NOI and the SOI* Computation
The indices are computed from NCEP sea level pressure anomalies (SLPA)
(monthly sea level pressure minus climatology) of
the North Pacific High (NPH) [35N,130W],
South Pacific High (SPH) [30S,95W],
Darwin [10S,130E], and Tahiti [18S,150W].
The NOI, SOI*, and SOI are created as
follows:
| NOI = SLPA_NPH - SLPA_DARWIN |
| SOI* = SLPA_SPH - SLPA_DARWIN |
| SOI = SLPA_TAHITI - SLPA_DARWIN |
The definitions used to calculate the NOI and SOI* differ slightly from the traditional
definition of the SOI (Chelliah 1990), in that neither the pressure series
nor the indices are normalized. We compute a version of the SOI
consistent with the NOI and SOI*. The base period we used for the climatologies is January 1948 to
December 1997.
http://www.pfeg.noaa.gov/products/PFEL/modeled/indices/NOIx/compute.html
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NOI Computation