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

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.