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The Hydrographic Department of the Maritime Satety Agency conducted an airborne magnetic survey from 1979 to 1980 to derive a regional field model around Japan at the epoch 1980.0. The regional field model, consisting of 3rd-degree polynomials, was compared with the models MGST (4/81) and IGRF 1980 for the earth's main geomagnetic field over the world. The comparison of the regional field model and MGST (4/81) or IGRF 1980 revealed the following differences:1) MGST (4/81) model approximates the actual magnetic field better than IGRF 1980, insofar as the RMS residuals for the region around Japan are concerned. The RMS residuals from MGST (4/81) are 18.1nT, 44.3nT, 47.3nT, and 42.3nT for the total intensity F and three components X, Y, Z respectively, whereas the residuals from IGRF 1980 are 23.6nT, 46.6nT, 67.6nT, and 50.4nT in the same order.2) Large negative residuals of the geomagnetic total intensity in the area of the Japan Sea and Okhotsk Sea (amounting to -300nT from the IGRF 1965 or IGRF 1975) are thought to be attributable to the insufficient representation of the core-field in these IGRF models. If MGST (4/81) is used as a reference model field, the residual map shows a positive deviation along the outer region of Island Arc and a negative one in the marginal sea. This indicates the existence of a significant long-wavelength magnetic anomaly around Japan.

A regional magnetic field model around Japan at the epoch 1980.0 and its comparison with world magnetic field models MGST(4/81) and IGRF 1980.