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ARRL Propagation Bulletin ARLP028 (2023)

ARLP028 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 28  ARLP028
From Tad Cook, K7RA
Seattle, WA  July 14, 2023
To all radio amateurs 

ARLP028 Propagation de K7RA


A glancing CME impact is expected late on 13-July and another CME
impact is expected early on 15-July. These impacts present the
possibility of geomagnetic storm activity over 13-15 July."

We saw a welcome rise in solar activity this reporting week, July

Referencing the previous seven days, average daily sunspot numbers
rose from 126.1 to 181.9, while average daily solar flux increased
from 164.5 to 179.4. On July 13 the solar flux was 202.9, well above
the average for the previous seven days.

Geomagnetic indicators did not change much, average planetary A
index going from 7.3 to 8.6 and average daily middle latitude A
index from 8 to 8.1.

The most active day was July 7 when University of Alaska's college A
index was 40.  The middle latitude A index on that day was only 11.
The college A index is from a magnetometer in Fairbanks.

What is the outlook for the next month?

Predicted solar flux looks great over the next few days, at 200,
202, 198, 200, and 204 on July 14-18, 202 on July 19-21, 160 on July
22-23, 155 on July 24-25, 160 on July 26-27, 165 on July 28-29, 170
on July 30-31, 165 on August 1-4, 170 on August 5, 175 on August
6-7, 170 on August 8, then 165 on August 9-11, 170 on August 12, 175
on August 13-14, 170 on August 15-17, and 160 on August 18-19.

Predicted planetary A index is 10 on July 14, 5 on July 15 through
August 2, then 10, 8 and 5 on August 3-5, then 8, 8, 5, 8 and 8 on
August 6-10, 5 on August 11 through the end of the month.

On July 12, reported: 

"A new hyperactive sunspot is producing M-class solar flares every
few hours. This is causing shortwave radio blackouts around all
longitudes of our planet. If current trends continue, an X-flare
could be in the offing."

See for updates.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere July 14-20, 2023 from OK1HH.

"Over the past week, we were surprised by two large groups of spots
that appeared on the eastern limb of the solar disk.

The first of these, AR3363, emerged in the southeast. Although it
remained large, there was nothing significant going on. Its opposite
was AR 3372 a few days later, which produced moderate-sized flares
almost daily.

In both cases, helioseismic echoes from the sun's far side suggested
that it may be the leading edge of a large active region.

But there was no indication that these would be areas with a
diametrically different type of activity.

The images of the two groups of spots were large enough to be
observed by the Mars rover Perseverance. Because of Mars' position,
it saw them a few days earlier than a terrestrial observer. For the
record: Perseverance observes the Sun daily, but mainly so that it
can tell from the drop in brightness that a Martian dust storm is

AR3372 activity is increasing, while on July 11 and 12 several
M-class solar flares (some with CMEs) have already occurred (X-class
flare appeared to be imminent). In particular, it was almost certain
that the Earth's magnetic field activity would increase in the
following days. The probability of magnetic storms increased
significantly as AR3372 rotated more and more toward the Earth."

Carl, K9LA had comments on the OK1HH report from last week.

"There have been many papers in recent years that have looked at the
trends in ionospheric parameters over the past decades. Although the
changes are small, they do show up in ionosonde data after much math
to eliminate solar activity and geomagnetic field activity. These
results show both positive and negative trends in the F2 region
electron density, likely due to neutral atmosphere dynamics and
electrodynamics that could give regional differences.

An interesting paper in 2008 Geophysical Research Letters modeled
the increased levels of CO2 (global warming) in the atmosphere
versus the impact on the ionosphere.


They used 2000 as the baseline with 365 ppmv of CO2, and doubled the
amount of CO2 for the year 2100. Their results showed that electron
densities in the E and F1 region would increase a couple percent in
2100 while the height of the E region peak would decrease a couple
km. In the F2 region, the electron density would decrease by several
percent in 2100 while the height of the F2 region would decrease 10
or so km."

Thanks to reader David Moore for this, on aurora hype:

Flare video (with music.)

Huge sunspot:

Tamitha Skov reports:

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 6 through 12, 2023 were 149, 147, 167, 183,
181, 227, and 219, with a mean of 181.9. 10.7 cm flux was 157.6,
161.4, 160.5, 179.2, 190.6, 213.5, and 193.3, with a mean of 179.4.
Estimated planetary A indices were 11, 18, 8, 4, 5, 8, and 6, with a
mean of 8.6. Middle latitude A index was 11, 16, 6, 4, 6, 8, and 6,
with a mean of 8.1. 


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