100 Years of Progress in Understanding the Dynamics of Coupled Atmosphere–Ocean Variability

Abstract

In situ observation networks and reanalyses products of the state of the atmosphere and upper ocean show well-defined, large-scale patterns of coupled climate variability on time scales ranging from seasons to several decades. We summarize these phenomena and their physics, which have been revealed by analysis of observations, by experimentation with uncoupled and coupled atmosphere and ocean models with a hierarchy of complexity, and by theoretical developments. We start with a discussion of 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 tropical phenomena that only exist because of the coupling between the atmosphere and the ocean: 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 further discuss the sources of irregularity and asymmetry between warm and cold phases of ENSO, and the response of ENSO to forcing. 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. These patterns include the North Atlantic Oscillation (NAO), the North Pacific Oscillation (NPO), and the Pacific–North American (PNA) pattern; they are most active in wintertime, with a temporal spectrum that is nearly white. 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; 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. We review the progress that has been made in the past 50 years in understanding each of these phenomena and the implications for short-term (seasonal-to-interannual) climate forecasts. We end with a brief discussion of advances of things that are on the horizon, under the rug, and over the rainbow.

Monsoons, ITCZs, and the Concept of the Global Monsoon

“…Precipitation data are from CMAP 1979-2017 (Xie & Arkin, 1997), SST data are from HADISST 1870-2017(Rayner et al, 2003, and wind data are from ERA-Interim 1979-2017(Dee et al, 2011. From Battisti et al (2019). ©American Meteorological Society.…”

Increasingly important role of numerical modeling in oceanic observation design strategy: A review

“…Over the past several decades, significant progress in ocean observation has been made due to the development of observational instruments and increasing efforts from global research communities (Schiller and Brassington, 2011;Davis et al, 2019). Such progress has significantly improved the understanding, simulation, and prediction of the oceans (Battisti et al, 2019). Because of these efforts, observing, understanding, and simulating/predicting the ocean have reached a status of coordinated development.…”

Monsoons, ITCZs and the Concept of the Global Monsoon

“…Precipitation data are from CMAP 1979-2017(Xie & Arkin, 1997a), SST data are fromHADISST 1870 (Rayner et al, 2003, and wind data are fromERA- Interim 1979 (Dee et al, 2011. FromBattisti et al (2019). ©American Meteorological Society.…”