Temporal and spatial evolution of the solar energetic particle event on 20 January 2005 and resulting radiation doses in aviation

Abstract

[1] The solar energetic particle event on 20 January 2005 was one of the largest ground level events ever observed. Neutron monitor stations in the Antarctic recorded count rate increases of several thousand percent caused by secondary energetic particles, and it took more than 36 h to return to background level. Such huge increases in high energetic solar cosmic radiation on the ground are obviously accompanied by considerable changes in the radiation environment at aviation altitudes. Measurements of 28 neutron monitor stations were used in this work to numerically approximate the primary solar proton spectra during the first 12 h of the event by minimizing the differences between measurements and the results of Monte-Carlo calculated count rate increases. The primary spectrum of solar energetic protons was approximated by a power law in rigidity and a linear angular distribution. The incoming direction of the solar energetic particles was determined and compared to the interplanetary magnetic field direction during the event. The effects on the radiation exposure at altitudes of about 12 km during that time were estimated to range from none at low latitudes up to almost 2 mSv/h for a very short time in the Antarctic region and about 0.1 mSv/h at high latitudes on the Northern Hemisphere. After 12 h, dose rates were still increased by 50% at latitudes above 60°whereas no increases at all occurred at latitudes below 40°during the whole event.

What Are Special About Ground-Level Events?

“…Tylka and Dietrich 2009;Matthiä et al 2009). Even for simpler quantities such as the onset time and peak flux, it is important to find a NM whose asymptotic look angle is nearly aligned with the interplanetary magnetic field.…”

Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005

“…Several investigators (e.g. Orus et al, 2007;Sreeja et al, 2009;Kane, 2009;Matthiä et al, 2009;McKenna-Lawlor et al, 2010) have studied different aspects associated with the geomagnetic storm or geomagnetic disturbed period around the third week of January 2005. Du et al (2008) have investigated the storm on 21-22 January 2005 and called it an "anomalous" geomagnetic storm as the storm main phase occurs during northward interplanetary magnetic fields (IMFs).…”

Radiation dose of aircrews during a solar proton event without ground-level enhancement

“…The most energetic events can be observed even at ground-based neutron monitors, and are called ground-level enhancements (GLE) (Forbush, 1946). Recently, Matthia et al (2009a) reported that the effective dose rate at a conventional flight altitude of 40 kft (∼ 12 km) reached 1.0 mSv h −1 during the largest GLE-69 during solar cycle 23. The total effective dose at flight altitude has been estimated for all of the GLE events during solar cycle 23, and ranged from 2.0 µSv to 0.3 mSv (Shea and Smart, 2012).…”