The authors acknowledge the use of the SSA-MTM Toolkit provided by the UCLA SSA-MTM group from their Web site (http://www.atmos.ucla.edu/tcd/ssa/), and the Matlab wavelet scripts provided by Christopher Torrence and Gilbert P. Compo from their Web site (http://paos.colorado.edu/research/wavelets/). Comments and suggestions from two anonymous reviewers have been helpful to the improvement of the original manuscript. The work of the first author forms part of his M.Phil. research, which is supported by a Postgraduate Studentship from the City University of Hong Kong. This research is partially supported by City University of Hong Kong Strategic Research Grant 7000010.
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