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ARRL Propagation Bulletin ARLP013 (2021)

ARLP013 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 13  ARLP013
From Tad Cook, K7RA
Seattle, WA  March 26, 2021
To all radio amateurs 

ARLP013 Propagation de K7RA

On March 21 and 22 two new sunspot groups, 2811 and 2812 appeared.
Average daily sunspot number this week faded a bit from 19 to 17.9,
but average daily solar flux went from 78.1 to 78.6. Neither change
is significant.

We haven't seen a day with no sunspots since March 1, so that brings
the percentage of spotless days so far this year to 38%, down from
57% last year and 77% in 2019.

Geomagnetic activity was steady throughout this week, with average
daily planetary A index rising from 10.3 to 13.3, and average middle
latitude A index from 7.3 to 10.4.

But geomagnetic conditions were disturbed at higher latitudes.
Alaska's College A index, measured near Fairbanks, was 40 and 45 on
March 20-21. This was reflected in a report from N6QEK/KL7 in North
Pole, Alaska (a town southeast of Fairbanks, not at the north pole)
who wrote, "HF frequencies here in the interior of Alaska were wiped
out for the BARTG RTTY contest. FT-8 signals were almost
non-existent as well."

Saturday was the first day of Spring in the Northern Hemisphere, and
Autumn in the Southern Hemisphere, positive indications for HF

Predicted solar flux over the next month is 80 on March 26-27, 75 on
March 28-31,  then 70 on April 1-2, 80 and 81 on April 3-4, 82 on
April 5-7, 81 on April 8, 80 on April 9-10, then 78 and 76 on April
11-12, 75 on April 13-14, 76 on April 15, 77 on April 16-17, 76 on
April 18-20, 77 on April 21, and 78 on April 22-28. Solar flux is
expected to peak at 82 on May 2-4.

Predicted planetary A index is 8 on March 26, 5 on March 27, 25 on
March 28, 20 on March 29-30, then 12 on March 31, then 8 on April
1-3, 5 on April 4-7, then 15, 18 and 20 on April 8-10, 5 on April
11-15, then 25, 22, 20, 15 and 8 on April 16-20, and 5 on April
21-23, then 25 on April 24 and 20 on April 25-26.

Geomagnetic activity forecast for the period March 26 to April 20,
2021 from F.K. Janda, OK1HH.

"Geomagnetic field will be:
quiet on: April 1, 6-7, 12-13
quiet to unsettled on: March 26-27, 31, April 5, 14, 18 
quiet to active on: April 2-4, 15, 20
unsettled to active: March 29, April 8, 11, 19
active to disturbed: March 28, 30, April 9-10, 16-17
"Solar wind will intensify on: March (28,) 29-30, (31,) April 2-3,
(4-6, 8-9,) 10-11, (12, 16-17,) 18-19, (20).
- Parenthesis means lower probability of activity enhancement.
- Predictability of changes remains very low, as there are irregular
  and ambiguous indications."

Jon Jones, N0JK, wrote on March 22:

"More on the March 13, 2021 sporadic-E opening. The month of March
has the LOWEST occurrence of sporadic-E propagation of any month of
the year. Thus, I consider any sporadic-E on 6 Meters in March

"There was some afternoon TEP (trans-equatorial propagation) on 6
meters between Florida and South America March 21. Stations such as
W4AS, KD4ESV, KV4HV, in Florida worked CX and LU stations around
2100z. K0GU (DN70) in Colorado spotted LU9FVS, perhaps a sporadic-E
to TEP link. The K index was 5, indicating 'storm' geomagnetic field

This article mentions solar cycle predictions, and they mentioned
predicted "peak rates of more than 200 sunspots at a time."  But
they may have made a common error, confusing the daily sunspot
number with the actual number of sunspots, two very different
numbers (as can be seen here):

To review, to calculate the sunspot number, we count a value of 10
for each sunspot group, then add a value of one for each sunspot
within those groups.

I noticed something strange about the NOAA SESC reported solar flux
of 79 on March 23. They get the solar flux values from the
Penticton, British Columbia Dominion Radio Astrophysical Observatory
noon reading, which is also my source (see ).
NOAA rounds off these values to the nearest whole number, which
should have been 82.

Now that it is March 2021, I will pause to reflect. The FCC issued
my Novice license (WN7CSK) on March 23, 1965 when I was 12 years
old. When the ticket finally arrived, I was very, very excited.

I asked my mother to hang her bright red sweater in the dining room
window when any envelope from the FCC arrived so I could see it from
my school bus. When I saw mom's sweater, I leaped from my seat, and
ran to the front of the bus, whooping and hollering. This only
confirmed for my schoolmates what they already knew, that I really
was crazy. Fifty-six years later, this vivid memory lingers.

It was 30 years ago (this week?) that I began writing this bulletin
when there was a sudden increase in solar flux that I felt was
noteworthy. But ARRL had just announced in an ARRL bulletin that Ed
Tilton, W1HDQ who authored this propagation bulletin was ill, so it
was suspended for the time being.

I fell into writing the bulletin when I called ARRL HQ because I
thought they should put out a bulletin with this solar news. The man
I spoke with wondered who might write this, so I offered. Then the
next week they asked for another bulletin.

I also called W1HDQ, who at that time was living in Florida. His
wife answered the phone, but said he was too ill to talk on the
phone. She asked what I was calling about, and when I told her the
solar flux value, she replied, "Oh he'll want to hear about this!"
and I spoke with Ed briefly, who seemed excited by the news.

Unfortunately, W1HDQ never recovered, so I kept writing the ARRL
Propagation Bulletin. I have since been unable to learn when he
began writing it. I recall copying the bulletin from W1AW on 20
meter CW in 1966, but before that? Nobody seems to know. I wish I
had asked Ed about this when we spoke.

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 March 18 through 24, 2021 were 12, 14, 12, 12,
23, 26, and 26, with a mean of 17.9. 10.7 cm flux was 73.4, 73.5,
80.3, 77.1, 80.4, 81.8, and 83.6, with a mean of 78.6. Estimated
planetary A indices were 4, 6, 29, 24, 8, 11, and 11, with a mean of
13.3. Middle latitude A index was 4, 6, 20, 17, 6, 9, and 11, with a
mean of 10.4.


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