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ARRL Propagation Bulletin ARLP037 (2018)

ARLP037 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 37  ARLP037
From Tad Cook, K7RA
Seattle, WA  September 15, 2018
To all radio amateurs 

ARLP037 Propagation de K7RA

We observed a return of sunspot activity during the past reporting
week (September 6-12), with spots on four days, but not consecutive.
Sunspots were visible on September 8-9 and 11-12. Average daily
sunspot numbers increased to 7.6, compared to zero over the previous
seven days.

Average daily solar flux increased from 67.8 to 68.6, and planetary
A index doubled from 6.3 to 12.6, while mid-latitude A index went
from 5.9 to 10.

The September 13 forecast predicted solar flux at 70 on September
14, 68 on September 15-22, 67 on September 23-24, 68 on September 25
through October 6, 70 on October 7-9, 68 on October 10-19, 67 on
October 20-21, 68 on October 22-28.

The same forecast over the same period supposes planetary A index at
8 on September 14-15, 10 and 8 on September 16-17, 5 on September
18-21, 12 and 8 on September 22-23, 5 on September 24-30, then 8 and
10 on October 1-2. 5 on October 3-6, then 12, 35, 15, 12, 12, 8, 5,
10 and 8 on October 7-15, 5 on October 16-18, then 12 and 8 on
October 19-20, 5 on October 21-27 and 8 on October 28.

As recently as September 9, the US Air Force predicted a rise of
solar flux to 75 on September 17 before dropping below 70, followed
by flux values of 70 on October 7-9. The day before, on September 8
the forecast showed flux values of 70 through September 16, 75 on
September 17, and 72 on September 18-22. Predicted solar flux was 75
for October 10-14. This was considerably more optimistic than the
latest forecast.

From OK1HH:

"Geomagnetic activity forecast for the period September 14 to
October 10, 2018

"Geomagnetic field will be:

"Quiet on September 17, 19
Quiet to unsettled on September 18, 20, 24, October 3
Quiet to active on September 14-15, 25-30, October 4-6, 10
Unsettled to active on September 16, 23, October 1-2, 9
Active to disturbed on September (21) -22, October 7-8

"Solar wind will intensify on September 14-16, (21,) 22-24, (25), 29.
October 1-2, 6-9

- Parenthesis means lower probability of activity enhancement.

"F. K. Janda, OK1HH"

Max White sent this link from the Financial Times about solar flares
on September 9:

The latest from Dr. Tamitha Skov, WX6SWW on September 11.

"Dear Tad:

"My newest 'forecast shortie' came out on You Tube today as we were
passing the peak of this solar storm. As I feared (and mentioned on
Twitter and on Patreon numerous times), we did reach G2-level storm
conditions. In fact we remained at G2-levels for over 6 hours. This
meant emergency communication over the amateur radio bands was
non-existent. Luckily, it looks like the worst is now over. This is
good news as several 'hurricane watch nets' are activating as early
as tomorrow in anticipation of Hurricane Florence. However, the bad
news is the fast solar wind is ongoing and it will take several days
yet for the radio bands to fully recover. Let's hope they do before
this Category 4 storm makes landfall.

"Since becoming an amateur radio operator myself this Summer (my
call sign is now WX6SWW), I have really begun to appreciate the
extent that Space Weather thwarts emergency responders during
hurricane season. Even though I do not live on a coast threatened by
hurricanes-- Los Angeles hardly gets any rain at all, let alone a
hurricane-class storm-- like many, I am beginning to dread this time
of year. The concern worsens when I read articles published in
reputable weather journals that talk about the intensification of
hurricanes in the coming years. For all of our sakes, I hope that
climate scientists determine a 'Category 6' for hurricanes is not
warranted. Until then, articles like this one will continue to make
me very nervous. It really makes me wonder what the peak of the
hurricane season will be like in a few years when solar activity
begins to rise.

"Again, a huge debt of gratitude goes to the Patreon members, who
are making these 'forecast shorties' possible. Frequent forecast
updates such as these prove so critical at times like now. Thank you
for helping to keep communities aware so they can stay safe. You are
my heroes."

If you would like to make a comment or have a tip for our readers,
email the author at, .

For more information concerning radio propagation, see the ARRL
Technical Information Service web site at, For an explanation of
numbers used in this bulletin, see

An archive of past propagation bulletins is at More good
information and tutorials on propagation are at

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 September 6 through 12, 2018 were 0, 0, 16, 12,
0, 14, and 11, with a mean of 7.6. 10.7 cm flux was 67.4, 67.5,
68.7, 68.4, 69, 69.4, and 69.7, with a mean of 68.6. Estimated
planetary A indices were 6, 5, 5, 7, 21, 35, and 9, with a mean of
12.6. Estimated mid-latitude A indices were 5, 5, 5, 6, 15, 24, and
10, with a mean of 10.


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