At 0134 UTC on April 27, The Australian Space Weather Forecasting Centre of the Australian Bureau of Meteorology issued a geomagnetic disturbance warning, stating, “An equatorial coronal hole is currently elevating solar wind speeds. Combined with the anticipated impact from a recent CME on April 27, geomagnetic activity is expected to be at G0-G1 levels over April 27 – 28, with a slight chance of an isolated period of G2.”

Solar and geomagnetic indicators moved in opposite directions this week. Average daily sunspot numbers over April 20 – 26 made a dramatic drop from 146.9 to 91.4, and average daily solar flux dropped from 164.5 to 139.4.

Average daily planetary A index more than tripled from 8.1 to 26.9, while average middle latitude A index more than doubled from 7.3 to 15.6.

Solar wind and explosions caused all of this grief.

Spaceweather.com reported that on April 21, a large magnetic filament on the sun exploded and hurled debris toward Earth.

Later, they reported that on April 23, at 1737 UTC a CME hit Earth, which sparked a severe G4-class geomagnetic storm. Aurora was visible as far south as southern New Mexico and Texas.

The planetary K index went as high as 8 over April 23 – 24.

Predicted solar flux over the next month is 135 on April 27 – 30; 140 on May 1 – 6, then 145, 150, 155, 160, and 165 on May 7 – 11; 170 on May 12 – 13, then 165, 160, 155, 150, 145, and 140 on May 14 – 19; 135 on May 20 – 21; 130 and 125 on May 22 – 23; 120 on May 24 – 25, and 125, 130, and 135 on May 26 – 28.

Predicted planetary A index is 18, 25, and 12 on April 27 – 29; 8 on April 30 through May 3, then 10, 8, 12, and 10 on May 4 – 7; 8 on May 8 – 9, then 5, 5, and 12 on May 10 – 12; 5 on May 13 – 15; 8 on May 16 – 17; 5 on May 18 – 22, then 15 and 18 on May 23 – 34, and 15 on May 25 – 27.

Here is a link to the aurora as observed in China:

https://bit.ly/41KyY3w

Here is a link to explaining the aurora:

https://bit.ly/3n7ROm2

Sunspot numbers for April 20 through 26, 2023, were 97, 114, 87, 86, 88, 87, and 81, with a mean of 91.4. 10.7-centimeter flux was 147, 151.2, 141.2, 135.2, 133.9, 130.7, and 136.5, with a mean of 139.4. Estimated planetary A indices were 5, 9, 7, 66, 76, 10, and 15, with a mean of 26.9. Middle latitude A index was 5, 8, 6, 32, 39, 7, and 12, with a mean of 15.6.

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.

For this week’s ARRL Propagation Bulletin ARLP016:

This week’s sunspot numbers and solar flux were higher than the week before.

Average daily sunspot numbers were more than doubled, from 70.6 to 146.9, and average daily solar flux increased from 141 to 164.5. Both figures represent a substantial increase in solar activity.

Planetary A index averages went from 7.6 to 8.1, while middle latitude A index advanced from 6.4 to 7.3.

Predicted solar flux over the next few weeks is 145, 140, and 135 on April 20 – 22; 130 on April 23 – 24; 125 on April 25 – 26; 160 on April 27 – 29; 165 on April 30; 172 on May 1 – 3; 170 on May 4; 172 on May 5 – 7; 178 on May 8; 182 on May 9 – 12, then 175, 178, and 170 on May 13 – 15; 168 on May 16 – 17; 175 on May 18, and 172 on May 19 – 21.

Predicted planetary A index is 20, 16, 12, and 10 on April 20 – 23, then 8, 5, 15, and 18 on April 24 – 27; 15 on April 28 – 30, then 12 and 10 on May 1 – 2; 8 on May 3 – 4; 5 on May 5 – 6; 12 on May 7; 5 on May 8 – 10, then 8 on May 11 – 12; 5 on May 13 – 18, then 10, 8, 5, and 5 on May 19 – 22.

Dan Handa, W7WA, commented on the news item last week about the current solar cycle reaching a peak earlier than predicted, perhaps by the end of this year.

I told him I hope it will not peak early because I want to see several more years of increasing activity.

Dan sent a detailed graph of Solar Cycle 19, from 1954 to 1966, and wrote, “I have read more than once [that] a slow rise means a low sunspot max. The previous [Solar] Cycle 24 took 5 years to reach a relatively low maximum. A rapid increase can mean a high sunspot maximum. The granddaddy of our lifetime, [Solar] Cycle 19, peaked in three years!” I was unaware of this.

Sunspot numbers for April 13 – 19, 2023, were 154, 153, 151, 155, 162, 140, and 113, with a mean of 146.9. 10.7-centimeter flux was 159.5, 171.3, 175.8, 177.8, 166.6, 153.2, and 147, with a mean of 164.5. Estimated planetary A indices were 6, 7, 9, 4, 6, 13, and 12, with a mean of 8.1. Middle latitude A index was 5, 10, 8, 4, 6, 9, and 9, with a mean of 7.3.

Solar activity was up for this reporting week, April 6 – 12.

