An Exploratory Analysis of the 20th Century Reanalysis Extra-Tropical Cyclone Track Density

Extra-tropical cyclones (ETCs) are responsible for much of the impactful surface weather in the middle latitudes. Given the influence ETCs have on atmospheric conditions, changes in ETC track density over time can have a strong influence on regional climate, and may help to explain some of the impacts inter-annual variations have on regional weather patterns. In order to investigate this further, track data from the 56-member 20th Century Reanalysis ensemble was used generate ETC track densities. The initial analysis focuses on the winter season (November to March) in the northern hemisphere when ETCs are generally stronger and presumably better captured by the model. To further improve confidence in the reanalysis dataset, only ETCs that appeared in a third (20) or more of the ensemble members within 200 km were included in this study. It is anticipated that an exploratory analysis will reveal changes in ETC track density over periods of time such as successive 30-year normal periods or inter-annual variations (i.e. Madden Julian Oscillation).