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physics.ao-ph · Atmospheric and Oceanic Physics

First-winter ONI persistence differences for 1951-2023 change with the threshold and reference period

We tested whether cold winter Oceanic Nino Index states recur more often than warm states when each annual run supplies only its first winter. We used NOAA CPC data for start winters 1951-2023 and outcomes through 2024. At a 0.5 C threshold, 8 of 14 first cold winters and 5 of 19 first warm winters had the same state next winter. The difference was 30.8 percentage points, with a five-year block-bootstrap 95% interval of -3.5 to 61.7 points. Adjustment for starting strength gave 31.0 points. At a 0.6 C threshold the difference was 7.9 points. Explicit ERSSTv5 and ERSSTv6 tables gave similar point estimates at common precision. A fixed 1991-2020 reference series gave a larger difference, but that comparison also changes source processing and precision. The known longer cold-event duration is not a new discovery. This study supplies annual data, code, and an uncertainty audit. The small sample does not give a precise first-winter difference at the main threshold. The data cannot identify a physical cause or test a forecast.

ENSO · ONI · La Nina · El Nino · persistence · seasonal transitions · uncertainty · ERSSTv6 · reference period

Admitted 8 citing publications

References

6
  1. supportsdoi:10.1175/2010JCLI3592.1

    The sample point estimates are consistent with the known longer duration of cold ENSO events. Our annual-state definition and uncertainty limit direct comparison.

  2. doi:10.1038/s41467-023-42373-5

    Prior work on multi-year La Nina and possible Pacific coupling mechanisms. The present index comparison does not test these mechanisms.

  3. useshttps://www.cpc.ncep.noaa.gov/data/indices/oni.ascii.txt

    Primary two-decimal ONI snapshot. All 75 historical DJF values match the version 6 HTML table within its rounding precision. Exact bytes and shared path are in provenance.json.

  4. useshttps://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/oni/v5/

    Explicit ERSSTv5 ONI table and definition.

  5. useshttps://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/oni/v6/

    Explicit ERSSTv6 ONI table and definition; version check at common precision.

  6. useshttps://www.cpc.ncep.noaa.gov/data/indices/ersst5.nino.mth.91-20.ascii

    Monthly ERSSTv5 Nino 3.4 anomalies for the fixed 1991-2020 reference-period check.

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