Secular variations of the geomagnetic field on litosphere plates of the Earth
The dependence of the value and sign of the geomagnetic secular variations (SV) refined of 3- and 11-year components on the position of observatories at different tectonic plates is investigated. The observatories of the long row observations were used for the studies. It is shown, that SV contain the components from internal and external sources. The values of the components change from plate to plate and even on the same plate. The secular variations have greater amplitudes in the regions with the intensive tectonic processes. Ten regions, having peculiar character of the SV, are distinguished. Secular variation may be of opposite phases in different tectonic plates, but extremes of their curves of hourly changes and the change of SV sign in most cases coincide with maximums and minimums of solar and geomagnetic activities. The assumption is made that internal and external sources of SV of the geomagnetic field are mutually connected. External sources play an important role in generation of SV. The maximal amplitudes of SV during all observational period were observed in two regions: the first region — the eastern part of the North-American plate, Caribbean plate and the northern part of the South-American plate, the second region — the western part of the Indian ocean. The value of SV component from the external sources depends on the geomagnetic latitudes of the observation places. Its amplitude increases with the increase of latitude of the observatories. The maximal values of SV components from external sources are observed at the magnetic and geomagnetic poles. The influence of the external sources on SV value is observed at the observatories placed under equatorial ionospheric electrojet. The main peculiarity of the nowadays geomagnetic field secular variations is decreasing the field intensity in the most regions of the Earth. In the second half of the twentieth century the regular small increasing of the field is observed only in the European part of Eurasian plate.
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