The Fourier method was carried out by performing a discrete Fourier transform on 21-yr (84-season) windows of the data. To prepare each window for spectral analysis, the mean of the window was subtracted, and the initial and final 5% of the data in the window was weighted with a cosine bell. The distance between the centers of neighbouring windows was 1 yr.
digital spectral analysis with applications marple pdf download
Download Zip: https://shoxet.com/2vznbK
The SST series (GISST 2.3a) provides a marked improvement in quality over the frequently used SST data from the Comprehensive Ocean Atmosphere Data Set (COADS). Wang and Wang (1996) analyzed central and eastern equatorial Pacific COADS SST data using wavelet analysis. They found that the spectrum from this data compared poorly with the Darwin sea level pressure anomaly series in the pre-1950 period. As was mentioned earlier, the Darwin pressure series produced similar spectral patterns to the series used in this investigation and we infer that the COADS SST data is of lower quality in the pre-1950 period.
The average spectrum of the SOI series has a broad spectral peak (Fig. 8), but the distribution of power over time is more sharply peaked in frequency and is not constant [Figs. 4, 6, and 7; Wang and Wang (1996)]. The persistence and distribution of power in the AR(3) spectrum (Figs. 8 and 9) are very reminiscent of those observed for the SOI and the other ENSO series. To test whether there are significant differences in structure between the real and synthetic SOI spectra, the probability distribution of wavelet coefficient amplitudes was calculated. This technique has been used before with discrete wavelet analysis (Yamada and Ohkitani 1991; Ivanov et al. 1996) to distinguish between wavelet spectra with different structures. For example, Yamada and Ohkitani (1991) found that while the distribution of wavelet coeffiecients of a phase-randomized turbulence time series was Gaussian, the turbulence series itself had an exponential distribution. The distribution of the wavelet coefficients of phase-randomized series is used as a null hypothesis for a completely random, structureless series. 2ff7e9595c
Comments