Solar cycle 25 explained

Cycle Num:25
Start Date:December 2019
End Date:about 2030
Max Count:131.1 (smoothed)
Max Count Date:January 2024 (progressive)[1]
Min Count:1.8
Prev Name:Solar cycle 24
Prev Dates:2008–2019

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.[2] It is expected to continue until about 2030.[3] [4]

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[5] to a weak cycle similar to previous cycle 24 and even a strong cycle.[6] 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[7] that solar cycle 25 will be similar to, 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).[8] However, observations from 2020 to 2022, the first three years of the cycle, significantly exceed predicted values.[9]

Cycle 25 predictions! Source! Date! Cycle max! Cycle start! Cycle end
Thompson, M.J. et al.August 2014Q4 2019
Zharkova, V. et al 2014, 2015.[10] (Northumbria U.)October 201465 (80% of cycle 24)
Upton, L.A. and Hathaway, D.H.[11] (Solar Observatories Group, Stanford University)December 201878 (95% of cycle 24)Late 2020 – Early 2021
Xu, J.C. et al.[12] (Chinese Academy of Sciences)August 2018168.5 ± 16.3 (2024)October 2020
Bhowmik, P. and Nandy, D. (IISER Kolkata)December 2018124 ± 15 (2023–2025)2020after 2031
Ozguc, A. et al.[13] (Harvard U-ty)December 2018154 ± 12 (2023.2±1.1)
NOAA / SSRC[14] April 2019117 ± 23 (2023–2026)mid-2019 – late 2020
NASA[15] June 201970 ± 29 (30–50% lower than Cycle 24 (2025))2020
NOAA / SSRC (update)[16] December 2019115 ± 10 (July 2025)April 2020 (± 6 months)
Mcintosh et al.[17] [18] June 2020229 ± 25
Mcintosh et al.December 2020190 ± 20
National Center for Atmospheric Research[19] December 2020233
de Jager, C. and Duhau, S. [20] December 2020160 ± 8 (2025 ± 1)
Actual, for comparisonPresent>131.1December 2019-

Progress

As of April 2018, the Sun showed signs of a reverse magnetic polarity sunspot appearing and beginning this solar cycle.[21] 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.[22] The first cycle 25 sunspot may have appeared in early April 2018[23] [24] or even December 2016.[22]

In November 2019, two reversed polarity sunspots appeared, possibly signaling the onset of cycle 25.[25] [26]

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.[27]

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.[28] A more recent supersynoptic map is available.[29]

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.

Counts
≥100
≥125
≥150
≥175
≥200
≥225
≥250
≥275
≥300

As at Aug 8, 2024, solar cycle 25 is averaging 35% more spots per day than solar cycle 24 at the same point in the cycle (Aug 8, 2013).

