Summary: The geomagnetic secularvariation timescale in observations
and numerical dynamo models
and Julien Aubert1
Received 3 March 2011; accepted 29 March 2011; published 5 May 2011.
 The knowledge of the spatial power spectra of the main
geomagnetic field and of its secular variation makes it possi-
ble to define typical timescales tn for each spherical harmonic
degree n. Investigating both observations and numerical
dynamos, we show that a oneparameter law of the form
tn = tSV/n is satisfied for the nondipole field, given the
statistical way the observed tn are expected to fluctuate.
Consequently, we determine the corresponding secular
variation timescale tSV from either instantaneous or time
averaged spectra, leading to a value of 415 ±45
yr for recent
satellite field models. In the broader context of geomagnetic