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The K7RA Solar Update


Sunspot numbers and solar flux rose this week. There were two new
sunspot groups on June 15, another on June 17 and one more on June
18, three more on June 19, two more on June 20 and another on June

Average daily sunspot number increased from 122 to 143, and average
daily solar flux rose from 154.8 to 165.4.

Average daily planetary A index jumped from 5.7 to 15.4, while the
middle latitude numbers increased from 6.7 to 13.1.

Predicted solar flux is 180 on June 23-24, 185 on June 25-27, 180 on
June 28, 175 on June 29 through July 1, 180 on July 2-3, 175 on July
4-5, 170 on July 6-10, then 165 on July 11, 160 on July 12-13, 165
on July 14-15, 160 and 155 on July 16-17, 160 on July 18-19, 165 on
July 20-24, 170 on July 25, 175 on July 26-28, and 180 on July

Predicted planetary A index is 14, 10 and 8 on June 23-25, then 5,
5, and 12 on June 26-28, then 5, 5, and 12 again on June 29 through
July 1, 8 on July 2, 5 on July 3-7, 12 on July 8, 5 on July 9-11,
then a dramatic increase to 20 and 30 on July 12-13, 8 on July
14-15, and 12 on July 16-17, 10 on July 18, 5 on July 19-23, 12 on
July 24-25, 5 on July 26-27, 12 and 8 on July 28-29, and 5 on July
30 through August 3.

These predictions are from forecasters Liming and Dethlefsen of the
US Air Force 557th Weather Wing at Offutt AFB.

See .

So, what does this forecast show for ARRL Field Day, which is this

Geomagnetic numbers are a bit more unsettled than what was shown in
last week's bulletin, which had an A index of 5 for Friday through
Sunday. The latest shows 14, 10 and 8. Predicted solar flux looks
excellent, at 180, 180 and 185.

Of course, Field Day does not begin until Saturday, but here we also
include data for the day prior.

Here is a X1.1 solar flare video:

Another report from South Asia regarding solar flares as some sort
of existential threat.  Don't worry. Nothing terrifying about what
they report, but there is a nice description of what the SOHO
observatory does.

Reader David Moore shared this video:

Don't know why, but no weekly report from OK1HH this time around.

On Thursday I attended an online event, the "Space Weather
Enterprise Forum," thanks to a tip from K6PFA.

Most of the sessions concerned threats from solar flares, but there
was great commentary from Bill Murtaugh of NOAA's Space Weather
Prediction Center.

He noted that the current solar cycle should peak in summer 2024
instead of 2025 and will peak much stronger than the consensus
forecast from earlier in the cycle. He also noted that increased
flare activity always occurs in the years following a sunspot cycle

John Dudley, Managing Director of Flight Operations at American
Airlines gave an interesting presentation about how space weather
affects routing of international flights.

He mentioned their expert on space weather at the airline, and I
looked him up. Yes, a ham, KC1ENP. Could not find an email address
for him, so I sent a QSL card to make contact.

Thanks to for this fascinating article about
setting up a personal space weather station.  It is under the
heading, "A New Way To Detect Solar Flares":

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 15 through 21, 2023 were 112, 120, 110,
133, 181, 155, and 190, with a mean of 143. 10.7 cm flux was 153.1,
157.2, 158.1, 164.1, 168.8, 180.1, and 176.4, with a mean of 165.4.
Estimated planetary A indices were 24, 38, 8, 10, 10, 10, and 8,
with a mean of 15.4. Middle latitude A index was 17, 24, 8, 12, 9,
13, and 9, with a mean of 13.1.




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