Events

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

Class Date Sunspot
region
Radio B. SR Storm GM Storm
X8.79 2024-05-14 3664 R3 - Yes ?
X6.37 2024-02-23 3590 R3 - No -
X5.89 2024-05-11 3664 R3 S2 Yes ?
X5.01 2023‑12‑31 3536 R3 S1 Yes -
X4.52 2024-05-06 3663 R3 - Yes G5
X3.98 2024-05-10 3664 R3 S2 Yes G5
X3.48 2024-05-15 3664 R3 - Yes ?
X3.38 2024-02-09 3575 R3 S2 Yes -
X2.99 2024-05-15 3685 R3 S1 Yes ?
X2.9 2024-05-27 3697 R3 - Yes -
X2.87 2023‑12‑14 3514 R3 S1 Yes G1
X2.56 2024-02-16 3576 R3 S0 Yes -
X2.28 2023‑02‑17 3229 R3 - Yes -
X2.25 2022‑04‑20 2992 R3 - Yes -
X2.25 2024-05-09 3664 R3 S2 Yes G5
X2.07 2023‑03‑03 3234 R3 - Yes -
X2.0 2024-07-16 3738 R3 - Yes ?
X1.98 2023‑01‑09 3184 R3 - No -
X1.9 2024-02-21 3590 R3 - No -
X1.72 2024-05-14 3664 R3 - Yes ?
X1.7 2024-02-22 3590 R3 - No -
X1.69 2024-05-02 3663 R3 - Yes -
X1.63 2023‑08‑05 3386 R3 S1 Yes -
X1.59 2021‑07‑03 2838 R3 - Yes -
X1.57 2024-07-29 3764 R3 - No -
X1.55 2024-06-10 3697 R3 - Yes ?
X1.54 2024-05-11 3664 R3 - No -
X1.51 2022‑05‑10 3006 R3 - No -
X1.51 2023‑08‑07 3386 R3 S1 Yes -
X1.45 2024-05-29 3697 R3 S0 Yes ?
X1.43 2024-06-01 3697 R3 - No -
X1.38 2022‑03‑30 2975 R3 S1 Yes G1
X1.32 2024-05-05 3663 R3 - No -
X1.29 2024-05-05 3663 R3 - No -
X1.27 2023‑03‑29 3256 R3 - Yes -
X1.27 2024-07-14 3738 R3 - No -
X1.25 2024-05-14 3664 R3 - Yes ?
X1.22 2023‑01‑06 3182 R3 - No -
X1.18 2024-05-31 3697 R3 - No -
X1.17 2022‑04‑17 2994 R3 - Yes -
X1.16 2023‑02‑11 3217 R3 - No -
X1.13 2022‑04‑30 2994 R3 - Yes -
X1.13 2022‑05‑03 3006 R3 - No -
X1.12 2024-03-23 3614 R3 S2 Yes G4
X1.12 2024-03-29 3615 R3 - Yes -
X1.12 2024-05-09 3664 R3 S2 Yes G5
X1.11 2023‑06‑20 3341 R3 - Yes -
X1.08 2023‑07‑02 3354 R3 - No -
X1.08 2024-05-08 3663 R3 - No -
X1.06 2022‑10‑02 3110 R3 - Yes -
X1.06 2023‑01‑10 3186 R3 - Yes -
X1.04 2024-05-08 3663 R3 - Yes G5
X1.03 2024-06-01 3697 R3 ? ? ?
X1.02 2024-05-08 3664 R3 - No -
X1.02 2024-05-12 3664 R3 - No -
X1.0 2021‑10‑28 2887 R3 S1 Yes -
M9.92 2024-07-28 3762 R3 - No -
M9.87 2024-05-08 3664 R3 - Yes G5
M9.82 2023‑11‑28 3500 R2 - Yes G3
M9.76 2024-03-28 3615 R2 - No -
M9.75 2024-06-08 3697 R2 S3 Yes ?
M9.67 2022‑03‑31 2975 R2 - Yes -
M9.66 2022‑04‑21 2993 R2 - Yes -
M9.62 2023‑05‑16 3310 R2 - No -
M9.56 2024-06-10 3697 R2 - Yes ?
M9.53 2023-04-30 3654 R2 - No -
M9.42 2024-03-30 3615 R2 - Yes -
M9.4 2024-07-30 3772 R2 - Yes -
M9.39 2024-03-30 3615 R2 - Yes -
M9.36 2024-06-23 3723 R2 - No -
M9.13 2024-05-04 3663 R2 - No -
M9.10 2024-05-04 3663 R2 - No -
M9.04 2024-02-10 3576 R2 S1 Yes -
M8.96 2023‑05‑20 3311 R2 - No -
M8.87 2024-05-11 3664 R2 S2 Yes -
M8.77 2022‑10‑02 3110 R2 - Yes G1
M8.77 2024-07-29 3762 R2 - Yes ?
M8.72 2023‑09‑21 3435 R2 - Yes G2
M8.69 2024-05-08 3664 R2 - Yes G5
