Use of the wavelet transform on hydro-meteorological data
A.F. Drago and S.R.Boxall
In ‘Physics and Chemistry of the Earth’ (2002) 27: 1387–1399
The advantages of utilising wavelet analysis to study the dependence of sea level variability on meteorological parameters are demonstrated on data collected at a sea level station on the northwestern coast of Malta. The strength of the method lies in the fact that time information is conserved and signal variability can be resolved up to levels which would equivalently require a much longer data set with Fourier transform methods. The validity of the wavelet transform is verified in its potential to decompose and identify in detail the synoptic variability of a parameter, as well as to follow the inter-dependence of more parameters by a quantitative comparison based on a correlation of their wavelet expressions.
The results of discrete wavelet analysis exhibit significant differences in the temporal development of the wavelet decompositions of residual sea level. This is even more evident in the air pressure field for which the variability is principally explained by wavelet decompositions corresponding to central frequencies of 0.56 and 0.28 cpd. The reduced activity in barometric pressure fluctuations during summer is particularly evident at these two decompositions.
This work also furnishes a contribution to studies concerning the validity of the inverted barometer effect. The position and extent of the frequency range at which the local sea level variation can be approximated by the inverted barometer effect is found to depend on the amplitude of the air pressure fluctuations. During the stronger pressure variations, the inverted correlation to the sea level occurs at practically the full range of synoptic frequencies and even lower.