Wavelet transform(WT) is an analysis tool well suited to the study of
multiscale, nonstationary processes occurring over finite spatial and temporal
domains.The earth climate system undoubtedly possesses these
Lau,K.M., and Hengyi Weng, 1995: Climate Signal Detection Using Wavelet Transform: How to Make a Time Series Sing. Bulletin of the American Meteorological Society, 76, No.12,2391-2402.