Correspondences

What is linked, what is not

Each arc joins two phenomena tested on this site. Green and animated: clear link (correlation significant at 5 % after correcting for autocorrelation, or a response outside chance in an event study). Grey: inconclusive test. A statistical link alone does not establish causation.

Clear link
Inconclusive

Hypotheses tested

Clear links

correlation p < 0.05 or epochs outside chance

Causation demonstrated

a correlation demonstrates none

Arc width from |r| of the stored result; several tests between the same phenomena are drawn as stacked arcs.

Hypothesis tested: During El Niño, stronger zonal winds raise the atmospheric angular momentum; by conservation the Earth’s rotation slows and the day lengthens by a few tenths of a millisecond, lagging by about one month (Chao, 1989).

Pearson correlation r (lag 1 month(s))

0.45

95% interval [0.35; 0.56] (block bootstrap)

Aligned points

760

effective n ≈ 164 (autocorrelation)

p-value

0.00000

two-sided, Fisher z transform, effective n

Period analysed

1962-01 → 2025-05

computed on Oct 23, 2026 · engine v1.0

Aligned series (standard deviations, after preprocessing)

Show the data as a table

Both series are drawn in standard-deviation units (z) after removing the seasonal cycle and slow variations, to compare their fluctuations; original values are in the table and the CSV export.

Correlation by lag (month(s))

Show the data as a table

Pearson coefficient for each lag; a positive lag means the second series follows the first. The table gives n, effective n and p for each lag.

Aligned series (CSV)

Method and sources

Aligned monthly series (PSL Niño 3.4; monthly mean of the C04 length of day), seasonal cycle removed by monthly climatology, then variations longer than five years removed by a running mean. Pearson correlation for lags from −12 to +12 months, effective n after Bretherton et al. (1999), confidence interval from a 12-month block bootstrap (1000 draws).

Computation parameters

{
    "n_eff": "Bretherton et al. (1999)",
    "max_lag": 12,
    "bootstrap": {
        "seed": 20261023,
        "block": 12,
        "draws": 1000
    },
    "statistic": "pearson",
    "deseasonalize": "monthly climatology",
    "high_pass_months": 60
}

Inputs : psl.nino34.anom.monthly (945 pts, run #42) · iers.lod.daily (23,136 pts, run #66)

Reading this result

The correlation is robust and its positive lag (length of day follows the index) matches the expected mechanism; its value depends on the chosen filtering (5-year windows here). Correlation is not causation: common factors (seasons, cycles, trends) or coincidence can produce it. The p-values account for autocorrelation (effective n) but not for preprocessing choices; the confidence interval comes from a block bootstrap. The limits of the source data apply.

SOURCES OF THIS PAGE

Niño 3.4 SST anomaly (NOAA PSL, ERSSTv5): NOAA PSL, Niño 3.4 index: monthly SST anomaly (5°N–5°S, 170°–120°W) from ERSSTv5, climatology 1991–2020. · source page ↗
Licence : U.S. Government work, public domain · retrieved on Oct 23, 2026 · SHA-256 879cf3cb31d7…
IERS EOP 20 C04 daily Earth orientation since 1962: IERS Earth Orientation Centre, EOP 20 C04 (IAU2000A) combined series, 1962–; Bizouard, C., et al. (2019), J. Geod. 93, 621–633. · doi:10.1007/s00190-018-1186-3 · source page ↗
Licence : IERS data, free use with citation (Bizouard et al., 2019) · retrieved on Oct 23, 2026 · SHA-256 395e94687b8a…
Chao (1989): Chao, B. F. (1989). Length-of-day variations caused by El Niño–Southern Oscillation and quasi-biennial oscillation. Science, 243(4893), 923–925. · doi:10.1126/science.243.4893.923
Licence : Published literature; cited
Bretherton et al. (1999): Bretherton, C. S., Widmann, M., Dymnikov, V. P., Wallace, J. M., & Bladé, I. (1999). The effective number of spatial degrees of freedom of a time-varying field. Journal of Climate, 12(7), 1990–2009. · doi:10.1175/1520-0442(1999)012<1990:TENOSD>2.0.CO;2
Licence : Published literature; cited

El Niño and length of day Atmospheric angular momentum slows the Earth

What is linked, what is not