Atmospheric Blocking and Sub-Arctic Climate: Insights from CMIP5

Abstract:

The wintertime weather in the northern North Atlantic sector is characterized by a succession of intense storms and blocking distortions of the jet stream which cause strong surface fluxes and wind-driven forces. This is also a region of strong oceanic advection of heat northward from the Atlantic into the Nordic Seas and Arctic Ocean. In this study we examine year to year variations in these surface exchanges and advective contributions through analysis of 14 CMIP5 coupled climate models. All models exhibit decadal ocean variability of Nordic Seas that is comparable in amplitude and timescale to observations. However, the roles of heat advection and surface fluxes in producing this variability are different: some models are heat flux controlled models, while others are advection controlled. We find that the frequency of wintertime blocking events over Greenland is closely linked to these differences. Models with low event frequencies have ocean variability which is mainly flux-driven, while models with high event frequencies, have oceans in which ocean advection is key. Low frequency of these blocking events is also associated with a northeastward shift of the northern surface air pressure center of the model’s representation of the North Atlantic Oscillation, and this connection is discussed. Finally, we discuss connections of ocean variability to sea ice variability in the Arctic Basin and to the Atlantic meridional overturning circulation.