Solar cycle 25

Solar cycle 25 is the current solar cycle, the 25th since 1755, when extensive recording of solar sunspot activity began. It began in December 2019 with a minimum smoothed sunspot number of 1.8. It is expected to continue until about 2030.

Predictions
Widely varying predictions regarding the strength of cycle 25 ranged from very weak with suggestions of slow slide in to a Maunder minimum like state to a weak cycle similar to previous cycle 24 and even a strong cycle. Upton and Hathaway predicted that the weakness of cycle 25 would make it part of the Modern Gleissberg Minimum.

The Solar Cycle 25 Prediction Panel predicted in December 2019 that solar cycle 25 will be similar to solar cycle 24, with the preceding solar cycle minimum in April 2020 (± 6 months), and the number of sunspots reaching a (smoothed) maximum of 115 in July 2025 (± 8 months). This prediction is in line with the current general agreement in the scientific literature, which holds that solar cycle 25 will be weaker than average (i.e. weaker than during the exceptionally strong Modern Maximum). However, observations from 2020 to 2022, the first three years of the cycle, significantly exceed predicted values.

Progress
As of April 2018, the Sun showed signs of a reverse magnetic polarity sunspot appearing and beginning this solar cycle. It is typical during the transition from one cycle to the next to experience a period where sunspots of both polarities exist (during the solar minimum). The polarward reversed polarity sunspots suggested that a transition to cycle 25 was in process. The first cycle 25 sunspot may have appeared in early April 2018 or even December 2016.

In November 2019, two reversed polarity sunspots appeared, possibly signaling the onset of cycle 25.

Nandy et al., analyzed the polarity orientation of bipolar magnetic regions observed in December 2019 and concluded that magnetic regions with the underlying orientation of solar cycle 25 toroidal field component were brewing in the solar convection zone, representing early signs of the new cycle.

Supersynoptic (time vs. solar latitude) map of the radial component of the solar magnetic field for cycles 24-25 based on observations from the Global Oscillations Network Group (GONG) shows magnetic activity of cycle 25 beginning November 2019 at about 30 degree latitudes in both solar hemispheres. A more recent supersynoptic map is available.

The following table gives the number of days so far in cycle 25 against the number up to the same point in cycle 24, which have passed various thresholds for the numbers of sunspots. As at Jun 2 2024, solar cycle 25 is averaging 29% more spots per day than solar cycle 24 at the same point in the cycle (Jun 2 2013).

Year 1 of SC25 (Dec 2019 to Nov 2020) averaged 101% more spots per day than year 1 of SC24. Year 2 of SC25 (Dec 2020 to Nov 2021) averaged 7% more spots per day than year 2 of SC24. Year 3 of SC25 (Dec 2021 to Nov 2022) averaged 8% more spots per day than year 3 of SC24. Year 4 of SC25 (Dec 2022 to Nov 2023) averaged 41% more spots per day than year 4 of SC24. Year 5 of SC25 (Dec 1 2023 to Jun 2 2024) is currently averaging 50% more spots per day than the corresponding period of SC24.

Events
The strongest flares of Solar Cycle 25 (above M5.0 class) and related events

Farside flares (above M5.0 class) observed by STIX

2020
On 29 May, the first C-class solar flares of Solar Cycle 25 took place, as well as the first M-class flare. Solar activity continued to increase in the following months, especially abruptly in October, with flares taking place on a near-daily basis by November. On 29 November, an M4.4 flare, the strongest of the cycle to date, took place, possibly indicating that the solar cycle would be more active than initially thought.

On 8 December, a small coronal mass ejection was found heading directly towards Earth shortly after a strong C-class solar flare, hitting the planet on 9–10 December and causing bright aurorae at high latitudes.

2021
The first X-class solar flare of the cycle took place on 3 July, peaking at X1.59.

On 22 July, a total of six different active regions were seen on the solar disk for the first time since 6 September 2017.

On 9 October, a M1.6 class solar flare erupted sending a coronal mass ejection that hit Earth on 12 October, triggering a (moderate) G2 geomagnetic storm.

The second X-class flare of the solar cycle erupted on 28 October, producing a CME and a S1 solar radiation storm. Reports initially predicted that the CME could graze Earth, however geomagnetic storms on 30–31 October only reached a moderate K$p$ index of 4.

On 3 and 4 November, the K$p$ index reached 8−, equivalent to a G4 geomagnetic storm. This was the most intense geomagnetic storm to hit Earth since September 2017.

2022
In late March, sunspot region 2975 released X1.3 and M9.6 flares, the former causing a G1 geomagnetic storm on 31 March despite being near the solar limb. The region rotated out of view of Earth on 5 April, but helioseismic measurements on April 8 showed it still active on the far side of the Sun. On 12 April, a Coronal Mass Ejection on the far side likely erupted from the region, with helioseismic measurements showing the region to have intensified since crossing over the limb. As the region began rotating into view from Earth, a possibly X-class flare occurred on 15 April.

After rotating to the visible hemisphere of the Sun, the regions of the sunspot complex were designated 2993 through 2996. On 17 April, sunspot group 2994 released an X1.2 flare. However, the complex's activity subsided slightly in the next few days. While crossing the solar limb, sunspot region 2992 emitted M7.3 and X2.2 flares, the latter being the strongest of the cycle up to that point.

2023
On 24 March, an intense geomagnetic storm hit Earth unexpectedly, reaching a level of G4 and producing auroras as far south as New Mexico. A minor CME from an M1 flare was predicted to hit the day earlier, but the timing and intensity were unexpected. Later, on 23 and 24 April, more G4 storms hit Earth, on the former day being tied with several days in solar cycle 24 for the strongest storm since 2005. Auroras were visible as far south as San Antonio, Texas.

On 14 December, a solar flare measuring X2.87 was recorded from sunspot region 3514, making it the strongest solar flare of the cycle for just 17 days, as on 31 December, a solar flare measuring X5.0 was recorded from sunspot 3536.

2024
On 9 February, region 3575 produced an X3.4 flare, the second strongest of the cycle up to that point, causing radiation levels to briefly exceed S2 over the following days. On 12 February, after rotating to the far side of the Sun, the same region released a strong CME. As it was invisible from Earth, it was impossible to assess the flare's strength, but it nonetheless caused proton storm levels to briefly reach S2 again on February 12–13.

On 22 February, region 3590 produced a solar flare measuring X6.3.

In May, the strongest solar storm in 20 years produced aurorae at far lower latitudes than usual. A few days later, on 14 May, region 3664 produced the strongest solar flare thus far of the solar cycle, measuring X8.7.

On 20 May 2024, an X12 solar flare - X-class are the strongest kind of solar flare - produced x-rays and gamma rays that hit Mars, while a coronal mass ejection launched a solar wind.