Analyses of geomagnetic field and its secular variation over China for 2005. 0 epoch using Spherical Cap Harmonic method

As a basic technological product describing the geomagnetic spatial distribution, the national geomagnetic chart should choose appropriate method to truly describe the geomagnetic field on standard epoch and its variation for coming 5 years. We used the Spherical Cap Harmonic (SCH) method to calculate the geomagnetic data at 1119 sites and 36 observatories in China on 2005. 0 epoch, and obtained the normal and abnormal geomagnetic spatial structure in China and built an SCH model for geomagnetic secular variation in China for 2005 similar to 2010 epoch. The results have showed that the error of geomagnetic field by IGRF could be 5' for declination and inclination and 100 nT for total intensity. By using better resolution and newer geomagnetic data, the geomagnetic chart on 2005. 0 epoch using SCH method should be better to describe the spatial structure of geomagnetic field. This method should be used in compiling Geomagnetic Chart for China stably.