Atmospheric blocking events: a review

Even though meteorologists have been aware of atmospheric blocking for more than 100 years, it is a phenomenon still not well forecast or completely understood. Also, while there is not one standard accepted definition, there are some commonalities known about the understanding of blocking behavior. Blocking occurs less often than other destructive phenomena, but globally their occurrence has increased since the beginning of the century. The longevity of blocking means it can negatively impact agricultural and economic activity and human comfort by bringing extreme conditions not only to the areas where they occur but also to locations well upstream and downstream. Additionally, while it is known where blocking occurs and their general character has been well described, operational models still struggle to replicate the intensity and duration even though improvement has been noted in the timing and location of onset. Climatologically, models still underestimate their occurrence. In the last 40 years, investigators have used case study analysis and numerical and theoretical models to understand the onset and maintenance of blocking. Comparatively few have examined block decay. This review endeavors to cover the highlights of the history of blocking investigations, especially in the last few decades, in order to provide an understanding for a more general scientific audience.