Interdecadal Changes in the Links Between Late-Winter NAO and North Atlantic Tripole SST and Possible Mechanism

The North Atlantic Oscillation (NAO) and North Atlantic tripole sea surface temperature (SST_tri) are important modes in the atmosphere and ocean over the North Atlantic, respectively. The link between the two is well-known. However, this link weakened during 1980-2001, which is particularly pronounced in late winter and was not detected in early winter. This phenomenon has not been well revealed. The role of NAO in the above correlation changes was discussed. In late winter, a significant eastward shift (up to 20 degrees longitude) of NAO south center during 1980-2001 was observed in both observation and CMIP6, accompanied by the eastward expansion of NAO north center. Spatial shift of the NAO forced the region of strong air-sea interactions to shift and resulting in the collapse of NAO-related SST_tri. These findings deepen our understanding of the NAO on the subseasonal scale. A significant correlation between the North Atlantic Oscillation (NAO) and the North Atlantic tripole sea surface temperature (SST_tri) is widely recognized. However, this study found that the correlation between the two was significantly weakened in late winter during 1980-2001 while no such change was detected in early winter. Therefore, this paper will focus on the late winter and discuss the role of NAO spatial structure in the above correlation changes. When the NAO south center is located over the North Atlantic, both observations and the climate models indicate that the corresponding North Atlantic SST shows a significant tripole pattern. However, during 1980-2001, the NAO south center shift significantly eastward from the North Atlantic toward Western Europe (up to 20 degrees longitude). At the same time, the NAO north center expanded eastward significantly. The eastward shift of the NAO results in the significant eastward shift of the turbulent heat flux and wind stress anomalies. Shift in the region of strong air-sea interaction led to the collapse of NAO-related SST_tri. These findings deepen our understanding of the NAO on the subseasonal scale and also provide implications for subseasonal-seasonal predictions of Eurasian climate extremes. The link between NAO and North Atlantic tripole SST weakened obviously during 1980-2001 late winter, which was not detected in early winter The eastward shift of similar to 20 degrees longitude in NAO south center forced the strong air-sea interactions region to shift in observations and CMIP6 NAO's spatial shift in late winter caused the changes in the link between NAO and North Atlantic tripole SST