Atmosphere-ocean interaction on weekly timescales in the North Atlantic and Pacific

Large-scale atmosphere-ocean interaction over the North Atlantic and North Pacific during winter using a 14-yr record of weekly sea surface temperature and atmospheric circulation fields is examined. Singular Value Decomposition is used to quantify objectively the degree of coupling between the sea surface temperature and 500-mb geopotential height fields as a function of time lag, from -4 weeks to +4 weeks. The authors show that the air-sea coupling is strongest when 500-mb height leads sea surface temperature by 2-3 weeks - twice as strong as the simultaneous covariability and nearly four times as large as when sea surface temperature leads 500-mb height by a few weeks. The authors believe the 2-3-week timescale may be a reflection of high-frequency stochastic forcing by the atmosphere on the ocean mixed layer, in the line with the theoretical model of Frankignoul and Hasselmann. Sensible and latent energy fluxes at the sea surface are shown to be an important component of the atmospheric forcing. The close spatial and temporal corresponding between the fluxes and SST tendencies on weekly timescales is a testament to the quality of the datasets.