Secular variations in geomagnetic field caused by the fluctuations in the fluid flow in the outer-core

The theoretical spatial power spectrum of a dipole located at ( r(0), theta(0), phi(0)) can be fitted by a straight line in logarithmic scale when n is larger than 2. Based on the spherical harmonic coefficients of geomagnetic field during 1900-1995, the depth( r(0)) of source-layer of every 5a is calculated. The results show that r(0) decreased from 1900 to 1960; abruptly changed from 1945 to 1950 related to some kind of disturbance; decreased again from 1960 to 1975; increased from 1975 to 1985; and kept stable after 1985. Then the mean energy density (MED) of each year is Induced to ifs corresponding r(0). We find that MED of dipole field kept nearly unchanged from 1900 to 1960. While, MED of non-dipole field increased. The change of r(0) coinciding with the geomagnetic secular variation, impulse and length-of-day happened around 1970, suggesting that the change of r(0) may be related to the impulse. The variation in the fluid flow in the outer-core caused by the core-mantle coupling is a plausible candidate in explaining the changes in geomagnetic Jerk, length-of-day, and r(0).