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: A positive dipole warms the western Indian Ocean and cools the east: convection shifts towards East Africa, whose October–December short-rains season turns wet (Saji et al., 1999; Black et al., 2003).

Spearman correlation ρ

0.55

95% interval [0.18; 0.77] (block bootstrap)

Pearson correlation r (lag 0 year(s))

0.55

at the strongest lag

Aligned points

effective n ≈ 36 (autocorrelation)

p-value

0.00039

two-sided, Fisher z transform, effective n

r without the El Niño part

0.46

p = 0.004; Niño 3.4 alone: r = 0.30

Period analysed

1961 → 1997

computed on Oct 25, 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 (year(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

DMI from NOAA NCEI, September–November mean; Nairobi rainfall (GHCN-Daily), October–December total, months kept when at least 90 % complete (total scaled to the whole month). Lag fixed at zero; Pearson and Spearman (skewed rainfall), 3-year block bootstrap on Spearman. To separate the dipole from El Niño, which often occur together, the DMI is regressed on Niño 3.4 of the same season and the correlation is repeated on the residual.

Computation parameters

{
    "x": "mean Dipole Mode Index of September–November (NOAA NCEI)",
    "y": "October–December rainfall total at Nairobi (GHCN-Daily KE000063740 area, months ≥ 90 % complete, total scaled to the month)",
    "lag": "fixed at 0",
    "enso": "Niño 3.4 of September–November; dipole residual after a least-squares fit on it",
    "bootstrap": {
        "seed": 20261023,
        "block": 3,
        "draws": 1000,
        "statistic": "spearman"
    }
}

Inputs : ncei.iod.monthly (2,073 pts, run #3722) · ghcn.nairobi.precip.daily (16,748 pts, run #3700) · psl.nino34.anom.monthly (945 pts, run #42)

Reading this result

The link is strong and persists without ENSO, which confirms the own role of the Indian Ocean. But the Nairobi series is complete only to the late 1990s in GHCN-Daily: the sample is short, and 1997 (record dipole and El Niño, floods) weighs heavily. A single station does not stand for the whole region. 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

Indian Ocean Dipole (Dipole Mode Index) from ERSSTv5 (NOAA NCEI): NOAA NCEI, ERSST v5 Indian Ocean Dipole: SST anomaly difference between the western (50–70° E, 10° S–10° N) and south-eastern (90–110° E, 10° S–0°) tropical Indian Ocean (Saji et al., 1999), climatology 1971–2000. · doi:10.7289/V5T72FNM · source page ↗
Licence : U.S. Government work, public domain · retrieved on Oct 25, 2026 · SHA-256 e1a515e8d331…
GHCN-Daily stations of the reference places (NOAA NCEI): Menne, M. J., Durre, I., Vose, R. S., Gleason, B. E. and Houston, T. G. (2012). An overview of the Global Historical Climatology Network-Daily database. J. Atmos. Oceanic Technol., 29, 897–910. Menne, M. J., et al. (2012). Global Historical Climatology Network - Daily (GHCN-Daily), Version 3. NOAA NCEI. · doi:10.7289/V5D21VHZ · source page ↗
Licence : U.S. Government work, public domain (data from national services under WMO Resolution 40); cite Menne et al. (2012) · retrieved on Oct 25, 2026 · SHA-256 fb525098ce40…
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…
Saji et al. (1999): Saji, N. H., Goswami, B. N., Vinayachandran, P. N., & Yamagata, T. (1999). A dipole mode in the tropical Indian Ocean. Nature, 401, 360–363. · doi:10.1038/43854
Licence : Published literature; cited
Black et al. (2003): Black, E., Slingo, J., & Sperber, K. R. (2003). An observational study of the relationship between excessively strong short rains in coastal East Africa and Indian Ocean SST. Monthly Weather Review, 131(1), 74–94. · doi:10.1175/1520-0493(2003)131<0074:AOSOTR>2.0.CO;2
Licence : Published literature; cited

Indian Ocean Dipole and East African rains Positive dipole, abundant short rains in Nairobi

What is linked, what is not