Atlantic Climate Variability Experiment Prospectus

Energetic, large-scale variability is observed in the atmosphere and ocean of the Atlantic Sector on interannual and decadal time scales. It is manifested as coherent fluctuations in temperature , rainfall, surface pressure and temperature reaching eastward to central Europe and northern Asia, southward to subtropical West Africa and westward to North and South America with a myriad of well documented impacts on society and the environment. The coordinated changes in the position of mid-latitude atmospheric pressure centers and winter storm tracks over the Atlantic , as well as the strength of the trade winds, are commonly referred to as the North Atlantic Oscillation (NAO). In the tropical Atlantic, surface temperature variability and associated changes in the inter-tropical convergence zone and the Hadley circulation occurs on interannual to decadal time scales, phenomena we collectively call Tropical Atlantic Variability (TAV). The NAO and TAV are reflected in marked changes in wind stress on the ocean, as well as air-sea heat and fresh water fluxes. These in turn induce substantial changes in the wind-and buoyancy-driven ocean circulations, water mass transformation and possibly poleward heat transport. Indeed many ocean properties show strong links to overlying atmospheric variability, suggesting that much of the observed ocean variability is driven by the atmosphere. Whilst it is known that the Atlantic ocean plays a central role, through its thermoha-line circulation, in the mean climate, its role in modulating atmospheric variability on interannual to decadal time scales is less clear. We propose an Atlantic Climate Variability Experiment (ACVE) to address the overarching question: In what ways does coupled atmosphere-ocean dynamics in the Atlantic sector play an active role in climate variability? Its primary goal is to quantitatively test and improve our understanding of mechanisms and models of atmospheric and ocean processes that lead to climate variability in the Atlantic and its global consequences. We must determine whether observed and simulated variability is fundamentally coupled, whether one component drives variability in the other, whether modeled variability bears any relation to observed variability, and whether modes of variability once identified are predictable. Improvement of atmospheric and oceanic circulation models, especially boundary layer formulations, is a central part of ACVE. The specific objectives of the Atlantic Climate Variability Experiment are to: • Describe and model coupled atmosphere-ocean interactions in the Atlantic sector, quantify their influences on the regional and larger scale climate system, and investigate their predictability. • Assemble a quantitative historical …