On the time evolution of declination at geomagnetic observatories with long records

Paper type: 
Oral presentation

The temporal evolution of the declination of geomagnetic field is shown, on data from  observatories with 100-150 years long time series, to be composed of several ingredients, which we call the steady, the ~80-year, the 22-year, and the 11-year variations. The analysis of the first time derivative of declination for the study observatories showed that the ~80-year variation dominated the secular variation in the last 100 years and that the 22-year variation is important in defining the time evolution of the first time derivative of declination, since 1960. The analysis of 400 years-long declination time-series from three European locations (London, Munich, Rome) resulted in tracing back of the ~80-year variation to the 15th century and showed that what we called ‘steady variation’, based on 150 years of observatory data, proves to be only a part of a larger timescale variation, when 400 years of data are available.

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