Hydromagnetic waves in Earth's core and their influence on ...

264 Appendix B — CALS7K.1B.6 Characteristics <strong>and</strong> evaluation of the model CALS7K.1An RMS misfit of 1.00 was achieved for the model CALS7K.1 after data rejection, us<strong>in</strong>ga spatial damp<strong>in</strong>g parameter of 3 ×10 −7 nT −2 (spatial norm was 40 × 10 9 nT 2 ) <strong>and</strong> atemporal damp<strong>in</strong>g parameter of 5 × 10 −1 nT −2 yr 4 (temporal norm was 63×10 3 nT 2 yr −4 ).The best way of assess<strong>in</strong>g the success of a model is to compare its predictions to theorig<strong>in</strong>al data. This has been carried out by Korte <strong>and</strong> Constable (2005) with lakesediment data <strong>and</strong> archeomagnetic data at a number of sites. In general the fit ofthe model to the data was found to be good, though there are some discrepancies, forexample <strong>in</strong> Lake Baikal <strong>in</strong> Japan where not even the trend was been well captured,suggest<strong>in</strong>g that this record may have some serious errors. The good fit of the modelto records <strong>in</strong> the Southern hemisphere was particularly encourag<strong>in</strong>g, given the sparsenature of data coverage there.B.7 Grid<strong>in</strong>g of CALS7K.1 for analysis on <strong>core</strong> surfaceIn order to carry out a space-time analysis of field features <strong>in</strong> CALS7K.1, the sphericalharmonic field model for the magnetic potential V supplied by Monika Korte (personalcommunication July 2004) was used along with equations (A.8)-(A.17) to evaluate B ron a regularly spaced grid <strong>in</strong> latitude, longitude <strong>and</strong> time at the <strong>core</strong> surface.In all cases a grid of spac<strong>in</strong>g 2 degrees <strong>in</strong> longitude by 2 degrees <strong>in</strong> latitude was used.This is considerably smaller then the resolution of a degree 10 spherical harmonic model,ensur<strong>in</strong>g that no <strong>in</strong>formation was lost through the grid<strong>in</strong>g procedure.For comparison to gufm1 a subset of CALS7K.1 runn<strong>in</strong>g from 1600A.D to 1950A.D(called CALS7K.1h) was gridded with a temporal spac<strong>in</strong>g of 2 years. This is obviouslymuch higher than the temporal resolution <strong>in</strong> CALS7K.1, but facilitates straightforwardcomparisons with the historical record. When study<strong>in</strong>g the full span of CALS7K.1 atemporal spac<strong>in</strong>g of 25 years was employed, aga<strong>in</strong> significantly less than the resolutionof CALS7K.1. The study of the <strong>in</strong>terval from 2000B.C to 1700A.D. employs a 25 yeargrid spac<strong>in</strong>g.