Title:Application of EMD method to river tide

Journal: Journal of Atmospheric and Oceanic Technology, 4: 809-819

Authors:PAN H. -D., G. Zheng, Y. -Y. Wang, and X. -Q. Lv*

Abstract: A lot of tidal phenomena, including river tides, tides in ice-covered bay, and internal tides in fjords, are non-stationary. These tidal processes present a severe challenge for the conventional tidal analysis method. The Empirical Mode Decomposition (EMD) method is useful for non-stationary and nonlinear time series and has been used for different geophysical data. However, application of EMD to non-stationary tides is rare. This report is meant to demonstrate a new tidal analysis tool that can help study of non-stationary tides, in this case, river tides. EMD is applied to a set of hourly water level records on the lower Columbia River, where the tides are greatly influenced by the fluctuating river flow. The results show that the averaged period of any EMD mode almost exactly doubles that of the previous one, suggesting that EMD is a dyadic filter. The highest and second highest frequency modes of the EMD represent the semidiurnal (D2) and diurnal (D1) tides, respectively. The sum of EMD modes except for the first two is mean water level (MWL). We find that EMD captured the non-stationary characteristics of D1 tides, D2 tides and MWL induced by river flow successfully.