IS CLIMATE VARIABILITY OVER THE NORTH PACIFIC A LINEAR-RESPONSE TO ENSO

Indices of the dominant spatial patterns of wintertime. Northern Hemis phere 500-mb height and North Pacific sea surface temperature are stro ngly correlated with one another on interannual and interdecadal times cales, and both are correlated with indices of the El Nino-Southern Os cillation. One possible interpretation of these relationships is that the tropical SST anomalies associated with ENSO force the atmospheric circulation over the North Pacific, and these atmospheric anomalies, i n turn, give rise to the observed SST anomalies over the extratropical North Pacific. In this study, linear relationships between ENSO and e xtratropical variables are examined in two different ways. First, the component of the observed extratropical variability that is Linearly d ependent upon ENSO is removed. The dominant spatial patterns in the re sidual variability of 500-mb height and SST anomalies over the North P acific are shown to be similar to their counterparts in the total fiel ds and remain strongly coupled on both interannual and interdecadal ti mescales. Second the 44 winters used in the analysis are divided into strong ENSO and weak ENSO group in accordance with the absolute magnit ude of ENSO SST anomalies during that winter. Consistent with tile ana lysis of the residual fields, the dominant patterns in extratropical 5 00-mb height and SST over be North Pacific are strongly coupled, even during winters in which tropical pacific SST anomalies are weak. An al ternative analysis, in which a 15-year record of MSU tropical precipit ation data is used as a basis for defining the ENSO signal, yields sim ilar results. The Linear relation between SST in the western tropical Pacific and extratropical circulation anomalies ic also examined and f ound to be weak.