Description:   The top monthly time series is the standardized Southern Oscillation Index (SOI), the difference between the standardized sea level pressure at Tahiti and the standardized sea level pressure at Darwin for the last five years. Positive values are represented by the red bars and negative values are represented by the blue bars. The next time series is the 5-month running average SOI value, followed by the standardized SOI for Jan 1951 to present, and the 5-month running average SOI for Jan 1951 to present. Links to time series graphs of monthly SOI and 5-month running average SOI for 1882 to 1996 are also available.   NCEP is an acronym for the US National Centers for Environmental Prediction.