The fourth generation comprehensive model of magnetic field CM4 was reasonably used in this paper to study the variation of external field in magnetic quiet periods over Chinese mainland during 1960-2000. The distribution and variation of ionospheric field and magnetospheric field separated from the external field in 1960-1970, 1970-1980, 1980-1990 and 1990-2000 were also calculated and analyzed. Results showed that X component of external field variation was increased firstly, then decreased with time. The change was about 32 nT. The variation of corresponding magnetospheric field was increased firstly, then decreased continuously. The change was about 23.7nT. The Y Component of external field variation was decreased, increased and decreased with time. The change was about 3.8 nT. The variation of corresponding magnetospheric field was generally decreased and then increased with time. The change was about 2.3 nT. The Z Component of external field variation was decreased and then increased with time. The change was about 4.6 nT. The variation of corresponding magnetospheric field was decreased then increased. The change was about 9.3 nT. The intensities of corresponding ionospheric field to the three components were all less than 1 nT during 1960-1970, 1970-1980, 1980-1990 and 1990-2000. They vary with interesting phenomenon between positive and negative values, which maybe have something to do with 11 years＇ solar activities.%利用第4代地磁场综合模型CM4，研究了中国大陆地区1960—2000年磁静日期间地磁外源场的变化情况，并进一步计算分析了外源场中的电离层场及磁层场的分布与变化．结果显示，北向分量x的外源场强度在40年间呈先增加后减小的趋势，共减少了约32nT，其磁层场强度呈先增大，然后逐年减小的趋势，共减少了约23．7nT；东向分量Y的外源场强度呈先减少后增加再减少的趋势，共增加了约3．8nT，其磁层场强度呈先减小，再逐年增加的趋势，共增加了约2．3nT；垂直分量z的外源场强度呈先减少后增加的趋势，共增加了约4．6nT，
展开▼
