Model projections of the changes in atmospheric circulation and surface climate over North America, the North Atlantic, and Europe in the Twenty-First Century

The impacts of climate change on the North America-North Atlantic-Europe sector are studied using a coupled general circulation model: the Climate Model, version 3 (CM3) and a high-resolution atmosphere-only model, the High Resolution Atmospheric Model (HiRAM)-both developed at the Geophysical Fluid Dynamics Laboratory. The CM3 experiment is conducted under two climate change scenarios for the 1860-2100 period. The sea surface temperature (SST) forcing prescribed in the "time slice" integrations with HiRAM is derived from observations for the 1979-2008 period and projection by CM3 for the 2086-95 period. The wintertime response in the late twenty-first century is characterized by an enhancement of the positive phase of the North Atlantic Oscillation in sea level pressure (SLP) and poleward and eastward displacements of the Atlantic jet stream and storm track. The forcing pattern due to eddy vorticity fluxes in the perturbed storm track matches well with the response pattern of the SLP field in the late twenty-first century. The model results suggest that the above circulation changes are linked to the gradient of the altered SST forcing in the North Atlantic. In summer, the projected enhancement of convection over the eastern tropical Pacific is accompanied by a wave train spanning the North America-North Atlantic-Europe sector. This quasi-stationary circulation pattern is associated with diminished storm track activity at 40°-50°N and an eddy forcing pattern similar to the summertime SLP response in the late twenty-first century.