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:

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.

Note change in SST dataset. We are now using the HadISST 1.1 The BEST 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 SLP JJA SLP DJF SST JJA SST

DJF U-Surf JJA U-Surf DJF Air T JJA Air T

DJF V-Surf JJA V-Surf DJF Precipitation Rate JJA Precipitation Rate