Secure Site Login

ARRL Propagation Bulletin ARLP035 (2019)

ARLP035 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7RA
Seattle, WA  August 30, 2019
To all radio amateurs 

ARLP035 Propagation de K7RA

The current stretch of spotless days is now over three weeks,
according to The continuing quiet seems
eerie. For this past reporting week, Thursday through Wednesday, the
average daily solar flux (10.7 GHz radiation recorded in Penticton,
British Columbia, which roughly tracks with sunspot activity) was
only 66. I couldn't recall when the weekly average reported in this
bulletin was last that low, and couldn't find any report during the
past year with such low activity.

I did an inspection of the numbers and had to go back to the Fall of
2007 to find average solar flux in that range. In 2007 we reported
an average of 66.5 in propagation forecast bulletin number 40:

Can anyone else find solar flux that low or lower in past bulletins?
We have them online going back to 1995:

If anyone has copies of propagation bulletins prior to 1995, I would
love to see them. I began writing the bulletin in March 1991. Before
that, W1HDQ was the author. I recall copying the bulletin as a
teenager in 1966 using CW but have not found anyone who knows when
the bulletin began. I should have asked W1HDQ before he became a
silent key.

Predicted solar flux for the next 45 days is 66 on August 30 through
September 6, 67 on September 7-11, 68 on September 12-15, 67 on
September 16 through October 8, and 68 again on October 9-12, then
67 on October 13.

Predicted planetary A index is 8, 20, 34, 16 and 8 on August 30
through September 3, 5 on September 4-5, 8 on September 6-7, 5 on
September 8-21, then 10, 15 and 8 on September 22-24, 5 on September
25-27, then 35, 18 and 10 on September 28-30, 5 on October 1-2, 10
and 8 on October 3-4, and 5 on October 5-13.

Note that the predicted planetary A index is 34 on September 1,
which according to W3LPL and the ARRL Letter is the 160th
anniversary of the infamous Carrington Event.

Http:// reported a large recurring coronal hole
facing Earth, and they expect the effects to be felt this Sunday,
September 1. A planetary A index value of 35 is predicted for the
next solar rotation, on September 28.

Geomagnetic activity forecast for the period August 30 to September
26, 2019 from OK1HH.

"Geomagnetic field will be
Quiet on: September 10-11, 20-21, (25-26)
Quiet to unsettled on: August 30, September 3-5, 7-8, 13, 17, 22, 24
Quiet to active on: August 31, September 6, 9, 12, 14-16, 18-19, 23
Unsettled to active on: September 2
Active to disturbed: September 1

"Solar wind will intensify on August (30)-31, September 1 (-2), (4-6)
Parenthesis means lower probability of activity enhancement."

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 page 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 August 22 through 28, 2019 were 0, 0, 0, 0, 0,
0, and 0, with a mean of 0. 10.7 cm flux was 65.7, 66.5, 66.3, 66,
65.8, 66.1, and 65.9, with a mean of 66. Estimated planetary A
indices were 6, 4, 5, 4, 6, 10, and 5, with a mean of 5.7. Middle
latitude A index was 7, 4, 5, 5, 6, 10, and 5, with a mean of 6.