Solar energetic particle cutoff variations during the 29-31 October 2003 geomagnetic storm

At low latitudes to midlatitudes the Earth's magnetic field usually shields the upper atmosphere and spacecraft in low Earth orbit from solar energetic particles (SEPs). During severe geomagnetic storms, distortion of the Earth's field suppresses geomagnetic shielding, allowing SEPs access to the midlatitudes. A case study of the 26-31 October 2003 solar-geomagnetic event is used to examine how a severe geomagnetic storm affects SEP access to the Earth. Geomagnetic cutoffs are numerically determined in model geomagnetic fields using code developed by the Center for Integrated Space Weather Modeling (CISM) at Dartmouth College. The CISM-Dartmouth geomagnetic cutoff model is being used in conjunction with the High Energy and Charge Transport code (HZETRN) at the NASA Langley Research Center to develop a real-time data-driven prediction of radiation exposure at commercial airline altitudes. In this work, cutoff rigidities are computed on global grids and along several high-latitude flight routes before and during the geomagnetic storm. It is found that significant variations in SEP access to the midlatitudes and high latitudes can occur on time scales of an hour or less in response to changes in the solar wind dynamic pressure and interplanetary magnetic field. The maximum suppression of the cutoff is similar to 1 GV occurring in the midlatitudes during the main phase of the storm. The cutoff is also significantly suppressed by the arrival of an interplanetary shock. The maximum suppression of the cutoff due to the shock is approximately one half of the maximum suppression during the main phase of the storm.