Earth Planets Space, Vol. 52 (No. 11), pp. 1073-1076, 2000LETTER
A. Yamamoto1, Y. Ohta2, T. Okuzawa2, S. Taguchi2, I. Tomizawa3, and T. Shibata2
1Japan Coast Guard Academy, Kure, Hiroshima 737-8512, Japan
2Department of Information and Communication Engineering, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
3Sugadaira Space Radio Observatory, University of Electro-Communications, Sugadaira, Nagano 386-2200, Japan
(Received January 14, 2000; Revised May 31, 2000; Accepted August 25, 2000)
Abstract: Since the middle of 1996, we have made a routine observation of TEC using GPS in Chofu (35.65°N, 139.54°E), Tokyo. We examine in this paper the relationship between the perturbation components of TEC and geomagnetic field variations during 11 storm events for 1997-1998 to clarify the mid-latitude characteristics of TEC variations at the time of magnetic storms. The perturbation components of TEC were derived every 20 seconds by subtracting quiet-time TEC values which are estimated as the average of both 3 days just before and after the storm period. The magnetic field data from Memambetsu Magnetic Observatory (45.92°N, 144.20°E) are used for the identification of the storm-time variations. Our results show that (1) the amplitude level of the TEC variation tends to increase during the first 24 hr of storm and then decrease below its usual-day level with recovery in one or two days later for the typical magnetic storm, and (2) during a negative-value phase of the TEC variation, which follows the initial positive hump structure, the perturbation amplitude of TEC shows a remarkable reduction in summer compared to in winter.