ARLP046 The ARRL Solar Report undefined

 

SB PROP @ ARL $ARLP046

ARLP046 The ARRL Solar Report

 

ZCZC AP46

QST de W1AW

Propagation Forecast Bulletin 46 ARLP046

From ARRL Headquarters

Newington CT December 12, 2025

To all radio amateurs

 

SB PROP ARL ARLP046

ARLP046 The ARRL Solar Report

 

Solar activity reached high levels this past week when Region 4299 produced an M1.1 (R1/Minor) flare on December 6. Shortly after, the region produced an M8.1/2b (R3/Strong) flare, also on December 6. Associated with the M8.1 flare was a 1,100 SFU Tenflare, a 1,143 km/s Type II sweep and a Type IV sweep. (A "sweep" is a solar radio burst that sweeps through the RF spectrum as the energy moves outward from the Sun.)

 

Some development was observed around the leader spot of Region 4299, while slight decay was noted among the trailer spots. Regions 4296 and 4294 remained the largest of the visible disk but have only produced C-class activity in the past 24 hours. Only minor changes were observed among the other numbered active regions and activity

is now moderate.

 

Coronal mass ejection (CME) activity was observed from both M-class flares. A slow, Earth-directed CME was observed from the M1.1 and a faster, full-halo, Earth-directed CME was observed from the M8.1 flare. According to Spaceweather.com, it touched off a G2 (moderate) geomagnetic storm on December 10, which has subsided.

 

Solar wind parameters reflected a disturbed near-Earth environment throughout the reporting period. Solar wind speeds showed little reaction to the magnetic transient, averaging 375 km/s throughout the reporting period. The phi angle was oriented towards-the-Sun (negative) for the majority of the reporting period, then slowly rotated around to away-from-the-Sun (positive) 1.5 hours after the arrival of the transient.

 

The electron flux is expected to become elevated through December 14 as a coronal hole high speed stream (CH HSS) originating from the negative polarity coronal hole in the northern hemisphere becomes geoeffective. The flux is likely to surpass the 1,000 pfu threshold during the diurnal maxima.

 

As complex regions in the western hemisphere move beyond the limb, chances for the proton flux to become elevated decrease. There is a 10% chance for an S1 (Minor) radiation storming event on December 12, with chances decreasing to 1% by December 14.

 

Spaceweather.com for December 12 reports on the Geminids Meteor Showers peaking this upcoming weekend.

 

A story on the Meteor Scatter QSO Party can be found on the ARRL website at, .

 

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere, December 4, 2025, by F. K. Janda, OK1HH:

 

"On December 1, an active sunspot group emerged on the southeastern limb of the solar disk, as expected. During the last solar rotation, it was designated AR4274. Astronomers renamed it now as AR4294, while produced the first in a series of energetically significant flares observed during the first third of December. In addition, AR4296 began to grow right next to it, and together they began to resemble the so-called Carrington region of 1859. However, the growth of both regions slowed down, but moderately powerful eruptions continued to occur in them, surprisingly contributed to by the relatively small group AR4299 in the north of the solar disk.

 

"Another energetically significant solar flare on December 8 came as a surprise. Given the speed of the ejected particles, the CME was expected to hit Earth on December 9. However, they apparently traveled to Earth along a longer path and arrived on December 10. Therefore, they encountered a slow and expected stream of particles that last hit Earth on November 12. The result of the encounter between the slow and fast particle streams was a so-called reverse shock at around 20:00 UT on December 10, which triggered a G2-class geomagnetic storm. However, these storms are usually short-lived and, apart from unusual, irregular (and interesting) developments, they did not have any significant consequences.

 

"Solar activity remains high, and the state of the ionosphere reflects this. However, the fact that the conditions for shortwave propagation are different from previous cycles is another story. Every eleven-year cycle is different."

 

The latest video from Dr. Tamitha Skov, WX6SWW, can be found on YouTube at, .

 

The Predicted Planetary A Index for December 13 to 19 is 12, 12, 8, 5, 8, 10, and 8, with a mean of 9. Predicted Planetary K Index is 4, 4, 3, 2, 3, 3, and 3, with a mean of 3.1. 10.7-centimeter flux is 140, 130, 130, 135, 135, 140, and 140, with a mean of 135.8.

 

For more information concerning shortwave radio propagation, see and the ARRL Technical Information Service web page at, . For an explanation of numbers used in this bulletin, see . Information and tutorials on propagation can be found at, .

 

Also, check this:

 

 

"Understanding Solar Indices" from September 2002 QST.

NNNN

/EX

 

 

ARRL The National Association for Amateur Radio®