Average daily sunspot number plummeted to 104.4.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere for December 12, 2024 from OK1HH:

"The high solar activity in October this year suggests that this may have been the peak of an 11-year cycle.  This is not to say that solar activity will not continue to rise.  On the contrary, it may well be that the first maximum of the cycle took place in October and that we can look forward to a second maximum.  This could take place in 2025 or 2026 at the latest, but it will be followed by a decline.

"Solar activity in November was lower and December's is even lower. The expected geomagnetic disturbance, predicted for 29 November, did not take place because the CME did not affect the Earth.  However, the almost daily occurrence of moderate solar flares continued and a large flare occurred.  It happened on 8 December at around 0906 UT. However, even after this eruption no major geomagnetic disturbance followed and the changes in ionospheric shortwave propagation were rather random."

In December, the Sun is quieter, and large sunspot groups do not occur in its photosphere.  The only major active regions we see are to the south of the solar equator, and their area is about half that of those seen in November.  However, the active area of AR3917 is slowly getting larger and with it the likelihood of a larger flare is increasing.

The Earth's ionosphere has been repeatedly affected in recent days by increased concentrations of solar-origin free electrons, which, while causing a slight rise in MUF, have been more pronounced in the ionosphere, causing scattering and hence attenuation, which has had a negative effect on the longer shortwave bands.

More meteors are arriving at Earth these days.  The swarm is called the Geminids and most meteors should arrive about December 14. Therefore we can observe more frequent occurrences of the sporadic E layer.  In addition to the occurrences of stronger signals on the longer shortwave bands, propagation through ionospheric waveguides is more frequent.  The sporadic layer may not only form one of the walls of the waveguide, but also enable its termination.  Which is a good chance, for example, for QRP devotees.

Predicted solar flux is 165 on December 13 to 15, 160 and 165 December 16 and 17, 160 on December 18 and 19, then 175, 185, and 190 on December 20 to 22, 185 on December 23 and 24, 180 on December 25 and 26, and 180 on December 30 through January 2, 2025.

Predicted planetary A index is 5 on January 13 and 14, 8 on January 15 and 16, 5 on January 17 to 20, then 8 on January 29.

Flare blasts South Africa:  https://bit.ly/3Do6nJJ

STCE Newsletter Online version:

http://www.stce.be/newsletter/newsletter.php

PDF version:

http://www.stce.be/newsletter/pdf/2024/STCEnews20241212.pdf

Send your tips, reports, observations, questions and comments to k7ra@rrl.net.  When reporting observations, don't forget to tell us which mode you were operating.  

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 .

An archive of past propagation bulletins is at

http://arrl.org/w1aw-bulletins-archive-propagation .

More information and tutorials on propagation are at http://k9la.us/

Check "Understanding Solar Indices" from September 2002 QST at  https://bit.ly/3Rc8Njt .

Instructions for starting or ending email subscriptions to ARRL bulletins are at http://arrl.org/bulletins .

Sunspot numbers for December 5 through 11 2024 were 101, 103, 91, 103, 94, 125, 114, with a mean of 104.4.  10.7 cm flux was 174.6, 177.5, 182.5, 177.7 172.5, 171.9, and 160.5 with a mean of 170.9. Estimated planetary A indices were 4, 8, 11, 7, 6, 13, and 7, with a mean of 8.  Middle latitude A Index was 3, 6, 9, 6, 6, 6, 10, and 5, with a mean of 7.3.