M8.67 2022‑08‑29 3088 R2 - No -
M8.62 2023‑02‑28 3234 R2 - Yes -
M8.42 2024-05-05 3663 R2 - No -
M8.29 2024-05-07 3663 R2 - No -
M8.24 2024-08-01 3772 R2 - No -
M8.23 2023‑09‑20 3435 R2 - No -
M7.92 2022‑09‑16 3098 R2 - No -
M7.92 2024-05-08 3664 R2 - No -
M7.88 2024-07-28 3766 R2 - No -
M7.79 2024-07-28 3762 R2 - No -
M7.75 2024-07-31 3772 R2 - No -
M7.48 2024-03-20 3615 R2 - No -
M7.47 2024-05-05 3663 R2 - No -
M7.43 2024-03-10 3599 R2 S0 Yes -
M7.43 2024-08-04 3768 R2 - Yes -
M7.35 2024-06-01 3697 R2 - Yes ?
M7.3 2024-08-04 3775 R2 - No -
M7.29 2022‑04‑20 2992 R2 - Yes -
M7.27 2023‑05‑03 3293 R2 - No -
M7.25 2024-05-17 3685 R2 ? Yes ?
M7.24 2022‑08‑26 3089 R2 - Yes -
M7.17 2024-05-08 3664 R2 - No -
M7.12 2023‑05‑01 3288 R2 - No -
M7.1 2024-03-28 3615 R2 - No -
M6.97 2023‑07‑12 3372 R2 - No -
M6.97 2023‑12‑15 3514 R2 - Yes G1
M6.83 2023‑07‑11 3368 R2 - No -
M6.83 2024-01-29 3559 R2 S2 Yes -
M6.77 2024-03-18 3615 R2 - No -
M6.73 2022‑08‑28 3088 R2 - Yes -
M6.66 2024-05-13 3664 R2 S2 Yes ?
M6.57 2023‑05‑09 3296 R2 - Yes -
M6.51 2024-07-29 3772 R2 - Yes -
M6.5 2023‑05‑20 3311 R2 - No -
M6.5 2024-02-12 3576 R2 - No -
M6.39 2023‑02‑07 3213 R2 - No -
M6.36 2022‑12‑14 3165 R2 - No -
M6.35 2023‑02‑25 3229 R2 S1 Yes G3
M6.2 2022‑09‑16 3098 R2 - No -
M6.14 2024-03-28 3615 R2 - No -
M6.12 2024-06-06 3697 R2 - No -
M6.07 2024-08-01 3772 R2 - No -
M6.04 2024-07-31 3772 R2 - No -
M6.03 2023‑01‑15 3191 R2 - Yes -
M6.01 2023‑09‑03 3413 R2 - Yes -
M5.97 2024-05-10 3664 R2 - No -
M5.86 2022‑10‑01 3110 R2 - Yes G1
M5.86 2023‑07‑11 3372 R2 - No -
M5.84 2023‑12‑14 3514 R2 - Yes G1
M5.8 2023‑03‑06 3243 R2 - Yes -
M5.76 2022‑05‑04 3004 R2 - No -
M5.76 2024-06-20 3719 R2 - No -
M5.74 2022‑12‑15 3165 R2 - No -
M5.73 2024-05-29 3691 R2 - No -
M5.72 2023‑07‑17 3363 R2 S2 Yes -
M5.68 2023‑05‑20 3311 R2 - No -
M5.67 2023‑01‑11 3184 R2 - Yes -
M5.54 2022‑05‑19 3014 R2 - No -
M5.51 2023‑08‑06 3386 R2 - Yes -
M5.5 2022‑01‑20 2929 R2 S1 Yes -
M5.49 2023‑12‑08 3511 R2 - No -
M5.47 2024-04-11 3639 R2 - Yes -
M5.46 2024-08-03 3775 R2 - No -
M5.41 2023‑03‑30 3256 R2 S0 Yes -
M5.39 2022‑08‑26 3089 R2 - No -
M5.39 2023‑05‑19 3311 R2 - No -
M5.39 2024-07-31 3772 R2 - No -
M5.35 2024-07-13 3738 R2 - No -
M5.34 2024-06-12 3697 R2 - No -
M5.32 2022‑05‑04 3006 R2 - No -
M5.27 2022‑03‑04 3234 R2 - Yes -
M5.25 2022‑11‑07 3141 R2 - No -
M5.2 2023‑05‑20 3311 R2 - No -
M5.18 2024-02-07 3575 R2 - Yes -
M5.18 2024-05-07 3663 R2 - No -
M5.15 2023‑01‑10 3186 R2 S0 Yes -
M5.12 2024-01-23 3559 R2 - Yes -
M5.09 2023‑02‑21 3234 R2 - Yes -
M5.08 2022‑08‑16 3078 R2 - No -
M5.07 2024-07-13 3738 R2 - No -
M5.05 2024-07-17 3743 R2 - No -
M5.04 2023‑03‑05 3243 R2 - No -
M5.02 2023‑05‑09 3296 R2 - No -

