\n<\/p>\n
Solar activity was at very low levels with only isolated B-class
flaring, mostly from Region 4416.
\u00a0
There are currently four numbered regions on the visible disk. Region
4416 remains the largest group by area but exhibited signs of
structural weakening, including flux submergence and a slight decay
of its intermediary pores. Region 4419 was the most complex group on
the disk and showed flux emergence, growth, and divergence within its
intermediary spots, leading to the development of a mixed-polarity
gamma configuration. Region 4418 is trending toward plage with only
two small bipolar pores remaining and Region 4415 remained stable.
CMEs observed in coronagraph imagery were determined to be directed
away from Earth.
\u00a0
Solar wind parameters reflected waning coronal hole high speed stream
influences toward a nominal regime. Solar wind speeds underwent a
gradual, albeit erratic, decline from early-period highs near 420
km\/s, to stabilize around 375 km\/s by the end of the reporting
period. The phi angle was predominantly oriented in a positive (away
from the Sun) direction.
\u00a0
Solar wind parameters are expected to remain primarily near nominal
levels through April 16. Significant enhancements are anticipated on
April 17 with the onset of a co-rotating interaction region (CIR)
that will precede the arrival of a negative polarity high-speed
stream (-CH HSS).
\u00a0
Spaceweather.com reports a large hole has opened in the sun’s
atmosphere, and it is directly facing Earth. High-speed solar wind
flowing from this coronal hole should arrive on April 18th,
potentially sparking G2-class geomagnetc storms. <\/p>\n
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s
Ionosphere, April 16, 2026, by F. K. Janda, OK1HH:<\/p>\n
It is as if we were not just past the 11-year solar activity maximum;
the solar flux fell and remained below 100 s,f,u for five days (April
9\u201313), while the number of sunspot groups dropped to just three.
Flare activity declined similarly. However, more significant for the
future development of solar activity\u2014and especially for its impact on
Earth\u2014is the large coronal hole No. 42, which is approaching the
central meridian from the northeast. Its western border\u00a0 can be
considered a potential source of solar wind that will reach Earth in
the coming days. <\/p>\n
Initially, it seemed that this would not happen until April 19, but
closer observation of its development shows that the Earth will be
hit by a fast solar wind as early as April 18 during the day. Or
perhaps as early as the late afternoon of April 17, in which case the
disturbance could begin with a positive phase (with an increase in
MUF) while should\u00a0 continue through the negative phase for much of
the weekend.<\/p>\n
The latest solar report from Dr. Tamitha Skov, WX6SWW, can be found
on YouTube.
https:\/\/www.youtube.com\/watch?v=cOcV9xp8qU8&pp=0gcJCdMKAYcqIYzv<\/p>\n
The Predicted Planetary A Index for April 18 to April 24 is 15, 20,
12, 10, 8, 5, and 8 with a mean of 11.1. The Predicted Planetary K
Index is 3, 4, 4, 3, 3, 2, and 3 with a mean of 3.1. 10.7 centimeter
flux is 110, 110, 120, 130, 140, 145, and 145 with a mean of 128.5.
For more information concerning shortwave radio propagation, see<\/span>
http:\/\/www.arrl.org\/propagation\u00a0<\/span>and the ARRL Technical Information<\/span>
Service web page at,\u00a0<\/span><\/span>http:\/\/arrl.org\/propagation-of-rf-signals. For<\/span>
an explanation of numbers used in this bulletin, see<\/span>
http:\/\/arrl.org\/the-sun-the-earth-the-ionosphere\u00a0<\/span>. Information and<\/span>
tutorials on propagation can be found at,\u00a0<\/span><\/span>http:\/\/k9la.us\/\u00a0<\/span>.<\/span><\/p>\n