What to Expect
The Arctic Oscillation (AO) is the leading mode of climate variability in the Northern Hemisphere winter. It is generally regarded as a zonally-symmetric pattern with one center over Pacific and two centers over the North Atlantic and North Pacific. Based on observational and reanalysis datasets with long records, the multidecadal fluctuations in the patterns and teleconnections of the winter mean AO are investigated. Results show that the Atlantic center of the AO pattern remains unchanged throughout the period 1920–2010, whereas the Pacific center of the AO is strong during 1920–59 and 1986–2010 and weak during 1960–85. Consequently, the link between the AO and the surface air temperature over western North America is strong during 1920–59 and 1986–2010 and weak during 1960–85. The time-varying Pacific center of the AO motivates a revisit to the nature of the AO from the perspective of decadal change. It reveals that the North Pacific mode (NPM) and North Atlantic Oscillation (NAO) are the inherent regional atmospheric modes over the North Pacific and North Atlantic, respectively. Their patterns over the North Pacific and North Atlantic remain stable and change little with time during 1920–2010. The Atlantic center of the AO always resembles the NAO over the North Atlantic, but the Pacific center of the AO only resembles the NPM over the North Pacific when the NPM–NAO coupling is strong. These results suggest that the AO seems to be fundamentally rooted in the variability over the North Atlantic and that the annular structure of the AO very likely arises from the coupling of the atmospheric modes between the North Pacific and North Atlantic. Analysis of model outputs from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) also reveals fluctuations in the Pacific center of the AO, and the possible mechanism is discussed.
Lin is a Professor at Institute of Atmospheric Physics, Chinese Academy of Sciences. His research is mainly about mid-latitude climate variability, its mechanism and impacts in boreal winter, focusing on the East Asia-North Pacific region. He is interested in monsoon dynamics, atmospheric teleconnections, climate extreme events, and troposphere-stratosphere dynamical coupling.