An Analysis of Large-Scale Regime Transition on the Spatiotemporal Distribution of Cyclone Clustering

Northern Hemisphere cool season atmospheric predictability for sub-seasonal time scales (1-4 weeks) is greatly affected by the structure and evolution of the North Pacific jet stream (NPJ). The NPJ is largely affected by tropical and polar disturbances such as longitudinally varying convection associated with the Madden-Julian Oscillation (MJO), re-curving tropical cyclones (TCs) especially those that undergo extratropical transition (ET), and arctic air masses originating from the Asian continent that dive south. Perturbation of the NPJ by these disturbances can create an eastward-propagating Rossby wave train (RWT), and downstream wave amplification. This downstream propagation further enhances the probability of extreme weather events (EWE) occurring, for example, the sequential clustering of cyclogenesis events, and early season artic air equatorward surges over the CONUS. These EWE have enormous societal impacts ranging from agricultural damage to public safety.

A seasonal cyclone clustering climatology over the Northern Hemisphere during the years 1979-2015 will be constructed and displayed using maps. Whether certain flow regimes, and their phase and amplitude produce more favorable environments for cyclone clustering will be examined using the clustering climatology and density. These results will be achieved by utilizing the Hodges tracking algorithm and an algorithm produced by ECMWF for the CFSR and the ERAI re-analysis datasets. An assessment of the three cyclone tracking datasets on the sensitivity of NH cyclone clustering will be created.