Empirical mode decomposition and correlation properties of long daily ozone records.

Correlations for daily data of total ozone column are investigated by detrended fluctuation analysis (DFA). The removal of annual periodicity does not result in a background-free signal for the tropical station Mauna Loa. In order to identify the remaining quasiperiodic constituent, the relatively new method of empirical mode decomposition (EMD) is tested. We found that the so-called intrinsic mode functions do not represent real signal components of the ozone time series, their amplitude modulation is very sensitive to local changes such as random data removal or smoothing. Tests on synthetic data further corroborate the limitations of decomposing quasiperiodic signals from noise with EMD. Nevertheless the EMD algorithm helps to identify dominating frequencies in the time series, which allows to separate fluctuations from the remaining background. We demonstrate that DFA analysis for the cleaned Mauna Loa record yields scaling comparable to a mid-latitude station.