All the indicators we track at the bottom of this bulletin fell last week.
Because there were no sunspots in six of the seven days (July 20-26) last week, average daily sunspot number dropped from 26.6 to 1.7. Average daily solar flux declined from 85.9 to 69.7.
Average daily planetary A index declined from 13 to 11.9, while the mid-latitude A index went the opposite direction, from 10.9 to 12.9.
The latest predicted solar flux (as of July 27) shows 68 on July 28-29, 72 and 76 on July 30-31, 80 on August 1-3, 82 on August 4-11, 80 and 75 on August 12-13, 70 on August 14-25, 80 on August 26, 82 on August 27 through September 1, 80 on September 2-4, 82 on September 5-7, and 80, 75 and 70 on September 8-10.
Predicted planetary A index is 7, 5, 6, 12, 10 and 8 on July 29 through August 2, 5 on August 3-5, 25 and 10 on August 6-7, 5 on August 8-15, 15 on August 17-18, then 12 and 8 on August 19-20, 5 on August 21-31, then 25, 10 and 8 on September 1-3, and 5 on September 4-10.
F.K. Janda, OK1HH of the Czech Propagation Interest Group sent this geomagnetic activity forecast for the period July 28-August 22, 2017.
Geomagnetic field will be:
Quiet on August 4, 9
Mostly quiet on July 30, August 2, 8, 10, 14-15
Quiet to unsettled July 28-29, August 1, 3, 16
Quiet to active on July 31, August 5, 7, 11, 13, 17-22
Active to disturbed on August 6, 12
Amplifications of the solar wind from coronal holes are expected on July 13-16 (-17), 20-21, (23-24, 28-29,) August 6-8
- Parenthesis means lower probability of activity enhancement and/or lower reliability of prediction due to irregular changes in position and area of coronal holes.
American Geophysical Union reports on 200 year old sunspot drawings discovered in Maine: http://bit.ly/2tPjuiI
Don’t miss the Solar Eclipse QSO Party on Monday, August 21 from 1400-2100 UTC. This is a wide-ranging propagation experiment intended to observe what happens when the moon blocks ionizing solar radiation from the ionosphere. The event is sponsored by ARRL and HamSCI, and the details are in the August 2017 QST, or you can read the same QST article at http://bit.ly/2tJ6EON .
Martin McCormick, WB5AGZ, of Stillwater, Oklahoma reported on July 23: "This has been one of the less spectacular sporadic E seasons so far with several openings but very few that are the type one will remember much after they occurred.
“After learning that WWV had installed a turnstile antenna on its 25 MHz transmitter, I began parking a receiver on that frequency to see if I could hear it in North-Central Oklahoma.
“During the first couple of weeks I heard nothing, but then WWV began coming in around 0000 UTC starting July 20.
“Whatever is ionizing the E layer to create this propagation is sticking around for a few days because once it started fading in, it has made numerous appearances this last week. It has mostly been in the mid to late evenings Central time, but on Sunday, July 23, it has been in with a fair signal since around 1200 UTC and is still somewhat audible at 1700 UTC as I write.
“It is good that WWV is transmitting on 25 MHz, as there are almost no steady identifiable signals in high HF and low VHF anymore to indicate when the bands are open.
“There is an announcement at 17 minutes past the hour stating that the turnstile antenna's configuration will not change until after the eclipse on 21 August.
“The theory that one of the possible triggers for a Sporadic E event has to do with clouds of iron and magnesium atoms from meteorites is interesting because we seem to have nothing for days at a time even though geomagnetic activity is not unusually low or high, and then we have several active days of Sporadic E and the numbers are not any different than they were when there was no Sporadic E at all."
Later, Martin provided this link: http://adsabs.harvard.edu/abs/2010JGRA..11512318K
He also commented, "The idea that a cloud of something such as magnesium or iron ions is one of the factors makes a lot of sense since we don't have sporadic E every day, all summer or all winter, even though the angle of Solar radiation is totally predictable and the geomagnetic activity indices are always present, if variable. So, something else, which is hard to see and slow-moving, must also contribute to causing sporadic E.
“Those of us who have been listening to both sporadic E and normal ionospheric propagation for years notice that the fading rate of signals always speeds up when there is lots of variation in the Sun's magnetic field and slows way down when things are quiet.
“The 25 MHz WWV signal was audible here last week almost every evening and most of last Sunday, but this week, there have been only a few seconds in which it pops in briefly and then everything goes dead again."
For more information concerning radio propagation, see the ARRL Technical Information Service 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/.
Monthly propagation charts between four USA regions and twelve overseas locations are at http://arrl.org/propagation.
Instructions for starting or ending email distribution of ARRL bulletins are at http://arrl.org/bulletins.
Sunspot numbers for July 20 through 26, 2017 were 0, 0, 0, 0, 0, 12, and 0, with a mean of 1.7. 10.7 cm flux was 70.2, 69.4, 69.5, 70.6, 70.1, 69.8, and 68.6, with a mean of 69.7. Estimated planetary A indices were 7, 14, 16, 14, 12, 9, and 11, with a mean of 11.9. Estimated mid-latitude A indices were 6, 13, 18, 16, 13, 9, and 15, with a mean of 12.9.