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 SHIMIZU
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.
(Received 19 November 2010; received in revised form 28 September 2011; accepted 4 November 2011)
