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

Abstract

[1] 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 ∼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.

The geomagnetic cutoff rigidities at high latitudes for different solar wind and geomagnetic conditions

“…Therefore, our simulation results suggest that the Dst index is not suitable for forecasting the entry of the energetic particles into the magnetosphere at high latitudes. It is compatible with the results of Kress et al (2004Kress et al ( , 2010; Leske et al (2001); Merkin and Goodrich (2007). This may be caused by the fact that Dst index represents the disturbed magnetic field at the dipole equator on the Earth's surface; when the geomagnetic storm is not strong enough to affect the ring current the Dst index does not vary much.…”

“…However, Kress et al (2004) found that the smallest cutoff rigidity did not happen at the time when Dst reached the smallest value but > 10 h prior to the minimum Dst. In addition, Leske et al (2001) and Kress et al (2010) found that in the main phase of a geomagnetic storm there is not an obvious correlation between variations of the Dst index and that of the cutoff rigidity.…”

Relationship between solar activity and Δ14C peaks in AD 775, AD 994, and 660 BC

“…Furthermore, if the first CME and/or the shocked plasma in front of it contain strong embedded southward-pointing magnetic fields, these southward fields reconnect with the north-directed fields on the front side of the magnetosphere, releasing a large amount of energy. The resulting magnetic storm acts to reduce the geomagnetic field, so that when SEPs accelerated by the second shock reach the neighborhood of the Earth, they may encounter greatly reduced geomagnetic cutoffs and hence can reach an abnormally large fraction of the atmosphere (Leske et al 2001;Kress et al 2010). …”

Solar Energetic Particles and Space Weather: Science and Applications

“…5). Variations in SEP access to latitudes can occur on time scales of an hour or less in response to changes in the solar wind dynamic pressure and IMF (Kress et al 2010). For this reason high inclination LEO satellites can at times be vulnerable to SEPs, as well as the International Space Station that has an orbital inclination of 51.64 ı .…”