Farside flares (above M5.0 class) observed by STIX[30]

Class Date Sunspot
region
Class
(seen from
Earth)
X14 2024-07-22 3738 -
X12 2024-05-20 3664 -
X9 2023-07-16 3368 -
X9 2024-05-15 3664 X3.48
X9 2024-05-15 3664 -
X7 2024-07-24 3738 -
X6 2023-01-03 3182 C4.06
X6 2023-07-16 3368 -
X6 2023-12-31 3536 X5.01
X6 2024-05-17 3664 -
X5 2024-05-16 3664 -
X4 2023-09-08 3413 -
X4 2023-09-11 3413 -
X4 2024-08-04 3738 -
X3 2024-04-03 ? -
X3 2024-06-11 3697 -
X3 2024-06-13 3697 -
X3 2024-06-17 3697 -
X2 2022-04-30 2994 M1.99
X2 2023-07-10 3354 -
X2 2024-02-02 ? -
X2 2024-05-14 3664 X1.25
X1 2020-11-18 2786 -
X1 2022-05-01 2994 C1.9
X1 2022-08-29 3088 M8.68
X1 2022-08-30 3088 M1.7
X1 2022-08-30 3088 C7.18
X1 2022-09-29 3112 C5.76
X1 2022-12-27 3180 -
X1 2023-05-14 3310 -
X1 2023-05-23 3323 -
X1 2023-07-07 3354 -
X1 2023-07-08 3354 -
X1 2023-07-13 3360 -
X1 2023-07-14 3372 -
X1 2023-07-18 3368 -
X1 2023-07-24 ? -
X1 2024-05-25 3664 -
X1 2024-06-16 3697 -
X1 2024-07-24 3738 -
X1 2024-07-25 3738 -
X1 2024-07-27 3738 -
X1 2024-07-28 3738 -
X1 2024-08-02 3738 M1.33
M9 2022-05-05 2994 -
M9 2022-08-29 3088 M4.71
M9 2022-09-05 3088 -
M9 2022-09-11 3089 -
M9 2023-05-30 3323 -
M9 2023-06-01 3310 -
M9 2023-07-15 ? -
M9 2023-07-18 3368 -
M9 2024-07-23 3738 -
M8 2022-05-01 2994 -
M8 2022-05-10 2994 -
M8 2022-08-31 3088 -
M8 2022-09-10 3089 -
M8 2022-12-27 3180 -
M8 2023-05-14 3310 -
M8 2023-06-04 ? -
M8 2023-01-10 3549 C9.64
M8 2024-07-30 3738 -
M7 2022-01-12 ? -
M7 2022-01-25 ? C3.79
M7 2022-05-05 2994 -
M7 2022-05-10 2994 -
M7 2022-08-30 3088 C7.57
M7 2022-09-11 3089 -
M7 2023-01-10 3190 -
M7 2023-05-25 3323 -
M7 2023-07-11 3354 -
M7 2024-06-10 ? -
M7 2024-06-17 3697 -
M6 2022-04-30 2994 M4.82
M6 2022-05-01 2994 -
M6 2022-05-01 2994 -
M6 2022-05-05 2994 -
M6 2022-09-17 3098 M2.61
M6 2023-02-14 3229 -
M6 2023-02-20 3234 M4.43
M6 2023-07-07 3354 -
M6 2023-07-09 3354 -
M6 2023-07-09 3354 -
M6 2023-07-09 3354 -
M6 2023-07-11 3372 M1.17
M6 2023-07-13 3360 -
M6 2023-07-19 3363 M3.81
M6 2023-07-22 3363 -
M6 2023-10-31 3477 -
M6 2024-01-10 3549 C7.01
M6 2024-06-13 3697 -
M6 2024-06-17 3697 -
M6 2024-07-29 3738 -
M5 2021-07-15 ? -
M5 2022-04-19 2992 M3.71
M5 2022-05-17 3014 C9.91
M5 2022-08-29 3088 M2.58
M5 2022-09-01 3088 -
M5 2022-09-14 3089 -
M5 2022-09-29 3112 -
M5 2022-12-28 3180 C6.09
M5 2023-05-12 3310 -
M5 2023-05-16 3310 -
M5 2023-06-08 ? -
M5 2023-07-16 ? -
M5 2023-08-08 3387 M3.67
M5 2023-08-08 3387 -
M5 2024-05-12 3685 -
M5 2024-05-14 3685 -
M5 2024-05-16 3664 -
M5 2024-05-16 3664 -
M5 2024-05-22 3664 -
M5 2024-06-28 ? -
M5 2024-07-03 ? -
M5 2024-07-24 3738 -

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.[31]

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.[32] [33]

2021

The first X-class solar flare of the cycle took place on 3 July, peaking at X1.59.[34]

On 22 July, a total of six different active regions were seen on the solar disk for the first time since 6 September 2017.[35]

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.[36]

