Variation of SEP event occurrence with heliospheric magnetic field

Recent work based on nitrate abundances in polar ice cores has shown that large fluence solar energetic (E > 30 MeV) particle (LSEP) events during the spacecraft era of observations (1960-present) are diminished in comparison with those of some preceding eras detected in the ice cores dating back to 1561. McCracken et al. [McCracken, K.G.. Dreschhoff, G.A.M., Smart, D.F., Shea. M.A. A study of the frequency of occurrence of large-fluence solar proton events and the strength of the interplanetary magnetic field, Sol. Phys., 224, 359 372, 2004] have reported an inverse correlation between LSEP events and the magnitudes of the associated reconstructed heliospheric magnetic fields (HMF). A physical working model by McCracken [McCracken, K..G. Changes in the cosmic ray and heliomagnetic components of space climate, 1428 2005, including the variable occurrence of solar energetic particle events. Adv. Space Res., 40. 107