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SB PROP @ ARL $ARLP038
ARLP038 Propagation DE K7RA
QST DE W1AW
ARRL Propagation Bulletin 38 ARLP038 From Tad Cook, K7RA
Seattle, Washington September 20 2024

Solar activity was quiet over the past week, but geomagnetic numbers were way, way up.

Average daily sunspot numbers dropped from 178.4 to 120, and average daily solar flux from 223.7 to 175.7.

Average daily planetary A index rocketed from 7.9 to 35.7, and middle latitude numbers from 11.1 to 23.4.

Six new sunspot groups emerged over the past week; one each on September 13 and 14, two on September 16, and two each on September 17 and 18.

Predicted solar flux is 160 and 155 on September 20-21, 150 on September 22-26, then a huge leap to 230 and 225 on September 27-28, 240 on September 29 through October 2, 230 on October 3, 220 on October 4-5, then 215, 205 and 207 on October 6-8, 201, 186 and 172 on October 9-11, 173 and 175 on October 12-13, 170 on October 14-16, 165 on October 17-18, 170 on October 19, 225 on October 20-21, then 230, 225, 230 and 225 on October 22-25, then 240 on October 26-29.

Predicted planetary A index is 5, 10 and 8 on September 20-22, 5 on September 23-26, then 25, 15 and 10 on September 27-29, then 5 on September 30 through October 4, 10 on October 5-6, and 5 on October 7-9, 10 on October 10, 20 on October 11-13, 15 on October 14, 10 on October 15-16, then 5 on October 17-22, 25 on October 23-24, and 15 and 10 on October 25-26..

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere September 19, 2024 from F.K. Janda, OK1HH.

Overall solar activity has decreased slightly in recent days, but before that AR3825 produced energetic flares, including two of the largest: X1.3 on September 12th and a very strong X4.5 on September 14th. The arrival of the CMEs and the onset of the disturbance, expected on the afternoon of UT Sept 16th, was delayed and registered as an influx of protons in the solar wind at 22:44 UT Sept 16th. After that, a geomagnetic disturbance started to develop, which significantly affected the shortwave propagation conditions, especially on 17 September.

A more pronounced upsurge in solar flux can be expected once the large active regions known to be present through helioseismology start to reappear at the eastern limb of the solar disk. This should happen around 26 September. However, a repeat of the August 28-29 disturbance is expected in the same period. Therefore, an improvement in propagation conditions can be expected before September 26, or better yet, shortly during the onset of the disturbance-after which a deterioration will occur.

New STCE newsletter.

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

Tamitha Skov video.

https://youtu.be/o0HWm0W-YRw

Send your tips, reports, observations, questions and comments to k7ra@arrl.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 good information and tutorials on propagation are at http://k9la.us/

Also, check this.

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

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

Sunspot numbers for September 12 through 18 2024 were 160, 127, 136, 68, 103, 140, and 106, with a mean of 120. 10.7 cm flux was 201.2, 185.8, 172.4, 172.8, 169.2, 165.4, and 163.3, with a mean of 175.7. Estimated planetary A indices were 67, 37, 21, 19, 23, 71, and 12, with a mean of 35.7. Middle latitude A Index was 36, 22, 22, 16, 19, 39, and 10, with a mean of 23.4. NNNN