The 25th Solar Cycle

This page is part of the project "Understanding HF Propagation."
by Doron Tal, 4X4XM | Rate site

Explanatory Tutorial

What is solar cycle?

A review of significat radio blackout events of the 25th solar cycle

The most significant blackout event of the 25th solar cycle

Significant Geomagnetic Storms during the 25th solar cycle

Current and predicted fadeouts

List of references

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 (X8.7 peaked on 14-May-2024) 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 space weather center:

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

Figure 1: A screenshot of NOAA's space weather 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.

Figure 2: A-indices recorded 30 days before that 11-May-2024 blackout event

Figure 3: K-indices before and after the 11-May-2024 blackout event

Figure 4: Kp-index 3 days after that 11-May-2024 blackout event

On 14 May 2024 X8.7 flare was observed.

Figure 5. 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

Figure 6: An X4.5 flare caused R3 (Strong) HF radio blackouts

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

Figure 7: 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

Figure 8: 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

Figure 9: Two simultaneous, yet separate R3 (Strong) radio blackout events
occurred on 30-December-2024, between 04:14 and 04:29 UTC.

The first event, an X1.5 flare, peaked at 04:14 UTC and originated from Region 3936 in the NW quadrant of the Sun. The second event, an X1.1 flare, began before the first flare had completely ended, and peaked at 04:29 UTC. This event originated from Region 3932 in the SW quadrant of the Sun. The associated coronal mass ejection was analyzed and determined to not have an Earth-directed component.

Table 1: Severe Geomagnetic Storms during the 25th solar cycle
Date	Storm Intensity	Kp Index	Geomag activity	Short Description
May 11, 2024	Extreme	9	G5	Strongest geomagnetic storm of Solar Cycle 25; peak of a multi-day event linked to a full-halo CME from AR13664.
Oct 11, 2024	Severe	8+	G4	High-speed solar wind with strong southward IMF produced widespread aurora.
Oct 10, 2024	Severe	9	G4–G5	Intense geomagnetic activity during a two-day October storm sequence.
Jan 1, 2025	Moderate	8	G3	New Year storm with elevated Kp and sustained activity.
Nov 12, 2025	Severe	9	G4	Triggered by multiple flares and CMEs; Fast solar wind and strong IMF drove a late-2025 storm.