How to Handle Polar and Auroral Zone Magnetic Data?
Alan Thomson1, Brian Hamilton1, Susan Macmillan1, Sarah Reay1 1British Geological Survey, Edinburgh Using a combination of 20-second sampled night-side Oersted and Champ data and night-side observatory hourly means we have constructed a new global geomagnetic field model for 1999-2008. The data selection principles are the same as in Thomson and Lesur (T&L, GJI, 169, 951-963, 2007) and the model parameterisation is similar. For example, we solve for a maximum internal spherical harmonic degree of 60, with piecewise linear (seven node) secular variation to degree 13. We use a degree one external field, again piecewise linearly time-dependent, and with added annual/semi-annual variation terms, to represent slower secular change in the quiet magnetosphere. Rapid (e.g. ring current) variations in degree one external and induced fields are parameterised by the VMD index, as first introduced by Lesur (T&L, 2007). No damping or constraints are used in the inverse problem and our new model ben
