Occurrence and transition probabilities of omega and high-over-low blocking in the Euro-Atlantic region

Abstract. Stationary, long-lasting blocked weather patterns can lead to extreme conditions such as anomalously high temperatures or heavy rainfall. The exact locations of extremes depend on the location vortices that form block. There are two main types blocking: (i) a high-over-low block with located poleward an isolated low and (ii) omega lows lie southeast southwest blocking in Northern Hemisphere. In this work, we refine novel method based kinematic vorticity number point vortex theory allows us distinguish between these types. Based National Centers for Environmental Prediction–Department Energy (NCEP–DOE) Reanalysis 2 data, study trends occurrence probability onset (formation), decay (offset) transition probabilities 30-year period from 1990 2019 Hemisphere (90∘ W–90∘ E) Euro-Atlantic sector (40∘ W–30∘ E). First, use logistic regression investigate long-term changes full years, seasons months. While small annual values, more visible also diverse when broken down seasonal monthly resolution, showing prominent increase February March decrease December. A three-state multinomial describing reveals different both Particularly December dominated by type. Additionally, Markov models describe two-state (unblocked, blocked) block, block) model. We find largest summer season, where towards blocks significantly increase, while unblocked state becomes less probable. Prominent winter decreasing transitions persistence latter. Moreover, show is likely occur be persistent than pattern.