Retrieval of the long-term trend of the volcanic geomagnetic field variations by using a wavelet analysis and its comparison with other methods
Sasaoka, M. & Shimizu, J.
Abstract
In order to retrieve the geomagnetic variations related to the volcanic activity， various methods for decomposing the geomagnetic field variations were developed at Kakioka Magnetic Observatory. The log-term trend of the volcanic geomagnetic field variations was investigated using these methods for the observation of the stations on Miyakejima Island. Using the wavelet analysis which extracts the long-term trend by removing the short-term variations attributed to the magnetic disturbances enables easy compare differences in annual variation and ocean dynamo effect at each station. While a comparison of the wavelet method， the stochastic difference method and the Kalman-filter method shows almost same variations in their long-term trends with the volcanic activity eliminating short-term variations. The differences between the trends of these methods are indicated in order of 1 month. It is inferred that 1-month trend of the reference data from the geomagnetic observatory affects to the estimated trends of the volcanic activity from the stochastic difference method and the Kalman-filter method.
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