Western Regional Climate Center

Overview

The Southern Oscillation Index (SOI) is one measure of the large-scale fluctuations in air pressure occurring between the western and eastern tropical Pacific (i.e., the state of the Southern Oscillation) and is one index of the magnitude of El Niño Southern Oscillation (ENSO) events. Redmond and Koch (1991) show the strongest relationships between SOI and precipitation for the Western US are typically lagged with summer/autumn SOI having the best association with fall/winter precipitation totals. Another ENSO index more commonly used in the 21st century is the Niño 3.4 index which provides an average of the sea surface temperature anomalies in the Niño 3.4 region (5N-5S, 170W-120W). The Niño 3.4 index has similar relationships to Western US precipitation as the SOI. This page provides scatter plots of June-November SOI and Niño 3.4 anomaly against October-March precipitation totals (based on Redmond and Koch, 1991) for each NCEI Climate Division in the US for the period 1933-present. Seasonal scatter plots (ENSO and precipitation for the same season) and lagged seasonal scatter plots (ENSO lagged one season behind precipitation) are also provided.

Resources

Redmond, K.T. and Koch, R.W. (1991): Surface Climate and Streamflow Variability in the Western United States and Their Relationships to Large-Scale Circulation Indices. Water Resources Research, 27(9), 2381-2399. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/91WR00690

Southern Oscillation Index: https://www.ncei.noaa.gov/access/monitoring/enso/soi

Niño 3.4 Index: https://www.ncei.noaa.gov/access/monitoring/enso/sst

Monthly Niño 3.4 Anomaly Values: https://psl.noaa.gov/gcos_wgsp/Timeseries/Data/nino34.long.anom.data

NCEI Climate Divisions Map: https://www.ncei.noaa.gov/access/monitoring/reference-maps/conus-climate-divisions

Scatter Plots

Select the desired model, state, and district from the dropdown options below to view scatter plots.