Future change in wintertime atmospheric blocking simulated using a 20‐km‐mesh atmospheric global circulation model

Abstract

Future change in the frequency of atmospheric blocking is investigated through present‐day (1979–2003) and future (2075–2099) simulations using 20‐, 60‐, 120‐, and 180‐km‐mesh atmospheric general circulation models (AGCMs) under the Intergovernmental Panel on Climate Change Special Reports on Emission Scenarios A1B emission scenario, focusing on the Northern Hemisphere winter (December–February). The results of present‐day climate simulations reveal that the AGCM with the highest horizontal resolution is required to accurately simulate Euro‐Atlantic blocking, whereas the AGCM with the lowest horizontal resolution is in good agreement with reanalysis data regarding the frequency of Pacific blocking. While the lower‐resolution models accurately reproduce long‐lived Pacific blocking, they are unable to accurately simulate long‐lived Euro‐Atlantic blocking. This result suggests that the maintenance mechanism of Euro‐Atlantic blocking is different from that of Pacific blocking. In the future climate simulations, both frequencies of Euro‐Atlantic and Pacific blockings are predicted to show a significant decrease, mainly in the western part of each peak in present‐day blocking frequency, where the westerly jet is predicted to increase in strength; no significant change is predicted in the eastern part of each peak. The number of Euro‐Atlantic blocking events is predicted to decrease for almost all blocking durations, whereas the decrease in the number of Pacific blockings is remarkable for long‐duration events. It is possible that long‐lived (>25 days) Euro‐Atlantic and Pacific blockings will disappear altogether in the future.