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ARRL Propagation Bulletin ARLP015 (2021)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 9, 2021
To all radio amateurs 

ARLP015 Propagation de K7RA

Sunspots were only visible on four days over the current reporting
week, on April 3-6. And now on Friday morning there are still no

As a result, average daily sunspot number declined from 11.9 last
week to 6.4 currently. Average daily solar flux also dropped from
77.4 to 73.4. On Thursday the daily solar flux was 74, just above
the average for the previous seven days, 73.4. The Sun remained

Average daily planetary A index declined from 8.9 to 6.6, and
average mid-latitude A index slipped from 7.7 to 5.6.

Predicted solar flux for the next month is 74 on April 9-15, 72 on
April 16-20, 74 on April 21-26, 73 on April 27 through May 1, 72 on
May 2-5, 70 on May 6-10, and 71 on May 11-12. 74 is not a high 10.7
cm flux value, but it should be there on May 18 and beyond.

Predicted planetary A index is 5, 10 and 8 on April 9-11, 5 on April
12-13, then 8 on April 14-15, 15 and 18 on April 16-17, 8 on April
18-19, 5 on April 20-21, 8 on April 22-24, 5 on April 25 through May
1, 8 on May 2-4, and 5 on May 5-12.

Geomagnetic activity forecast for the period April 9 to May 4, 2021
from F.K. Janda, OK1HH:

"Geomagnetic field will be,
quiet on: April 25, May 1-3
quiet to unsettled on: April 18, 20, 22, 26, 28-30
quiet to active on: April 19, 23-24, 27
unsettled to active: April (9-11,) 17, 21-22
active to disturbed: April 16, May 4
"Solar wind will intensify on: April (9-11, 16,) 18-19, (21-22, then
irregularly between April 23-May 1,) May 3-4.
- Parenthesis means lower probability of activity enhancement.
- Predictability of changes remains very low, as there
  are a lack of indications and contradictions between them."

Des, ND3L wrote: "I was off the air for 28 years. Got back on a year
ago. I'm in the process of inputting my old logs into QRZ.COM
logbook. Back in 1989 I had a stretch of 11 pages of all 10 meter
contacts with 25 contacts per page! Found 5 new countries that I
never had confirmed. Operators were still around and had old logs
and confirmed. Took me from 284 to 289 confirmed in 1 week!

"In early 1989 daily sunspot numbers ranged from 134 to 161. We
didn't know we had it so good!"

Ken Brown, N4SO on Alabama's Gulf Coast reports on 17 meter FT8 on
March 28, he worked ZD8HZ on Ascension Island at 2117 UTC, over a
distance of 5,509 miles.

Later from 2207-2345 UTC he worked "JA5AQC, JR7VHZ, JG1SRB, JR1FYS,
JA3APV, JA2QXP, and on the 29th and 30th worked a total of ten more
Japanese, some call signs repeated from the 28th."

WB8VLC in Salem, Oregon is seeing consistent 10 meter activity,
which is a nice surprise considering the very low solar activity and
probably too early in the year for e-skip.

He reported: "As usual 10 meters has been open here in NW Oregon
pretty much every week to South America, but the interesting
openings were 2 weekends in March when E51JD in Rarotonga South Cook
Islands has been in on 10 meter SSB along with KH6ZM on RTTY and the
usual South Americans." (KH6ZM is on the Hawaii Big Island).

JQ2UOZ wrote:

"Hi, Tad-san, K7RA. Thank you very much for mentioning me in the
latest bulletin.

"By the way, I have found a very interesting article about the solar
cycle: 'Gradual onset of the Maunder Minimum revealed by
high-precision carbon-14 analyses.' Scientific Reports volume 11,
Article number: 5482 (2021): ."

The author describes in the Abstract, "Here we show that the 11-year
solar cycles were significantly lengthened before the onset of the
Maunder Minimum (1645-1715 CE) based on unprecedentedly
high-precision data of carbon-14 content in tree rings. It implies
that flow speed in the convection zone is an essential parameter to
determine long-term solar activity variations. We find that a 16
year-long cycle had occurred three solar cycles before the onset of
prolonged sunspot disappearance, suggesting a longer-than-expected
preparatory period for the grand minimum. As the Sun has shown a
tendency of cycle lengthening since Solar Cycle 23 (1996-2008 CE),
the behavior of Solar Cycle 25 can be critically important to the
later solar activity. I hope to have active Solar Cycle 25."

Some of you may find this article interesting:

A recent video update from Dr. Tamitha Skov, WX6SWW:

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

For more information concerning shortwave 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

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

Sunspot numbers for April 1 through 7, 2021 were 0, 0, 12, 11, 11,
11, and 0, with a mean of 6.4. 10.7 cm flux was 77.9, 72.1, 72.8,
70, 71.9, 73.6, and 75.7, with a mean of 73.4. Estimated planetary A
indices were 8, 6, 4, 3, 5, 3, and 17, with a mean of 6.6 Middle
latitude A index was 8, 4, 2, 2, 5, 3, and 15, with a mean of 5.6.


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