Sensitivity of Blocks and Cyclones in ERA5 to Spatial Resolution and Definition

ERA5, the fifth‐generation reanalysis of the European Center for Medium‐Range Weather Forecasts, provides long time series of atmospheric fields at high spatial and temporal resolution. It allows detailed studies of atmospheric flow features such as blocks or cyclones. We investigate characteristics of blocks and cyclones in ERA5 using different algorithms, compare the results to ERA5's predecessor, ERA‐interim, and investigate how these characteristics depend on spatial resolution. Generally, ERA5 and ERA‐interim characterize blocks and cyclones similarly. For Lagrangian detection and tracking methods, blocks are more robust than cyclones to changes in resolution and reanalysis choice. Eulerian methods are robust to changes in resolution. Thus, ERA5 provides a state‐of‐the‐art reanalysis for the synoptic‐scale extratropical circulation. We find that Lagrangian cyclone characteristics are strongly dependent on spatial resolution and therefore recommend that model and reanalysis data should be mapped to a common resolution for verification.