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ARRL Propagation Bulletin ARLP011 (2021)

ARLP011 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 11  ARLP011
From Tad Cook, K7RA
Seattle, WA  March 12, 2021
To all radio amateurs 

ARLP011 Propagation de K7RA

Although solar activity remains low, lately as a sunspot rotates to
the west off the visible solar disc a new one emerges in the east.
Sunspot group 2807 recently moved over the Sun's western horizon,
but on March 9 new sunspot group 2808 moved across the eastern
horizon, and a newer group (2809) has now emerged just south of the
center of the solar disc. This brought the daily sunspot number
higher from 11 on Wednesday to 23 on Thursday, March 11.

Recent sunspot activity and solar flux still seem soft when compared
to activity toward the end of 2020.

In Propagation Forecast Bulletins ARLP048, 049, and 050 in 2020,
(covering November 19 through December 9), average sunspot numbers
were 27.9, 57.6 and 28.9 and average daily solar flux was 90.1,
108.1 and 91.9. For the past three weeks overall average daily
sunspot numbers were 19 (the two weeks prior to that had no
sunspots) and average daily solar flux was 77.1.

We can't do anything except to wait and watch, but we can look
forward to the Vernal Equinox next week on Saturday, March 20. Like
the Autumnal Equinox in the Fall, this is always a positive
influence on HF propagation when the northern and southern
hemispheres are bathed in approximately equal amounts of solar
radiation. You can count on it.

Average daily sunspot numbers this week hardly changed, from 18.9
last week to 18.4.

Average daily solar flux shifted marginally higher from 76.7 to

Solar wind has slackened, so average daily planetary A index went
from 14.7 to 7.6, and the middle latitude numbers changed from 10.4
to 6.1.

Predicted solar flux for the next 30 days is 78 on March 12-19, then
75, 76, 78 and 81 on March 20-23, 80 on March 24-25, then 78 and 76
on March 26-27, then 75 on March 28 through April 1, then 78 on
April 2-3, and 70, 74, 76, 72, 71, 72 and 70 on April 4-10. After
April 18, solar flux may rise again above 80, then back to 75 by
April 24.

Predicted planetary A index is 12, 20 and 10 on March 12-14, 5 on
March 15-17, 12 on March 18-19, then 20, 18, 12 and 8 on March
20-23, 5 on March 24-27, then 25, 20, 20 and 10 on March 28-31, then
5, 15 and 8 on April 1-3, 5 on April 4-7, then 18, 12, 5 and 15 on
April 8-11. A recurring coronal hole may rotate into a geo-effective
position on April 15-16 and another around April 24-25, raising the
planetary A index again to around 20-25.

Geomagnetic activity forecast for the period March 12 to April 6,
2021 from F.K Janda, OK1HH.
"Geomagnetic field will be:
quiet on: March 17, (26-27,) April 1, 6
quiet to unsettled on: March 12-13, 16, 25, April 3-5
quiet to active on: March 21-24, 31
unsettled to active: March 14-15, 18, 29 April 2
active to disturbed: March 19-20, 28, 30

"Solar wind will intensify on: March (12-14, 18-19,) 20-23, (27,)
28-31, April (1-2).

"Parenthesis means lower probability of activity enhancement.
Predictability of changes remains very low, as there are ambiguous

Dennis, K7BV, reported:

"March 7, while checking the bands for DX, I went to 15m FT8 about
1650z. The strongest signal by a huge margin was S79KW (LI75rj
Seychelles) at +27 dB!  After a quick contact, I moved to a clear
frequency to CQ.  Almost immediately 4S6RSP at -8 dB strong called.
A few minutes later VU2AMW at -1 dB called. I also noticed YC5YZ
calling CQ. Nothing else heard from the region but S79KW remained
strong well after this brief 15 meters opening to Southern and
Southeast Asia."

Unfortunately the averages at the end of this bulletin sometimes
change from the preview in Thursday's ARRL Letter. This is my fault
and happens from time to time. Thanks so much to Don Wright, AA2F,
who catches these every time, and makes sure the correct averages
appear in Friday's bulletin.

Aurora season in Colorado:

David Moore sent this from Science News: "The aurora's very high
altitude booster."

If you would like to make a comment or have a tip for our readers,
please 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

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

Sunspot numbers for March 4 through 10, 2021 were 32, 14, 23, 14,
12, 23, and 11, with a mean of 18.4. 10.7 cm flux was 81.4, 73.2,
77, 77.5, 79.9, 83.7, and 79.4, with a mean of 78.9. Estimated
planetary A indices were 11, 5, 16, 10, 6, 3, and 2, with a mean of
7.6. Middle latitude A index was 11, 5, 11, 7, 5, 2, and 2, with a
mean of 6.1.


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