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ARRL Propagation Bulletin ARLP012 (2021)

ARLP012 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 12  ARLP012
From Tad Cook, K7RA
Seattle, WA  March 19, 2021
To all radio amateurs 

ARLP012 Propagation de K7RA

Average daily sunspot numbers this week rose just a little, from
18.4 to 19, and average daily solar flux changed from 78.9 to 78.1.
Solar activity remains low.

Note the vernal equinox, (the first day of spring in the Northern
Hemisphere) occurs at 0937 UTC on Saturday, March 20.  Both the
Southern and Northern hemispheres will be bathed in approximately
equal amounts of solar radiation, which has a positive effect of HF

On March 17 and 18, the daily sunspot number was only 12 on both
days, but the total sunspot area rose from 50 to 200
micro-hemispheres.  Sunspot area was last at this level on February
25.  You can see daily sunspot area along with sunspot numbers and
solar flux at .

Average daily planetary A index rose from 7.6 to 10.3, and average
daily middle-latitude A index increased from 6.1 to 7.3.  Solar wind
on March 14 drove the planetary A index to 25, and Alaska's College
A index was 37.

On Wednesday March 17 warned that minor geomagnetic
unrest is expected on March 18, due to a co-rotating interactive
region that will disturb our magnetic field.  "CIRs are transition
zones between fast and slow-moving solar wind streams.  Plasma piles
up in these regions, creating shock-like density gradients that
often do a good job sparking auroras."

On March 18 reported, "NOAA forecasters say that a
minor G1-class geomagnetic storm is likely on March 20 and 21 when a
stream of high-speed solar wind hits Earth's magnetic field.  The
gaseous material is flowing faster than 600 km/s from a southern
hole in the sun's atmosphere."

The latest forecast from the US Air Force Space Weather Squadron
predicts solar flux at 72 on March 19 to 21, 70 on March 22 to 26,
76 on March 27, 75 on March 28 through April 1, 78 on April 2 and 3,
then 70, 74, 76 and 72 on April 4 to 7, 71, 72 and 70 on April 8 to
10, 71, 72 and 71 on April 11 to 13, then 73, 76, 75 and 76 on April
14 to 16.  Solar flux is expected to hit a high of 81 on April 19.

Predicted planetary A index is 12, 24, 20, 15, 12, 8 and 10 on March
19 to 25, 5 on March 26 to 27, 25 on March 28, 20 on March 29 to 30,
then 10, 5, 15 and 8 on March 31 through April 3, 5 on April 4 to 7,
then 15, 18, 20, and 15 on April 8 to 11, then 8, 5 and 8 on April
12 to 14, and 20 on April 15 and 16 and 18 on April 17.  The A index
may peak at 25 again on April 24.

More about the Air Force and space weather:

Geomagnetic activity forecast for the period March 19 to April 13,
2021 from F. K. Janda, OK1HH.

"Geomagnetic field will be
Quiet on:  March (27,) April 1, 4, 6, 12
Quiet to unsettled on:  March 25 and 26, April 3, 5, 7
Quiet to active on:  March 22 to 24, 31, April 13
Unsettled to active:  March 21, April 2, 8 and 9, 11
Active to disturbed:  March (19 and 20,) 28 to 30, April 10

Solar wind will intensify on:  March (19,) 20 to 22, (23, 27,) 28
and 29, (30, April 1 and 2, (3 to 5, 8,) 9 and 10, (11)

Parenthesis means lower probability of activity enhancement.
Predictability of changes remains very low, as indicators remain

At 2358 UTC on March 17 Australia's Space Weather Services sent this

"A large Southern Polar coronal hole with low latitude extensions
will become geoeffective with the CIR possibly arriving from late on
UT day 19 March, causing unsettled to active conditions.  The HSS
from the coronal hole is expected to follow on UT day 20 March,
causing active conditions with the possibility of a G1 minor storm.
Active conditions are expected to continue on 21 March, Auroras may
be visible from Tasmania at night on 19-20 March."

Dave Bono, K6OAK in Fremont, California reports:

"On Monday March 15th just before 1900 UTC 6 and 10 meters were
dead, but I noticed a few signals on 12M FT8, one being a fairly
strong signal from VP8NO in the Falklands.  After a few attempts I
was able to make contact and received a respectable -10 report.  I
was running 50 watts into a ground mounted vertical antenna.  Not
bad for a few minutes in the shack."

Mike, KA3JAW in Easton, PA (FN20jq) reports six meter activity:

On March 13 at 1627 UTC six meter sporadic-e began to appear on FT8
50.313 MHz with stations from the central states of IL, MO, KY, NE,
IA and KS for over 3.5 hours from the first Es cloud formation.

1659 UTC heard VO1SIX in Newfoundland, Canada (GN27jd) at 1090 miles
coming in from 065 degrees azimuth from a second Es cloud formation.

1830 UTC Es starts to spread out directly west into the central
states of NE, IA and KS.

The farthest distance came from KQ0P (EM19wf) at 1109 miles, 271
degrees azimuth with a signal of -6 dB while the radio power output
was 15 watts using a half wave dipole at 6 feet above ground.

Remembering the 1989 Quebec event:

This article on solar activity has some interesting links:

Historic sunspot activity going way, way back:

VA7JW gives an overview of the Dominion Radio Astrophysical
Observatory at Penticton which supplies us with solar flux data:

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 March 11 through 17, 2021 were 23, 15, 12, 24,
24, 23, and 12, with a mean of 19.  10.7 cm flux was 78.2, 76.9,
81.1, 78, 74.8, 79.2, and 78.2, with a mean of 78.1.  Estimated
planetary A indices were 4, 12, 17, 25, 7, 4, and 3, with a mean of
10.3.  Middle latitude A index was 3, 9, 13, 17, 5, 2, and 2, with a
mean of 7.3.


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