Variations in cutoff latitude during the January 2012 solar proton event and implication for the distribution of particle energy deposition



[1] Protons in the energy range 1–20 MeV deposit most of their energy in the middle atmosphere (60–100 km). Knowledge of their magnetic latitudinal and local time distribution is crucial for determining their effect on the chemistry and dynamics in the atmosphere. Using POES 16–19 and METOP02 satellites, we investigate the latitudinal cutoff boundaries and the energy deposition during the January 2012 solar proton event. The dayside cutoff latitudes show high correlation with the Dst index even when Dst turns positive, leading to an abrupt poleward movement of more than 5°. In the same time interval, the nightside cutoff latitudes move equatorward resulting in vastly asymmetric energy deposition into the atmosphere on the dayside and nightside. The differences are sustained for almost a day in the middle atmosphere at 65° corrected geomagnetic latitude. These features cannot be taken into account by applying the frequently used GOES particle data.