Causal dependences between the coupled ocean–atmosphere dynamics over the tropical Pacific, the North Pacific and the North Atlantic

Abstract

Abstract. The causal dependences (in a dynamical sense) between the dynamics of three different coupled ocean–atmosphere basins, the North Atlantic, the North Pacific and the tropical Pacific region (Nino3.4), have been explored using data from three reanalysis datasets, namely ORA-20C, ORAS4 and ERA-20C. The approach is based on convergent cross mapping (CCM) developed by Sugihara et al. (2012) that allows for evaluating the dependences between variables beyond the classical teleconnection patterns based on correlations. The use of CCM on these data mostly reveals that (i) the tropical Pacific (Nino3.4 region) only influences the dynamics of the North Atlantic region through its annual climatological cycle; (ii) the atmosphere over the North Pacific is dynamically forcing the North Atlantic on a monthly basis; (iii) on longer timescales (interannual), the dynamics of the North Pacific and the North Atlantic are influencing each other through the ocean dynamics, suggesting a connection through the thermohaline circulation. These findings shed a new light on the coupling between these three different regions of the globe. In particular, they call for a deep reassessment of the way teleconnections are interpreted and for a more rigorous way to evaluate dynamical dependences between the different components of the climate system.

Response to the Reviewer's comments

“…The code for CCM and the time series are available upon request to the authors. The data are made available on https://zenodo.org/ (Vannitsem, 2018).…”

Atmospheric and Ocean Dynamics May Explain Cycles in Oceanic Oscillations

“…The cycle length for the NAO when smoothed to identify multidecadal variability is about 60 years [31,32]. On an interannual time scale, the dynamics of the North Pacific and the North Atlantic probably influence each other through thermocline circulation [20]. The Privalsky and Yushkov [24] characteristics were AR(p) = 0 and r e = 0.…”

“…Furthermore, results may be distorted by additional methodical assumptions, like using frequencies that belong to a discrete harmonic set for windowed Fourier transforms [27]. A second type of method uses covariance estimates [20,40], and with increasing sample length the method gives more reliable results. The window length for the LL method is only used to establish confidence intervals by applying a Monte Carlo test to stochastic data.…”

“…Detailed mechanisms can be found in articles that include model descriptions (e.g., Jackson et al [19] on salinity and the AMOC). Williamson et al [5] discuss the relationship between temperature dipoles and wind stress, Vannitsem and Ekelmans [20] discuss thermohaline circulation, and Busecke and Abernathey [21] discuss ocean mesoscale mixing driven by variations in large-scale flow.…”

The North Atlantic Oscillations: Cycle Times for the NAO, the AMO and the AMOC

“…In Seip and Wang [5] it was shown that current climate models appear to describe ocean oscillation interactions fairly well, although those interactions are not directly implemented in the models. Furthermore, studies of teleconnections across basins suggest that basins will show similar cycle times, but that the cycles are phase shifted [6][7][8][9].…”