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ARRL Propagation Bulletin ARLP027 (2023)

ARLP027 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 27  ARLP027
From Tad Cook, K7RA
Seattle, WA  July 7, 2023
To all radio amateurs 

ARLP027 Propagation de K7RA

The average daily sunspot number for June, 2023 was the highest in
21 years, according to

From a July 3 email alert from

"SUNSPOT COUNTS HIT A 21-YEAR HIGH:  It's official:  The average
sunspot number in June 2023 hit a 21-year high.  Solar Cycle 25 has
shot past its predecessor, Solar Cycle 24, and may be on pace to
rival some of the stronger cycles of the 20th century."

Could we see another Cycle 19, the biggest in recorded history, even
back before the birth of radio?

Not too long ago, we heard that this cycle should peak in summer
2025.  Later that was revised to 2024.  Now I am seeing occasional
references to a cycle peak at the end of this year.
From my own records, average daily sunspot numbers for April through
June 2023 were 93.7, 125.8 and 143.9, a nice upward trend.

Some popular news outlets seem confused by the difference between
sunspot number and number of sunspots, and have quoted another
higher average.

Here is the difference.  If they are just counting the total number
of sunspots for the month, this is far different from average daily
sunspot numbers.  The sunspot number is somewhat subjective, but it
gets ten points for each sunspot group, and one point for each
sunspot in those groups.

But I stand by my numbers.  They are all from NOAA and appear at the
end of each bulletin.

But they may be referencing International Sunspot Number, which may
be different from the SESC numbers from NOAA.

Here is an example of confusing sunspot numbers with number of

This one is also confusing, saying there were 163.4 sunspots in

But what does this mean?  It could be either 163 or 164 sunspots,
but not a fractional number, unless it expresses an average.  The
minimum sunspot number is 11.  This would be one sunspot group
containing one spot.  They are always whole, not fractional

There was one new sunspot region (group) on June 30, three more on
July 1, one more on July 2, another on July 4, and one more on July

Sunspot and solar flux data again this week did not track together.
Average daily sunspot number declined from 170 to 126.1, while
average daily solar flux rose slightly from 160.3 to 164.5.

Geomagnetic indicators were lower, with average daily planetary A
index declining from 10.7 to 7.3, and middle latitude averages from
9.9 to 8.

Predicted solar flux is 155 on July 7, 150 on July 8 to 10, then 155
on July 11, 160 on July 12 to 13, 175 on July 14 to 18, 170 on July
19 to 21, 160 on July 22 and 23, 155 on July 24 and 25, 160 on July
26 and 27, 165 on July 28 and 29, then 170, 170 and 165 on July 30
through August 1, 155 on August 2 to 6, then 160, 165 and 170 on
August 7 to 9, and 175 on August 10 to 14.

Predicted planetary A index is 5, 12 and 8 on July 7 to 9, 5 on July
10 and 11, then 20 and 30 on July 12 and 13, 8 on July 14 to 22, 5
on July 23 to 30, 8 on July 31 through August 1, then 5 on August 2
to 4, 12 and 8 on August 5 and 6, then 5, 20 and 30 on August 7 to
9, and 8 on August 10 to 18.

Note those big numbers are about one solar rotation apart, which is
about 27.5 days.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere for July 6, 2023 from F. K. Janda, OK1HH.

When the current 25th solar cycle began in December 2019, solar
astronomers thought it would be a weak cycle similar to its
immediate predecessor, solar cycle 24.  But now we have a twenty-one
year peak.  And we expect a continued increase for about two more

The misfortune is that ongoing global changes are reducing the
ionization rate of the ionosphere.  Yet the current conditions for
shortwave or decameter wave propagation do not match the amount of
solar activity - they are worse.

But that's not all.  Not only is solar cycle 25 likely to rival some
of the more powerful cycles of the 20th century, but we're likely to
see even more powerful solar flares and magnetic storms.  History
repeats itself cyclically, and we need only think of the great
Halloween storm of 2003, including the strongest solar flare ever
recorded in X-ray (X45).

The giant sunspot group AR3354 (only about four times smaller than
the giant sunspot group of early September 1859) made its last
appearance on July 2 with an X-class flare.  Two days later it

We won't lose the source of the stronger flares, however - the
growing AR3359, with its Beta-Gamma magnetic configuration, crossed
the central meridian toward active western longitudes on July 6 and
will continue to grow.  With its predicted higher activity, we could
see an increase in the Earth's magnetic field activity as early as
the middle of next week.

Tamitha Skov, from July 1.


Stormy weekend?

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 June 29 through July 5, 2023 were 112, 187, 119,
126, 117, 121, and 101, with a mean of 126.1.  10.7 cm flux was
162.2, 158.6, 165.5, 170.2, 173.2, 167.2, and 154.6, with a mean of
164.5.  Estimated planetary A indices were 17, 8, 5, 5, 5, 4, and 7,
with a mean of 7.3.  Middle latitude A index was 13, 8, 6, 8, 7, 5,
and 9, with a mean of 8.


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