Shannon Information of the geomagnetic field during the excursions

The Shannon Information or Information Content is a statistical measure of a system characterising its properties of organisation (maximum value) or disorder (minimum value). Once it is introduced the scalar potential of the geomagnetic field in terms of a spherical harmonic expansion, it is straightforward to define the Shannon Information by an expression including the Gauss coefficients [De Santis et al., EPSL, 2004]. Some recent models of the past geomagnetic field, including also the two most recent excursions, i.e. Laschamp (~41 ka) and Mono Lake (~34 ka) events, allow us to calculate the Shannon Information in the periods of those events and compare each other. It is expected that when approaching to excursions, the Shannon Information decreases, i.e. the disorder of the system increases. From the behaviour in time of the Shannon Information calculated from the Gauss coefficients of three geomagnetic field reconstructions that span the last excursions, i.e. IMOLE, GGF100k and LSMOD2, it is observed a decrease of the Shannon Information that seems to anticipate the occurrence of the impending excursions some time in advance. This result must be taken with caution because the reconstructions used are based on sedimentary data, which could present some smoothing effects related to the acquisition of the magnetisation mechanism.