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ARRL Propagation Bulletin ARLP028 (2020)

ARLP028 Propagation de K7RA

Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7RA
Seattle, WA  July 10, 2020
To all radio amateurs

ARLP028 Propagation de K7RA

We saw a new sunspot on July 4, but it was from old Solar Cycle 24,
and lasted only through July 5. Sunspot numbers were 12 and 11,
giving us an average daily sunspot number of 3.3 for the week. Prior
to this, no sunspots were observed since June 15.

Average daily solar flux was 68.5, and the previous week it was

Average daily planetary A index changed from 4.7 to 5.1, and average
daily middle latitude A index shifted from 4.7 to 6.4.

The 45 day outlook for solar flux does not look promising, with no
predicted values at 70 or above.  Predicted solar flux is 68 on July
10-24, 69 on July 25 through August 8, 68 on August 9-20, and 69 on
August 21-23.

Predicted planetary A index is 5 on July 10-12, 8 on July 13, 5 on
July 14-26, 8 on July 27-28, 5 on July 29-30, then 12, 10, 8 and 8
on July 31 through August 3, 5 on August 4-22 and 8 on August 23.
Both the solar flux and A index forecasts are the same as the
forecasts released on July 8.

You can check daily updates provided by the US Air Force Space
Weather Squadron at, .
They are provided each day around 2130 UTC.

It seemed to me recently that solar flux values have been depressed
compared to recent flux values. But when compared to last year's
solar flux, the numbers are actually higher, but only marginally.

A year ago the average weekly solar flux in 2019 Propagation
Forecast Bulletins ARLP023 to ARLP028 were 69.5, 69. 67.1, 67.4,
67.5 and 67.1. But this year the weekly averages for bulletins 23-28
are 69.6, 71.3, 70, 67.7, 68.6 and 68.5, so each week they are
higher than in the same period last year, but just barely.

And in 2018? 73.2, 69.4, 74, 75.3, 68.2, and 71.5, so the bottom
really seems to be spread over this year and last year, at least
when considering solar flux.

Geomagnetic activity forecast for the period July 10 to August 5, 2020
from F.K. Janda, OK1HH.
"Geomagnetic field will be 
quiet on: July 15, 18-20, 29-30, August 4-5 
quiet to unsettled on: July 10, 12-14, 21-22, 25-28, August 3 
quiet to active on: (July 11, 16-17, 23-24, 31, August 1-2) 
unsettled to active on: nothing predicted
active to disturbed: nothing predicted
"Solar wind will intensify on: July (16-18, 21-22,) 23-25, (26-27,)
August 1-2, (3-4).
- Parenthesis means lower probability of activity enhancement. 
- The predictability of changes remains in the long run lower as
there are very few indications."

Regular contributor David Moore forwarded this piece from PBS about
what our nearby Star is made of:

Jim Wilson, K5ND of Grapevine, Texas reported on July 6:

"There was an incredible 6 meter opening yesterday along with a few
making 2 meter Es contacts. I managed to find a few new 6 meter
grids, thanks in part to rover AG6EE, who has added a number of new
grids to my log over the past couple of weeks. Surprisingly there
have been a number of 6 meter grid rovers in action, despite our
stay-at-home moment: AC0RA, W7GJ, K8JH, and others."

Jim wonders if there might be a correlation between 6 meter openings
and recent sightings of noctilucent clouds? NLC have been widely
reported recently on

Dr. Tamitha Skov, WX6SWW has a new video. See .

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 and 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 July 2 through 8, 2020 were 0, 0, 12, 11, 0, 0,
and 0, with a mean of 3.3. 10.7 cm flux was 68, 69.3, 69.5, 69.4,
68.5, 67.7, and 67.2, with a mean of 68.5. Estimated planetary A
indices were 4, 4, 7, 10, 5, 4, and 2, with a mean of 5.1. Middle
latitude A index was 5, 5, 9, 13, 6, 5, and 2, with a mean of 6.4.


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