Variation of SEP Event Occurrence with Heliospheric Magnetic Field Magnitudes
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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Recent work based on nitrate abundances in polar ice cores has shown that large fluence solar energetic 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 and others have reported an inverse correlation between LSP events and the magnitudes of the associated reconstructed heliospheric magnetic fields HMF. A physical working model by McCracken is that the lower HMF and coronal magnetic field B imply that fast coronal mass ejections CMEs produce shocks with enhanced Alfvenic Mach numbers and higher compression ratios, leading to shock production of more numerous and energetic LSEP events. From a possible decline of the HMF over the next several solar cycles he has urged a watch for a return to the environment of high-frequency, high-fluence LSEP events preceding the current spacecraft era. His LSEP event watch involves three independent questions about 1 the physical model. 2 the prediction of decreasing solar-cycle sunspot numbers and heliomagnetic fields, and 3 the inferred anti-correlation between LSEP events and HMFs. Here we discuss observational evidence bearing on the last question and find little support for the claimed LSEP-HMF anticorrelation.
- Electricity and Magnetism