High solar activity continued this week, with average daily sunspot number changing from 208.1 to 208.9 and average daily solar flux from 193 to 207.3.  Average daily planetary A index shifted from 6 to 14, and average middle latitude A index from 7.3 to 13.1.

The Penticton observatory in British Columbia reported a solar flux of 400.7 at noon on July 30, which we threw out due to obvious overload at the facility.  We used values from the morning and afternoon to come up with our estimate instead.

Nine new sunspot regions emerged.  There was one on July 25, two on July 26, another on July 28 and another on July 29, two more on July 30 and another two on July 31.

Predicted solar flux is 235 on August 2, 230 on August 3, 220 on August 4 to 8, 190 on August 9 to 11, 195 on August 12 and 13, 190 on August 14 to 17, 185 on August 18, then 180 on August 19 to 24, 190 on August 25 to 31, 180 on September 1 and 2, 185 on September 3 and 4, and 190 on September 5 to 7.

The planetary A index prediction calls for 10, 30, 25 and 8 on August 2 to 5, 5 on August 6 to 21, then 10 and 8 on August 22 and 23, and 5 on August 24 to September 11.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's Ionosphere for August 1, 2024 from OK1HH.

The largest solar flare so far in the 25th 11-year cycle occurred on July 23 on the far side of the Sun.  Fortunately, it was observable by the Solar Orbiter (SolO), a solar probe designed to study the Sun from a heliocentric orbit.  The spacecraft was manufactured by Airbus for ESA.  The individual measuring instruments and sensors were supplied by ESA Member States, including the Czech Republic, while the US NASA is also involved in the probe.  The spacecraft was launched on 10 February 2020 on Atlas V rocket from Cape Canaveral.

Solar Orbiter was in an ideal position to observe the eruption, directly invisible from Earth now.  On July 24, SolO was directly hit by particles from the CME, accelerated in a shock front, which increased their energy (a similar ESP event caused the "Great Quebec Blackout" in March 1989, but fortunately only SolO was hit this time).

Over the past seven days, the Sun's rotation has shifted the sunspot active regions from the southeast quadrant of the solar disk to the southwest, or the area where Earth is more likely to be hit by particles ejected from the Sun.  Strong eruptive activity has continued.  If we just had the Sun overhead, we could register the Dellinger effect, a shortwave blackout, which almost always hit the lower shortwave bands and only rarely the entire shortwave range.

Even a G3 geomagnetic disturbance was predicted, but so far it has been a G2.  It could have been worse due to "cannibal CMEs" that made way for other CMEs from subsequent eruptions.  Even so, due to  "appropriate" timing, there was a significant drop in daily MUF values and an overall worsening of shortwave propagation conditions.  

The worst days were 26 and 30 and 31 July.  We continue to observe several unstable sunspot regions on the Sun.  Therefore, further similar disturbances are very likely.

Recent report from Tamitha Skov: https://bit.ly/3A6XClU  

How current storm differs from May 11:

https://bit.ly/46thuvr

Are we at solar max? https://bit.ly/3yuxMYn (Thanks to NN4X.)

Frank Donovan, W3LPL sent this URL, commenting that it contains much more detail about July 23 solar events:

https://www.stce.be/newsletter/pdf/2024/STCEnews20240801.pdf

Kepler's sketches: https://bit.ly/3SB5gvg

Stormy: https://bit.ly/3YozbdL

Send your tips, reports, observations, questions and comments to [email protected] .  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

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

Sunspot numbers for July 25 through 31 2024 were 171, 181, 178, 189, 211, 261, and 271, with a mean of 208.9.  10.7 cm flux was 176.2, 176.3, 203.6, 214.4, 223.1, 222.3, and 235.1, with a mean of 207.3. Estimated planetary A indices were 9, 23, 13, 7, 6, 23, and 17, with a mean of 14.  Middle latitude A Index was 9, 23, 14, 8, 7, 18, and 13, with a mean of 13.1.