Proton Penetration Efficiency over Sierra Negra (Mexico) and Oulu (Finland)

On November 7, 2004, a large solar flare was observed, which had a notable impact on the solar neutron detectors located at Mt. Chacaltaya (5,250 m) in Bolivia and Mt. Sierra Negra (4,600 m) in Mexico. In addition, the neutron monitor at Oulu, Finland, recorded a 5-sigma enhancement. In order to determine the causes of these enhancements, we performed trajectory simulations ejecting anti-protons from 20 km above each location, and checked whether or not these anti-protons could reach the magnetopause (∼8R_E). Then, we understand that the Chacaltaya enhancement was caused by solar neutrons themselves, while the Mt. Sierra Negra event may have been produced by high-energy solar neutron decay protons (SNDPs) with energies ≥ 6 GeV. Based on our antiproton trajectory analysis, we suggest that the enhancement at Oulu may also have been produced by solar neutron decay protons with energies around ≥ 200 MeV. During this flare, protons were accelerated up to 10 GeV within one minute, leading to the production of SNDPs.