Antarctic Record (Feb 1982)

Geomagnetic secular variation in the Antarctic region during 1960-1975

  • Takesi Nagata

Journal volume & issue
no. 74
pp. 27 – 44


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The annual mean values of the geomagnetic three components (X, Y, Z) at 20 stations located between the South Pole and the 30°S latitude circle during 15 years from 1960 to 1975 are examined to study on the geomagnetic secular variation in the southern polar region. In each of three periods, 1960-1965,1965-1970 and 1970-1975,the maximum positive annual rate, Z, over 150 nT/year, was located in a polar area of 70°-85°S in latitude and 20°W-60°E in longitude, as shown in Figs. 1(a), (b) and (c). The major parts of the geomagnetic secular variation in the Antarctic region can be attributed to a decrease of the centered geomagnetic dipole intensity and the northward shift of the geomagnetic dipole, both effects resulting in a decrease of the total geomagnetic force (F) and an apparent increase of Z (Z>0). In the north polar region, the two effects tend to cancel each other, but they are added to each other in the southern polar region. The two effects estimated from Yukutake-Cain's global analysis of the geomagnetic field (1979) are subtracted from the observed values of (X, Y, Z) at the Antarctic region stations. The residuals still show a considerably systematic regional secular variation pattern which can be represented by a positive anomaly of Z (Z>50nT/year) between 20°W and 50°E in longitude and a negative anomaly (Z≲-50nT/year) between 70°E and 180°E in longitude in the southern polar region (Figs. 4(a), (b), (c)). The geomagnetic non-dipole field in the southern polar region has a characteristic distribution pattern which has a focus of a positive anomaly of ΔZ>20,000nT in an area of 60°-70°S in latitude and 10°E-70°W in longitude and a focus of a negative anomaly of ΔZ~-15,000 nT around 30°S in latitude and 140°E in longitude. Roughly speaking, it appears that the non-dipole field is growing up gradually in the southern polar region.