Solar activity was down again this week, with average daily sunspot numbers dropping from 105.9 to 78.7, and the average daily solar flux dropping from 149.4 to 140.9. Only three sunspot groups appeared, occurring on August 25, 28, and 30.

There has been a gradual transition from summer to fall conditions, with 10 and 12 meters opening more frequently. The autumnal equinox is only 3 weeks away.

Geomagnetic indicators were a little lower. The average planetary A index went from 8.4 to 7, and average middle latitude numbers went from 10.1 to 8.9.

Predicted solar flux shows a peak around 168 on September 18 – 21.

Forecast values are 145 on August 31 through September 1; 150, 150, and 145 on September 2 – 4; 150 on September 5 – 6; 156 on September 7 – 8; 150 on September 9; 147 on September 10 – 11; 145, 150, 155, 150, 155, and 160 on September 12 – 17; 168 on September 18 – 21; 165, 160, and 148 on September 22 – 24; 150 on September 25 – 26, and 152, 150, 145, and 140 on September 27 – 30.

Predicted planetary A index is 5, 10, and 10 on August 31 through September 2; 5 on September 3 – 6; 8 on September 7 – 8; 5 on September 9 – 13; 12, 10, 10, and 8 on September 14 – 17; 5 on September 18 – 22; 10, 10, and 8 on September 23 – 25, and 5 on September 26 to October 2.

Read about India’s solar mission at https://bit.ly/3PiPJ1N.

Check out a video about solar flares at https://bit.ly/47X6gzC. Sunspot numbers for August 24 through 30, 2023, were 86, 77, 75, 69, 68, 82, and 94, with a mean of 78.7. The 10.7-centimeter flux was 144.1, 138.9, 139.3, 141.5, 141.7, 142.2, and 138.6, with a mean of 140.9. Estimated planetary A indices were 9, 5, 7, 11, 6, 5, and 6, with a mean of 7. The middle latitude A index was 9, 7, 9, 13, 8, 7, and 9, with a mean of 8.9.

Five new sunspot groups emerged this week: one on August 17, another on August 18, two more on August 21, and another on August 22.

Average daily sunspot numbers rose slightly from 95.7 to 105.9, while the average daily solar flux declined from 154.2 to 149.4.

There weren’t any big geomagnetic events this week to report. The average daily planetary A index changed from 6 to 8.4, while the average daily middle latitude index changed from 7.7 to 10.1.

Predicted solar flux is 150 on August 24; 155 on August 25 – 26; 160, 165, and 165 on August 27 – 29; 160, 165, and 165 on August 30 through September 1; 163 and 160 on September 2 – 3; 162 on September 4 – 5; 158 on September 6 – 7; 160 and 162 on September 8 – 9; 158 on September 10 – 11; 155 on September 12; 152 on September 13 – 15; 153 on September 16 – 18; 155 on September 19, and 158 on September 20 – 23.

Predicted planetary A index is 8 on August 24 – 25; 5, 10, and 8 on August 26 – 28; 5 on August 29 through September 5; 10, 8, and 8 on September 6 – 8; 5 on September 9 – 13; 12 on September 14; 10 on September 15 – 17, and 5 on September 18 through the end of the month.

Jeremy Gill of Seattle, Washington, shared the article, “Laboratory measurements of the physics of auroral electron acceleration by Alfvén waves,” which has information on aurora activity and the ionosphere. Read it at https://bit.ly/44sRGgh.

Read some shrill warnings of solar activity at https://bit.ly/3qHy6za, https://bit.ly/3YLsoci, https://bit.ly/3QNx8w3, and https://bit.ly/3OJRCTP.

Sunspot numbers for August 17 – 23, 2023, were 135, 112, 104, 93, 102, 96, and 99, with a mean of 105.9. The 10.7-centimeter flux was 151.9, 150.6, 150.6, 146.3, 148.7, 150.9, and 147, with a mean of 149.4. Estimated planetary A indices were 8, 11, 8, 11, 9, 8, and 4, with a mean of 8.4. Middle latitude A index was 10, 14, 8, 12, 10, 12, and 5, with a mean of 10.1.

Eleven new sunspot groups emerged over the past week, August 10 – 16, 2023, but average solar indicators declined.

There were two new sunspot groups on August 11, three more on

August 13, another on August 14, two more on August 15, and three more on August 16.

The average daily sunspot numbers declined from 108.9 to 95.7, while the average daily solar flux dropped from 166.4 to 154.2.

Predicted solar flux is 160 on August 17 – 24; 162, 160, and 164 on August 25 – 27; 168 on August 28 – 31; 165, 163, and 160 on September 1 – 3; 158, 155, 152, and 150 on September 4 – 7; 148, 142, 140, and 130 on September 8 – 11; 135 on September 12 – 14, and 145, 150, and 155 on September 15 – 17.

Predicted planetary A index is 15, 12, and 8 on August 17 – 19; 5 on August 20 – 25; 12 on August 26; 5 on August 27 through September 5; 10, 8, and 8 on September 6 – 8; 5 on September 9 – 11, and 12, 15, 12, and 8 on September 12 – 15.

Look for comments from readers concerning the transition from summer to fall conditions in Friday’s bulletin.