Seven new sunspot groups appeared: one on April 6, another on April 9, two more on April 10, another on April 11, and two more on April 12.

The average daily sunspot number rose from 53.4 to 70.6, and the average daily solar flux increased from 132.5 to 141.

Geomagnetic conditions were calm. The average daily planetary A index dropped from 15 to 7.6, and the middle latitude average dropped from 11.7 to 6.4.

Predicted solar flux is 155 and 160 on April 13 – 14; 165 on April 15 – 16; 160 on April 17 – 18, then 155 and 152 on April 19 – 20; 155 on April 21 – 22; 158 on April 23; 155 on April 24 – 25, then 152, 148, 145, and 142 on April 26 – 29; 140 on April 30 and May 1; 142 and 140 on May 2 – 3; 135 on May 4 – 5, then 130, 140, 145, 150, 152, 155, and 158 on May 6 – 12, and 160 on May 13 – 15.

Predicted planetary A index is 5 on April 13 – 15; 12 on April 16; 8 on April 17 – 18, then 5, 10, 15, and 10 on April 19 – 22; 5 on April 23 – 25, then 15 and 18 on April 26 – 27; 15 on April 28 – 30, then 12 and 10 on May 1 – 2; 8 on May 3 – 4; 5 on May 5 – 6, then 8, 10, and 8 on May 7 – 9, and 5 on May 10 – 13.

Spaceweather.com released this news on Wednesday:

“Evidence is mounting that Solar Cycle 25 might peak much earlier than expected. New research by a leading group of solar physicists predicts maximum sunspot activity in late 2023 or early 2024 with a peak that could be twice as strong as the previous solar cycle.”

It is all explained in this paper:

https://bit.ly/41gZnW4

Look in the Spaceweather.com archive for April 12 – 13 to read more.

I noticed some odd 10-meter propagation at 2000 UTC on April 11. While running FT8 and a one wavelength end-fed wire at my home in Seattle, the only stations that heard me, according to pskreporter.info, were one in New Zealand, another in Hawaii, and only five stations in Florida over a 200-mile strip from 2,512 to 2,712 miles. Checking again at 2015 UTC, it was still the same.

Sunspot numbers for April 6 – 12, 2023, were 33, 38, 49, 52, 92, 103, and 127, with a mean of 70.6. 10.7-centimeter flux was 137.1, 136.3, 135.9, 140.3, 139.8, 143.4, and 154, with a mean of 141. Estimated planetary A indices were 9, 8, 6, 6, 14, 6, and 4, with a mean of 7.6. Middle latitude A index was 7, 7, 5, 5, 11, 6, and 4, with a mean of 6.4.

HAM is a short documentary that follows a group of Montanan amateur radio enthusiasts that show the loyal community of amateur radio, explore what it means to be a ham, and how they are trying to keep the hobby alive. Thank you to everyone who made this documentary happen, to all of our peers at UM, to the awesome people who let us into their lives, and to everyone who cheered us on the whole way. Special thanks to the School of Visual and Media Arts at the University of Montana and Montana PBS. Produced by students from the School of Visual and Media Arts program at the University of Montana in 2022. Aired on Montana PBS on November 24th, 2022.

Here is the link to that documentary: https://www.youtube.com/watch?v=wt5wZhC5crI

Average solar flux and sunspot numbers went down this week. Sunspot numbers are down by half, from 112.6 last week to 53.4 this week. Average daily solar flux declined from 156.1 to 132.5.

Geomagnetic indicators also declined this week. The average daily planetary A index went from 23.3 last week to 15 this week. Average daily middle latitude A index went down from 13.7 to 11.7.

The middle latitude A index for April 1 was not available, so my guess for it is 11.

Predicted solar flux is 140 on April 6 – 8; 135 on April 9 – 11; 140 on April 12 – 13; 130 on April 14; 135 on April 15 – 17; 140 on April 18 – 20; 135 on April 21 – 23, then 130, 125, and 120 on April 24 – 26; 115 on April 27 – 29; 125 on April 30; 120 on May 1 – 2; 115 on May 3 – 4, and 110 on May 5 – 7.

Predicted planetary A index was 8 on April 6; 5 on April 7 – 10, then 8, 8, and 5 on April 11 – 13; 8 on April 14 – 15, then 12, 10, and 15 on April 16 – 18, then 5, 20, 15, and 10 on April 19 – 22; 5 on April 23 – 25, then 15 and 18 on April 26 – 27; 15 on April 28 – 29; 8 on April 30; 10 on May 1 – 2; 8 on May 3, and 5 on May 4 – 6.

This video from Tamitha Skov features flares and wind, and came out right after last week’s bulletin:

https://youtu.be/F8ERhLiOK88

Sunspot numbers for March 30 through April 5, 2023, were 99, 61, 23, 54, 56, 44, and 37, with a mean of 53.4. 10.7-centimeter flux was 140.3, 129.3, 125.3, 126.9, 133.6, 135.7, and 136.6, with a mean of 132.5. Estimated planetary A indices were 17, 21, 13, 15, 15, 13, and 11, with a mean of 15. Middle latitude A index was 11, 17, 11, 13, 11, 10, and 9, with a mean of 11.7.