Eduardo Zorita, Viacheslav Kharin, and Hans von Storch
Max-Planck-Insitut für Meteorologie, Hamburg, Germany.
ABSTRACT
The ocean surface-atmosphere relationships in the North Atlantic in northern winter are empirically examined by canonical correlation analysis (CCA). This analysis is performed from two different points of view. First, the connection between atmospheric circulation anomalies, in terms of monthly mean sea level pressure (SLP) and monthly standard deviation of SLP (σSLP), and sea surface temperature (SST) anomalies of the Atlantic Ocean are idrectly examined. Second, the air-sea relationships are indirectly studied through their influence upon precipitation in a area likely to be determined by the North-Atlantic, the Iberian peninsula.
The canonical correlation analysis yields two pairs of patterns that describe the coherent variations of the combined SST-SLP fields; one pair of patterns for the SST-sigmaSLP fields and one pair of patterns for the SLP-sSLP fields. All patterns are dominant in describing variance. A lag-correlation analysis of the time coeffcients indicates that monthly SLP varies simultaneously with sslp but is leading monthly SST slightly. These results are consistent with the hypothesis that anomalies of the atmospheric circulation are mainly responsible for the appearance of anomalous wintertime SST and with the notion that the intramonthly variability of the atmosphere (sigmaSLP) is coupled to the mean flow (SLP).
With respect to Iberian pr4ecipitation, one-well defined CCA pair of patterns of regional rainfall and, respectively, SLP and SST is found. Above-normal Iberian precipitation is connected with a "high index" North Atlantic SLP distribution and below-normal SST in most of the Atlantic north of 200N. The dominant process responsible for the variability of rainfall appears to be the intensity of the westerly wind and the frrequency of storms imbedded in it, not the presence of regional or remote SST anomalies.
It is concluded that a large-scale SLP pattern in the North Atlantic, similar to the first EOF of the SLP field, is instrumental in generating both the Iberian precipitation and the Atlantic SST variability on the seasonal time scale.