Regional features of the secular variation of the geomagnetic field in China for 2000

On the basis of magnetic survey data during 1998-2001, the China Geomagnetic Reference Field Secular Variation model for 2000, CGRF-SV2000, is established. The model shows a slow and smooth variation of the magnetic field in China. The unsigned average annual rates are 12.2 nT/a, 8.2 nT/a, 43.8 nT/a, 11.8 nT/a, 0.96(')/a, 2.99(')/a and 22.4 nT/a for X, Y, Z, H, D, I and F, respectively. These rates are less than the global rates of IGRF by 1/2 to 1/3. The variations of different elements show an unified SV pattern in China: the north geomagnetic pole is moving to China, or China is moving toward high latitudes at a rate 3(')/a. In addition, the variation of declination D shows that the contrast of D between eastern and western China is enhanced. As a comparison and test, The 8th generation of the International Geomagnetic Reference Field (IGRF) model is used to analyze the secular change of the global geomagnetic field. The global SV estimated by the IGRF model shows similar characteristics compared with CGRF-SV2000, although the annual rates of IGRF-SV are greater than those of CGRF-SV, and some regional (or local) anomalies are noted.