The ARRL Solar Update
Solar activity has remained low this past week. The largest flare
was a C9.9 on November 19 from a region just beyond the NE limb near
N17. Region 4284 grew slightly in the early part of the period but
was in decay after November 19.
New Region 4287 was numbered. A Type II radio sweep (estimated at
695 km/s) was observed on November 19 at 2215 UTC, likely associated
with a B9.0 flare from just beyond the east limb. No Earth-directed
CMEs were observed. Solar activity is expected to be at low levels,
with slight chance for moderate levels (R1-R2/minor-moderate) to
November 21.
Solar wind parameters were at nominal levels. Solar wind speed
ranged from 346 - 421 km/s. Total field ranged from 4-8 nT while the
Bz component was between +8/-2 nT. Phi angle was predominantly
negative. By late November 20, a negative polarity coronal hole high
speed stream (CH HSS) is expected to become geoeffective, causing a
minor enhancement in the solar wind.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere, November 20, 2025, by F. K. Janda, OK1HH:
"Solar activity over the last three months has fluctuated fairly
regularly within an approximately 27-day period, determined by the
rotation of the Sun. The positions of active longitudes do not
change much, which makes it relatively easy to predict not only
solar but also geomagnetic activity. However, we are still close to
the 11-year maximum, so the large solar flares on November 9, 10,
and 11 were not a major surprise.
"However, the fact that the coronal plasma clouds from the first two
flares merged (the second, faster one caught up with the first) and
caused a massive geomagnetic disturbance on November 12 could have
been a surprise.
"The massive disturbance lasted only until November 13, followed by
alternating calm days on November 14-15 and November 18-19 with
turbulent days, for which a more accurate forecast was not possible.
We are likely to see an increase in solar activity during the third
3rd of November and the first 3rd of December, with increased
geomagnetic activity most likely expected in the last days of
November and the first days of December. However, the regularity of
fluctuations in solar and geomagnetic activity will end during this
period, while it is advisable to pay attention to newly emerging
active regions and the shift of coronal holes on the Sun."
High Speed Stream activity is expected to wane through November 22.
Solar wind speeds in the 450-550 km/s range are likely based on
recurrent values. The geomagnetic field is likely to reach
unsettled conditions on November 22 due to waning solar wind
enhancements. Mostly quiet conditions are expected on November 23.
Spaceweather.com for November 21 reports that Sunspot 4274, which
caused the Veteran's Day aurora and radiation storm, will be back
after Thanksgiving.
The latest video report from Dr. Tamitha Skov, WX6SWW, can be found
on YouTube at, https://www.youtube.com/watch?v=FOLDm_N6ft8 .
The current Solar Cycle Progression from the NOAA/Space Weather
Prediction Center can be found at,
https://www.swpc.noaa.gov/products/solar-cycle-progression .
The Predicted Planetary A Index for November 22 to 28 is 8, 5, 15,
18, 25, 20, and 10, with a mean of 14.4. Predicted Planetary K
Index is 3, 2, 4, 5, 5, 5, and 3, with a mean of 3.9.
10.7-centimeter flux is 110, 105, 110, 110, 110, 120, and 130, with
a mean of 113.6.
For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and the ARRL Technical Information
Service web page at, 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 . Information and
tutorials on propagation can be found at, http://k9la.us/ .
Also, check this:
https://bit.ly/3Rc8Njt
"Understanding Solar Indices" from September 2002 QST.
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