire dayside. Where Rz is Earth’s radius; and hmax is the height of the ionospheric F2-layer maximum
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