Sunspot numbers for August 10 through 16, 2023, were 83, 105, 61, 89, 85, 107, and 140, with a mean of 95.7. The 10.7-centimeter flux was 155.7, 152.8, 148.3, 150.4, 154, 158.1, and 160.1, with a mean of 154.2. Estimated planetary A indices were 7, 5, 8, 5, 5, 5, 5, 5, 5, 4, and 8, with a mean of 6. The middle latitude A index was 8, 6, 10, 7, 6, 7, and 10, with a mean of 7.7.

A comprehensive Solar Update is posted Fridays on the ARRL website. For more information concerning radio propagation, visit the ARRL Technical Information Service, read “What the Numbers Mean…,” and check out the Propagation Page of Carl Luetzelschwab, K9LA.

A propagation bulletin archive is available. For customizable propagation charts, visit the VOACAP Online for Ham Radio website.

Share your reports and observations.

A weekly, full report is posted on ARRL News.

Two new sunspot groups appeared on August 3, and then three more appeared on August 7, followed by another on August 9.

But solar activity was lower during our current reporting week of August 3 – 9, with the average daily sunspot number dropping from 154.3 to 108.9, and average solar flux from 173 to 166.4.

The average daily planetary A index rose from 8.3 to 12.3, and the average middle latitude A index rose from 9.3 to 10.1.

The middle latitude A index on August 3 – 4 was not available, so I estimated the value based on the planetary A index and remaining five middle latitude readings for the rest of the week.

Predicted solar flux is 150 on August 10 – 12; 145, 140, 130, and 135 on August 13 – 16; 162 on August 17 – 18; 164 on August 19 – 20; 168 on August 21 – 23; 172, 172, and 170 on August 24 – 26; 172, 172, and 174 on August 27 – 29; 172, 172, and 170 on August 30 – September 1; 168, 168, 166, and 164 on September 2 – 5, and 162, 162, 164, and 164 on September 6 – 9.

Predicted planetary A index is 12 on August 10; 5 on August 11 – 14; 12 and 8 on August 15 – 16; 5 on August 17 – 25; 12 on August 26, and 5 on August 27 – September 4.

On August 9, Spaceweather.com wrote about a 1940 geomagnetic storm that sounds similar to the infamous Carrington Event.

Two coronal mass ejections hit Earth, each 109 minutes apart. Read a recent scientific paper on the event at https://bit.ly/3s1VrMh.

Check out the following articles on solar flares:

https://bit.ly/3KXlUl1

https://bit.ly/3qj0pE6

https://bit.ly/3QPYPV9

https://bit.ly/45naVsF

Space weather forecaster Dr. Tamitha Skov, WX6SWW, recently uploaded this video:

https://youtu.be/Olfjss8GmSI Sunspot numbers for August 3 – 9, 2023, were 124, 122, 100, 97, 101, 115, and 103, with a mean of 108.9. The 10.7-centimeter flux was 162.9, 170.8, 175.8, 173.5, 169.7, 158.9, and 153.4, with a mean of 166.4. Estimated planetary A indices were 6, 13, 36, 4, 12, 8, and 7, with a mean of 12.3. Middle latitude A index was 5, 12, 24, 4, 11, 7, and 8, with a mean of 10.1.

The Australian Space Weather Forecasting Centre issued a geomagnetic disturbance warning at 0233 UTC on August 3, 2023:

“Two recent coronal mass ejections (CMEs) are expected to impact Earth on UT day 05-Aug, with the second possibly arriving early 06-Aug. G0-G1 geomagnetic conditions may be expected on 05-Aug, with a chance for isolated periods of G2 towards the end of the UT day on 05-Aug. Geomagnetic storm conditions may persist over 06-Aug.”

Solar activity was up during this reporting week, July 27 through August 2.

Average daily sunspot numbers increased from 128.1 to 154.3, but the average daily solar flux was about the same as last week, moving from 172.2 to 173.

Geomagnetic indicators were quiet, with the average daily planetary A index shifting from 11 to 8.3, while middle latitude numbers went from 11.1 to 9.3.

Predicted solar flux is 170 and 165 on August 3 – 4; 160 on August 5 – 7; 155, 145, and 168 on August 8 – 10; 168 on August 11 – 12; 170 on August 13 – 16; 172 on August 17 – 18; 170 and 168 on August 19 – 20; 170 on August 21 – 22; 172 on August 23; 170 on August 24 – 27, and 165 on August 28 – 31.

Predicted planetary A index is 10, 20, 28, 15, and 8 on August 3 – 7; 5, 5, and 10 on August 8 – 10; 8 on August 11 – 12; 5 on August 13 – 25; 12 and 10 on August 26 – 27, and 5 on August 28 – 31.

ARRL published an excellent new book, Here to There: Radio Wave Propagation, written by a team of experts, including Frank Donovan, W3LPL; Nathaniel Frissell, W2NAF, and Carl Luetzelschwab, K9LA. It’s a great reference on all aspects of HF and VHF propagation and it includes a survey of the various propagation prediction computer programs.

Sunspot numbers for July 27 through August 2 were 154, 148, 147, 139, 197, 160, and 135, with a mean of 154.3. The 10.7-centimeter flux was 165.3, 168.2, 178.6, 174.4, 177.1, 174.7, and 172.9, with a mean of 173. Estimated planetary A indices were 7, 6, 9, 9, 6, 9, and 12, with a mean of 8.3. Middle latitude A index was 7, 5, 8, 18, 8, 9, and 10, with a mean of 9.3.