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ARRL Propagation Bulletin ARLP009 (2024)

ARLP009 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 9  ARLP009
From Tad Cook, K7RA
Seattle, WA  March 1, 2024
To all radio amateurs 

ARLP009 Propagation de K7RA


"A filament eruption was observed at 28/0855UT from the solar
southeast quadrant. The associated CME has been determined to
contain an Earth-directed component, with an arrival to Earth's
magnetosphere at 02/1100 UTC +/- 12 hours. G1 geomagnetic conditions
are expected.


Seven new sunspot groups emerged this week, four on February 23, one
on February 25, another on February 26 and one more on February 28.

Solar activity increased this reporting week, February 22-28,
compared to the week before. Average daily sunspot number rose from
84.4 to 108.4, and solar flux from 164 to 175.

Geomagnetic conditions were quiet, though the numbers rose.
Planetary A index went from 4.4 to 8.4, and middle latitude numbers
from 3.3 to 7.4.

The predicted solar flux is 160, 155, and 160 on March 1-3, 165 on
March 4-5, 160 and 165 on March 6-7, 165 on March 8-9, 168 on March
10, then 165 on March 11-12, 160 on March 13-14, then 168 and 172 on
March 15-16, then 175, 175 and 178 on March 17-19, 180 on March
20-24, and 175 on March 25-26, then 180 and 175 on March 27-28, 170
on March 29-30, 172 on March 31 to April 1, 170 on April 2, and 165
on April 3-5.
The predicted planetary A index is 8, 12, 12 and 10 on March 1-4,
then 5 on March 5-23, then 15, 12 and 12 on March 24-26, and 5 on
March 27 to mid-April. reported on giant sunspot AR3590:  "In only 23
hours spanning February 21-22, the active region unleashed three
powerful X-class solar flares (X1.8, X1.7 and X6.3). The X6.3 flare
is the strongest of Solar Cycle 25, so far, and the most powerful
flare since the great solar storms of September 2017."

Because there were no CMEs, there were no geomagnetic storms, but
extreme ultraviolet radiation ionized the top of Earth's atmosphere
and caused several shortwave blackouts over Hawaii and Australia on
February 21-22.

Sunspot group AR3590 is the largest of the current solar cycle.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - February 29, 2024 from OK1HH:

"Over the past seven days, we have seen the deflection of an active
region of AR3590 on the Sun, 760 millionths of the size of the solar
disk. On February 25, it already occupied an area of 1450
millionths, making it the largest group of spots so far since the
beginning of the 25th cycle. It produced its largest and extra
proton flares on February 21-22, including three X-class flares in
23 hours. The largest of these, X6.3 on 22 February, with a maximum
at 2324 UT, was the most important flare since the beginning of
Solar Cycle 25.

"Proton flares were no exception and caused an absorption in the
polar cap (PCA). The first of these was recorded on 9 February in
the already setting region AR3575. At the same time, there was a
region AR3576 in the southeast of the solar disk, which will rise
again in the next few days, so we do not have to worry about a
decrease in solar activity.

"With the exception of the unsettled days of February 25-27, the
geomagnetic field was mostly calm. We expect a similar pattern in
the coming weeks. Ideally, the mostly calm development could last
until the Spring Equinox. If this happens, shortwave propagation
conditions will be mostly above average."

This weekend is the ARRL International DX SSB contest. For details

Some articles about solar basics:

Popular Science article about a Solar Minima:

I do not trust the data or the correlations in this article, but
there is some interesting content here:

Latest video from Dr. Tamitha Skov, WX6SWW:

Send your tips, reports, observations, questions and comments to When reporting observations, don't forget to tell us
which mode you were operating.

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 .

Also, check this QST article about Solar Indices:

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

Sunspot numbers for February 22 through 28 2024 were 46, 116, 106,
114, 133, 103, and 127, with a mean of 106.4. 10.7 cm flux was
173.3, 172.9, 179.2, 180.8, 171.7, 168.3, and 179.1, with a mean of
175. Estimated planetary A indices were 6, 3, 7, 13, 11, 13, and 6,
with a mean of 8.4. Middle latitude A index was 6, 2, 6, 14, 10, 9,
and 5, with a mean of 7.4.


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