QST de W1AW  
Propagation Forecast Bulletin 13  ARLP013
>From Tad Cook, K7RA
Seattle, WA  March 28, 2016
To all radio amateurs 

SB PROP ARL ARLP013
ARLP013 Propagation de K7RA

All of the indicators we track were lower over the past week (March
17-23), compared to the previous seven days. Average daily sunspot
numbers declined from 51.7 to 28.4, and average daily solar flux was
88.8, compared to 98.6 during the prior seven days. Planetary A
index was lower by 3.8 points to 11.9, and average mid-latitude A
index (measured in Wallops Island, Virginia) was down from 12 to
8.6. Lower geomagnetic indices are generally considered a good thing
for HF propagation.

Looking at the record at ftp://ftp.swpc.noaa.gov/pub/indices/DSD.txt
we can see that until March 24, there were no new sunspot regions
since March 17 when there was one, which followed two on the day
before.

Even though our Sun is quiet, there is a seasonal variation which
produces aurora around the Vernal and Autumnal Equinox. (Vernal, or
Spring Equinox was on Sunday, March 20, 2016 and the next Autumnal
or Fall Equinox this year will occur on Thursday, September 22,
2016.)

Spaceweather.com supplied this article a few days ago explaining how
this works:

www-ssc.igpp.ucla.edu/personnel/russell/papers/40/ .

>From NOAA and the USAF, predicted solar flux is 88, 90, 92 and 88 on
March 25-28, 90 on March 29 through April 3, 95 on April 4-11, 90 on
April 12-17 and 85 on April 18-20. Flux values are predicted to go
back to 95 again after April 30.

Also via NOAA, planetary A index for March 25-29 is predicted at 5,
8, 8, 10 and 8, then 5 on March 30 through April 1, then 30, 20 and
8 on April 2-4, 5 on April 5-7, then 10, 5, 15, 24, 22, and 20 on
April 8-13, and 8 on April 14-15. The A index then jumps to 30 on
April 29.

F.K. Janda, OK1HH sends us his geomagnetic forecast, but this week I
want to test a different format. You can see the format we've been
using in past bulletins at
arrl.org/w1aw-bulletins-archive-propagation. See below for a
link to my survey.

Here is the proposed format:

Geomagnetic activity forecast for the period March 25-April 20, 2016

Geomagnetic field will be: 
Quiet on March 25-26, April 1, 14, 17-18
Mostly quiet on March 30-31, April 6, 10, 15-16, 19 
Quiet to unsettled on March 27, 29, April 7, 20 
Quiet to active on March 28, April 5, 8-9, 11, 13 
Active to disturbed on April 2-4, 12

Increases in solar wind are expected on March (30), April 4-6, 9,
11, 14

Remarks: - Parenthesis means lower probability of activity
enhancement.

See examples and vote at, https://www.surveymonkey.com/r/BP9FMTZ .

Ray Soifer, W2RS in Green Valley, Arizona on March 24 sent this info
about working 30 meter grayline propagation yesterday morning:

'Interesting propagation. I heard nothing from VK0EK until half an
hour before sunrise. He peaked 579 around sunrise, then faded and
was gone 30-40 minutes after. Quite a grayline.'

Ray didn't tell me that VK0EK is on Heard Island, but maybe I should
already know that:

vk0ek.org/

The distance from Ray's QTH to Heard Island is 10,945 miles, short
path.

More info about Heard Island, from the Australian government:

heardisland.antarctica.gov.au/

Max White, M0VNG, and earlier David Moore sent this link to an
ultraviolet image of our Sun: bit.ly/1RqC0Ar .

Martin McCormick, WB5AGZ of Stillwater, Oklahoma sent this piece in
a message titled 'Is it F2, or E?'

'One of the first things a person notices when listening to HF
signals coming from afar is a characteristic sound as if someone was
continuously playing with tone controls. It is especially noticeable
on AM signals and the wider the receiver passband, the more
pronounced is the effect. This is known as selective fading because
different frequencies fade in and out at different times.

'The Earth's ionosphere is a shell or several shells of
electrically-charged air molecules and atoms ranging from around 38
miles above us to about 310 miles high. The Sun and cosmic rays
cause the molecules and atoms to loose electrons which gives them a
positive charge. They can reflect radio signals and give us
world-wide radio communication.

'The reflecting layers are the E layer at about 56-93 miles plus the
F layer complex which consists of several shells or layers that
come, go and move around based on Solar and Geo magnetic activity.

'The f2 layer is mostly responsible for short wave communications
and the selective fading is due to more than one layer reflecting
the same signal back to Earth. If the layers happen to be half of a
wavelength apart, one receives two versions of the same signal in
which one version is delayed enough to cause the carrier of an AM or
FM signal to be cancelled out. Mother Nature just turned a normal AM
signal in to a double-sideband suppressed carrier transmission.

'FM signals are also altered. It is possible to receive FM on an AM
receiver by tuning slightly off from center. It is called slope
detection and has existed for as long as there has been FM. If you
tune right on to the frequency, the audio is faint and muffled. F2
propagation, however, can cause a selective fade just below or above
the carrier frequency such that if you are on the center frequency,
the amplitude of the signal matches the deviation and you can hear
fairly good audio as if the signal was both AM and FM. Nature
automatically did that, also but the effect may not last more than a
fraction of a second.

'When sporadic-E is involved, signals still fade up and down but the
E layer acts like a single thin film and there is no selective
fading. Except for fades, signals sound local.'

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

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at,
arrl.org/propagation-of-rf-signals. For an explanation of the
numbers used in this bulletin, see
arrl.org/the-sun-the-earth-the-ionosphere. An archive of past
propagation bulletins is at
arrl.org/w1aw-bulletins-archive-propagation. More good
information and tutorials on propagation are at k9la.us/.

My own archives of the NOAA/USAF daily 45 day forecast for solar
flux and planetary A index are in downloadable spreadsheet format at
bit.ly/1VOqf9B and bit.ly/1DcpaC5 .

Click on 'Download this file' to download the archive, and ignore
the security warning about file format. Pop-up blockers may suppress
the download.

Monthly propagation charts between four USA regions and twelve
overseas locations are at arrl.org/propagation.

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

Sunspot numbers for March 17 through 23 were 66, 29, 26, 26, 25, 13,
and 14, with a mean of 28.4. 10.7 cm flux was 91.6, 90.3, 89.4,
87.6, 88.9, 87.3, and 86.8, with a mean of 88.8. Estimated planetary
A indices were 21, 8, 18, 10, 8, 8, and 10, with a mean of 11.9.
Estimated mid-latitude A indices were 16, 6, 12, 6, 7, 6, and 7,
with a mean of 8.6.