| SB PROP @ ARL $ARLP015
ARLP015 The ARRL Solar Report
ZCZC AP15
QST de W1AW
Propagation Forecast Bulletin 15 ARLP015
From ARRL Headquarters
Newington CT April 25, 2025
To all radio amateurs
SB PROP ARL ARLP015
ARLP015 The ARRL Solar Report
Solar activity has been at low levels with only minor C-class flaring through April 24, 2025, and is expected to be moderate with a chance of M-class flares (R1-R2, Minor-Moderate) through April 26. No Earth-directed Coronal Mass Ejections (CMEs) have been observed. A southwest CME was observed on April 23 and is considered to be far-side due to the lack of any on-disk plasma motion/flare activity.
Solar wind parameters continued to be slightly enhanced due to the Coronal Hole High-Speed Streams (CH HSS) associated with the positive polarity coronal holes in the southern hemisphere. Solar wind parameters are expected to continue to be influenced by positive polarity, with CH HSS conditions through April 26. Nominal conditions are expected thereafter.
On April 25, Spaceweather.com reported the Earth was struck by an interplanetary shockwave on April 24 around 0700 UTC. An interplanetary shock wave is an abrupt change in the solar wind – probably caused by the Coronal Mass Ejection.
Overall, solar activity remained at low levels. Region AR4064 remained the largest sunspot group on the disk. The regions intermediate spots grew in penumbral area over the past 24 hours.
The geomagnetic field is expected to remain at mostly quiet to unsettled levels, with active conditions likely on April 27 due to the influence from multiple positive polarity CH HSS.
There are currently 11 numbered sunspot regions on the solar disk.
Solar activity is expected to be low with a chance for M-class flares on April 26 and 27.
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
The Predicted Planetary A Index for April 26 to May 2 is 8, 8, 6, 6, 6, 25, and 35, with a mean of 13.4. The Predicted Planetary K Index is 3, 3, 2, 2, 2, 5, and 6, with a mean of 3.3. Predicted 10.7 centimeter flux is 165, 165, 170, 170, 170, 170, and 175, with a mean of 169.3.
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