Two Lagrangian approaches to atmospheric blocking

In the last decade, boreal summers have been marked by a number of extreme weather events such as heat waves, droughts and extreme precipitations with significant social, economical and environmental impacts. One of the most outstanding example occurred in the summer of 2010 when an anomalously strong heatwave persisted over Eastern Europe for several weeks while extreme rainfalls struck Pakistan, leading to the country’s worst floods in record history. This combination of events was due to the presence of an anomalously persistent atmospheric block - a large-scale pressure pattern.

Despite numerous studies, a complete understanding and prediction of atmospheric blocking events is still missing. In this work, we use two Lagrangian-based approaches to highlight distinctive circulation patterns associated with blocking. Firstly, taking a geometric perspective, we identify transport barriers present in and around the blocking region. These barriers, so called Lagrangian Coherent Structures, are computed from the Finite-Time Lyapunov Exponent field which measures local stretching in the atmospheric flow. Secondly, we construct a complex-network description of the flow based on a probabilistic approach and characterize the behavior of the flow network measures during blocking situations.