Before revision:  In contrast with classical methods, the surrogate data used here are realisations of a non-stationary linear stochastic process, preserving both the amplitude and time-frequency distributions of original data . These surrogate data are used in combination with an extension of the wavelet coherence to multivariate signals to detect short-lived coherent spatial patterns .
After revision:  In contrast with classical methods, the surrogate data used here are realisations of a non-stationary linear stochastic process, preserving both the amplitude and time-frequency distributions of original data .