Comment on 'Can core-surface flow models be usedto improve the forecast of the Earth's main magneticfield?' by Stefan Maus, Luis Silva, and GauthierHulot

摘要

[1] Maus et al. [2008a] (hereinafter referred to as paper 1)test the idea of forecasting the geomagnetic field by using acore flow model defined at the top of Earth's liquid outercore. In their approach they start from a magnetic fieldmodel at a time to = 2003.0, namely, the POMME-3 [Mauset al., 2006], estimate for the same epoch a model of theflow including its time derivative and finally, hindcast thefield using the induction equation from 1990 to 2002. Theseestimates of the magnetic field at different epochs are thencompared with the CM4 model [Sabaka et al., 2004].Although the idea of using a core flow model to forecastthe magnetic field is in itself very attractive, we would liketo comment on two major points: (1) The accuracy of theused magnetic field model is not such that the time variationof the flow can be reasonably estimated. (2) The processproposed to predict the field is very unlikely to improve onthe usual approach, where the magnetic field is extrapolatedin time using estimates of its secular variation. We discussthese two points in sections 2 and 3.