J. Aarons, M. Mendillo, and B. Lin

Center for Space Physics Boston University Boston, MA 02215



A magnetic storm which reached the Kp level of 9-, took place in the time period May 1-6, 1998. Phase fluctuation data from a variety of Global Positioning System sites were used to map the development of irregularities at both high and equatorial latitudes. At high latitudes, the storm from 2156 UT on May 1 to ~0300 UT on May 4 produced auroral irregularities. Within the storm time, the dominant parameter overall until May 4 was magnetic local time. The irregularities were probably produced from structured precipitation in both the E and lower F layers. At 03 UT on May 4 with the extremely large magnetic perturbation that brought Kp levels to 9- and 8+, strong intensity irregularities were observed simultaneously all across the auroral zone, even sites in daylight.

At equatorial latitudes, there was no clear indication of effects of the early storm. The only distinct effect was noted by the appearance of strong irregularities on May 4 when in the post midnight time period, the Eastern Pacific anomaly stations of Galapagos Island and Easter Island showed strong phase fluctuation activity. No other stations in South America, in Western Pacific longitudes or in African longitudes showed activity. The hypothesis is that the longitudinally narrow effect overcame shielding and succeeded in lifting the F layer in the post midnight time period for Galapagos and Easter Islands; the subsequent falling of the layer at the magnetic equator developed into a plume structure.