| Abstract: | The latitudinal dependence of the westward drift in the main geomagnetic field is examined by using the correlation analysis
of moving random pattern. The study reveals the characteristics in the differential rotation of the main field. The results
show that the global geomagnetic field drifts westward with an average speed of 0.18°/a during 1900 –2000. The westward drift
rate is not symmetrical with respect to the equator. The maximum westward drift rate, 0.31°/a, occurs at the latitude φ=−15°,
forming a Rapid Westward Drift Belt (RDB) around this latitude. Going northward and southward from this belt, the drift rate
decreases and reaches the minimum (0.12°/a) at φ= 50° and the minimum (0.14°/a) at φ= −56°, forming a Northern Hemisphere
Slow Westward Drift Belt (N-SDB) and a Southern Hemisphere Slow Westward Drift Belt (S-SDB). Three phases can be detected
in the evolution of the westward drift. In the first phase (1900–1940), the RDB dominates the global drift pattern. The westward
drifts in this belt are much faster than those in other areas. In the second phase (1940–1960), the drift rates in the RDB
are less than those in the first phase, while the drifts in the N-SDB and S-SDB are relatively large. In this phase, the differential
rotation becomes less obvious. In the third phase (1960–2000), the westward drift in the RDB increases again and the differential
rotation gradually becomes apparent. |
