Variations in geomagnetic shielding of solar energetic particles associated with the arrival of an interplanetary shock at the Earth's magnetosphere

The Earth's magnetic field usually shields latitudes below approximately 60 degrees from direct penetration by solar energetic particles (SEPs). Geomagnetic storms suppress geomagnetic shielding and lower the cutoff latitude up to ~15 degrees, predominantly due to a reduction in field strength in the inner magnetosphere caused by ring current buildup. Significant variations in SEP cutoffs may also occur during storm onset with the arrival of an interplanetary shock. In this work we examine how sudden increases in solar wind dynamic pressure affect geomagnetic cutoffs. SAMPEX energetic particle observations and numerical model results will be presented and directly compared. In most cases, large increases in solar wind dynamic pressure are found to increase the cutoff near local noon and suppress the cutoff at dawn, dusk and midnight local times. An application of the numerical cutoff model used for this work will also be discussed, involving a nowcast prediction of radiation exposure on high altitude polar flights for the safety of airline crews and passengers.