The representative recent secular variation of the geomagnetic field on the Croatian territory

The four consecutive geomagnetic surveys performed from 2004 to 2007 at Pokupsko (POKU) repeat station, which is located in the central part of Croatia, were depicted. The resulting geomagnetic field secular variation, and its time change, was chosen as being representative for the whole Croatian territory. In doing so, two models of data reduction using Tihany (THY), as the closest reference geomagnetic observatory were considered. First data reduction model assumed simply that the secular variation at the repeat station and observatory were the same all the time throughout the year for which the secular mean was calculated. Second data reduction model took into the consideration the difference in secular variation at both repeat station and observatory for the concerned year. In addition, the reduction to a quiet level, according to procedure used at Edinburgh, and in reference to Tihany and L’ Aquila observatories, was performed. All three reductions methods were compared. Obtained geomagnetic field values, as well as its secular variation were compared to those computed from the global geomagnetic models. In addition, Mokrovics’ historical data were used in order to determine the geomagnetic field variation. Herewith, the first geomagnetic field secular variation obtained from terrestrial surveys of the Republic of Croatia is presented.