Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm31a0741h&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM31A-0741
Physics
2752 Mhd Waves And Instabilities, 2788 Storms And Substorms, 2794 Instruments And Techniques
Scientific paper
The present study proposes a new method to identify ground Pi2 onsets. The Pi2 wave is usually examined by applying a linear band-pass filter or something equivalent, such as wavelet convolution, to ground magnetometer data, and its onset is determined based on the amplitude of the extracted wave component. The proposed method is distinguished from such conventional methods in terms of the following points. First, the proposed method does not filter or smooth data, rather it analyzes the original data. Second, the proposed method determines the Pi2 onset so that the intervals before and after the onset can be optimally described by different time-series models. The optimal partition is determined by minimizing the Akaike information criterion (AIC). The time-series models adopted are general enough to apply to any nonstationary time series irrespective of its waveform, frequency, amplitude, and signal-to-noise ratio. As a result, the proposed procedure is free from the choice of a threshold and is therefore objective. The procedure is applied to simulation data, and it is confirmed that the procedure can determine the onset with the precision of the time resolution of data. An application to magnetic field data from 210o magnetic meridian (MM) stations suggests that our procedure can be used for examining the latitudinal and longitudinal dependence of the onset time.
Higuchi Takeo
Ohtani Shin
Uozumi Teiji
Yumoto Kiyo
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