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The K7RA Solar Update


Solar activity declined over the past reporting week, August 13-19. Average daily sunspot numbers went from 82.3 during the previous seven days, to 37.4 in the most recent period.

Average daily solar flux also declined over the same two weeks, from a mean of 112.4 to 91. Average planetary A index went from 11.7 in the previous week to 21.4 in the recent seven days. Activity over August 15-17 drove these numbers higher, with planetary A index at 44, 36 and 27 during those three days. This was caused by a CME, a coronal mass ejection.

The latest predicted solar flux from NOAA/USAF over the near term is 105 and 110 on August 21-22, 115 on August 23-24 then 110, 115, 110 and 100 on August 25-28, 95 on August 29 through September 2, 100 on September 3-4, 105 on September 5, 100 on September 6-7, then 95 and 90 on September 8-9, and 85 on September 10-18. Solar flux then rises to 100 after September 29.

Predicted planetary A index is 12 on August 21-22, 28 on August 23, then 12, 8, 12 and 14 on August 24-27, 10 on August 28-29, 5 on August 30 through September 1, then 12, 22, 15 and 12 on September 2-5, 10 on September 6-7, then 8 on September 8-9, 5 on September 10-11, then 10, 20 and 15 on September 12-14, 5 on September 15-16 and 8 on September 17-18.

OK1MGW sent a geomagnetic forecast for August 21 to September 16. He sees quiet to unsettled conditions August 21-22, quiet to active August 23, quiet to unsettled August 24, mostly quiet August 25, and active to disturbed August 26 (although he is unsure of the reliability of that prediction).

On August 27-28 he sees quiet to active conditions, quiet to unsettled August 29-30, mostly quiet August 31 through September 1, quiet to active September 2, active to disturbed September 3, quiet to active September 4, mostly quiet September 5-8, quiet September 9-10, mostly quiet September 11, quiet to unsettled September 12-15 and quiet to active September 16. He expects increases in solar wind August 23, 25-28 and September 1-4.

At 0636 UTC on August 19 Australia’s Space Weather Services released a geomagnetic disturbance warning, which said, “A large Coronal Hole (CH 683) is located in the solar Northern Hemisphere and is taking geoeffective position. A high speed solar wind stream emanating from CH 683 is driving a Co-rotating Interaction Region (CIR) and this will affect Earth's geomagnetic environment over the next 1-2 days. Minor geomagnetic storms could occur in the high latitude regions and possibly extend into the mid latitudes. The aurora may be visible from the southern parts of Australia at the local night hours on 19 and 20 August.”

Jon Jones, N9JK, of Kansas wrote: “A surprising amount of late season sporadic E propagation on 50 MHz this third week of August.

“Six meters was open for strong sporadic E the afternoon and evening of August 16. In addition to strong single hop, some double hop E-skip was noted by W9RM DM58 to FM18, and K1TOL FN44 to N3AIU in DM45 around 0200z August 17.

“The next day and afternoon sporadic E appeared again. This time multi-hop Es spanned the Atlantic Ocean between North America and Europe.

“CT1HZE IM57 worked into W5, W9 and WØ around 1600z, then again to the Midwest starting at 2245z on 6 meters. NØLL EM09 and KQØJ EN11 worked CT1HZE around 2315z. KQØJ was using just a single loop antenna! I did not hear CT1HZE in eastern Kansas, but picked up W7LFB on 50.160 MHz in very rare DN83! Finally NØLL also worked a rare grid, VE9IQ FN67 for Larry's last grid to complete the FFMA (Fred Fish Memorial Award) at 2327z!

“The geomagnetic field had been active all weekend due to a CME impact August 15, which caused a strong G3-class geomagnetic storm and bright auroras around the Arctic Circle. The storm persisted as a G1-class through August 17, perhaps enhancing sporadic E conditions.”

For more information concerning radio propagation, see the ARRL Technical Information Service at For an explanation of the numbers used in this bulletin, see An archive of past propagation bulletins is at More good information and tutorials on propagation are at

My own archives of the NOAA/USAF daily 45 day forecast for solar flux and planetary A index are in downloadable spreadsheet format at and .

Click on “Download this file” to download the archive and ignore the security warning about file format. Pop-up blockers may suppress download. I’ve had better luck with Firefox than IE.

Monthly propagation charts between four USA regions and twelve overseas locations are at

Instructions for starting or ending email distribution of ARRL bulletins are at

Sunspot numbers for August 13 through 19 were 51, 46, 33, 32, 20, 44, and 36, with a mean of 37.4. 10.7 cm flux was 94.8, 93.2, 89.4, 85.6, 87, 88.7, and 98.2, with a mean of 91. Estimated planetary A indices were 11, 4, 44, 36, 27, 9, and 19, with a mean of 21.4. Estimated mid-latitude A indices were 14, 4, 24, 27, 27, 10, and 18, with a mean of 17.7.




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