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


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 (Bz) and the "rectified" electric field V Bs 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. Bz 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 Bz (or  V Bs) 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, Dstmin are: Dstmin = 0.83 + 7.85 X Bzmin and Dstmin = -16.48 -12.89 X V Bsmax. (3) The velocity dependence of the Dstmin prediction relationship will improve the accuracy for a Bz-base prediction result. (4) For the V Bsmax based prediction relationship, the prediction accuracy of Dstmin becomes worse when a velocity-dependent prediction relationship is used.

submitted,  JASTP, 2003