The second X-class flare of the solar cycle erupted on 28 October, producing a CME and a S1 solar radiation storm.[37] Reports initially predicted that the CME could graze Earth,[37] however geomagnetic storms on 30–31 October only reached a moderate K index of 4.[38]

On 3 and 4 November, the K index reached 8−, equivalent to a G4 geomagnetic storm.[39] 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.[40] 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.[41] On 12 April, a Coronal Mass Ejection on the far side likely erupted from the region,[42] 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.[43]

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.[44] [45] However, the complex's activity subsided slightly in the next few days.[46] 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.[46]

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.[47] 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.[48] Auroras were visible as far south as San Antonio, Texas.[49]

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,[50] as on 31 December, a solar flare measuring X5.0 was recorded from sunspot 3536.[51]

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.[52] 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.[53]

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.[54] [55]

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. [56]

See also

External links

Notes and References

  1. Web site: SILSO, World Data Center . Sunspot Number and Long-term Solar Observations: on-line Sunspot Number catalogue . Royal Observatory of Belgium . https://web.archive.org/web/20230405200033/https://www.sidc.be/silso/ . 2023-04-05 .
  2. Web site: Hello Solar Cycle 25. National Weather Service. National Weather Service. 15 September 2020. 18 March 2021. https://web.archive.org/web/20210318003150/https://www.weather.gov/news/201509-solar-cycle. live.
  3. News: Odenwald . Sten . Waiting for the next sunspot cycle: 2019-2030 . . 2016-09-02 . 2017-11-22 . 2018-12-12 . https://web.archive.org/web/20181212022245/https://www.huffingtonpost.com/dr-sten-odenwald/waiting-for-the-next-suns_b_11812282.html . live .
  4. McIntosh . Scott W. . Wang . Xin . Leamon . Robert J. . Davey . Alisdair R. . Howe . Rachel . Krista . Larisza D. . Malanushenko . Anna V. . Markel . Robert S. . Cirtain . Jonathan W. . Gurman . Joseph B. . Pesnell . William D. . Thompson . Michael J. . Deciphering Solar magnetic activity: On the relationship between the sunspot cycle and the evolution of small magnetic features . The Astrophysical Journal . 8 August 2014 . 792 . 1 . 12 . 10.1088/0004-637X/792/1/12 . 1403.3071 . 2014ApJ...792...12M. 118418019 .
  5. Kitiashvili et al.
  6. McIntosh. Scott W.. Chapman. Sandra C.. Leamon. Robert J.. Egeland. Ricky. Watkins. Nicholas W.. 2020-06-26. Overlapping Magnetic Activity Cycles and the Sunspot Number: Forecasting Sunspot Cycle 25 Amplitude. Solar Physics. 295. 12. 163. 10.1007/s11207-020-01723-y. 2006.15263. 2020SoPh..295..163M. 220250556.
  7. Web site: Solar Cycle 25 Forecast Update | NOAA / NWS Space Weather Prediction Center . 2020-01-09 . 2021-03-21 . https://web.archive.org/web/20210321013820/https://www.swpc.noaa.gov/news/solar-cycle-25-forecast-update . live .
  8. Bhowmik . Prantika . Nandy . Dibyendu . Prediction of the strength and timing of sunspot cycle 25 reveal decadal-scale space environmental conditions . Nature Communications . 6 December 2018 . 9 . 1 . 5209 . 10.1038/s41467-018-07690-0 . 30523260 . 6283837 . 2018NatCo...9.5209B . 1909.04537 .
  9. Web site: climateimpactcompany.com . Solar Cycle 25 Continues to Strengthen Rapidly . 10 July 2022 . 2022-12-21 . 2022-12-21 . https://web.archive.org/web/20221221161332/https://climateimpactcompany.com/solar-cycle-25-continues-to-strengthen-rapidly-3/ . live .
  10. Shepherd . Simon J. . Zharkov . Sergei I. . Zharkova . Valentina V. . Prediction of solar activity from solar background magnetic field variations in cycles 21–23 . The Astrophysical Journal . 13 October 2014 . 795 . 1 . 46 . 10.1088/0004-637X/795/1/46 . 2014ApJ...795...46S . 10454/10790 . 29947523 . free .
  11. Upton . Lisa A. . Hathaway . David H. . An updated solar cycle 25 prediction with AFT: The modern minimum . Geophysical Research Letters . 45 . 16 . 28 August 2018 . 8091–8095 . 10.1029/2018GL078387. 1808.04868 . 2018GeoRL..45.8091U . 118913702 .
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