Spherical Cap Harmonic Analysis of the Geomagnetic Residual Field in China for 1950‐1990

Abstract

AbstractBased on the geomagnetic 3‐component absolute survey data of China during 1950~1990, and using the method of spherical cap harmonic (SCH) analysis, the SCH models of the geomagnetic residual field in China for 1950~1990 are calculated, and the corresponding geomagnetic residual field charts are drawn. The root mean square (RMS) deviations of SCH models of the geomagnetic residual field are 93.1nT(1950), 128.9nT(1960), 107.2nT(1970), 107.6nT(1980), and 95.2nT(1990) for ΔX, 74.8nT(1950), 98.1nT(1960), 89.2nT(1970), 89.9nT(1980), and 84.0nT(1990) for ΔY , 122.2nT(1950), 135.0nT(1960), 137.7nT(1970), 110.1nT(1980), and 107.5nT(1990) for ΔZ, respectively. Based on the SCH models of the geomagnetic residual field in China and the DGRF models of the global geomagnetic field, the SCH models of the geomagnetic field in China for 1950~1990 are given, and the corresponding geomagnetic charts are plotted. The pole of the spherical cap is at 36°N and 104°E, and its half‐angle is 30°, the truncation order of the SCH models is 8. The SCH models of the geomagnetic field can better express the spatial‐temporal variation of the geomagnetic field in China. The boundary effect of the SCH models is analyzed and discussed.