Calculations and Analyses of the Geomagnetic Field Models for East Asia

According to the geomagnetic data from repeat stations and observatories of China, former Soviet Union and Mongolia, and using the methods of Taylor polynomial and spherical cap harmonic analysis, the Taylor polynomial models and spherical cap harmonic models for both the geomagnetic field (X,Y,Z) and the residual magnetic field (ΔX,ΔY,ΔZ) over East Asia are calculated, the corresponding geomagnetic field charts and residual magnetic field charts are drawn, too. The expansion origin point of Taylor polynomial is at 45°N and 100°E, the truncation order of Taylor polynomial models is 7. The root mean square (RMS) deviations of Taylor polynomial models of the geomagnetic field are 133.0nT for X, 107.4nT for Y , 148.0nT for Z; those of the residual magnetic field are 133.8nT for ΔX, 108.3nT for ΔY , and 144.9nT for ΔZ, respectively. The pole of the spherical cap is at 45°N and 100°E, and its half-angle is 42°, the truncation order of the spherical cap harmonic model is 10. The RMS deviations of the spherical cap harmonic model of the residual magnetic field are 131.2nT for ΔX, 112.6nT for ΔY , and 138.7nT for ΔZ; those of the geomagnetic field are 134.6nT for X, 112.7nT for Y , and 141.1nT for Z, respectively. The comparisons between Taylor polynomial models and spherical cap harmonic models are made. The criteria of decision of the truncation order of the regional models are discussed.