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, http://arrl.org/news/operators-monitors-wanted-for-meteor-scatter-qso-party-december-12-13
[ http://arrl.org/news/operators-monitors-wanted-for-meteor-scatter-qso-party-december-12-13
] .


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, https://www.youtube.com/watch?v=zsh1fLbrUjk [ https://www.youtube.com/watch?v=zsh1fLbrUjk ] .


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 http://www.arrl.org/propagation [ http://www.arrl.org/propagation?utm_source=Informz&utm_medium=Email&utm_campaign=ARRL
] and the ARRL Technical Information Service web page at, http://arrl.org/propagation-of-rf-signals [ http://arrl.org/propagation-of-rf-signals ] . For an explanation of numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere [ http://arrl.org/the-sun-the-earth-the-ionosphere ] . Information and
tutorials on propagation can be found at, http://k9la.us/ [ http://k9la.us/ ]
.


Also, check this:

https://bit.ly/3Rc8Njt [ https://bit.ly/3Rc8Njt ]

"Understanding Solar Indices" from September 2002 QST.
NNNN
/EX

ARRL The National Association for Amateur Radio(R)


--- PyGate Linux v1.5.2
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)