The Coupled Patterns between Sea Level Pressure and Sea Surface Temperature in the Midlatitude North Atlantic

Abstract

Monthly variability of atmosphere-ocean interactions in the midlatitude North Atlantic during the winter months (November?April) is examined. Composite and singular value decomposition (SVD) analyses are applied to the observed sea level pressure (SLP) and sea surface temperature (SST) anomalies of each winter month for the period 1950?1987. The SLP anomaly composites (i.e., SLP differences between selected warm and cold SST months) are constructed based on the averaged SST anomalies over the RM region (60°?40°W and 50°?40°N). These composites shift from a positive monopole pattern in early winter to a dipole pattern in midwinter and then back to a monopole pattern in late winter. A complementary SVD analysis reveals that the first SVD mode is dipole structured and especially dominant in midwinter. The second SVD mode is monopole featured and more dominant in early and late winter than in midwinter. By examining the spatial distributions of the SVD modes and especially their similarities to the patterns derived from other model simulations, two coupling processes are suggested. The dipole mode is suggested to be related to an atmosphere driving the ocean process and the monopole mode to an ocean forcing the atmosphere process. The month-dependency and the statistical significance of the SVD modes are subjected to two Monte Carlo tests. The results are used to further explain the shifts in the SLP anomaly composites and to indirectly estimate the predominance of the proposed coupling processes during each winter month.