Technical Report of the Kakioka Magnetic Observatory, Vol. 9, No.1-2, pp. 19-24, February, 2012


Retrieval of the long-term trend of the volcanic geomagnetic field variations by using a wavelet analysis and its comparison with other methods


Masahiro SASAOKA and Jumpei SHIMUZU


Abstract

   In order to retrieve the geomagnetic variations related to the volcanic activityC 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C 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.


Received 19 November 2010; received in revised form 28 September 2011; accepted 4 November 2011




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