Performance of Different Digital Filters in Storm Track Study
The performance of Butterworth filter(BF) and symmetrical filter with different truncation modes in filtering the synoptic-scale(2.5--6 d) transient wave is compared in storm track study. Result reveals that, when the cutoff parameter n is greater than and equal to 9, the symmetrical filter can better reserve the synoptic-scale signal and suppress the non-synoptic scale signal than BF does. In the study of storm track with day-to-day observations, the symmetrical filter is comparative well-performed when the cutoff parameter equals to 15. The performance of symmetrical filter using sinusoidal cutoff is better than that using trapeziform cutoff in the condition presented above;meanwhile, their performance is both superior to that of BF, especially in El Nino years with stronger storm tracks. If the size of samples is not large enough,it is worthy to use BF to get the transient wave with the band-pass of 2.5-8 d.
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