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ARRL Propagation Bulletin ARLP031 (2023)

ARLP031 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7RA
Seattle, WA  August 4, 2023
To all radio amateurs 

ARLP031 Propagation de K7RA

The Australian Space Weather Forecasting Centre issued a geomagnetic
disturbance warning at 0233 UTC on August 3.

"Two recent coronal mass ejections (CMEs) are expected to impact
Earth on UT day 05-Aug, with the second possibly arriving early
06-Aug. G0-G1 geomagnetic conditions may be expected on 05-Aug, with
a chance for isolated periods of G2 towards the end of the UT day on
05-Aug. Geomagnetic storm conditions may persist over 06-Aug."

Solar activity was up during this reporting week, July 27 through
August 2.

Average daily sunspot numbers increased from 128.1 to 154.3, but
average daily solar flux was about the same as last week, moving
just from 172.2 to 173.

Geomagnetic indicators were quiet, with average daily planetary A
index shifting from 11 to 8.3, while middle latitude numbers went
from 11.1 to 9.3.

Predicted solar flux is 160 on August 4-5, 162 on August 6, 164 on
August 7-8, 162 and 160 on August 9-10, 168 on August 11-12, 170 on
August 13-16, 172 on August 17-18, then 170 and 168 on August 19-20,
170 on August 21-22, 172 on August 23, and 170 on August 24-27, then
165 on August 28-31, then 168, 170, 168, 165, 168, and 165 on
September 1-6, 168 on September 7-8, and 170 on September 9-12.

Predicted planetary A index 15, 26, 15 and 8 on August 4-7, 5 on
August 8-10, 8 on August 11-12, 5 on August 13-25, then 12 and 10 on
August 26-27, and 5 on August 28-31, 12 and 10 on September 1-2, 5
on September 3-5, 10 on September 6, 8 on September 7-8, and 5 on
September 9-17.

No report from OK1HH this week as he vacations in the mountains in

See for an image of him on vacation

Here are reports from two of his colleagues at Czech observatories.

"Solar activity forecast for the period August 4-10, 2023.

Activity level: mostly low to moderate 
X-ray background flux (1.0-8.0 A): in the range C1.1-C2.5 
Radio flux (10.7 cm): a fluctuation in the range 155-185 
Events: class C (2-15/day), class M (0-3/day), class X (0-2/period), 
proton (0-1/period) 
Relative sunspot number (Ri): in the range 124-220

Martina Pavelkova RWC Prague, Astronomical Institute, Solar Dept.,
Ondrejov, Czech Republic"

"Geomagnetic activity forecast for the period August 4-10, 2023

Quiet: Aug 3, 5-8 
Unsettled: Aug 4-5, 9-10 
Active: Jul 10 
Minor storm: 0 
Major storm: 0 
Severe storm: 0

Next week, we do not expect any storming event. Currently  we expect
quiet to unsettled conditions. The most unsettled episode is
expected at the end of current forecast period, August 9-10.

Tomas Bayer RWC Prague Institute of Geophysics of the ASCR, Prague
Department of Geomagnetism Budkov observatory (BDV)"

Look at all the sunspots on August 3!


In an exchange with Carl Luetzelschwab, K9LA and OK1HH, Carl
commented, "Many papers show that climate change has affected the
ionosphere. Is the change enough to actually notice it in
predictions and in on-the-air operations? To answer the prediction
aspect, I looked at Millstone Hill (Massachusetts) foE and foF2
ionosonde data at 1700 UTC (around local noon) for October 1998 (V1
smoothed sunspot number = 70) and January 2023 (V2 smoothed sunspot
number = 114, which gives a V1 number of 80). The data is 24 years
apart, and I figured a trend due to climate change might show up if
there was one. I compared the ionosonde data to what VOACAP
predicted for those two months."

His conclusion? No effect.

V1 and V2 refer to the new and old version sunspot numbers,
explained here:

This relates to the statement in the OK1HH report in last month about
global changes affecting propagation.

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 July 27 through August 2, 2023 were 154, 148,
147, 139, 197, 160, and 135, with a mean of 154.3  10.7 cm flux was
165.3, 168.2, 178.6, 174.4, 177.1, 174.7, and 172.9, with a mean of
173. Estimated planetary A indices were 7, 6, 9, 9, 6, 9, and 12,
with a mean of 8.3. Middle latitude A index was 7, 5, 8, 18, 8, 9,
and 10, with a mean of 9.3.


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