Properties of baroclinic Rossby waves in the North Atlantic from eddy-resolving simulations of ocean circulation

Abstract. The teleconnections between the North Atlantic Oscillation (NAO) and the variability of the Gulf Stream (GS) were extensively studied these last years, often exhibiting time delays between both phenomena. These time lags, usually ranging between 0–2 years, are sometimes explained by the hypothesis of baroclinic Rossby waves generated by the NAO in the central North Atlantic (NA) and travelling westward before interacting with the GS. In this study, we use a numerical hindcast at an eddy-resolving resolution (1/12°) from the DRAKKAR project to examine the occurrence and properties of such Rossby waves between 1970–2015, thus including a large pre-TOPEX/Poseidon period. Through the use of a two-dimensional Radon Transform (2D-RT) on Hovmöller diagrams of the Sea Surface Height (SSH), a methodology easily portable to other oceanic model outputs, we show evidence of baroclinic Rossby waves travelling at 39° N at a speed of 4.17 cm s⁻¹. This is the first time Rossby waves are found that much north during such an extended period. These results are consistent with the time lags observed between the NAO and the GS transport while the GS latitudinal shifts might obey additional processes.