Fig. 11From: COV-OBS.x2: 180 years of geomagnetic field evolution from ground-based and satellite observationsAuto-correlation function for the external dipole field coefficient \(q_{1d}^0\) in dipole coordinates, superimposed with the fit obtained with (top) the 3-parameter function \(C_2(\tau )\), and (bottom) a 5-parameter function \(C_2(\tau )+C_1(\tau )\)Back to article page