Investigation of geomagnetic-field secular variation around the Sverdlovsk magnetic observatory

summary . The magnetic observatories at Vysokaya Dubrava and at Arti in Sverdlovsk region have operated in parallel since 1972 January. In spite of the rather small distance between them (160 km), it has been established that during that time, there have been differences in the geomagnetic field variations over a wide range of frequencies. The secular variation also differs appreciably. Over a period of four years the difference in the horizontal component between the observatories increased by 3 nT, the difference in the vertical component by 4 nT and the difference in the total intensity by 6 nT, while the difference in declination decreased by 0.6 min. Besides the normal geomagnetic secular variation, governed by processes in the Earth's core, secular-variation anomalies (SVA) linked with processes in the lithosphere may also take place. The intensity of the local SVAs reaches 10–2 nT/yr, whilst their size does not exceed 15 km. It is undesirable to locate an observatory in a region where an SVA exists since this will distort the normal secular-Variation pattern. It is therefore important to know to what extent observations at the observatory reflect the mean value of the secular variation for that area. For this purpose we would recommend performing a highly accurate survey, for example the total intensity in a network of radial lines in a region around the observatory of radius 50–100 km. Such investigations have been performed around the Arti observatory with an accuracy of the repeated measurements of ±0.3 nT in 1974 and ±0.2 nT in 1975. Ten local SVAs with intensities from 2–14 nT/yr were revealed around the observatory. The observatory of Arti is situated in a quiet region.