QST de W1AW
Propagation Forecast Bulletin 37 ARLP037
From Tad Cook, K7RA
Seattle, WA September 15, 2023
To all radio amateurs
SB PROP ARL ARLP037
ARLP037 Propagation de K7RA
Like last week, eight new sunspot groups emerged this reporting week, September 7-13.
One appeared on September 7, another September 9, four more on September 10, another on September 11 and one more on September 12.
Solar activity made a nice comeback, with average daily sunspot numbers rising from 95.4 to 138.1, and solar flux from 137.6 to 159.9.
The most active geomagnetic day was September 12, when the planetary A index was 25. Spaceweather.com reported a "stealth CME" (unexpected) that had aurora visible down as far as Missouri.
Average daily planetary A index decreased from 15.4 to 10.4, and middle latitude numbers from 16.3 to 11.3.
The Autumnal Equinox in the Northern Hemisphere is just a week away, on September 22.
It seems that the next sustained short term peak in solar flux is a few weeks off, with values between 150 and 155 over October 12-17, although it is expected to reach 150 on September 23-24.
The forecast shows solar flux at 145, 148, 145 and 145 on September 15-18, 140 on September 19-21, 145 on September 22, 150 on September 23-24, 145 on September 25, 140 on September 26-27, 135 on September 28-30, then 130, 135, 130 and 135 on October 1-4, 140 on October 5-6, 135 on October 7-8, 140 on October 9, 145 on October 10-11, 150 om October 12-13, then 155, 150, 155 and 150 on October 14-17, 145 on October 18-19, and 150 on October 20-21.
Predicted planetary A index is 15 on September 15, 8 on September 16-17, then 5, 5, and 10 on September 18-20, 5, 8 and 12 on September 21-23, 5 on September 24-27, then 8, 12 and 8 on September 28-30, and 5 on October 1-8, then 15, 12, 10 and 8 on October 9-12, 5 on October 13-19, 12 on October 20, and 5 on October 21-24.
Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere - September 15-22, 2023 from OK1HH.
"A week ago, the active sunspot group AR3414 dominated the solar disk. It is now on the far side of the Sun. This role has been taken over by AR3423, now approaching the western limb of the solar disk. It will be followed the next day by the slightly smaller AR3425. The important information is that we observe a coronal hole near both of them (closer to AR3425). This configuration was the likely cause of the surprise: Few people expected the Earth to be hit by a CME on September 12 at 1237 UT.
"Then a massive disturbance of the Earth's magnetic field developed. Its initial positive phase increased the MUF values on September 12. This was followed by a negative phase, which in turn caused a significant decrease in MUF, with worsened shortwave propagation conditions on 13 September. This was followed by a gradual improvement on 14 September, when the magnetic filament connecting sunspots AR3423 and AR3425 erupted. The consequence could be a G1 to G2 class geomagnetic storm in the Earth's vicinity on 17 September."
Jon Jones, N0JK wrote from Kansas:
"Sunday afternoon and evening (September 10-11) strong sporadic-E on 6 meters took place.
"This set up links to TEP on to South America.
"The hot spot seemed to be south Central Kansas and northeast Oklahoma. KF0M in EM17 worked many South American stations. From EM28, the Es was not lined up that well.
"Had many strong stations in south Texas and northern Mexico. Around 2250 UTC LU1MQF (FF55) and CE4MBH (FF44) appeared for a few minutes on 50.313 MHz FT8.
"Any sporadic-E is a treat in the September ARRL VHF contest (which was last weekend). With Solar Cycle 25 picking up, the Es can link to TEP."
An article about the Sun from IFLScience:
The latest from Dr. Tamitha Skov, WX6SWW:
Send your tips, reports, observations, questions and comments to email@example.com.
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.
Also, check this article from September, 2002 QST:
An archive of past propagation bulletins is at http://arrl.org/w1aw-bulletins-archive-propagation. More good information and tutorials on propagation are at http://k9la.us/.
Monthly propagation charts between four USA regions and twelve overseas locations are at http://arrl.org/propagation.
Sunspot numbers for September 7 through 13, 2023 were 135, 123, 119, 167, 173, 141, and 109, with a mean of 138.1. 10.7 cm flux was 160.8, 160.9, 161.4, 163.9, 176.4, 153.5, and 142.6, with a mean of 159.9. Estimated planetary A indices were 6, 6, 8, 4, 7, 25, and 17, with a mean of 10.4. Middle latitude A index was 11, 8, 12, 6, 8, 17, and 17, with a mean of 11.3.
Source: W1AW Bulletin via the ARRL.