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 full-halo CME is heading towards the Earth or directly away from it. The fastest reach the magnetosphere in one to three days and cause most large storms: Dst should drop. Fast CMEs seen at the limb leave sideways and should have no effect (Gopalswamy et al., 2007).

Events used

389

minimum composite anomaly -13.38 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

Control: composite minimum (nT)

-0.6

285 days of limb CMEs, 3 day(s) outside the band

Period analysed

1996-01-01 → 2026-10-16

computed on Oct 23, 2026 · engine v1.0

Superposed epochs

Show the data as a table

Mean anomaly around the 389 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).

Control group: fast CMEs seen at the limb

Show the data as a table

Aligned series (CSV)

Method and sources

For each day on which the CDAW catalogue lists a full halo of at least 1000 km/s, the daily minimum Dst (OMNI2) is expressed as a 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.

The control group gathers the days of equally fast CMEs narrower than 120°, not halos, halo days removed: they leave towards the limb, across the Sun–Earth line.

Computation parameters

{
    "draws": 1000,
    "events": "days with a full-halo CME ≥ 1000 km/s (SOHO/LASCO CDAW)",
    "control": "days with a non-halo CME ≥ 1000 km/s narrower than 120° (limb events), halo days removed",
    "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 : cdaw.cme.fast_halo.yearly (31 pts, run #10) · omni.dst.hourly (559,191 pts, run #133)

Reading this result

The dip of the composite after fast halos is clear and comes around day two, the travel time of a fast CME. The control group stays almost flat: the direction of the ejection matters, not only its speed. Some halos leave towards the far side and have no effect, which dilutes the mean. The orientation of the CME’s magnetic field (southward Bz) then sets the strength of the storm. 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

SOHO/LASCO CME catalogue (CDAW Data Center): Yashiro, S., Gopalswamy, N., et al. (2004). A catalog of white light coronal mass ejections observed by the SOHO spacecraft. JGR 109, A07105; Gopalswamy, N., et al. (2009), Earth Moon Planets 104, 295. The CME catalog is generated and maintained at the CDAW Data Center by NASA and The Catholic University of America in cooperation with the Naval Research Laboratory. SOHO is a project of international cooperation between ESA and NASA. · doi:10.1029/2003JA010282 · source page ↗
Licence : NASA, public domain; acknowledgement requested (CDAW, SOHO is an ESA/NASA project) · retrieved on Oct 23, 2026 · SHA-256 7f74bca5d28a…
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 et al. (2007): Gopalswamy, N., Yashiro, S., & Akiyama, S. (2007). Geoeffectiveness of halo coronal mass ejections. Journal of Geophysical Research, 112, A06112. · doi:10.1029/2006JA012149
Licence : Published literature; cited
Yashiro et al. (2004): Yashiro, S., Gopalswamy, N., et al. (2004). A catalog of white light coronal mass ejections observed by the SOHO spacecraft. Journal of Geophysical Research, 109, A07105. · doi:10.1029/2003JA010282
Licence : Published literature; cited

Halo CMEs and geomagnetic storms Fast halos hit the Earth two days later

What is linked, what is not