Mid-latitude effects of the May 15, 1997 magnetic storm

We investigate the May 15, 1997 magnetic storm effects on the mid- and low-latitude ionosphere. The study is based on using the data from three chains of ionospheric stations located approximately along the meridians 20degrees, 140degrees and 280degreesE in the geomagnetic latitude range 13-65degreesN. Variations in f(0)F2 are considered. Estimates of the zonal electric fields are made. Results of our analysis show that the main ionospheric effects of the storm under consideration are: ( I) long-lasting intense negative disturbances during the storm main and recovery phases at subauroral and mid-latitudes; (2) positive disturbances at stations of the European and American chains observed prior to the storm, regardless of the local time; (3) a positive peak of Deltaf(0)F2 at stations of the Asian chain during the storm main phase in the evening hours; (4) a similarity of the form of the Deltaf(0)F2-variations at different latitudes and (5) the largest effect on the F region is observed at the Asian chain. The resulting differences of the Deltaf(0)F2-variations can be driven both by the local time of the sudden storm commencement and by magnetic dip. It is not mere chance that the largest differences are observed along the meridian 140degreesE where the difference between the geographic and magnetic poles is the largest. (C) 2002 Elsevier Science Ltd. All rights reserved.