Patrick MARTINEAU, Hisashi NAKAMURA, Bunmei TAGUCHI, Yu KOSAKA and Masato MORI 

Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan 

The relationship between the frequency of weather extremes and the slowly-varying ocean state is still elusive. In this study, statistical modes of covariability between sea surface temperature (SST) and wintertime subseasonal temperature variability in the lower troposphere midlatitudes over decadal timescales are identified by applying singular value decomposition analysis to reanalysis data. The dominant mode of covariability identified by this analysis highlights an important connection between wintertime SSTs over the North Atlantic Ocean, with a pattern similar to the Atlantic Multidecadal Oscillation, and subseasonal surface temperature variability over Northeastern America and Europe. The associated atmospheric circulation anomaly, which is reminiscent of the negative phase of the North Atlantic Oscillation, is partly maintained by the propagation of a Rossby wave train forced by anomalous heat fluxes between the ocean and atmosphere in the subtropics. In addition, the atmospheric anomaly pattern is found to maintain itself efficiently in the midlatitudes through a transfer of energy from the mean flow by baroclinic processes. This interdecadal variability of the wintertime circulation is found to modulate transfers of energy between the time-mean flow and the subseasonal eddies that are responsible for the occurrence of surface temperature extremes.