Dynamic geomagnetic rigidity cutoff variations during a solar proton event
Article first published online: 29 APR 2006
Copyright 2006 by the American Geophysical Union.
Journal of Geophysical Research: Space Physics (1978–2012)
Volume 111, Issue A4, April 2006
How to Cite
2006), Dynamic geomagnetic rigidity cutoff variations during a solar proton event, J. Geophys. Res., 111, A04222, doi:10.1029/2005JA011395., , , , , and (
- Issue published online: 29 APR 2006
- Article first published online: 29 APR 2006
- Manuscript Accepted: 12 JAN 2006
- Manuscript Revised: 16 DEC 2005
- Manuscript Received: 31 AUG 2005
- geomagnetic field;
- rigidity cutoff;
- solar proton event
 Solar proton events (SPE) are major, though infrequent, space weather phenomena that can produce hazardous effects in the near-Earth space environment. A detailed understanding of their effects depends upon knowledge of the dynamic rigidity cutoffs imposed by the changing total magnetic field. For the first time we investigate detailed comparisons between theoretical cutoff rigidities and ground-based measurements during the large geomagnetic disturbance of 4–10 November 2001. We make use of the imaging riometer (IRIS) at Halley, Antarctica, fortunately situated such that the rigidity cutoff sweeps back and forth across the instrument's field of view during the SPE period. The Kp-dependent geomagnetic rigidity cutoff energies are determined from satellite observations combined with previously reported particle-tracing results. We find that the predicted absorption levels show good agreement with those experimentally observed for low and middle levels of geomagnetic disturbance (Kp < 5). However, during more disturbed geomagnetic conditions the cutoff modeling overestimates the stretching of the geomagnetic field, underestimating the rigidity cutoff energies, and hence leading to riometer absorption predictions that are too high. In very disturbed conditions (Kp ≈ 7–9) the rigidity energy cutoffs indicated by the IRIS observations appear to be equivalent to those predicted for Kp ≈ 6 by the particle-tracing approach. Examples of changing rigidity cutoff contours for increasing levels of geomagnetic disturbance are presented.