| Summary: | Blocking events are large-scale, quasi-stationary, high-pressure anomalous systems that last for weeks and block or divert the midlatitude (40◦ N-70◦ N) winds, blowing from west to east. Due to their persistence and size, depending on the season and the region, blocking events can cause, or contribute to, various types of extreme events such as heat waves, cold spells, droughts, and heavy rainfall episodes. Understanding the response of atmospheric blocking events to climate change has been of great interest in recent years. However, potential changes in the blocking area (size), which can affect the spatio-temporal characteristics of the resulting extreme events, have not received much attention. Using two large-ensemble, fully-coupled General Circulation Model (GCM) simulations, we show that the size of blocking events increases with climate change, particularly in the northern hemisphere (by as much as 17%). Using a two-layer quasi-geostrophic model and a dimensional analysis technique, we derive a scaling law for the size of blocking events, which shows that area mostly scales with width of the jet times the Kuo scale (i.e., the length of stationary Rossby waves). The scaling law is validated in a range of idealized GCM simulations. Predictions of this scaling law agree well with changes in blocking events’ size under climate change in fully-coupled GCMs in winters but not in summers. To better understand the dynamics and impacts of blocking events, their 3D structure needs to be further investigated. We present a comprehensive composite analysis of the 3D structure of blocks and its response to future climate change over North Pacific, North Atlantic, and Russia in summers and winters using reanalysis and two large-ensemble climate models. In reanalysis, over both ocean and land, the anomalous winds are equivalent-barotropic in the troposphere and stratosphere, and temperature anomalies are positive throughout the troposphere and negative in the lower stratosphere. The main seasonal and regional differences ...
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