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ARRL Propagation Bulletin ARLP015 (2023)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 14, 2023
To all radio amateurs 

ARLP015 Propagation de K7RA

Solar activity was up for this reporting week, April 6-12.

Seven new sunspot groups appeared, one on April 6, another on April
9, two more on April 10, another on April 11, and two more on April
12. Then on Thursday, April 13, three new sunspot groups emerged.
The sunspot number rose to 154, the highest value in the past month.

Average daily sunspot number rose from 53.4 to 70.6, and average
daily solar flux increased from 132.5 to 141.

On Thursday, the noon solar flux reading was 159.5 and was well
above the average for the previous seven days, perhaps indicating an
upward trend.

Geomagnetic conditions were calm, with average daily planetary A
index dropping from 15 to 7.6, and the middle latitude average from
11.7 to 6.4.
Predicted solar flux was 155 and 160 on April 13-14, and 165 on
April 15-16.

The Thursday prediction was well above that.

Predicted solar flux is 168 on April 14-16, 165 and 160 on April
17-18, 155 on April 19-22, 158 on April 23, 155 on April 24-25, then
152, 148, 145 and 142 on April 26-29, 140 on April 30 and May 1, 142
and 140 on May 2-3, 135 on May 4-5, then 130, 140, 145, 150, 152,
155 and 158 on May 6-12, then 160 on May 13-15, and 150 and 152 on
May 16-17, 155 on May 18-19, then 158, 155 and 155 on May 20-22.

Predicted planetary A index is 8, 12, 10 and 8 on April 14-17, 5 on
April 18-20, then 8 and 10 on April 21-22, 5 on April 23-25, then 15
and 18 on April 26-27, 15 on April 28-30, then 12 and 10 on May 1-2,
8 on May 3-4, 5 on May 5-6, then 8, 10 and 8 on May 7-9, and 5 on
May 10-13, then 10, 15 and 5 on May 14-16, 20, 15 and 10 on May
17-19, and 5 on May 20-23. released this news on Wednesday:

"Evidence is mounting that Solar Cycle 25 might peak much earlier
than expected. New research by a leading group of solar physicists
predicts maximum sunspot activity in late 2023 or early 2024 with a
peak that could be twice as strong as the previous solar cycle."

Look in the Spaceweather archive for April 12-13 to read more.  It
is all explained in this scientific paper:

I noticed some very odd 10 meter propagation at 2000 UTC on April
11. Running FT8 and a one wavelength end fed wire at my home in
Seattle, the only stations that heard me according to were one in New Zealand, another in Hawaii, and in
North America, only 5 stations (NK5B, AD4ES, K4RMM, KB4FB and AA4CB)
in Florida, all within a 200 mile strip from 2,512 to 2,712 miles
from me. Checking again at 2015 UTC, it was still the same. It
looked quite dramatic on the map.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - April 13, 2023, from F.K. Janda, OK1HH.

"Relatively frequent C-class solar flares, sporadic M-class flares
in one or two sunspot groups, and the appearance of two or three
relatively small coronal holes - that's how the Sun looked between
April 6 and 13.

"The solar wind speed dropped to 340 km/s by April 9, rose
significantly to 550 km/s on April 10, and then slowly dropped
again. The Earth's magnetic field was unsettled on April 10, then
mostly calm on the other days.

"MUF values were slightly higher on 10 April. This was followed by
11 April with irregular daily MUF and irregular occurrences of
attenuation. Since 12 April onward there was a transition to a
regular daily course of ionospheric parameters.

"Now we can expect higher solar activity in the southern hemisphere.
The rise should continue in the coming days at first. A slight
decrease will follow after the weekend.

"A slight increase in geomagnetic activity with consequent
fluctuations in shortwave propagation conditions can be expected
rather since the middle of next week."

Here is a video about the Termination Event:

A story on NASA using AI to predict geomagnetic storms:

Here is a story about Radio Blackout:

Mike Mason, WB4MM in Daytona Beach, Florida wrote:

"On April 9 2023 FT8 mode 12 meters beginning at 2254 UTC and ending
at 2328 UTC I worked 12 JA stations plus 2 South Korean stations in
a row. I was calling CQ AS WB4MM EL99.

"My station has 100 watts to an attic 15M dipole. I believe the SFI
at the time was 135. Not sure of the type of prop. This occurred
within an hour of sunset at my QTH."

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 April 6 through 12, 2023 were 33, 38, 49, 52,
92, 103, and 127, with a mean of 70.6. 10.7 cm flux was 137.1,
136.3, 135.9, 140.3, 139.8, 143.4, and 154, with a mean of 141.
Estimated planetary A indices were 9, 8, 6, 6, 14, 6, and 4, with a
mean of 7.6. Middle latitude A index was 7, 7, 5, 5, 11, 6, and 4,
with a mean of 6.4.


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