RONI gave no clear pressure reconstruction gain over ONI in 2000-2024 separate-month linear tests

We compared ERSSTv5 RONI and ONI as inputs to a linear estimate of three-month standardized SOI. Separate fits for each center month used years from 1952 through test year minus two. At 300 held-out centers in 2000-2024, RONI reduced mean squared error by 3.70%, from 0.18784 to 0.18089. The conditional 95% five-year block interval was -28.14% to +25.69%. Mean absolute error rose slightly. A common-slope check and two time halves also had intervals that included zero. Planned trend and last-30-year fits gave larger gains, which shows dependence on the fitting method. These data do not establish a clear main-test advantage, real-time forecast skill, or a change in physical coupling. Revised reference periods, one pressure measure, shared SST observations, 25 test years and conditional uncertainty limit inference. The package includes code, aggregate losses, hashes, audits and a figure. Exact external source snapshots are required for reproduction.

ENSO · RONI · ONI · SOI · ocean atmosphere coupling · held-out reconstruction · null result