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: The strongest flares are often accompanied by coronal mass ejections that reach the Earth in one to three days and compress the magnetosphere: Dst should drop in the following days (Gopalswamy, 2009).

Events used

484

minimum composite anomaly -13.30 nT

Days outside chance

out of 7 days tested after the event

Verdict

Clear effect

clear effect: two consecutive days outside the 5–95 % band

Period analysed

1976-01-01 → 2026-10-16

computed on Oct 23, 2026 · engine v1.0

Superposed epochs

Show the data as a table

Mean anomaly around the 484 events, relative to the mean of the days before each event (x axis in days); dashed lines are the 5th and 95th percentiles of composites built on randomly drawn dates (Monte-Carlo).

Aligned series (CSV)

Method and sources

For each day with at least one X flare in the GOES catalogue, the daily minimum Dst (OMNI2) is expressed as the departure from the mean of the five previous days, then averaged over all events. The 5–95 % band comes from 1,000 draws of random dates. The link is called clear if the composite leaves the band on two consecutive days.

Computation parameters

{
    "draws": 1000,
    "events": "days with an X-class flare (GOES)",
    "response": "daily minimum Dst (OMNI2), nT",
    "after_days": 6,
    "before_days": 5,
    "significance": "at least two consecutive days outside the Monte-Carlo 5–95 % band"
}

Inputs : goes.flares.x.yearly (51 pts, run #111) · omni.dst.hourly (559,191 pts, run #133)

Reading this result

Not every X flare launches an Earth-directed ejection: the mean composite (about −13 nT) is much weaker than individual storms, which can exceed −300 nT. The result illustrates the Sun–Earth chain; it does not forecast a given storm. X flares often come in series from the same active region: Dst already drops slightly before day 0, under the effect of the previous flares. 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

GOES X-ray flare lists (NOAA SWPC/NGDC events, yearly compilations by NASA GSFC): NOAA SWPC/NGDC GOES X-ray flare event lists (1975–), yearly compilations by K. Tolbert, NASA GSFC Hesperia. Flare classes as reported by NOAA at the time: until December 2019 the XRS-B flux carried a 0.7 scaling factor (Janssens et al., 2025). · source page ↗
Licence : U.S. Government work, public domain (NOAA/NASA) · retrieved on Oct 23, 2026 · SHA-256 9c4ca1a2c018…
OMNI2 hourly near-Earth solar wind and geomagnetic indices: King, J. H., & Papitashvili, N. E. (2005). Solar wind spatial scales in and comparisons of hourly Wind and ACE plasma and magnetic field data. J. Geophys. Res., 110, A02104. OMNI2 data from NASA/GSFC SPDF OMNIWeb; Kp/ap from GFZ Potsdam, Dst from WDC Kyoto, F10.7 from NRC Canada (Penticton). · doi:10.1029/2004JA010649 · source page ↗
Licence : NASA data, public domain; acknowledge SPDF/OMNIWeb and the index providers · retrieved on Oct 23, 2026 · SHA-256 6de9b217bd4b…
Gopalswamy (2009): Gopalswamy, N. (2009). Coronal mass ejections and space weather. In Climate and Weather of the Sun-Earth System (CAWSES), Terrapub, 77–120.
Licence : Published literature; cited
Gonzalez (1994): Gonzalez, W. D., et al. (1994). What is a geomagnetic storm? Journal of Geophysical Research, 99(A4), 5771–5792. · doi:10.1029/93JA02867
Licence : Published literature; cited

X flares and geomagnetic storms The Earth responds two to three days later

What is linked, what is not