Spherical cap harmonic analysis of the geomagnetic field and its secular variation in China for 2000

According to the three component absolute survey data of 118 geomagnetic stations observed during 1998 similar to 2000 and 39 geomagnetic observatories and IGRF 2000, the spherical cap harmonic models of the geomagnetic field for 2000(the truncation order is 8), and the geomagnetic secular variation for 2000 similar to 2005(the truncation oder is 6) are calculated. The pole of the spherical cap is at 36degreesN and 104degreesE, and its half-angle is 30degrees. The spherical cap harmonic models of the geomagnetic field and its secular variation can better express the spatial-temporal variation of the geomagnetic field in China. The root mean square (RMS) deviations of the geomagnetic model are 104.4 nT for X, 103.3 nT for Y and 123.9 nT for Z. Based on the spherical cap harmonic models of the geomagnetic field and its secular variation, the geomagnetic charts (F, X, Y, Z), the anomaly charts (DeltaF, DeltaX, DeltaY, DeltaZ) for 2000 and the secular variation charts ((F) over dot, (X) over dot, (Y) over dot, (Z) over dot,) for 2000 similar to 2005 are drawn. The ways of improving the boundary effect of the geomagnetic model and arranging the repeat stations are suggested.