The 3D Structure of Atmospheric Blocking: Climatology and Response to Climate Change

Abstract:

Atmospheric blocking is a large-scale weather phenomenon that interrupts the prevailing eastward progression of pressure systems and can result in weather extremes in the midlatitudes. Due to their devastating consequences, understanding the changes of blocking in response to climate change has been of great interest in recent years. In this study, we investigate the 3D structure of blocking events in reanalysis and two large-ensemble, fully coupled GCM simulations. Here we compare the climatology of blocks in the models with reanalysis and show that the models are able to well capture the overall structure of blocks. The results of our composite analysis indicate that the blocks exhibit an equivalent-barotropic structure in both summer and winter seasons over both oceans and continents in the northern hemisphere. However, the intensity of blocks is stronger in winters compared to summers. There is also a barotropic convergence of the eddy field on the downside of the blocks. We also notice the significant contribution of latent heating and vertical velocity in warming up the upward upstream of the blocks. Finally, we study the response of the blocks to climate change (RCP8.5) and find that blocking events will be weakened in the summer of three different northern hemisphere regions. However, wintertime blocks’ responses to climate change are more complex than those in summers and depend on the regions and atmospheric pressure levels, thus a region by region analysis is needed to understand the winter responses.