Progress in Understanding the Dynamics of Coupled Atmosphere/Ocean Variability

Well defined, large scale patterns of coupled climate variability exist on time scales ranging from seasons to several decades; these phenomenon and their physics are the foci of our review paper. In the first two-thirds of the talk, we highlight the key topics covered in our review paper. The first section presents the seasonal cycle in the equatorial tropical Pacific and Atlantic Oceans, which are clearly affected by coupling between the atmosphere and the ocean. We then discuss the Pacific and Atlantic Meridional Modes, the El Niño-Southern Oscillation (ENSO) in the Pacific and a phenomenon analogous to ENSO in the Atlantic. For ENSO, we summarize the sources of irregularity and asymmetry between warm and cold phases of ENSO. Fundamental to variability on all time scales in the midlatitudes of the Northern Hemisphere are preferred patterns of uncoupled atmospheric variability that exist independent of any changes in the state of the ocean, land or distribution of sea ice: the North Atlantic Oscillation (NAO), the North Pacific Oscillation (NPO), and the Pacific North American / Aleutian Low (PNA) pattern. Stochastic variability in the NPO, PNA and NAO force the ocean on days to interannual times scales by way of turbulent heat exchange and Ekman transport, and on decadal and longer time scales by way of wind stress forcing. The PNA is partially responsible for the Pacific Decadal Oscillation (PDO); the NAO is responsible for an analogous phenomenon in the North Atlantic subpolar gyre. In models, stochastic forcing by the NAO also gives rise to variability in the strength of the Atlantic Meridional Overturning circulation (AMOC) that is partially responsible for multidecadal anomalies in the North Atlantic climate known as the Atlantic Multidecadal Oscillation (AMO); observations do not yet exist to adequately determine the physics of the AMO. The remainder of the talk will be dedicated to categorizing advances in coupled atmosphere-ocean variability and predictability that we believe are (i) on the horizon, (ii) under the rug, and (iii) over the rainbow.