Size of the atmospheric blocking events: A scaling law and response to climate change

Understanding the response of atmospheric blocking events to climate change has been of great interest in recent years. However, potential changes in the area (size) of blocking events, which can affect the spatio-temporal characteristics of the resulting extreme events, have not received much attention. Using two large-ensemble, fully-coupled GCM simulations and two blocking indices, we show that the size of blocking events increases with climate change, particularly in summers of the northern hemisphere (by as much as 17%). Using a two-layer quasi-geostrophic model and the Buckingham-PI dimensional analysis technique, we derive a scaling law for the size of blocking events, which shows that area mostly scales with the 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. This scaling's predictions agree well with changes in blocking events' size under climate change in fully-coupled GCMs in winters but not in summers. These results, recently published in Nabizadeh et al. (2019 GRL) suggest that future studies should focus on investigating the consequences of larger blocks on the size, magnitude, and persistence of extreme weather events, and on improving the understanding of summer blocks. Our more recent work using an idealized moist GCM (MiMA) with aquaplanet lower boundaries and seasonal cycle shows that, again, the scaling law works remarkably well in winters but not in summers, which points to diabatic processes as the likely source of discrepancy. Using MiMA to extend the scaling law to account for diabatic processes is currently underway. Nabizadeh, E., Hassanzadeh, P., Yang, D. and Barnes, E.A., 2019. Size of the atmospheric blocking events: Scaling law and response to climate change. Geophysical Research Letters.