A method for representing a geomagnetic total force field in a small region with special attention to discontinuities of data

In order to represent the total force field variation in a narrow region as precisely as possible, the calculation process of NOC, which is frequently used in geomagnetic field modeling, was improved. An iterative procedure was introduced to avoid the effect of data missing in some time series. The presented procedures are applied to monthly averaged data of the geomagnetic total force field during 1980–1997 in Japan. Some local changes are detected using this model. One of them may be related to an earthquake that took place near the site.