Open AccessDynamic geomagnetic rigidity cutoff variations during a solar proton event
Author(s) -
Rodger Craig J.,
Clilverd Mark A.,
Verronen Pekka T.,
Ulich Thomas,
Jarvis Martin J.,
Turunen Esa
Publication year - 2006
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2005ja011395
Subject(s) - earth's magnetic field , riometer , cutoff , rigidity (electromagnetism) , physics , geomagnetic storm , space weather , south atlantic anomaly , magnetosphere , ionosphere , atmospheric sciences , cutoff frequency , computational physics , geophysics , magnetic field , optics , van allen radiation belt , quantum mechanics
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 K p ‐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 ( K p < 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 ( K p ≈ 7–9) the rigidity energy cutoffs indicated by the IRIS observations appear to be equivalent to those predicted for K p ≈ 6 by the particle‐tracing approach. Examples of changing rigidity cutoff contours for increasing levels of geomagnetic disturbance are presented.