Identifying Rossby wave trains and quantifying their properties

A novel method is introduced to automatically identify upper‐level Rossby wave trains and to objectively diagnose their properties. Based on the envelope of the upper tropospheric meridional wind represented in a Hovmöller diagram, the algorithm identifies individual Rossby wave trains as objects. These depend to some extent on user defined parameters. The utility of the method is demonstrated in two areas of application. First, the skill of a particular numerical weather prediction model is analysed for a specific case of a long‐lived Rossby wave train. For this purpose, a novel diagnostic is designed based on a Hovmöller diagram of the Rossby wave train objects that contains forecast data with the same lead time throughout the diagram. Automatically calculated properties of the different forecast Rossby wave trains are compared. Second, the climatological behaviour of Rossby wave train objects is investigated in long time series from reanalysis data. There are preferred regions for the generation and the decay of Rossby wave trains, and these regions show significant differences for Rossby wave trains of different minimum lifetimes; in addition there are substantial differences between the seasons.