Future change in Southern Hemisphere summertime and wintertime atmospheric blockings simulated using a 20-km-mesh AGCM

Abstract

Future changes in the frequency of Australia-New Zealand (AU; winter and summer) and Andes (AN; winter) blockings are investigated via present-day (1979-2003) and future (2075-2099) simulations using 20-, 60-, and 180-kmmesh atmospheric general circulation models (AGCMs) under the IPCC SRES A1B emission scenario. The presentday climate simulations reveal that the AGCM with the highest horizontal resolution is required to accurately simulate AU and AN blockings in both winter and summer. The future climate simulation predicts a significant decrease inAUblocking frequency in both summer and winter, mainly on the west side of the peak in present-day blocking frequency, where the westerly jet is predicted to increase in strength. The decrease in the AU blocking frequency during winter is more remarkable than that during summer. The number of long-lived AU blocking events is predicted to decrease with the possibility that events ≥13 days will disappear altogether. In contrast, no significant changes are predicted in AN blocking frequency and duration. © Copyright 2010 by the American Geophysical Union.