Secular variation of the Earth's magnetic field revealed by Mexican Geomagnetic Repeat Stations during the last two centuries

Abstract

Modeling of the recent geomagnetic secular variation in terms of both directions and intensity is commonly based on observatory data, available for the last four centuries in Europe but less than 100 years in most part of our planet. Geomagnetic Repeat Stations provide invaluable supplementary data for such purpose allowing largely extend the magnetic record. Here, we compile database retrieved from 32 localities in Mexico providing 257 values of magnetic declinations, 239 inclinations, 236 data for the horizontal component and other 233 for the vertical component of intensity. The selected dataset consists of twenty-six repeat stations providing 216 declinations, 234 inclinations, 140 intensities, 213 values for horizontal and 209 vertical components. An agglomerative hierarchical grouping tree method and Chebyshev metrics were used to mitigate the measurement errors while the relocation error exercise was also implemented. The Bootstrap method and penalized cubic splines were used to build the secular variation curve which show rather similar trends comparing to the global model data for the most time interval involved. Several potential geomagnetic jerks are observed for 1958, 1969 and 1978 most likely corresponding with those detected in French observatories in Chambon la Forêt and in Tucson in North America.