TELECONNECTIVE RESPONSE OF THE PACIFIC-NORTH AMERICAN REGION ATMOSPHERE TO LARGE CENTRAL EQUATORIAL PACIFIC SST ANOMALIES

A prominent year-round ensemble response to a global sea surface tempe rature (SST) anomaly held fixed to that for January 1992 (near the pea k of a major warm El Nino-Southern Oscillation episode) was observed i n a 20-yr integration of the general circulation model used for operat ional seasonal prediction by the U.S. National Weather Service. This m otivated a detailed observational reassessment of the teleconnections between strong SST anomalies in the central equatorial Pacific Ocean a nd Pacific-North America region 700-hPa heights and U.S. surface tempe ratures and precipitation. The approach used consisted of formation of monthly mean composites formed separately from cases in which the SST anomaly in a key area of the central equatorial Pacific Ocean was eit her large and positive or Large and negative. Extensive permutation te sts were conducted to test null hypotheses of no signal in these compo sites. The results provided a substantial case for the presence of tel econnections to either the positive-or negative-SST anomalies in every month of the year. These signals were seasonally varying (sometimes w ith substantial month to month changes) and, when present for both SST -anomaly signs in a particular month, usually were not similarly phase d patterns of opposite polarity (i.e., the SST-teleconnected variable relationships were most often nonlinear). A suite of 13 45-yr integrat ions of the same model described above was run with global SST analyse s reconstructed from the observational record. Corresponding composite s from the model were formed and compared visually and quantitatively with the high-confidence observational signals. The quantitative compa risons included skill analyses utilizing a decomposition that relates the squared differences between two maps to phase correspondence and a mplitude and bias error terms and analyses of the variance about compo site means. For the latter, in the case of the model runs it was possi ble to estimate the portions of this variance attributable to case to case variation in SSTs and to internal variability. Comparisons to mon thly mean maps and analyses of variance for the 20-yr run with SSTs fi xed to January 1992 Values were also made. The visual and quantitative comparisons all revealed different aspects of prominent model systema tic errors that have important implications for the optimum exploitati on of the model for use in prediction. One of these implications was t hat the current model's ensemble responses to SST forcing will not be optimally useful until after nonlinear correction of SST-field-depende nt systematic errors.