Abstract
ABSTRACT In late 1940 March, at least five significant solar flares were reported. They likely launched interplanetary coronal mass ejections (ICMEs), and were associated with one of the largest storm sudden commencements (SSCs) since 1868, resulting in space weather hazards that would have significant societal impacts should it occur today. The initial solar activity is associated with a solar proton event. Afterwards, another flare was reported in the eastern solar quadrant (N12 E37-38) at 11:30–12:30 ut on March 23, with significant magnetic crochets (up to ≈ |80| nT at Eskdalemuir) during 11:07–11:40 ut. On their basis, we conservatively estimate the required energy flux of the source solar flare as X35 ± 1 in soft X-ray class. The resultant ICMEs caused enormous SSCs (up to >425 nT recorded at Tucson) and allowed us to estimate an extremely inward magnetopause position (estimated magnetopause stand-off position ≈3.4 RE). The time series of the resultant geomagnetic storm is reconstructed using a Dst estimate, which peaked at 20 ut on March 24 at ≈ −389 nT. Around the storm main phase, the equatorward boundary of the auroral oval extended ≤46.3° in invariant latitudes. This sequence also caused a solar proton event and Forbush decrease (≈3 per cent). These sequences indicate pile-up of multiple ICMEs, which even achieved a record value of inward magnetopause position. Our analyses of this historical pioneer event bring more insights into possible serious space weather hazards and provide a quantitative basis for future analyses and predictions.
Highlights
ED Solar eruptions frequently release interplanetary coronal mass ejections (ICMEs)
These N ICMEs occasionally interact with the terrestrial magnetic field with sufficient mass
to their potential to create IN space weather conditions
Summary
ED Solar eruptions frequently release interplanetary coronal mass ejections (ICMEs). These N ICMEs occasionally interact with the terrestrial magnetic field with sufficient mass, U velocity, and southward interplanetary magnetic field (IMF) to cause geomagnetic storms and equatorward extensions of the auroral oval ED despite its significance, the lack of Dst index data for the 1940s makes a N quantitative analysis a challenge (Balan et al, 2019) Such extreme geomagnetic storms U (including this storm) have frequently been recorded incompletely, as their extraordinary magnitudes exceed the recording range of early magnetograms D considered a solar flare at N12 E37-38 from the centre of the solar disk on the previous E day, 23 March (Newton, 1940), when the sunspot area reached 1017 MSH This flare IT was recorded at a minimum of three observatories, i.e., in Greenwich (class 3), Zürich (class 3), and Cambridge (class 2+), according to D‘Azambuja (1940). USCRIPT AN M ITED ED N U Figure 3: Time series of the extreme SFE reported at Eskdalemuir ΓH (blue curve) and the modelled SXR flux of the source solar flare (red curve), following Curto et al. AL (2016).
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