Thursday, 13 February 2003
Interannual and interdecadal variability in the predominant Pacific Region SST anomaly patterns
Previous research by Kung and Chern (Atmosfera, 1995) has demonstrated that Pacific Region SSTs and SST anomalies can be separated into seven general synoptic classifications (“clusters”) for Pacific Region SSTs and SST anomalies (A-G). Each of these clusters is shown to have a distinct impact on the barotropic component of the mean tropospheric height distributions as well. Clusters A, B, E, and G (C, D, and F) are shown to be representative of La Nina (El Nino) type SST distributions. Further, an analysis of the SST patterns from 1955 – 1993 demonstrated that clusters A – D (especially A and B-type) were prominent from 1955 – 1977, while types E and F dominated the later period. Type G clusters were comparatively rare, but occurred in both periods. In retrospect, this shift in prominent patterns during 1977 corresponds roughly with a change in phase of the Pacific Decadal Oscillation (PDO). Thus, it is suggested that in updating the analysis to include the 1994 to 2002 period will correspond to a change in phase of the PDO during 1999 and 2000. Initial results have shown that during this period, SST patterns did evolve from predominantly E and F-type anomalies during 1994 to A, B, and G-type anomalies through 2001 and into mid-2002. By June 2002, the incipient El Nino resulted in the transition of the SST distributions to a D-type pattern. Thus, these results suggest that A through D-type SST clusters are characteristic of the negative phase of the PDO, while C, E, and F type are more characteristic of the positive phase of the PDO. These results will also be extended backward in time in order to obtain a longer period of record.