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ARRL Propagation Bulletin ARLP035 (2023)

ARLP035 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 35  ARLP035
From Tad Cook, K7RA
Seattle, WA  September 1, 2023
To all radio amateurs 

ARLP035 Propagation de K7RA

First, this alert from Australia.


A filament eruption and associated coronal mass ejection (CME) were
observed on UT day 30-Aug. This CME is expected to impact Earth from
1800 UT +/- 12 hours on 02-Sep, with impacts possibly rolling into
UT day 03-Sep. G1-G2 geomagnetic conditions are expected over this
time, with a chance for periods of G3."

Solar activity was down again this week, with average daily sunspot
numbers dropping from 105.9 to 78.7, and average daily solar flux
from 149.4 to 140.9.

Only three sunspot groups appeared, one each on August 25, 28 and

But I have noticed a gradual transition from summer toward fall
conditions, with 10 and 12 meter openings more frequent. The
autumnal equinox is only three weeks from now.

Geomagnetic indicators were a little lower. Average planetary A
index went from 8.4 to 7, and average middle latitude numbers from
10.1 to 8.9.

What is the outlook?

Predicted solar flux shows a peak around 168 on September 18-21.

Forecast values are 140 on September 1, then 150, 150 and 145 on
September 2-4, 150 on September 5-9, 147 on September 10-11, then
145, 150, 155, 150, 155 and 160 on September 12-17, 168 on September
18-21, then 165, 160, and 148 on September 22-24, 150 on September
25-26, then 152, 150, 145,and 140 on September 27-30, then 145 on
October 1, 150 on October 2-3, 152 on October 4, 156 on October 5-6,
150 on October 7. and 148 on October 8-9.

Predicted planetary A index is 10, 12 and 35 on September 1-3, then
15, 10 and 8 on September 4-6, 5 on September 7-13, then 12, 10, 10
and 8 on September 14-17, 5 on September 18-22, then 10, 10 and 8 on
September 23-25, 5 on September 26 to October 2, then 10, 8 and 8 on
October 3-5, and 5 on October 6-10.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere for September 1-7, 2023 from OK1HH.

"On 27 August, we predicted a rise in geomagnetic activity,
triggered by the arrival of particles from the filament solar flares
three days earlier. It did occur, but to a lesser extent than we
expected. No significant solar flare (at least of M-class) was
observed until 25 August, which is somewhat surprising for the
current phase of Cycle 25 development.

We did not see a major flare until August 26 at 2250 UTC, and it was
an M1-class solar flare, hidden behind the Sun's eastern edge, but
it was a long duration eruption (LDE). It was accompanied by a CME,
which of course was not heading toward Earth, but in this case Mars
(which it should hit on September 1).

The coronal mass ejection (CME) was observed on August 29 at about
1748 UTC near the coordinates N05W35. Another major solar flare, C3,
was observed on August 30 with a maximum at 2334 UTC at AR 3413.

Prior to that, a filament of solar plasma disappeared near S18W24 at
2015 UTC.

Still, we expect only a slight increase in Earth's magnetic field
activity in the next few days.

Ionospheric propagation has varied erratically, with partial credit
due to the sporadic E layer that occurred irregularly in Earth's
northern hemisphere late this summer."

India's solar mission:


Four hours of Tamitha Skov and extreme space weather events:

This weekend is the phone portion of the All Asia DX Contest: 

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 at . For an
explanation of numbers used in this bulletin, see .

Also, check this article from September, 2002 QST:

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 August 24 through 30, 2023 were 86, 77, 75, 69,
68, 82, and 94, with a mean of 78.7.  10.7 cm flux was 144.1, 138.9,
139.3, 141.5, 141.7, 142.2, and 138.6, with a mean of 140.9.
Estimated planetary A indices were 9, 5, 7, 11, 6, 5, and 6, with a
mean of 7. Middle latitude A index was 9, 7, 9, 13, 8, 7, and 9,
with a mean of 8.9.


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