Geomagnetic storms cause significant variations in the shielding of energetic solar ions by the Earth’s magnetic field, Dartmouth physics and astronomy professor Brian Kress explained at the College’s Plasma Seminar on Sept. 30.
The Earth’s magnetic field usually shields latitudes below 60 degrees from direct penetration by energetic solar ions of energies up to several hundred mega electron-volts. However, distortion of the Earth’s magnetosphere due to disturbances in the solar wind may allow access to greater numbers of energetic solar ions. Since the Earth’s magnetic field is not a pure dipole field, but a distorted dipole, it is particularly susceptible to geomagnetic distortions.
According to Kress, geomagnetic storms resulting from disturbances in the solar wind may alter the cut-off latitude of energetic solar ions by a significant amount. Observations from spacecrafts showed that in most cases, large increases in solar wind dynamic pressure suppressed geomagnetic shielding of energetic solar ions at dawn, dusk, and midnight local times. However, solar wind dynamic pressure was observed to enhance geomagnetic shielding near noon local times.
Information on variations in geomagnetic shielding is highly valuable to the aviation industry. In his lecture, Kress discussed his on-going collaboration with researchers at the NASA-Langley Research Center, where a model is being developed to predict radiation exposure on high altitude polar flights. The model, called the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS), will enable airlines to monitor radiation doses inside commercial aircraft on high altitude polar flights. NAIRAS will obtain a real-time estimate of the radiation dose by propagating energetic solar ions down through the atmosphere. This will allow airlines to take appropriate measures to protect the health of crew and passengers.
Kress and other Dartmouth researchers are also currently developing a dynamic model of geomagnetic shielding. Unlike the NASA-Langley model, the Dartmouth model will propagate energetic particles from points beyond the Earth’s atmospheric boundary. The particles will then be picked up at the atmospheric boundary by the NASA-Langley model and move down through the Earth’s atmosphere where they will be used to predict radiation doses. This arrangement, according to Kress, will allow the Dartmouth model to serve as an outer boundary condition for the NASA-Langley model.
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