The Climatological and Dynamic Character of Simultaneously Occurring Blocking Events

Previous climatologies examining the topic of blocking anticyclones generally study the global occurrence of blocking over a certain time period or a geographically defined subset of these events. There are few studies that are associated with particular blocking characteristics such as duration or intensity, or some other quantity outside of occurrence. In this work, the climatological and dynamic character of simultaneously occurring blocking events will be examined. Some previously published papers have proposed without strong evidence that simultaneously occurring blocking events are stronger and more persistent than those that occur in isolation. Simultaneous blocking events are defined as those that occur at around the same time but in different parts of the Northern or Southern Hemisphere. Other work has postulated that the relative paucity of these events in the mid-20^th century indicated that simultaneous events were likely coincidental as blocking is due to a combination of large- and synoptic-scale atmospheric process. These have also postulated that a greater frequency of block occurrence would lead to a greater probability of these events occurring in tandem. Using the NCEP reanalyses, the character of simultaneously occurring blocking events is examined from the mid-20^th century through 2024. This work found that in the Southern Hemisphere, simultaneous blocking events are significantly stronger and longer-lived than solitary events. In the Northern Hemisphere, blocking is not necessarily stronger; however, they are more persistent.