SPRG Seminars

September 23, 2008:

"Prospects for Future Enhanced Solar Energetic Particle Events and the Effects of Weaker Heliomagnetic Fields"

Steve Kahler, Air Force Research Laboratory, Hanscom AFB, MA

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Have we been lucky? Solar energetic (E ≥ 10 MeV) particle (SEP) events are a hallmark of solar activity and have been observed from space for nearly five solar cycles. For space physicists they are a topic of fundamental importance and fascination, but for some of the world (airlines, GPS users, astronauts, and my employer) SEP events are detrimental to their essential activities. A recent report in the journal Space Weather (McCracken, 2007) has compared the space era SEP activity with large historical SEP events inferred from nitrate deposits in polar ice cores dating back to 1561. Periods were found of much more frequent SEP events than we have observed in the space age. Why is that, and are we due for a resurgence of high SEP activity as the report suggests? SEP events appear to be inversely correlated with both the sunspot numbers and reconstructions of the heliomagnetic field magnitudes, leading to a proposed model based on SEP production by coronal shocks. I will review the genesis of the SEP event record and reconstructions of the heliomagnetic fields, assess the validity of the inverse correlation between SEP events and heliomagnetic fields, and examine the feasibility of the proposed shock model. The goal is to present a critical overview of this rather complicated topic.