| SB PROP @ ARL $ARLP047
ARLP047 The ARRL Solar Report
ZCZC AP47
QST de W1AW
Propagation Forecast Bulletin 47 ARLP047
From ARRL Headquarters
Newington, CT December 19, 2025
To all radio amateurs
SB PROP ARL ARLP047
ARLP047 The ARRL Solar Report
Solar activity has been at low levels with only a few C1 flares from Region 4307. Slight growth and consolidation were observed in that region as it neared the southwestern limb. Slight decay and separation were observed in Region 4311. The rest of the spotted regions were either stable or in decay. CME analysis will be conducted as imagery becomes available. Solar activity is expected to be low with a slight chance for M-class flares (R1-R2, minor-moderate) on December 18 to 20.
Solar wind parameters continued to be under the influence of a negative polarity coronal hole high-speed stream (CH HSS). Solar wind speed was mostly in the 550 to 650 km/s range. HSS influences are expected to gradually diminish on December 19 – 20.
Solar activity is expected to continue at low levels over December 19 to 21. There is a chance for R1/R2 (Minor-Moderate) events through December 21. The solar wind environment is expected to remain mildly enhanced over December 19 to 21 as negative polarity CH HSS influences diminish.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth’s Ionosphere, December 18, 2025, by F. K. Janda, OK1HH:
The occurrence of an extensive coronal hole in the western half of the solar disk is consistent with the increased speed of the solar wind, as measured by geostationary satellites. The edges of another relatively large coronal hole in the east are likely to be the source of the next period of enhanced solar wind during the coming week. However, overall solar activity is low, as reflected in the low values of the critical frequencies of the F2 ionospheric layer.
The decline in geomagnetic activity in mid-December did, however, have a positive effect on shortwave propagation conditions, albeit mainly at lower frequencies. This included the occasional formation of ionospheric waveguides.
Although solar activity is likely to increase next week, the activity of the Earth’s magnetic field is also likely to increase. Therefore, unstable conditions can be expected in the Earth’s ionosphere, with short intervals of improvement followed by longer intervals of deterioration in shortwave propagation conditions.
The current Solar Cycle Progression from the NOAA/Space Weather Prediction Center can be found at www.swpc.noaa.gov/products/solar-cycle-progression.
The Predicted Planetary A Index for December 20 to 26 is 10, 5, 20, 20, 25, 20, and 20, with a mean of 17.1. Predicted Planetary K Index is 3, 2, 5, 5, 5, 5, 5, with a mean of 4.2. 10.7-centimeter flux is 115, 115, 125, 135, 145, 155, 165, with a mean of 136.4.
For more information concerning shortwave radio propagation, see www.arrl.org/propagation and the ARRL Technical Information Service web page at www.arrl.org/propagation-of-rf-signals. For an explanation of numbers used in this bulletin, see www.arrl.org/the-sun-the-earth-the-ionosphere. Information and tutorials on propagation can be found at http://k9la.us.
Also, check this: ”Understanding Solar Indices” from September 2002 QST. https://bit.ly/3Rc8Njt
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