Nine new sunspot groups appeared this week, but the average daily sunspot numbers were lower.

A new sunspot group appeared every day on September 15 – 17; four more appeared on September 18, and one appeared each day on September 19 – 20, 2023.

The average daily sunspot numbers declined from 138.1 to 118.4, while the average daily solar flux declined from 159.9 to 149.3.

The autumnal equinox in the Northern Hemisphere is Friday, September 22, 2023. The change in seasons has been evident with improving conditions on 10 and 12 meters.

A fast-moving coronal mass ejection (CME) hit Earth on September 18, sparking dramatic displays of aurora across the northern tier of North America, and in Europe as far south as France.

Alaska’s college A index was 49 and 61 on September 18 – 19, while the planetary A index was 30 and 49.

Predicted solar flux is 155, 152, 153, and 155 on September 21 – 24; 160 on September 25 – 27; 135 on September 28 – 30;130, 135, 130, and 135 on October 1 – 4; 140 on October 5 – 6; 135 on October 7 – 8; 140, 145, and 145 on October 9 – 11, 150, 150, 155, and 150 on October 12 – 15, and 155, 150, 145, and 145 on October 16 – 19.

Predicted planetary A index is 8 and 15 on September 21 – 22; 12 on September 23 – 26; 5, 8, 12, and 8 on September 27 – 30; 5 on October 1 – 11; 8 on October 12, and 5 on October 13 – 19. Sunspot numbers for September 14 – 20, 2023, were 110, 96, 88, 94, 139, 143, and 159, with a mean of 118.4. The 10.7-centimeter flux was 145.2, 139.1, 140.4, 144.6, 154.5, 166.1, and 155.5, with a mean of 149.3. Estimated planetary A indices were 18, 7, 7, 16, 30, 49, and 16, with a mean of 20.4. Middle latitude A index was 13, 7, 5, 14, 21, 38, and 15, with a mean of 18.1.

Like last week, eight new sunspot groups emerged this reporting week, September 7 – 13, 2023.

One appeared on September 7, another on 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 increasing from 137.6 to 159.9.

The most active geomagnetic day was September 12, when the planetary A index was 25. A “stealth CME” with an aurora visible as far south as Missouri was reported on spaceweather.com.

The average daily planetary A index decreased from 15.4 to 10.4, and middle latitude numbers decreased from 16.3 to 11.3.

The autumnal equinox in the Northern Hemisphere is on September 22 — just a week away.

It seems that the next sustained short-term peak in solar flux is a few weeks off, with values between 150 and 155 on October 12 – 17, although it’s expected to reach 150 on September 23 – 24.

The forecast shows the solar flux at 145, 145, 148, 145, and 145 on September 14 – 18; 148 on September 19 – 20; 145 on September 21 – 22; 150 on September 23 – 24; 145 on September 25; 140 on September 26 – 27; 135 on September 28 – 30; 130, 135, 130, and 135 on October 1 – 4; 140 on October 5 – 6, and 135 on October 7 – 8.

Predicted planetary A index is 12 and 15 on September 14 – 15; 8 on September 16 – 17; 5, 5, and 10 on September 18 – 20; 5, 5, and 12 on September 21 – 23; 5 on September 24 – 27; 8, 12, and 8 on September 28 – 30, and 5 on October 1 – 8. Sunspot numbers for September 7 – 13, 2023, were 135, 123, 119, 167, 173, 141, and 109, with a mean of 138.1. The 10.7-centimeter 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. The middle latitude A index was 11, 8, 12, 6, 8, 17, and 17, with a mean of 11.3.

Seven new sunspots emerged this week: one on September 2, two on September 3, two more on September 4, one on September 5, and one on September 6.

The average daily sunspot number was up from 78.7 to 95.4, while the average daily solar flux decreased from 140.9 to 137.6.

Geomagnetic activity was higher. On September 2, the planetary A index was 38 when Earth moved through a high-speed solar wind. In Alaska, the college A index at Fairbanks was 59.

The average daily planetary A index increased from 7 to 15.4, and the average middle latitude A index rose from 8.9 to 16.3.

Predicted solar flux is 150, 155, 155, and 150 on September 7 – 10; 140 on September 11 – 13; 145, 150, 150, and 155 on September 14 – 17; 150, 155, and 150 on September 18 – 20; 145 on September 21 – 22; 150 on September 23 – 24; 145 on September 25; 140 on September 26 – 27; 135 on September 28 – 30; 130, 135, 130, and 135 on October 1 – 4, and 140 on October 5 – 6.

Predicted planetary A index is 12, 10, 5, and 5 on September 7 – 10; 8 on September 11 – 13; 10, 8, 12, 8, and 8 on September 14 – 18; 5 on September 19 – 22; 12 on September 23; 5 on September 24 – 27; 8, 12, 5, and 12 on September 28 through October 1; 12, 10, 12, and 10 on October 2 – 5, and 5 on October 6 – 10.

