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ARRL Propagation Bulletin ARLP033 (2018)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 17, 2018
To all radio amateurs 

ARLP033 Propagation de K7RA

Australia's Space Weather Services issued a Geomagnetic Disturbance
Warning at 0022 UTC on August 16: "Geomagnetic activity is expected
to be at Quiet to Active levels due to coronal hole effects. A
period of significant southward Bz component could produce isolated
Minor Storm levels."

What is the Bz component? It is a component of the interplanetary
magnetic field, or IMF.  The site explains:

"The IMF is a vector quantity with three directional components, two
of which (Bx and By) are oriented parallel to the ecliptic. The
third component--Bz--is perpendicular to the ecliptic and is created
by waves and other disturbances in the solar wind. When the IMF and
geomagnetic field lines are oriented opposite or 'antiparallel' to
each other, they can 'merge' or 'reconnect,' resulting in the
transfer of energy, mass, and momentum from the solar wind flow to
magnetosphere. The strongest coupling --with the most dramatic
magnetospheric effects-- occurs when the Bz component is oriented

A high-speed solar wind stream is expected to emerge from the
coronal hole.

Solar activity is still very weak. The previous propagation forecast
bulletin (ARLP032) reported two days with a sunspot number of 11, on
each day, for August 2-8, yielding the average daily sunspot number
for the week at 1.6. This week's average was 3.4, based on a sunspot
number of 12 on both August 14 and 15. That activity continued on
Thursday, August 16, also with a daily sunspot number of 12.

Average solar flux went in the other direction, changing to 68.7
from 69.7 in the previous week. Geomagnetic indicators were higher,
with average daily planetary A index shifting from 5.7 to 6.9, and
mid-latitude A index from 6.9 to 7.3.

Activity is weak and should get weaker, at least until two years
from now in 2020 when we will probably reach the bottom of Solar
Cycle 24.

Predicted solar flux (August 16 forecast from USAF via NOAA) is 69
on August 17-23, 70 on August 24 through September 5, 68 on
September 6-18, and 70 on September 19-30.

Predicted planetary A index from the same forecast is 10 on August
17, 5 on August 18-20, 15 on August 21-22, 10 on August 23, 5 on
August 24 through September 2, then 12, 8, 5, 5, 10, 8 and 8 on
September 3-9, then 5 on September 10-11, then 12, 15, 8, 5, 15 and
12 on September 12-17, 5 on September 18-28, 8 on September 29 and
12 on September 30.

F.K. Janda, OK1HH sends us his Geomagnetic Activity Forecast for the
period August 17 to September 12, 2018.

Geomagnetic field will be:

Quiet on August 22-24, 31, September 5, 9
Quiet to unsettled on August 18, 25, 30, September 1-2, 4, 6
Quiet to active on August 17, 19, 26-29, September 3, 8
Unsettled to active on August 21, September 7, 10, 12
Active to disturbed on August 20, September 11

Solar wind will intensify on August (16-19), 20-22, 28-30,
September 10-12

- Parenthesis means lower probability of activity enhancement.
- Reliability of predictions remains low.

Interesting article about cosmic rays can be found at, .  This article was written by Dr. Tony
Phillips of

On Tuesday, August 14, Dr. Tamitha Skov sent this message and video:

"Dear Tad,

"Another quick note to let you know my latest 'forecast shortie' is
up for viewing on You Tube. However, I can report some good news
since I shot the forecast. A new, albeit tiny active region is
emerging on the Earth-facing Sun and is growing fast! This means
both solar flux and amateur radio propagation might be getting a
much needed boost over the next couple of days. I will be sure to
keep you updated on how this new region is progressing when I shoot
my full length forecast in the next couple of days. Again, a huge
*THANK YOU* to the Patreon members during this pre-launch phase, who
are making these 'forecast shorties' possible!"

Dr. Skov mentioned the Parker Solar Probe, which launched August 12:

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 August 9 through 15, 2018 were 0, 0, 0, 0, 0,
12, and 12, with a mean of 3.4. 10.7 cm flux was 70.3, 69.5, 67.4,
68.1, 67.8, 68.7, and 68.8, with a mean of 68.7. Estimated planetary
A indices were 5, 4, 11, 5, 5, 4, and 14, with a mean of 6.9.
Estimated mid-latitude A indices were 6, 4, 11, 6, 6, 6, and 12,
with a mean of 7.3.


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