摘要：In this paper, a study is made to determine the effect of sudden commencement (SC) on the power spectrum of geomagnetic data using multiresolution analysis (MRA) of the discrete wavelet transform (DWT).The results of this study provides a guide to develop a new technique to automatically detect the SC because it could be an indicator of the onset of a geomagnetic storm.This new technique divides the original time series into different frequency sub-bands using the MRA of the DWT.Then it detects the change in a certain sub-band which shows a large change due to the SC.The geomagnetic records used in this study were 3-s resolution data collected from the Circum-Pan Pacific Magnetometer Network (CPMN).Using such high-resolution data enables us to minimize the detection error and the processing time to make a decision.The proposed algorithm is tested on one sample every three seconds of data sets collected from the CPMN.The maximum standard deviation of the algorithm detection times is observed to be fifty four seconds of the corresponding arrival times as determined by the National Geophysical Data Center (NGDC). Key words Automatic detection geomagnetic storms DWT sudden commencement CPMN.
