Northern Hemispheric atmospheric blocking representation in Community Earth System Model Large Ensemble 2

Abstract Atmospheric blocking, a persistent high-pressure system that disrupts the westerly flow of jet streams, plays a critical role in driving extreme weather events but remains poorly represented in climate models. For the first time, this study assesses the representation of blocking in a large ensemble (100 members) using the Community Earth System Model Large Ensemble 2 (LENS2). A two-dimensional blocking detection method is used to analyze blocking frequency in LENS2 for the present-day (1980–2014) and future (2066–2100) periods. Comparisons with reanalysis datasets (ERA5 and NCEP2) reveal that LENS2 successfully reproduces the spatial distribution of blocking events over the Northern Hemisphere but exhibits region-dependent biases in frequency. Overall, winter blocking representation in LENS2 is found to be better than in previous models, while significant biases persist for the summer season.Future projections in LENS2 under the SSP370 scenario suggest a decrease in summer (winter) blocking by 2.5% (20%) by the end of the 21st century. However, summer blocking frequency is projected to increase over certain existing blocking-prone regions, such as Europe (+ 22%), the Pacific (+ 20%), and Russia (+ 12%), accompanied by an overall eastward shift in blocking centers in the future.