Browsing by Subject "Radiation belts"

In this study we use mutual information to characterise statistical dependencies of seed and rel- ativistic electron fluxes in the Earth’s radiation belts on ultra-low frequency (ULF) wave power measured on the ground and at geostationary orbit. The benefit of mutual information, in com- parison to measures such as the Pearson correlation, lies in its capacity to distinguish non-linear dependencies from linear ones. We replicate the methodology in Simms et al. [2014] andwe also calculatethe conditional mutual information, CMI, between ULF spectral power and the electron fluxes, when conditioned on the solar wind speed V . The results of the replication are similar to those presented in Simms et al. [2014] and show low to moderate correlations between ULF Pc5 waves (2-7 mHz electromagnetic waves) and both relativistic and seed electron fluxes, with the correlations ranging from 0.18 to 0.65. The mutual information between ULF Pc5 spectral power and the relativistic electron flux is between 0.17 and 0.22 depending on whether it is evaluated for a storm’s main or recovery phase. The corresponding values of mutual information between ULF Pc5 spectral power and the seed electron flux are between 0.33 and 0.41. All the values of mutual information are statistically significant with a confidence interval of at least 8 standard deviations, except for the mutual information between ground-based ULF measurements and the relativistic electron flux. Highest values of CMI are obtained for roughly V > 600km/s, which also give the largest significance ratios for CMI, implying that under conditions with high solar wind speeds the dependence between ULF Pc5 spectral power and the electron fluxes at the outer radiation belts is higher than for lower solar wind speeds. The mutual information and CMI between the ULF spectral power and the seed electron fluxes is larger and up to twice as high as between ULF spectral power and the relativistic electron flux. The mutual information between average ULF spectral power and the peak electron flux after a storm is also higher than the regular mutual information, giving indication of a dependence whose timing might vary on a scale of days.