E-mail: edward.bolton@yale.edu

Wavelet Analysis of Climate

Working with K. A. Maasch and J. M. Lilly, I recently implemented a continuous wavelet analysis of the Earth's climate record of the last 2 million years. The local nature of the wavelet basis functions enables the computation of a transform in which the time dependence of modal amplitudes is clearly apparent. I created a new normalization of the wavelet bases which allows "period" to have a meaning consistent with that of Fourier analysis. The comparison of insolation forcing with oxygen isotopic variations in sediment cores shows that both series exhibit a beating pattern of the 20 kyr periodicity. In addition, the dominance of the ~100 kyr periodicity during the last million years, is seen to enter in the records with a beating pattern of successively longer periods. I am collaborating with Mike Mann, Jonathan Lees, and Kirk Maasch on a paper in which we compare wavelet analysis with evolutive and envelope multitaper analyses to highlight their relative advantages and disadvantages when applied to nonstationary processes.

Bolton, E.W., K.A. Maasch and J. M. Lilly (1995), A wavelet analysis of Plio-Pleistocene climate indicators: A new view of periodicity evolution, Geophysical Research Letters, 22, 2753-2756