Simultaneous response of the mid-latitude ionosphere to a sudden commencement of strong magnetic storms

Using the new technology of global GPS detection of ionospheric disturbances (GLOBDET), it is found that a sharp increase of the time derivative of the magnetic field strength during magnetic storms is accompanied by a simultaneous decrease of the mid-latitude total electron content (TEC) over the entire day-side of the globe. The corresponding negative correlation coefficient is no less than 0.8, and the delay relative to the sudden commencement of magnetic storm is about 3-10 min. The effect is especially clearly pronounced for magnetic storms with sudden commencements (SSC). The analysis is carried out for a set of 90 to 300 GPS stations for 10 days (January 6 and April 23, 1998; April 6, June 8, July 13, 14, and 15, 2000; March 31, April 4 and 11, 2001) with various levels of geomagnetic activity (D-SI and K-P varied from -6 to -295 nT and from 0 to 9, respectively). The amplitude of the response in the total electron content for the events considered was 0.1-0.4 x 10(16) m(-2) (which is a deviation of 0.2-2.6% from the TEC background value). The velocity of the disturbance motion from the dayside to the nightside was about 10-20 km/s. The results obtained agree with the data of ionospheric parameter measurements conducted earlier by methods with high temporal resolution.