Predicting the State of the Southern Oscillation Using Principal Oscillation Pattern Analysis

Abstract

Abstract Principal oscillation pattern (POP) analysis is a diagnostic technique for deriving the space-time characteristics of a dataset objectively. A multiyear dataset of monthly mean sea level pressure (SLP) in the area 15°S to 40°S is examined with the POP technique. In the low-frequency band one physically significant pair of patterns is identified, which is clearly associated with the Southern Oscillation (SO). According to the POP analysis, the 50 may be described as a damped oscillatory sequence of patterns …→P1→P2→-P1→-P2→P1… having a time scale of two to three years. The first pattern, P1, representative of the “peak” phase of ENSO, exhibits a dipole with anomalies of opposite sign over the central and eastern Pacific and over the Indian Ocean/Australian sector. The second, P2, pattern is dominated by an anomaly in the SPCZ region and describes an intermediate, or “onset” phase. The time coefficients of the two patterns, P1 and P2, may be interpreted as a bivariate index of the SO. Generalizing ...