Spherical Cap Harmonic Analysis of the Geomagnetic Field and its Secular Variation in China for 2000

Abstract According to the three component absolute survey data of 118 geomagnetic stations observed during 1998~2000 and 39 geomagnetic observatories and IGRF2000, spherical cap harmonic models of the geomagnetic field for 2000 (the truncation order is 8) and geomagnetic secular variation for 2000~2005 (the truncation order is 6) are calculated. The pole of the spherical cap is at 36°N and 104°E, and its half‐angle is 30°. 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) deviation of the geomagnetic models is 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 (∆F, ∆X, ∆Y, ∆Z) for 2000 and the secular variation charts (Ḟ, Ẋ, Ẏ, Ż) for 2000~2005 are drawn. The ways of improving the boundary effect of the geomagnetic model were pointed out, some suggestions to arrange the geomagnetic repeat stations were given too.