Annual, 11-year period and aperiodic variations of the induction vector by eight observatories of Intermagnet network
A large amount of geomagnetic data of Intermagnet network observatories for 1991-2014 years have been processed and time series of induction vector components for every month were obtained. This paper presents the results of processing of eight observatories, located in different parts of the globe. For these observatories graphs of monthly values of induction vector components for four intervals of periods from the range 5-60 minutes are shown. Periodic changes in vector components (from semiannual to 11-years) are detected, as well as trends. After 2007 some increase of annual variations is seen. The most intense variations are at high geomagnetic latitudes and in the equatorial zone; they arc minimal in the middle latitudes. The nature of variations is affected both by global and regional/local factors. Investigation of these periodic changes can give an unique information on the substance and the structural features of the Earth's interior. At Polish observatories long aperiodic variation is obtained after 2008, clarifying the nature of which requires further research.