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ARRL Propagation Bulletin ARLP020 (2023)

ARLP020 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 20  ARLP020
From Tad Cook, K7RA
Seattle, WA  May 19, 2023
To all radio amateurs 

ARLP020 Propagation de K7RA

This reporting week, May 11-17, average daily sunspot number was
nearly the same as last week, 118.6 compared to 119.3, only
marginally lower.

But average daily solar flux dropped from 167.8 to 143.2.

Geomagnetic indicators were quieter, both planetary and middle
latitude A index at 9.6. Last week the two numbers were 15.1 and
11.9, respectively.

What is the outlook for the next few weeks?

10.7 cm solar flux is forecast to have a peak of 165 on June 8.

The predicted numbers are 145 on May 19, 140 on May 20-21, 135 on
May 22-24, 140 on May 25-26, 145 on May 27, 155 on May 28-30, 160 on
May 31 and June 1, 155 on June 2-3, 160 on June 4-7, then 165, 160,
150, 145, and 150 on June 8-12, then 155 on June 13-17, 150 on June
18, 145 on June 19-21, 140 and 145 on June 22-23, and 155 on June
24-26 then 160 on June 27-28.

Predicted planetary A index is 5, 8, 12, 15 and 5 on May 19-23, 12
on May 24-25, 15 on May 26, 10 on May 27-28, 8 on May 29, 5 on May
30 through June 1, then 16, 12, 16 and 12 on June 2-5, 8 on June
6-8, then 5 on June 9-18, 12 and 20 on June 19-20, 15 on June 21-22,
10 on June 23-24, 8 on June 25, and 5 on June 26-28.

These numbers are updated daily here:

Thanks to reader David Moore for this:

"How 1,000 undergraduates helped solve an enduring mystery about the


"For three years at the height of the COVID-19 pandemic, a group of
students spent an estimated 56,000 hours analyzing the behavior of
hundreds of solar flares. Their results could help astrophysicists
understand how the Sun's corona reaches temperatures of millions of
degrees Fahrenheit."

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - May 18, 2023, from F.K. Janda, OK1HH.

"On May 12, we expected a CME impact from the flare on the evening
of May 9. It was indeed registered - at 0635 UTC the geomagnetic
storm began. However, it was weaker than expected, of G1 class.

"On 13 May at 1915 UTC, an unexpected CME impact followed for a
change, which again triggered another G1 class geomagnetic storm.

"On 16 May, we expected another smaller CME. The particle cloud has
been slowly approaching Earth since the magnetic filament eruption
in the southern hemisphere of the Sun on 12 May.

"The next solar flare on May 16, with a maximum at 1643 UTC, was
M9.6 class. It came from a sunspot group still hiding behind the
southeastern limb of the Sun. In fact, it may have been an X flare,
partially obscured by the solar horizon. Yet it caused the strong
Dellinger effect (shortwave fade) over North America. After the
sunspot group came out on the solar disk, we could observe it as AR
3310. It's about three times wider than Earth, and its magnetic
configuration promises more flares.

"Not only was solar flare activity quite high, but the Sun was
hurling so many CMEs into space that hardly a day went by without
one hitting Earth. Therefore, the frequency of geomagnetic storms
was also higher, followed by frequent deterioration of shortwave
propagation conditions. In summary, the 25th solar cycle continues
to evolve nicely."

Frank, VO1HP sent this from St. Johns, Newfoundland:

"On May 12 1957-2113 UTC, there was a strong 6M Es opening into mid
South America. Logged 20 stations using FT8. No CW or SSB heard.
Stations worked at VO1HP remote station: LU3CQ, CE3SX, 2SV, LI7DUE,

"Antenna 4el Yagi at 35ft overlooking ocean. K3 + PR6, KPA500
KAT500. Other VO1s seen: VO1CH, VO1SIX, and VO1AW."

On April 24, Rocky Riggs, W6RJK in Truckee, California wrote:

"I was not very active until recently when I was introduced to POTA.
The park I frequent the most would typically give me 40-60 contacts
in a 2 hour period.

"On Monday, April 24th, I went to the same park, and in 30+ minutes
had no contacts and couldn't hear anyone either. I later found out
that the solar storm was causing most of our radio problems. Until
then, I had never considered much about solar flares, or how the Sun
influences radio propagation. Now, finally, I'm trying to learn as
much as I can. The K7RA Solar Update in the ARRL Newsletter is
FANTASTIC and will be my source going forward to help me learn and

"Here's my question.  Is there a 'real time' place where I can go to
determine if a particular band has good propagation (I typically use
20m and 40m)?

"You know, like before I go out and get all set up and it's a 'goose

As I first reported in Propagation Forecast Bulletin ARLP017, I told
him that a very useful tool (to use) is to check real time
geomagnetic indices with this:

Nice quiet conditions show a planetary A index at 1 or 2, unsettled
conditions at 3, then above 3 conditions are disturbed. The scale is
logarithmic, so each point in either direction is important.

Another approach is to use pskreporter at which is handy if you live
in a grid square that has many active hams, or a nearby grid that is
more populated.

You can check FT8 activity on any band. There is also a "Country of
Callsign" selection so you can check activity across your nation of
choice. Recently when I have raised nobody on 10 meter FT8 this
option showed no activity here in the Pacific Northwest but plenty
of 10 meter activity in the southeast United States.

Here is a new video from Dr. Tamitha Skov, WX6SWW:

NASA sunspot picture:

A video of a recent eruption:

Here are articles about Radio Blackout:

NASA warning of a Solar Storm threat:

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 .

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 May 11 through 17, 2023 were 152, 134, 120, 109,
103, 106, and 106, with a mean of 118.6. 10.7 cm flux was 163.4,
149.1, 143.8, 139.7, 134.5, 134.3, and 137.9, with a mean of 143.2.
Estimated planetary A indices were 9, 19, 13, 8, 6, 8, and 4, with a
mean of 9.6. Middle latitude A index was 10, 15, 12, 9, 6, 10, and
5, with a mean of 9.6.


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