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ARRL Propagation Bulletin ARLP013 (2024)

ARLP013 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 13  ARLP013
From Tad Cook, K7RA
Seattle, WA  March 29, 2024
To all radio amateurs 

ARLP013 Propagation de K7RA

A dramatic increase in solar activity emerged over the past week,
and geomagnetic activity reacted as well.

Two new sunspot groups appeared on March 21, then one new group
emerged each day over March 22-25.

Average daily solar flux rose from 153.3 to 191.9, and average daily
sunspot numbers increased from 94.3 to 147.

The highest sunspot number over last week was 171 on March 22, which
was the highest sunspot number since November 22-25, 2023 when the
numbers were 174, 176, 184, and 179.

Average daily planetary A index jumped from 5.9 to 25.4, and middle
latitude numbers from 5 to 19.

On March 24 the college A index in Fairbanks, Alaska reached 100!
The planetary A index was 64.

Looking ahead, solar flux is predicted to reach a peak of 210 on
April 23-24.

The projected solar flux is 175, 170 and 155 on March 29-31, 150 on
April 1-2, 155 on April 3-4, 185 on April 5, then 180 and 185 on
April 4-5, 190 on April 6-7, then 185, 180, 175 and 180 on April
8-11, 185 on April 12-13, then 190, 185, 190, 185 and 180 on April
14-18, then 175 on April 19-20, then 200 and 205 on April 21-22, 210
on April 23-24, then 205, 190 and 180 on April 25-27, 175 on April
28-29, then 170, 180 and 185 on April 30 through May 2, and 190 on
May 3-4.

The planetary A index forecast shows 8 and 6 on March 29-30, 10 on
March 31 through April 1, then 8, 5, 5 and 12 on April 2-5, 5 on
April 6-8, 8 on April 9-11, 5 on April 12-18, then 8, 10, 10 and 8
on April 19-22, 5 on April 23-29, then 15, 12, and 12 on April 30
through May 2, and 5 on May 3-5.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere for March 28, 2024 from F. K. Janda, OK1HH: 

 The period without stronger disturbances in the Earth's magnetic
field was incredibly long: 19 December 2023 to 20 April 2024, or
three whole months.  But it had to end at some point.  Especially
since we're near the peak of the 11-year solar cycle.

 Around March 20, we were expecting the rise of a larger sunspot
group in the northeastern solar disk, AR3614.  The bigger surprise,
however, was the simultaneous emergence of another group, designated
AR3615, which surprised us both by its size and dispersion and by
the number of moderate flares produced, which totaled eleven on
March 23.

 Although AR3614 was the source of a much smaller number of flares,
it made up for everything with a large proton flare, accompanied by
a CME, on 23 March with a maximum at 0133 UT.  The Earth was
bombarded by energetic protons on the following days, while
simultaneously being hit by particle clouds from flares in both
active regions.  Which couldn't have resulted in anything other than
the development of a magnetic storm.  Its intensity was greatest on
April 24.

 The disturbance began on April 23, however, with an increase in
MUF, or so-called positive phase.  A significant decrease in MUF and
an increase in the attenuation of radio waves in the ionosphere
occurred since 24 March.  The significant deterioration of shortwave
propagation conditions lasted until 26 March.

 A return to slightly above-average propagation is expected after
March 28.

In a March 28 email titled "Big CME impact ignites 6 meters", Jon
Jones, N0JK in Kansas wrote:

"The CME that struck March 24 ignited 6 meters for the Midwest USA
through Wednesday March 26.

"On March 24 I logged 9Y4D on 6 Meter FT8 and had good copy on VP8WA
up to +4 dB.  Had a psk flag from CE8EIO at -5 dB.  The planetary K
index went to 8.

"March 25 copied HD8MD from my fixed mobile (1/4 wave whip) around
1930 UTC up to -7 dB on FT8.

"March 26 worked HC5VF, copied HD8MD, LU1WFU, HC2AP/P, HC1BI,
LU8DRH, CX4DSAE and many others on FT8.  Big pileups on the DX

Jon N0JK EM28 KS"

Shortwave blackout:

Check out the KN8DMK page on QRZ.COM.  Using a VLF receiver on 40.75
KHz, he monitored US Navy transmitter NAU in Puerto Rico during a
solar flare.

Tamitha Skov video:

This weekend is the CQ World Wide WPX SSB Contest.  See for info.  The CW weekend is May 25-26.

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 web page 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

Also, check this:

Instructions for starting or ending email distribution of ARRL
bulletins are at .

Sunspot numbers for March 21 through 27 2024 were 141, 171, 146,
145, 163, 149, and 114, with a mean of 147.  10.7 cm flux was 196.9,
197.6, 210.7, 195.1, 190.1, 178.2, and 174.6, with a mean of 191.9. 
Estimated planetary A indices were 27, 11, 36, 64, 22, 11, and 7,
with a mean of 25.4.  Middle latitude A index was 20, 10, 25, 43, 17,
11, and 7, with a mean of 19.


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