Secular variation from the historical repeat stations of the Italian magnetic network

Abstract

The study of geomagnetism OII the basis of large dat.a seeies is a very important tool: it helps to extclld our knowledge of the geomagnetic secular variatiaD ta a langet time interval aud caD bring informa'hon an geophysical phenomclla linked Dat ooly ta geomagnetism. Following these consideratioDs, we have tried ta extend the Italian repeat stations data. backwards with the indusion of the historical Italian geomagnetic data ca.talogue (Cafarella el al., 1992a). We obta.ined several data sels [rom about 1800 till nawadays for different. localities aod the analysis of secular variatioll both in space aud time over the last two centuries revealed interesting features. In this framework it Îs shown that the contribution of the observatories is very important for the accurate definition of the secular variation pattern; the study of the repeat station data together with the observatory series, can bring fundamental information to improve the knowledge of the upper core fluid flow structure that is responsible of the secular variation.