SM41A-04 0830h POSTER

Interplanetary Features of May 2-7, 1998, and Aspects of Their Effects on the Magnetosphere


C. Cocheci1
C. Farrugia1 (farrugia@monet.sr.unh.edu); V. Jordanova1; R. Arnoldy1; L F Burlaga2; K. Ogilvie 2; R. Lepping2; J. Scudder3; M. Freeman4; M. Thomsen5; G. Reeves5; G. Rostoker6

1University of New Hampshire, Durham, NH 03824, United States
2NASA/Goddard Space Flight Center, Greenbelt, MD 20771, United States
3University of Iowa, Iowa City, IA 52240, United States
4British Antartic Survey, Cambridge, CB3 OET, United Kingdom
5Los Alamos National Laboratory, Los Alamos, NM 87545, United States
6University of Alberta, Edmonton,
   AB T6G 2JI, Canada



When the corotating stream on May 4, 1998, reached Earth, an unprecedentedly high and short-lived powering of the magnetosphere took place. Three episodes of this stream were observed by WIND at a separation of about 25 days two of which were fairly innocuous, causing, e.g., weak ring current enhancements and moderate and short-lived Kp activity. The May 4 edition, however, caused the largest geomagnetic storm seen in the last 4 years (Dst less than -200 nT) and a Kp index which peaked at 8. On May 4, the leading edge of the stream reached 900 km/s, compared to 650 km/s and 550 km/s in its two later apparitions on May 29 and June 24. Behind the stream, the interplanetary magnetic field increased to 40 nT and the GSM By and Bz components were -25 nT and -30 nT, respectively. The electromagnetic energy deposited into the magnetosphere in just 2.5 hours was 7.2 mJ/m which may be compared with that deposited during 2 days when the magnetic cloud of October 1995 (itself the strongest event during the last solar minimum), and its trailing corotating stream passed Earth (5.0 mJ/m2). The May 4, 1998 stream may have interacted with a solar ejecta preceding it. This ejecta, gave rise to 2 days of average Dst of-100 nT and a sustained Kp index of ~6, but the energy input due to the 3-hour burst of high speed and compressed magnetic field exceeded that of the ejects by far and intensified the Dst activity from -100 nT to -200 nT. In our study of aspects Of the geomagnetic response in the period May 2-7, 1998, we (a) compare the powering of the magnetosphere during this event with that of other large events; (b) simulate the temporal variation of the Dst index; (c) study ground magnetograms, using a network of stations covering a wide range of magnetic latitudes and all local times; (d) describe magnetopause motions using a moddel based on Shue, et al. [1998]; and (e) discuss POLAR/HYDRA particle observations of polar cap precipitation.

Shue, J.-H., et al., J. Geophys. Res., 103, 17691, 1998