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ARRL Propagation Bulletin ARLP036 (2022)

ARLP036 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 36  ARLP036
From Tad Cook, K7RA
Seattle, WA  September 9, 2022
To all radio amateurs 

ARLP036 Propagation de K7RA

This week (September 1 to 7) two new sunspot groups emerged on
September 1, two more on September 2, one more on September 5,
another on September 6 another on September 7 and one more on
September 8 when the sunspot number rose to 75, 7 points above the
average for the previous seven days.

But average daily sunspot numbers declined from 74.9 to 68, while
average daily solar flux rose just two points from 123.8 to 125.8.

On Thursday night the sun is peppered with spots, but none are
magnetically complex and solar flux seems listless at 126.6, barely
above the average for the previous seven days.

Geomagnetic indicators were way up, average daily planetary A index
rose from 10.1 to 24.6, while middle-latitude numbers increased from
9.4 to 17.4.

September 4 was the most active day, when planetary A index was 64.
On that day the college A index in Fairbanks, Alaska was 91.

Predicted solar flux is 125 on September 9 to 13, 120 on September
14, 115 on September 15 and 16, then 125, 126 and 120 on September
17 to 19, 125 on September 20 and 21, 115 on September 22 to 24, 120
on September 25 to 28, 118 on September 29 and 30, 115 and 125 on
October 1 and 2, 120 on October 3 and 4, 122 on October 5, 120 on
October 6 and 7, 125 on October 8 to 11, 126 on October 12, 125 on
October 13 and 14, and 126 on October 15.

Predicted planetary A index is 50 on October 1.  Otherwise,  8 on
September 9 to 11, 5 on September 12, 20 on September 13 and 14, 15
on September 15, 8 on September 16 and 17, 5 on September 18 to 22,
then 12 and 10 on September 23 and 24, 14 on September 25 to 27, 8
on September 28 and 29, then 22, 50, 25, 16, 12 and 10 on September
30 through October 5, 8 on October 6 to 8, then 5, 12, 15 and 10 on
October 9 to 12, 8 on October 13 and 14, and 5 on October 15 to 19.

OK1HH writes:

"Over the past seven days, a large coronal hole moved from the
central meridian to the western limb of the solar disk.  Its
position relatively close to sunspot group AR3089 meant a high
probability of a geomagnetic disturbance in the following days,
since September 4.  Its onset as early as 3 September (class G1) was
related to the intensification of the solar wind and the opening of
a rift in the Earth's magnetic field.  The solar wind flow from the
large coronal hole finally hit Earth's magnetic field on September 4
and triggered a G2 class geomagnetic storm.

At the same time, two sunspot groups so large that they affected the
Sun's vibrations developed on the far side of the Sun.  These were
AR3088, which had last left the Sun a week earlier and was the
source of a large CME heading for Venus on September 5.

On September 7, AR3092 crossed the central meridian and had a really
long tail above the surface of the Sun.  It was a filament coming
out of the core of the spot and curling up into the solar
atmosphere.  Inside the filament was a long tube of relatively cool,
dark plasma.

Thereafter the Sun was relatively quiet.  The solar disk was dotted
by sunspots, but these have a stable magnetic field, so the chance
of flares was low.

Earth's magnetic field was mostly disturbed on the 3rd to the 6th.
Thereafter was unsettled to active on the remaining days.  Shortwave
propagation was below average, worst at the end of the disturbance
on September 6.  An increase in f0F2 occurred at the beginning of
the disturbance on September 4.

Now a few quiet days followed by another disturbance on 13 and 14
September is expected."

I (K7RA) have been seeing more strange 12 meter propagation
recently.  Over and over for several days using FT8 as a propagation
test tool with, I would call CQ and see that only
stations in Florida were receiving my signal.  It looks very odd on
the map.  Florida does have a very large ham population, but this
just seems so peculiar.

Regarding the recent overloading of the sensors at Penticton, I
noted I had seen this before, but didn't realize how rare it was.  I
paged back through the DRAO archives, and unless I missed something,
the last one was in 2015 on June 22 when the 2000 UTC flux reading
was 246.9.  The noon solar flux the following day was only 116.1.

Tamitha Skov's report is a week old, but too late for last week's

Two massive sunspots:

Longtime contributor David Moore sent this:

Big explosion:

Our angry sun:

So huge:

Send your tips, reports, observations, questions and comments to

For more information concerning shortwave radio propagation, see and the ARRL Technical Information
Service 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

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bulletins are at

Sunspot numbers for September 1 through 7, 2022 were 67, 71, 68, 62,
79, 56, and 73, with a mean of 68. 10.7 cm flux was 116.3, 129.8,
123.4, 128.3, 130.2, 126.2, and 126.1, with a mean of 125.8.
Estimated planetary A indices were 9, 8, 25, 64, 32, 20, and 14,
with a mean of 24.6.  Middle latitude A index was 9, 10, 23, 33, 21,
14, and 12, with a mean of 17.4.


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