Evidence of the ring current effect in geomagnetic observatories annual means

Abstract

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.