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The details of the scaling factors (s in the following equation) used at ECMWF to produce these relative indices are shown below, and some additional details of how they were computed are available in the blog post linked above.
| LaTeX Formatting |
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$$RNINO_{anom} = s(NINO - TROP)_{anom}$$ |
Niño3.4 Niño3 Niño4 Niño1+2
month
1 1.233 1.239 1.300 1.208
2 1.262 1.291 1.264 1.154
3 1.303 1.297 1.246 1.067
4 1.306 1.213 1.243 1.049
5 1.219 1.138 1.275 1.070
6 1.152 1.112 1.294 1.073
7 1.079 1.080 1.150 1.055
8 1.092 1.110 1.107 1.074
9 1.155 1.150 1.184 1.114
10 1.185 1.189 1.233 1.158
11 1.194 1.199 1.256 1.197
12 1.212 1.213 1.296 1.222
...