Solar Physics Division Meeting 2000, June 19-22
Session 2. Corona, Solar Wind, Flares, CMEs, Solar-stellar, Instrumentation, Other
Display, Chair: J. Krall, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[2.85] A Look at the Modest Geomagnetic Response to the Rise of Cycle 23: Coronal Transients With Less Geoeffectiveness?

J.G. Luhmann, Y. Li (University of California Berkeley), C.T. Russell, T. Mulligan (IGPP, UCLA), N. Arge (CIRES and NOAA-SEC), J.T. Hoeksema (Stanford University), D.J. McComas (LANL), C.W. Smith (Bartol Research Inst.)

Using the combination of ACE archived plasma and field data, and the Burton et al. (JGR 1975) formula for Dst, as modified by Fenrich and Luhmann (GRL 1998), we examine the magnetic storm producing potential of the local interplanetary medium during the unusually quiet approach to the Cycle 23 maximum. While the SOHO-LASCO coronagraph reported an increasing number of halo CMEs during this period, the number of following interplanetary disturbances, or ICMEs, was small. Moreover, those ICMEs that did occur tended to have small or short-lived North-South interplanetary magnetic field signatures. Part of the explanation is probably the configuration of the coronal helmet streamer belt source since 1998. The main helmet streamer belt has been either significantly warped by a substantial quadrupole moment of the large scale solar field, or dipolar but highly inclined to the rotation axis. These conditions in the primary CME source region are expected to favor large East-West interplanetary field disturbances in the leading edge of the ICME where the field is strengthened by compression. Comparisons with the ISEE-3 interplanetary data obtained during a similar phase of the rise to the more active Cycle 21 maximum provide some insights from a contrasting example of a more geoeffective case. These comparisons illustrate how the combination of solar magnetic field behavior and solar wind stream structure can conspire to make more or less geoeffective cycles.


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