North Atlantic variability driven by stochastic forcing in a simple model

This study investigates the mechanisms driving North Atlantic (NA) variability using a simple model that incorporates the time evolution of interactive upper ocean temperature anomalies, horizontal (Gyre, Ψ_g) and vertical (meridional overturning circulation, Ψ_m) circulation. The model is forced with multicentury long synthetic time series of external stochastic forcing that captures key statistical properties of observations such as the range of fluctuations and persistence of processes. The simulated oceanic response may be viewed as a delayed response to a cumulative atmospheric forcing over an interval defined by the system damping properties. Depending on the choice of parameters, the model suggests either compensatory mechanism (Ψ_m and Ψ_g are anti-correlated) or amplification mechanism (Ψ_m and Ψ_g are positively correlated). The compensatory mechanism implies that an increase of heat supplied by an anomalously strong Ψ_g would be balanced by a decrease of heat provided by a weaker Ψ_m and vice versa. The amplification mechanism suggests that both Ψ_m and Ψ_g maintain the heat budget in the system compensating its damping properties. Some evidence for these mechanisms is found in a global climate model. Further investigations of NA variability mechanisms are important as they improve understanding of how the NA climate system functions.