The data are calculated from the meridional wind in ERA-Interim. A lowpass filter of 15-days is applied and the daily climatology (also lowpass filtered) subtracted. The method of Zimin et al. 2003 with a latitude dependent wavenumber range is then applied. The description of this method and the discussion about the climatology of quasi-stationary waves (this dataset) and their connection to European temperature anomalies and extreme events can be found in the attached methodology statement.