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Solar storm

May 2024: a recap of the solar storm that lit up France

Published 28 April 2026 · 8 min read · Pulsar team

The weekend of 10-12 May 2024 will stay in the memory of anyone who looked up: a G5-class geomagnetic storm - the strongest since 2003 - made the northern lights visible to the naked eye as far south as the Old Port of Marseille. A recap of an exceptional event, what the science says, and how Pulsar covered it.

What happened

It all started on 8 May 2024. Active region 13664, a complex of sunspots 16 times the size of Earth, fired off a series of Earth-bound coronal mass ejections (CMEs). The event was flagged G4 on 9 May, then bumped to G5 (extreme) overnight on 10-11 May - the highest level on the geomagnetic scale, last reached in 2003. Pulsar tracked the progression in real time and pushed alerts to its users the moment their city's threshold was crossed.

The Kp index peaked at 9 of 9 for several consecutive 3-hour intervals. Magnetometers around the world recorded perturbations above 500 nT - enough to rattle Quebec power transformers and temporarily knock some Starlink satellites offline.

Aurora visible as far as Marseille

In France, the aurora started taking over the sky around 11 PM local time. From Lille, green ribbons appeared on the northern horizon. An hour later, from Paris, the aurora turned red and purple, photographed even from the ring road. Around 12:30 AM, sightings poured in from Lyon, Bordeaux, Toulouse. And the unexpected: from the Calanques near Marseille, the heights of Menton, Cap Canaille, photographers captured red columns above the Mediterranean.

At those latitudes (43-44° N), you usually have to go back to the 1957-1959 solar cycle to find a naked-eye aurora. The Carrington Event (1859), more powerful still, lit up the sky as far south as Cuba. May 2024 didn't reach Carrington, but it's the most striking event for France in over 60 years.

Why such striking colours?

The "classic" aurora is green: it comes from atomic oxygen at 100-300 km altitude emitting at 557.7 nm. But on 10 May, the dominant colour over France was red and purple. Three reasons:

  • At high altitude (300-500 km), oxygen emits red at 630 nm - the colour of extreme auroras.
  • Purple comes from ionised nitrogen (391-470 nm), excited only when the deposited energy is very intense.
  • At low latitudes (southern France), only the top of the auroral arc is visible - and that's exactly where red dominates.
For the first time in decades, tens of thousands of French people saw a northern aurora. Many first mistook it for light-pollution glare - until the columns started to dance.

What it teaches us for next time

Solar cycle 25, of which May 2024 was a peak, reaches its maximum between 2025 and 2026. Several practical lessons emerge:

  • Watch live Kp. When it crosses 7-8, head out immediately, regardless of your latitude. The window is short (a few hours) and unpredictable.
  • Don't trust the naked eye alone. A faint aurora looks grey. Take a 5-10 second exposure on your phone: if the colour pops on the sensor, the aurora is there.
  • Get away from streetlights. 30 km from a major city you gain 1-2 magnitudes - the difference between seeing nothing and seeing everything.
  • Look north. Even from Marseille in May 2024, the aurora was to the north, not over the sea.

Economic and technical impacts

Beyond the visual spectacle, May 2024 had significant technical fallout on several infrastructures. Total losses estimated by space and energy insurers exceed $500 million globally, split roughly across:

  • Precision agriculture: RTK GPS service used by autonomous tractors was disrupted for 24-48 hours across North America. Several Canadian cooperatives had to stop seeding mid-critical-window - Midwest losses alone estimated at $50 M.
  • Starlink constellation: SpaceX temporarily moved some satellites into "safe mode" to limit attitude losses from the expanded upper atmosphere. A few dozen satellites in descending orbit never recovered nominal altitude.
  • North American power grid: no major outages, but geomagnetically induced currents (GIC) briefly saturated transformers in Quebec and New England, triggering automatic protections without permanent damage.
  • Polar aviation: several transpolar flights (notably Air Canada and Lufthansa) were rerouted to avoid HF radio blackouts and elevated radiation exposure at high altitude.

These impacts illustrate why space weather is no longer purely a scientific topic but an operational continuity issue. That's exactly Pulsar's mission: turn scientific data into actionable alerts and recommendations for the operators concerned.

Field testimonials and data from France

Over 25,000 users visited the Pulsar app and API during the peak of the storm (10-12 May 2024), with spikes of 3,200 concurrent connections the moment the aurora pushed over Marseille. Some retrospective figures collected via our feedback form:

  • 87 % of respondents saw the aurora with the naked eye; 42 % from a major city (Paris, Lyon, Bordeaux, Toulouse).
  • 61 % were alerted by a notification (Pulsar, a weather app, social network) before stepping outside.
  • 34 % initially mistook the aurora for light pollution and only identified it after taking a long-exposure photo.
  • The southernmost département to report a naked-eye sighting: Bouches-du-Rhône (13), from the heights of Cap Canaille near La Ciotat at around 1:15 a.m.

A recurring theme in the feedback: it was hard to judge in real time whether the aurora was worth the trip. A grey haze seen from a city balcony often turned out to be - on a long exposure - a vivid coloured aurora. Always test with a long exposure before giving up.

FAQ: what you asked most

Why was May 2024 more visible than previous G4-class storms?

Three factors converged: (1) a succession of CMEs (at least 4 between 8 and 11 May) whose arrivals overlapped instead of spreading out - a cumulative "punch" effect; (2) a strongly negative Bz of the solar magnetic field (down to -50 nT), maximising coupling with Earth's magnetosphere; (3) exceptional weather luck in France, with clear skies over most of the country on the night of 10-11 May.

Can we predict an equivalent storm in advance?

With 18 to 96 hours of lead time we can detect that a CME is heading Earth-ward, but we only know its exact magnetic polarity (Bz) 30-60 minutes before arrival, when it crosses the DSCOVR satellite at 1.5 million km. Polarity decides whether the storm is moderate or extreme - hence the importance of real-time alerts rather than long-range forecasts.

Should I worry about internet or communications in a recurrence?

Not for the general public. Wi-Fi, 4G/5G and fibre are not affected by geomagnetic storms. The few real impacts hit HF communications (ham radio, polar aviation) and centimetre-precision GPS (RTK farming, geodesy). The "total blackout" scenario stays an extreme outlier (Carrington 1859 class), not statistically expected in 2026 even at cycle peak.

How many similar events to expect through 2027?

Based on previous solar cycles and the descending phase of cycle 25, a reasonable range is 1 to 3 G4-G5 class events between now and the end of 2027. Statistics show the most violent storms often arrive 1-2 years after the official maximum - so 2026-2027 remains a high-potential window.

How Pulsar covered the event

Throughout the storm, the Pulsar app and API streamed indices, thresholds, and per-city recommendations in real time. Pulsar users received a notification the moment Kp crossed their personalised threshold. Several user feedback messages told us the alert pulled them off the sofa just in time for the activity peak - exactly what the app is built for.

For the next major storm - there will likely be more in 2026 if the cycle holds - you can subscribe to free alerts via the contact form, or via the mobile app (launching 15 May 2026 on the App Store and Google Play).

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