I observed some interesting 12-meter propagation via PSK Reporter while using FT8 at 1745 UTC on September 4. My signal was received only over a narrow, 300-mile band hugging the east coast from Maine to Florida. The signals were between 2,200 – 2,500 miles away, and nowhere else.

Three hours later, at 2045 UTC, the reception reports along the coast expanded to 600 miles, and then 2,000 – 2,600 miles.

Later, at 2300 UTC, there was the same pattern, but it was a 200-mile band spanning 2,300 – 2,500 miles wide.

The next day, at 1700 UTC, there was an arc from Virginia to south Texas stretching 1,700 – 2,300 miles wide. At 1715 UTC, it drifted to a coverage of 1,750 – 2,600 miles.

Before FT8 and PSK Reporter, there was no practical way to observe propagation. Sunspot numbers for August 31 through September 6, 2023, were 77, 83, 77, 79, 100, 121, and 131, with a mean of 95.4. The 10.7-centimeter flux was 139.9, 135.8, 131.2, 130.5, 136, 142.9, and 147.1, with a mean of 137.6. Estimated planetary A indices were 6, 12, 38, 25, 8, 11, and 8, with a mean of 15.4. Middle latitude A index was 8, 15, 25, 28, 14, 14, and 10, with a mean of 16.3.

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.

Average daily sunspot numbers declined from 130.6 to 128.1 over the past week of July 20 – 26.

Average daily solar flux declined significantly from 190.5 to 172.2.

The solar flux forecast sees values at 168, 165, and 162 on July 27 – 29; 158 on July 30 – 31; 155 and 158 on August 1 – 2; 165 on August 3 – 4; 170 and 175 on August 5 – 6; 180 on August 7 – 10; 175 on August 11 – 13; 180 on August 14 – 15; 175 on August 16 – 18; 170 on August 19; 165, 165, and 160 on August 20 – 22, and 155 on August 23 – 26.

Predicted planetary A index is 20, 10, 5, 10, and 8 on July 27 – 31; 5, 5, 10, and 8 on August 1 – 4; 5 on August 5 – 9; 10 on August 10; 8 on August 11 – 13; 5 on August 14 – 19, and 10, 8, and 5 on August 20 – 22.

Read about sunspots, flares, and aurora at the following link:

https://bit.ly/44JxcRp

Check out a story about the Mars rover seeing the far side of the sun at the link below:

https://bit.ly/3KbRV8b

Also, see the report of a rocket punching a hole in the ionosphere at:

https://bit.ly/3KceBFB

Nearly 5 decades ago in Marin County, California, I, too, witnessed a rocket penetrating the ionosphere. It was a huge, dramatic display. My friend had seen a similar thing before, and said it was created by a rocket launch from Vandenberg Air Force Base in Southern California.

Sunspot numbers for July 20 – 26, 2023, were 131, 121, 103, 117, 141, 137, and 147, with a mean of 128.1. The 10.7-centimeter flux was 184.3, 172.8, 174.4, 172.5, 165.1, 169, and 167.4, with a mean of 172.2. Estimated planetary A indices were 10, 13, 9, 6, 7, 11, and 21, with a mean of 11. Middle latitude A index was 10, 11, 9, 5, 8, 12, and 23, with a mean of 11.1.

Average daily sunspot numbers declined, but the average daily solar flux increased. Sunspot averages were 181.9 last week and 130.6 this week. The average daily solar flux increased from 179.4 to 190.5.

Two new sunspot groups emerged on July 14, as well as three more on July 17, and another two on July 19.

The average daily planetary and middle latitude A indices were both 12.9 this week, rising from 8.6 and 8.1.

Predicted solar flux is 188 on July 20 – 23; 186, 184, 186, and 160 on July 24 – 27; 165 on July 28 – 29; 170 on July 30 – 31; 165 on August 1 – 4; 170, 175, 175, and 170 on August 5 – 8; 165 on August 9 – 11; 170 on August 12; 175 on August 13 – 14, and 170 on August 15 – 19.

The predicted planetary A index is 28, 20, and 12 on July 20 – 22; 5 on July 23 through August 2; 10 and 8 on August 3 – 4; 5 on August 5 – 14, then 12, 8, and 8 on August 15 – 17.

CNN presented a smart piece on the sunspot cycle peaking sooner than expected:

https://bit.ly/3rzNJJ6

Cosmos published an article about a double-peaked solar flare:

https://bit.ly/46ZoznE

Sunspot numbers for July 13 – 19, 2023, were 146, 141, 96, 99, 149, 142, and 141, with a mean of 130.6. The 10.7-centimeter flux was 202.9, 180.6, 178.5, 184.3, 180, 218.5, and 188.9, with a mean of 190.5. Estimated planetary A indices were 7, 20, 8, 10, 24, 16, and 5, with a mean of 12.9. Middle latitude A index was 9, 17, 9, 13, 19, 16, and 7, with a mean of 12.9.

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.