Simultaneous analysis of space-time variability: Principal Oscillation Patterns and Principal Interaction Patterns with applications to the Southern Oscillation

The merits of the analysis techniques "POP" (Principal Oscillation Pattern) and "PIP" (Principal Interaction Pattern) are demonstrated by applying it to a combined data set of surface wind and sea surface temperature along the equator. The POP analysis detects a dominant low—frequency oscillatory mode with a time scale of about 2 to 3 years which can be identified as the Southern Oscillation. With respect to SST, the mode behaves approximately as a standing patttern with maximum extremes in the Central and Eastern Pacific. In the zonal surface wind, however, a eastward propagating feature can be detected. The meridional wind component is less organized, except for the occurrence of southerly winds in the Eastern Pacific during the "peak phase" of E1 Nifio. The result of the PIP analysis is essentially the same as that of the POP analysis. except for a seasonal dependence of the system’s stability: disturbances tend to be amplified during April to July and damped throughout the rest of the year.