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ARRL Propagation Bulletin ARLP015 (2018)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 13, 2018
To all radio amateurs 

ARLP015 Propagation de K7RA

No sunspots were seen over the past reporting week, April 5-11, so
average daily sunspot number declined from 3.3 to 0. Average daily
solar flux declined from 68.6 to 67.7. Average daily planetary A
index increased from 5 to 9.4, and average daily mid-latitude A
index went from 4 to 8.1.

But on Thursday, April 12, a new sunspot appeared, AR2704, and it is
a small one. However this one is three times the size of new sunspot
groups appearing on March 30, March 17, March 15, and March 2. reported:

"A minor G1-class geomagnetic storm is in progress on April 11th as
Earth moves through a high speed stream of solar wind. This is
causing bright auroras around the poles, with Northern Lights
sighted as far south as the Dakotas in the USA.  The gaseous
material is flowing from a wide hole in the Sun's atmosphere--so
wide that the stream could continue to influence our planet for the
next two to three days.

"Visit for updates."

Predicted planetary A index is 15, 12, 8 and 5 on April 13-16, 8 on
April 17-18, 12 on April 19, 15 on April 20-21, 12 and 10 on April
22-23, 5 on April 24 to May 5, 8 on May 6, 18 on May 7-8, 15 on May
9, 12 on May 10-11, 8 on May 12-13, 5 and 8 on May 14-15, 15 on May
16-18, 12 and 10 on May 19-20, and 5 on May 21-27.

Predicted solar flux is 70 on April 13-19, 69 on April 20, 67 on
April 21-22, 68 on April 23 to May 5, 67 on May 6-19, and 68 on May

Interesting article about the next solar minimum:

I do not know if this claim about the biggest sunspot is accurate or
not: .

Another interesting article. Note there seems to be no correlation
between geomagnetic storms and troubled whale navigation:

Geomagnetic activity forecast for the period April 13 to May 8, 2018
from F.K. Janda, OK1HH.

"Geomagnetic field will be:
Quiet on April 24-25, 28 
Mostly quiet on April 23, 26, May 4 
Quiet to unsettled on April 17-18, 27, 29-30, May 1, 3, 5, 9 
Quiet to active on April 13, 15-16, 19, May 2, 6, 8 
Active to disturbed on April 14, (20-21,) May 7 

"Solar wind will intensify on April (24-25,) May 5-7, (8)

- Parenthesis means lower probability of activity enhancement.
- With regard to ongoing changes, current forecasts are less reliable again.
- Beware of paraskavedekatriafobia!"

Dr. Tamitha Skov wrote:

"We are enjoying a mild solar storm due to some fast solar wind from
a large coronal hole that will be gracing much of the Sun's face
over the next few days. The strongest part of this storm has already
hit, bringing aurora down to mid-latitudes. Although the back half
of this coronal hole is not as well formed as the front half, we
should continue to see pockets of fast solar wind causing sporadic
boosts in activity through the weekend. Amateur radio operators
might take advantage of auroral propagation modes, since the solar
flux remains low with our near-solar-minimum Sun.

"Speaking of, talk of the approaching solar minimum has been hot and
heavy as of late, even in scientific circles. We have seen a faster
drop towards solar minimum than many expected. This bolsters my
hopes that we are indeed crossing through the solar minimum phase
more rapidly than predicted. In fact, some recent analyses are
indicating we might reach solar minimum as early as sometime this

"As if on cue, the Sun gives us a glimpse into the future this week
by birthing a sunspot with a signature that confirms it belongs to
the upcoming solar cycle. These new-cycle regions are perfectly
normal and will become more common as time goes on. They also serve
as comforting reminders that the Sun is not diving into a new
Maunder minimum (with no sunspots for 70 years), nor is it plunging
us into another ice age. These regions are heralding the coming of a
new cycle. So rest easy. Sunspots will return and likely sooner than
most people think."

Note that Dr. Skov said a new spot has a polarity suggesting it is
from the next solar cycle, which is Cycle 25.

If you would like to make a comment or have a tip for our readers,
email the author at, .

For more information concerning radio propagation, see 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

Monthly propagation charts between four USA regions and twelve
overseas locations are at

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

Sunspot numbers for April 5 through 11, 2018 were 0, 0, 0, 0, 0, 0,
and 0, with a mean of 0. 10.7 cm flux was 66.4, 67.3, 66.8, 67.9,
68.7, 68.5, and 68.3, with a mean of 67.7. Estimated planetary A
indices were 9, 4, 5, 5, 11, 18, and 14, with a mean of 9.4.
Estimated mid-latitude A indices were 8, 3, 4, 5, 11, 14, and 12,
with a mean of 8.1.


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