Spatiotemporal patterns between the coupled modes of 500-mb geopotential height and sea surface temperature anomalies in the wintertime North Atlantic

The variation in the time lag and the transformation of the most coupled spatial patterns between atmospheric forcing and the oceanic response over the wintertime North Atlantic are studied depending on the time scale of the data under consideration. The singular value decomposition (SVD) of 500-mb geopotential height and sea surface temperature (SST) anomaly fields lagged relative to one another is used for this purpose. The monthly mean SST anomalies are found to lag behind the forcing monthly mean 500-mb height anomalies by half a month. This lag is described well by a simple ST-anomaly evolution model that relates the half-month lag to a quarter of a two-month oscillation period. This result suggests the presence of significant oscillations with a period of about two months in the midlatitude atmosphere. In addition, spurious oscillations with shorter periods may be observed in monthly mean data obtained at the Nyquist frequency corresponding to this period. Among such oscillations, SVD analysis of daily fields lagged in time distinguishes oscillations that correspond, in their spatiotemporal characteristics, to blocking situations in the North Atlantic. The transformation of the spatial 500-mb height and SST patterns of the first SVD mode is investigated on intraseasonal to interannual time scales. Parallel analysis of results produced by a coupled atmosphere-upper ocean model revealed their good agreement with those obtained from observational data.