ARLP014 Propagation de K7RA

ARLP014 Propagation de K7RA

Propagation Forecast Bulletin 14 ARLP014
From Tad Cook, K7RA
Seattle, WA April 2, 2015
To all radio amateurs

ARLP014 Propagation de K7RA

This bulletin is being posted a day early because ARRL headquarters
is closed tomorrow April 3 for Good Friday.

This week’s numbers have average daily solar flux and sunspot
numbers headed in opposite directions.

For the March 26 through April 1 period, average daily sunspot
numbers fell 6 points to 77.9, and average daily solar flux
increased 13.3 points to 135.7, compared to the previous seven days.

Geomagnetic indices were quieter, with average daily planetary A
index declining 10.7 points to 8.7, and average daily mid-latitude A
index dropping 6.6 points to 7.7.

We saw four new sunspot regions over the past week, one each on
March 26, 28, 29 and April 1.

The latest short term prediction for solar flux has 130 and 135 for
April 2 and 3, 125 on April 4 to 6, 130 on April 7 and 8, 140 on
April 9, 145 on April 10 to 13, 140 on April 14, 135 on April 15 to
18, 130 on April 19, and 125 on April 20 to 22. Then solar flux
sinks to a low of 120 on April 23 to 25 and hits a high of 150 on
April 28 before declining again.

Predicted planetary A index is 12, 20 and 15 on April 2 to 4, 8 on
April 5 to 8, 5 on April 9 to 11, then 15 and 30 on April 12 and 13,
20 on April 14 to 16, 15 on April 17, 20 on April 18 and 19, 12 on
April 20, 5 on April 21 and 22, 8 on April 23 and 24, 25 on April 25
and 29 on April 26 and 27.

At 2328 UTC on March 31 the Australian Space Forecast Centre issued
a geomagnetic disturbance warning. Increased geomagnetic activity is
expected due to a high speed solar wind from a coronal hole. The
geomagnetic activity forecast is for active conditions on April 2
and unsettled conditions April 3.

At the beginning of April we can look back at various averages of
daily sunspot numbers ending on March 31.

For monthly averages, the period since December 2014 shows a steady
decline. The monthly averages for daily sunspot numbers in the past
four months were 120, 101.3, 70.7 and 61.7. Our three month moving
averages of daily sunspot numbers centered on February 2014
(averaging for the period January 1 through March 31) through
February 2015 were 146.4, 148.4, 129.6, 118.4, 112.8, 109.2, 115.6,
108.4, 107, 104.7, 107.8, 98.2 and 78.1.

What does this lower activity mean in practical terms for HF? It
means that on average, the HF bands, particularly at the higher end
(20 to 30 MHz) will be open less often and less reliably. Of course
we can see big differences from day to day.

Using W6ELprop to get a general picture, on today’s date last year
we would see a path from Atlanta to Germany on 15 meters with an A
rating (75 percent or better chance of communication) from 1230 UTC
to 2330 UTC with signals at 29 db above a half microvolt at 1230 to
1800 UTC, then increasing to 33 db at 2030 to 2100 UTC and 38 db at
0030 UTC.

For today, although there is a small possibility of an opening after
1200 UTC, (especially at 1330 UTC) the opening begins with a 50
percent chance of reliable communication at 1500 UTC with signals at
just 16 db and gradually increasing to 20 db at 2000 UTC.

This propagation model has a funny anomaly though, with possibly
stronger signals on 20 and 17 meters than last year during early
morning hours on the Atlanta end. I don’t know why this is.

For instance, last year at this time on 20 meters at 1130 UTC
(around sunrise) we see signals at 12 db with an A rating, declining
to 7 db at 1330 UTC and 6 db from 1400 to 1530 UTC. But for today we
see 20 meter signals at 1130 UTC with an A rating at 15 db,
declining to 10 db at 1430 to 1530 UTC. But signals really pick up
at 2230 UTC (around sunset in Atlanta) with signals at 37 db last
year and 25 db this year.

For a graphic comparison of the latest four solar cycles, check .

At are many other comparisons.

For more information concerning radio propagation, see the ARRL
Technical Information Service at For an explanation of the
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 March 26 through April 1 were 103, 109, 82, 73,
56, 53, and 69, with a mean of 77.9. 10.7 cm flux was 136.1, 137.8,
145.6, 144.5, 133.6, 128.1, and 124.1, with a mean of 135.7.
Estimated planetary A indices were 8, 9, 9, 14, 5, 9, and 7, with a
mean of 8.7. Estimated mid-latitude A indices were 7, 7, 9, 11, 5,
7, and 8, with a mean of 7.7.


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