Response of the Earth’s lower ionosphere to the Ground Level Enhancement event of December 13, 2006

Abstract

In this study we analyze the Ground Level Enhancement Event No 70 observed on December 13, 2006, by correlating the observations from two research topics: Cosmic rays and Very Low Frequency (VLF<30kHz) wave propagation, as two ground based techniques for the detection of solar proton events, and their impact on the lower ionosphere. The observations have been endorsed from recordings of worldwide network ground based Neutron Monitors as well as by satellite data from the satellites GOES 12 (www.swpc.noaa.gov) and Pamela (www.pamela.roma2infn.it).We have evaluated the ionization rate for protons in the altitude range relevant to VLF propagation, and for galactic cosmic ray (GCR) background, finding that at energies up to ∼2GeV the ionization rate of solar protons exceeded the GCR ionization by 1.5 orders of magnitude.We have applied the Long Wave Propagation Capability (LWPC) code to evaluate the enhancement of the electron density from VLF signal perturbation and have inferred corresponding electron densities from the evaluated ionization rates and effective recombination coefficients from literature, to find the two independent sets in good agreement.