Relationships for predicting geomagnetic storm intensity

C.-C. Wu and R. P. Lepping

The University of Alabama in Huntsville, CSPAR, Huntsville, AL 35899, also Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771

Abstract:

Studying geomagnetic storm activity during 135 interplanetary magnetic cloud periods from 1965 to 1998, Wu and Lepping [2002b] found that the storm Dst index correlated well with both the interplanetary magnetic field z-component (B_z) and the "rectified" electric field V B_s but does not correlate well with solar wind speed, indicating that the role of magnetic cloud speed in predicting storm intensity is a minor one. They also found that the correlation coefficient for Dst vs. B_z increases dramatically when the solar wind speed exceeds 600 km/s. This implies that solar wind speed is also important indirectly for predicting the storm intensity when using B_z (or V B_s) as a direct predictor. Using the same data set of 135 magnetic cloud-associated storms, two Dst prediction-relationships are developed: one is velocity independent and the other is velocity dependent. In this study, (i) both Dst prediction-relationships will be presented and (ii) some recent storm events will be presented and discussed by (as examples) using both Dst prediction-relationships.

The results of this study also show: (1) the intensity of a magnetic storm which is associated with a magnetic cloud is predictable. (2) The prediction relationships for storm intensity, Dst_min are: Dst_min = 0.83 + 7.85 X Bz_min and Dst_min = -16.48 -12.89 X V Bs_max. (3) The velocity dependence of the Dst_min prediction relationship will improve the accuracy for a Bz-base prediction result. (4) For the V Bs_max based prediction relationship, the prediction accuracy of Dst_min becomes worse when a velocity-dependent prediction relationship is used.

submitted, JASTP, 2003