Bivariate EnSo Timeseries or the
"BEST" ENSO Index
Created by Prashant Sardeshmukh and Catherine Smith
index values | enso years | variable correlations
Please reference timeseries using the paper:
Note change in SST dataset. We are now using the HadISST 1.1
Smith, C.A. and P. Sardeshmukh, 2000, The Effect of ENSO on the Intraseasonal Variance of Surface Temperature in Winter.,
International J. of Climatology, 20 1543-1557.
index was designed to be simple to calculate and to provide a long time period ENSO index for research purposes.
Nino 3.4 has traditionally been used as a measure of ENSO strength in the tropical Pacific.
However, it's use alone neglects explicit atmospheric
processes. By adding the SOI or Southern Oscillation Index (the pressure difference between Tahiti and Darwin), these processes
are more directly included. In addition, older SST values are at least partially reconstructed and not explicitly measured.
By including the SOI, which is better measured historically,
the effect of biases in the SST data introduced by the reconstruction technique are reduced. A more detailed explanation how the index was created is available.
Based on 1871-2001 SST and SOI indices
Get 5-mo running mean time series
Get 3-mo running mean time series
Get 1-mo running mean time series
(contains most recent monthly value)
Details on creating and reading the timeseries.
El Nino/La Nina years
Table of years
Alternative (less stringent definition) table of years
El Nino/La Nina events can be taken from high/low values of the best index. Since
either of the 2 variables in the index may dominate, a "better" method
might be to use those months that correspond to both high Nino3.4 years
and low SOI values (or vice versa). The table lists the months where both the SST and the SOI exceeded the 20th percentile (+/-1.28). El Nino=1, La Nina=-1, 0 for other,-9 is missing). It was created using the 1871-2001 data with a 5 month running mean applied. A less stringent definition uses the top/bottom 33% events or std=+/-.96 and is here.
Correlation of Index with Atm/Ocean variables
Winter(DJF) and Summer(JJA) 1958-2000
|DJF Air T
|JJA Air T
|DJF Precipitation Rate
|JJA Precipitation Rate