Efekti prstenaste struje u opservatorijskim godišnjim srednjacima

The purpose of this study is to identify the physical sources of the major disturbance in the observatory annual means caused by the external geomagnetic field. The observatory annual means are widely used, especially in the modeling of the main field and its secular variations, although it is known that they are contaminated by parts of the field that come from outside the Earth. We consider data from 46 European observatories spanning the time period 1960–2001. The core field was removed using the Comprehensive Model, CM4 (Sabaka et al., 2004). With a suitable parameterization of the POMME model (Maus et al., 2005), we were able to reconstruct the signal of the residuals which can be linked to the ring current. This investigation paves a way for the more detail study of the external field influence on the observatory annual means, which as a consequence can bring a proposal for their correction.Cilj ovog rada je identificirati fizikalne izvore glavnih poremećaja u godišnjim srednjim vrijednostima s opservatorija, a uzrokovanih vanjskim magnetskim poljem. Opservatorijske godišnje srednje vrijednosti su u širokoj uporabi, posebno pri modeliranju glavnog polja i njegovih sekularnih promjena, mada je poznato da sadrže utjecaje polja čiji su izvori izvan Zemlje. Razmatramo podatke s 46 Europskih opservatorija u razdoblju 1960–2001. Polje jezgre je otklonjeno koristeći Comprehensive Model, CM4 (Sabaka et al., 2004). S adekvatnom parametrizacijom POMME modela (Maus et al., 2005) uspjeli smo rekonstruirati signal reziduala koji se može povezati sa prstenastom strujom (ring current). Ovo istraživanje otvara put detaljnijoj studiji utjecaja vanjskog magnetskog polja na opservatorijske godišnje srednje vrijednosti, koja nadalje može pridonijeti njihovoj korekciji