Average daily sunspot number this week declined just 1.7 to 26.6, even though there were two days in the reporting week with no sunspots, July 18-19. The blank Sun condition continued at least one more day on Thursday, July 20 which lands it on the first day of the next reporting week, July 20-26.

Average daily solar flux was 85.9, down 1.1 from the previous week.

Average planetary A index rose 3.9 points to 13, average mid-latitude A index rose from 9.6 to 10.9.

A coronal mass ejection (CME) on July 16 struck at 0545 UTC driving the planetary A index to 41, and 27 the following day.

Predicted solar flux is 70 on July 21-27, 75 on July 28, 90 on July 29 through August 11, 85 on August 12-13, 80 on August 14, 74 on August 15-19, 75 on August 20-24, and 90 on August 25 to September 3.

Predicted planetary A index is 8, 12 and 8 on July 21-23, 5 on July 24 through August 4, then 25, 10 and 8 on August 5-7, 5 on August 8-14, 8 on August 15-16, then 15 and 12 on August 17-18, 5 on August 19-31, and 25, 10 and 8 on September 1-3.


F. K. Janda, OK1HH of the Czech Propagation Interest Group sent us this geomagnetic activity forecast for the period July 21-August 8, 2017

“Geomagnetic field will be:
Quiet on July 25 -26, August 1-2
Mostly quiet on July 24, 27, 30-31, August 4, 8
Quiet to unsettled July 23, August 3
Quiet to active on July 21-22, 28-29, August 7
Active to disturbed on August 5-6

Amplifications of the solar wind from coronal holes are expected on July 21, (23-24, 28-29), August 6-8

Remark:
- Parenthesis means lower probability of activity enhancement and/or lower reliability of prediction.”


David Moore sent a link to an excellent NY Times science article titled “Unlocking Mysteries in the Sun’s 11-Year Cycle”: http://nyti.ms/2tdddgv


Another interesting article: https://cosmosmagazine.com/space/studying-the-solar-cycle

And the latest from Tamitha Skov: http://bit.ly/2uOPeob

http://bit.ly/2vqusbs



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 13 through 19, 2017 were 55, 58, 34, 26, 13, 0, and 0, with a mean of 26.6. 10.7 cm flux was 92.3, 93.9, 91.6, 86.5, 85.6, 78.2, and 73.1, with a mean of 85.9. Estimated planetary A indices were 4, 4, 4, 41, 27, 7, and 4, with a mean of 13. Estimated mid-latitude A indices were 5, 3, 4, 29, 23, 7, and 5, with a mean of 10.9.