Ionospheric manifestations of the magnetic storm on May 15-16, 1997, in different longitudinal sectors of the Northern Hemisphere

The effects of the May 15-16, 1997, magnetic storm in the midlatitude and low-latitude ionosphere of the Northern Hemisphere have been studied. The observations at three chains of stations extended approximately along the 20degrees, 140degrees, and 280degrees E meridians in the 13degrees-65degrees N range of geomagnetic latitudes have been used. Zonal electric fields have been estimated. An analysis provided the following results. Durable intense negative disturbances during the growth and recovery phases of the storm were observed at all stations. Before the storm, positive disturbances were observed at all stations of the European and American chains regardless of local time. The positive peak in DeltafoF2 during the storm growth phase ("the dusk effect") was seen only at the Asiatic chain of stations in evening hours. The strongest response to the storm in the F region was registered at the Asiatic chain where the difference between the geographical and magnetic poles is maximum. The obtained differences in the DeltafoF2 variations could be caused by the local time of the sudden storm commencement and by the magnetic dip.