What are Radio Blackouts?

1. Radio blackout phenomenon
2. Current and predicted fadeouts
3. How does a fadeout happen?
4. A review of significat radio blackout events of the 25th solar cycle
5. The first significant blackout event of the 25th solar cycle May 2024

Under normal conditions, HF radio waves from 3 to 30 MHz provide long-distance communication by reflecting off the ionosphere. However, suddenly the signal vanishes, and you hear nothing but static. This sudden loss of signal is what's known as a radio blackout.

An artist view

Fig 1. A radio blackout or fadeout refers to a major signal loss

The drop in signal affects in particular the lower HF bands.

Fig 2. Fadeout signal strength vs. time, courtesy of Australian Space Weather Services

Effects of Radio Blackouts

Communication Disruption: Radio blackouts can interrupt communication, especially affecting airplanes, ships, and emergency services that rely on certain radio frequencies.

Navigation Issues: GPS signals might become unreliable, which can be a problem for navigation systems.

Space weather events in the last three days The recent 3 days of Space Weather - RSG Scales Published by NOAA SWPC services Fig 3. Space weather events in the last three days Reference: Space Weather images at (US) NOAA SWPC

Current and predicted fadeouts as reported by ASWFC

Flare alarm   Fig 4. Flare alarm

Observed fadeout now present

Predict possible fadeouts near future

How does a fadeout happen?

Blackouts happen when the Sun releases "Solar Flares" (X-Ray radiation) and / or "Solar Particle Events" (SPE).

Fig 5. Solar Flares and Coronal Mass Ejections
are components of suden solar storms that may
affect skywave radio propagation on Earth.

Flashes of radiation

Fig 6. A Solar Flare courtesy of NOAA, May 2023

Solar flares reach Earth at the speed of light, taking approximately 8 minutes and 20 seconds. However, the ejected particles can take anywhere from a few hours to up to four days to reach Earth, depending on their speed.

Ejection of solar matter

A CME is a shock-wave of highly charged particles emitted by the sun.

Fig 7. Solar wind, CME and Earth magnetosphere

---

When a CME enters the magnetosphere, it causes a Geomagnetic Storm

Fig 8. An artist view of a Geomagnetic Storm

Major magnetic storms can block HF propagation from 3 to 30 MHz by altering the distribution of free electrons in the ionosphere. These storms can increase ionization in the D-region of the ionosphere, which blocks HF radio transmissions. Unexpected bursts on the Sun's surface cause Sudden Ionospheric Disturbances (SIDs) on Earth, with recovery times ranging from minutes to hours.

The 25th Solar Cycle Reaches Peak

On February 22, 2024, a X6.3 flare from region 3590 peaked. Then series of significat radio blackout events began on May 1, 2024, starting within region 3664. This spot was 17 times the size of Earth, triggered powerful solar flares and coronal mass ejections, leading to breathtaking auroras. NASA hailed this as the most intense geomagnetic storm in 500 years.

Since then, the Sun has unleashed multiple M-class and mild X-class flares. On October 3, it released an immense X9.0 flare, which caused a G4 geomagnetic storm, disrupting communications and creating vivid auroras. NASA later confirmed the arrival of the solar maximum with the Sun’s magnetic field flip.

A detailed review of the most significant radio blackout events since May 1, 2024

See below a screenshot of NOAA's spaceweather center:

The first dramatic radio blackout event for the 25th solar cycle has occurred
in May 2024


Fig 9. A screenshot of NOAA's spaceweather center on May 11, 2024 at 11:34 UTC

NASA’s Solar Dynamics Observatory captured images of the two solar flares on May 10 and May 11, 2024. These flares were part of a series of strong solar activities, classified as X5.8 and X1.5-class flares, respectively.

Another flare from region 3664 reached X8.7 on May 14, 2024.

The recorded geomagnetic storms were the most powerful to affect Earth since March 1989, and produced aurorae at far more equatorial latitudes than usual in both the Northern and Southern Hemispheres.

Fig 10. A-indices recorded 30 days before that 11-May-2024 blackout event

Fig 11. K-indices before and after that 11-May-2024 blackout event

Fig 12. Kp-index 3 days after that 11-May-2024 blackout event

On 14 May 2024 X8.7 flare was observed.

Fig 13. A screenshot: X8.7 flare (region 3664) was observed on 14-May-2024, followed by a strong HF radio blackout.

It was the largest flare since the beginning of cycle 25 until 14-May-2024.

Due to its location, any CME associated with this flare did NOT have any geomagnetic impact on Earth.

R3 HF Radio Blackout Observed X4.5 flare on 14-Sep-2024

Fig 14. An X4.5 flare caused R3 (Strong) HF radio blackouts

Sun released the strongest X9.0 solar flare (since 2017) on October 3, 2024

Fig 15. An X9.0 flare occurred at sunspot region 3842 causing R4 strong HF radio blackouts

R3 HF Radio Blackout Observed X3.3 flare at Region 3869 on 24-Oct-2024

Fig 16. An R3 X3.3 Radio Blackout occurred on 24 October from Sunspot region 3869

Pair of R3 HF Radio Blackout Events X1.5 flare at Regions 3936 & 3932 on 30-Dec-2024

Fig 17. Two simultaneous, yet separate R3 (Strong) radio blackout events
occurred on 30-December-2024, between 04:14 and 04:29 UTC.

* Read more about radio blackouts, SID phenomena, and how they affect lower HF bands, as well as the prediction model.

* Stay up to date with the latest forecast discussions.

References:
1. Communications blackout. ^Wikipedia
2. Radio Blackout ^UNDRR
3. Search the term "Blackout" at NOAA website.
  Reports:
4. Strong Solar Flare Activity: May 10-14, 2024 ^NASA
5. May 2024 Solar Storms ^Wikipedia
6. Biggest solar flare since 2019 erupted today along with more radio blackouts ^{Eric Ralls, Earth.com staff writer}
7. Geomagnetic Storm Watch for May 12, 2024 ^NOAA
8. Geomagnetic Storm Watch for May 14, 2024 ^NOAA
9. An X12 flare on the Sun's farside by Solar-Terrestrial Centre of Excellence (STCE)
10. R3 HF Radio Blackout Observed X4.5 flare on 14-Sep-2024
11. R3 HF Radio Blackout Observed X3.3 flare at Region 3869 on 24-Oct-2024
12. Pair of R3 HF Radio Blackout Events X1.5 flare at Regions 3936 & 3932 on 30-Dec-2024
  Analysis:
13. Historic Geomagnetic Storm Dazzles ^NASA
14. Geomagnetic and Atmospheric Response to May 2024 Solar Storm ^NASA
15. Solar storms of May 2024 ^ESA
16. May 2024 super geomagnetic storm challenges current space weather prediction models ^Phys.org
17. Super-Intense Geomagnetic Storm on 10–11 May 2024: Possible Mechanisms and Impacts ^AGU
18. The Solar and Geomagnetic Storms in May 2024: A Flash Data Report ^{Arxiv, Cornell Univ.}
19. The Strongest Solar Storm in 20 Years Did Little Damage, but Worse Space Weather Is Coming ^{Scientific American}