Splinter Group - Chairs: Daniel Baker (University of Colorado) & Mervyn Freeman (British Antarctic Survey, Cambridge, UK)

Session Synopsis:

In late April and early May, a combination of coronal mass ejections, solar flares, and high speed solar wind streams led to a powerful sequence of solar wind drivers of magnetospheric processes at the Earth. The result of the compounding solar wind disturbances was to produce a deep, powerful, and long-lasting enhancement of the highly relativistic electron population throughout the outer terrestrial radiation zone. Such enhancements have been shown to have caused spacecraft anomalies due to deep dielectric charging.

Session Aims:

To inter-relate solar, interplanetary and terrestrial observations during April/May 1998.

To identify original scientific studies arising from the observations.

To put the event into the context of approaching solar maximum.

Key Observations:

SOHO observed a large CME on 2 May 1998. SOHO and GOES sensors also observed a series of large solar flares.

From 1-19 May, WIND recorded four separate solar wind streams in which peak speeds exceeded 600km/s. In particular, on 4 May, the solar wind speed peaked at ~850 km/s. This is the highest solar wind speed that has been measured near 1 AU in the past several years.

On 4 May, the planetary magnetic index Kp reached 9, the ring current index Dst reached -218 nT (a major geomagnetic storm), the provisional auroral electrojet index (AE) briefly exceeded 2500 nT (WDC-C2, Kyoto University), and the local magnetic field perturbation at Halley, Antarctica exceeded 4000 nT.

SAMPEX and POLAR data revealed a remarkably strong acceleration of relativistic electrons exceptionally deep in the magnetosphere. On 4 May, there was a huge increase of the flux of highly relativistic electrons very deep in the magnetosphere (L~< 3). The slot region was filled and another radiation belt feature appeared at L~- 2.2 q 0.2 . The relativistic electrons remained high throughout the outer zone for at least the subsequent two weeks. LANL measurements at geostationary orbit show that the fluence of 1-6 MeV electrons peaked on or just before 19 May 1998. This May 1998 interval was the longest duration and spectrally hardest electron event seen in the past three years. Several spacecraft anomalies were reported in this interval.

Visit the ISTP event page for the May 98 CMEs

Russell et al. COSPAR paper on the POLAR magnetometer observations during the May CME event.

The session chairs welcome advance contributions and suggestions for the session. (E-mail: Dan Baker Mervyn Freeman)