Understanding the extremes in geomagnetic activity is an important component in understanding just how severe conditions can become in the terrestrial space environment. Extreme activity also has consequences for technological systems. On the ground, extreme geomagnetic behavior has an impact on navigation and position accuracy and the operation of power grids and pipeline networks. We therefore use a number of decades of one‐minute mean magnetic data from magnetic observatories in Europe, together with the technique of extreme value statistics, to provide a preliminary exploration of the extremes in magnetic field variations and their one‐minute rates of change. These extremes are expressed in terms of the variations that might be observed every 100 and 200 years in the horizontal strength and in the declination of the field. We find that both measured and extrapolated extreme values generally increase with geomagnetic latitude (as might be expected), though there is a marked maximum in estimated extreme levels between about 53 and 62 degrees north. At typical midlatitude European observatories (55–60 degrees geomagnetic latitude), compass variations may reach approximately 3–8 degrees/minute, and horizontal field changes may reach 1000–4000 nT/minute, in one magnetic storm once every 100 years. For storm return periods of 200 years the equivalent figures are 4–11 degrees/minute and 1000–6000 nT/minute.

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ABSTRACT

Approximately 51 000 observations made between 1955 and 1973 were used to produce the magnetic charts of Canada for 1975. A least-square method was used to derive sixth degree polynominals for the rectangular components X(north), Y(east), and Z(vertical). Cubic time terms were included to eliminate the customary laborious method of updating the data to the desired epoch.To reflect desired wavelengths of approximately 1000 km it was necessary to divide the map area of 31 × 106 km2 into quadrants with a unifying overlap of 10%. For consistency, X and Y were analysed together using Maxwell's curl-free relation (curl F)Z = 0. All data were weighted according to type and age.From the derived polynomials, values of D (magnetic declination), H (horizontal intensity), and Z were computed at 2° geographic grid intervals. These values were used to derive the final charts using a standard contouring package.The overall root mean square (rms) fit of the model to the input data is 174 nT. In the auroral zone, an area of high magnetic activity, the fit is generally poor. The fit to over 8500 supplementary observations is 170 nT, confirming the reliability of the model.