Application of Empirical Models for Assessment of the Atmospheric Ionization During a Geomagnetic Reversal

Abstract

<p><span>The most recent geomagnetic reversal of Earth’s magnetic dipole field, the Matuyama-Brunhes reversal event, took place 0.78 Ma ago. Detailed spatio-temporal paleomagnetic data have been made available for this time period. Geomagnetic reversals would be expected to impact the cosmic ray flux and in turn affect ionization rates of the atmosphere. In this study, empirical models are used to produce ionization rates for the entire globe during the Matuyama-Brunhes reversal.</span></p><p><span>The model takes the paleomagnetic timeseries data as input, and outputs 3D time series of the ionization rates of the atmosphere. It is shown, that ionization rates increase at low latitudes as the dipole field weakens. The increase is ~25% at the surface, and up to a factor of 5 in the upper atmosphere. The globally averaged ionization rate increase ranges from 13% at the surface and up to a factor of 2 in the upper atmosphere. Polar regions are largely unaffected. Lastly, we find that the reversal has a big influence on the much faster ionization rate changes caused by the solar 11-year cycle: The change in ionization between solar minimum and solar maximum increases up to two orders of magnitude depending on the strength of the geomagnetic dipole field, such that a weaker dipole field causes a stronger 11-year cycle and vice versa.<span> </span></span></p>