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ARRL Propagation Bulletin ARLP040 (2023)

ARLP040 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 40  ARLP040
From Tad Cook, K7RA
Seattle, WA  October 6, 2023
To all radio amateurs 

ARLP040 Propagation de K7RA

At 2308 UTC on October 5, the Australian Space Weather Forecasting
Centre issued a geomagnetic disturbance warning.

"A recent, mild CME impact, combined with the expected arrival of a
coronal hole high speed wind stream on 7 Oct, gives the chance for
G1 geomagnetic conditions over 6 and 7 Oct."

Seven new sunspot groups emerged over the past week, but overall
solar activity declined.

With consecutive dates you can initiate an animation using the back
and forward buttons on your browser.

We are currently enjoying improved HF propagation with the change of
seasons after the autumnal equinox.  This is particularly noticeable
on 12 and 10 meters.

Here is an optimistic news story about the current solar cycle.

One new sunspot group appeared on September 30, three more on
October 1, and one on each of the following days, October 2, 3 and
4.  On October 5, two more sunspot groups appeared, and the daily
sunspot number shot up to 179, the highest since September 26.
Previously, a high of 219 was on July 12.

Average daily sunspot number declined from 170.6 to 128.6, while
average daily solar flux went from 168.8 to 155.6.

Geomagnetic indicators were quieter.  Average daily planetary A
index went from 17 to 9.1, and average daily middle latitude A index
declined from 13.7 to 8.9.

The outlook for the next month has predicted solar flux at 158 on
October 6 and 7, 155, 152, 152, 150 and 145 on October 8 to 12, 158
on October 13 and 14, 156 on October 15 to 17, 154 on October 18 to
20, 152 on October 21, 154 on October 22 and 23, 156 and 158 on
October 24 and 25, 160 on October 26 to 28, 162 on October 29 to 31,
then 164 on November 1 to 3, 168 on November 4, 165 on November 5
and 6, 162 and 160 on November 7 and 8, 158 on November 9 and 10,
and 156 on November 11 to 13.

Predicted planetary A index is 18, 25, 10 and 5 on October 6 to 9, 8
on October 10 and 11, 5 on October 12 to 21, then 10 and 8 on
October 22 to 23, 5 on October 24 to 28, then 15, 12, 8, 15 and 8 on
October 29 through November 2, and 5 on November 3 through the
middle of the month.

Flares in the news:

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere -- October 5, 2023 from Frantisek K. Janda, OK1HH.
"After witnessing a number of solar flares (though at most of
moderate magnitude) during the past month, plus three solar plasma
cloud impacts (CMEs), late September and early October, which were a
bit quieter.

However, the development of solar and especially geomagnetic
activity was so irregular that it was difficult to make predictions
for the following days.  The geomagnetic calm on 28 September did
not mean an improvement in shortwave propagation conditions, but
rather a deterioration compared to the previous day, which was not
calm.  The improvement on 2 and 3 October was the result of a
relative calm with non-declining solar activity.

Subsequent developments were mostly quieter.  Nevertheless, there
were significant fluctuations in MUF on 4 October with a slight
deterioration.  The explanation for the causes can be found mainly
in the timing of the overall development.  Specifically,
deterioration often occurred after geomagnetic activity increased
overnight.  In addition, sporadic layer E activity increased at
times (especially on 4-5 October).  There was also a slight increase
in the concentration of protons in the solar wind on 3 October and
especially still on 5 October.

Irregular propagation conditions can be expected to continue, yet
there should already be less of a difference between expectations
and actual developments in October than there was in September."

W2BEE sent this about aurora:

Time lapse animation of sunspot:

Max White M0VNG sent this, about the solar atmosphere:

Check these links for the upcoming HamSCI propagation tests during
upcoming solar eclipses, the first on October 14, 2023:

New report 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.

An archive of past propagation bulletins is at .  More good
information and tutorials on propagation are at

Also, check this article from September, 2002 QST:

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

Sunspot numbers for September 28 through October 4, 2023 were 109,
102, 106, 136, 146, 150, and 151, with a mean of 128.6.  10.7 cm
flux was 147.8, 155, 159.1, 161.1, 157.4, 153.7, and 155, with a
mean of 155.6.  Estimated planetary A indices were 6, 12, 10, 9, 9,
8, and 10, with a mean of 9.1.  Middle latitude A index was 5, 13,
11, 9, 10, 6, and 8, with a mean of 8.9.


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