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ARRL Propagation Bulletin ARLP015 (2011)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 15, 2011
To all radio amateurs 

ARLP015 Propagation de K7RA

The daily sunspot number reached a new high for Solar Cycle 24 on
Wednesday, April 13, 2011, when it hit 153. I looked back over this
calendar year, and saw that the previous high was 137 on March 8,
2011, 16 points lower than Wednesday.  That week was reported in our
Propagation Forecast Bulletin ARLP010 (see,
which said, "The last time the daily sunspot number was higher than
this was July 7, 2005, when it was 149."

I knew I would have to inspect sunspot numbers prior to that date to
find something higher, which would be on the after-the-peak
down-side of Solar Cycle 23. I went to the
link and only had to look two days earlier to July 5, 2005, when it
was 181. In fact, the day prior to that was even higher, 192.  If
you look at that table, you can see that around the end of June and
early July 2005 the Sun produced a good burst of activity on Cycle
23's down side. You can read a bulletin from early July 2005 at

Apparently at that time we must have assumed that we were already
near a low point in the sunspot cycle, but did not know that five
years later we would still be waiting for a significant increase in
sunspot activity. The bulletin mentions this was the most activity
seen since November 26, 2003.

The average sunspot number for the past week rose 21.6 points, from
68.3 to 89.9.  Average daily solar flux declined though, by 2.6
points to 109.2.

Eight new sunspot groups emerged this week.  There was one new group
on April 7, two more on April 8, another new one on April 11, two
more on April 12, and another new group on Wednesday, April 13, and
yet another on April 14.

Predicted solar flux values from NOAA/USAF for the near term have
increased since the forecast in the ARRL Letter on Thursday.
Predicted solar flux is 125 and 128 on April 15-16, 130 on April
17-19, and 135 on April 20-21 and 115 on April 22-23.  Planetary A
index for the same period is predicted to be 5 on April 15-17, 7 and
10 on April 18-19, and 5 on April 20-27. Geophysical Institute
Prague predicts quiet geomagnetic conditions April 15-17, quiet to
unsettled April 18, active conditions April 19, and unsettled
conditions April 20-21.

On April 12 a solar wind stream hit Earth, causing aurora to be
visible across the northern tier states in the U.S.  The high
latitude College A index hit 39, and planetary A index was 23. The
next period of higher geomagnetic activity predicted by NOAA/USAF is
April 28-29, with a planetary A index of 12 and 15.

Jon Jones, N0JK of Wichita, Kansas reports, "I heard OA4TT (Peru) on
50.135 MHz on April 4 at 2020z. KN5O in LA had OA4TT in strong, was
weak for me.  Perhaps direct F2 to the Gulf Coast then weak Es on to
KS. KN5O is on my great circle bearing to Peru."

Jeff Hartley, N8II of Shepherdstown, West Virginia reports, "There
have been plenty of recent propagation surprises. Last Friday, April
8, K3SWZ near Harrisburg, PA reported to me working DU9RG on 10
meter SSB at 2348z. Sunset here was 2343Z. I didn't find Robin, but
did work first VK6 of Cycle 24 on 10 meters, VK6DU on SSB around
2350z. There were several other eastern VKs and ZLs with good
signals on 10 around the same time.

"I have worked 5N7M around 2300z on 10 CW and he is frequently on 10
and 12 meters very late for him right around the bottom of the band.
I heard him as late as 0044z with a good signal on 12 meters last
night, then he went down to the bottom of 15 CW around 0100z. 5M2TT
(Liberia) was running a big pile-up on 17 meters SSB around 0000z
and was worked on Monday around 2330z on both 10 meters phone and
CW. 15 has been regularly open to JA in our evenings this week and
was still open at 0110z last night. Earlier in the week I had a
'run' of JAs on 15 CW around 2330z with signals up to S9, not an
every day event for this QTH with about the poorest prop to JA in
the USA (beam heading is 330)."

To Japan, Jeff is over 6,800 miles. From K7RA in Seattle it is about
4,900 miles at 300 degrees.

Dick Grubb, W0QM of Boulder, Colorado suggested that in addition to
the STEREO web site at, another view is
at  This image shows the same data that are
displayed at the first site, but flattened out instead of the
spinning globe.

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 the
numbers used in this bulletin, see An archive of past
propagation bulletins is at Find more good
information and tutorials on propagation 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 7 through 13 were 73, 97, 56, 56, 80, 114,
and 153, with a mean of 89.9. 10.7 cm flux was 112.3, 108.7, 105,
104.8, 105.8, 110.3, and 117.8, with a mean of 109.2. Estimated
planetary A indices were 6, 8, 10, 5, 9, 23, and 14, with a mean of
10.7. Estimated mid-latitude A indices were 4, 5, 4, 3, 5, 14, and
10, with a mean of 6.4.


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