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ARRL Propagation Bulletin ARLP018 (2011)

ARLP018 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 18  ARLP018
From Tad Cook, K7RA
Seattle, WA  May 6, 2011
To all radio amateurs 

ARLP018 Propagation de K7RA

Currently seven sunspot groups are visible. The average daily
sunspot number is down more than seven points over the past
reporting week (April 28 to May 4) when compared to the previous
seven days.  Average daily solar flux was off nearly five points
compared to the earlier period.

Sunspot group 1201 first exhibited spots on Thursday, May 5,
although it was first numbered as a plage without spots back on
April 28.  A plage is a bright area on the Sun where sunspots may
appear.  Group 1207 was also new on Thursday.  You can see a daily
summary of sunspot groups, including their total area, at

A solar wind stream from a coronal hole induced a high latitude
geomagnetic storm at the end of April.  Middle-latitude geomagnetic
K indices measured at Fredericksburg, Virginia went as high as 4,
and the April 30 to May 2 middle-latitude A index was 17, 13 and 14.
The planetary K index hit 5 on April 30, and the planetary A index
over the same 3-day period was 24, 19, and 20.  High latitude areas
were more sharply affected, and Alaska's college K index rose as
high as 7, and the same 3-day period saw the college A index at 43,
56 and 37.

A bulletin received at 5:19 PM local time on Friday, April 29 (0019
UTC April 30) from IPS Radio and Space Services in Australia told of
the impending geomagnetic disturbance.  It read, "INCREASED
STREAM FOR 30 APRIL 2011."  You can subscribe to these alerts at

The latest prediction shows more geomagnetic activity coming May
9-10, when the predicted planetary A index is 18, then 15.  The
USAF/NOAA prediction shows a planetary A index of 7 on May 6-8, 18
and 15 on May 9-10, 7 on May 11-12, and 5 on May 13-16, rising again
to 15 on May 17, then 5 on May 18-25, and 12, 22, 18, 18 and 15 on
May 26-30.  The same prediction shows solar flux at 105 on May 6-8,
100 on May 9-13, and 115 on May 14-21.

Geophysical Institute Prague predicts quiet conditions on May 6-7,
quiet to unsettled May 8, unsettled to active May 9, unsettled May
10 and quiet again on May 11-12.

Now that we are in the first week of May, it is time to look at the
3-month moving average of sunspot numbers.  The latest value is
another increase, from 30.1 at the end of January to 35.3 at the end
of February, 55.7 at the end of March, and 72.3 at the end of April.
The monthly average of daily sunspot numbers for April was 80.8,
about the same as March, which was 81.1.

We calculate this average by summing all of the daily sunspot
numbers for three calendar months, then dividing by the number of
days.  Every month we incorporate a new month of data and drop off
one old month. The three-month moving averages of daily sunspot
numbers ending on April 2010 through April 2011 were 22.3, 18.5,
16.4, 20.4, 23.2, 28.9, 33, 35.6, 31, 30.1, 35.3, 55.7 and 72.3.

There has been very little change in the predicted smoothed sunspot
numbers from NOAA/SESC in the past month.  Compare page 14 on the
beginning of April table at with the latest
table, also on page 14, at and only August
through October 2011 have changed, each being one point lower.  Each
of these smoothed values represents an average of a year's worth of
data, either known numbers, or predicted.  For May 2011, about half
of the value is based on predicted numbers.  November 2010 is
probably the latest date that shows a number based on all known
values, as are all previous months.

Bob Scaife, G7PAF offers an interesting propagation tool, the
ability to monitor 20 meter PSK activity from his station in
England.  Go to his web page at and click on the live screen
on the left, which takes you to

Not sure how well this works if multiple bulletin readers try to
hook up at the same time, but Bob says one possible utility is to
send a PSK signal and monitor it from his QTH.

During ten minutes of casual monitoring I copied SQ3LMY, UA9WRG,
CT2FPY, EA3AJY, EA3AHH, YU1LC, CT4RC and I6MBK. Many of those
stations have photos of their radios and antenna systems on QRZ.COM,
and some even have links from their QRZ.COM page to monitor their
station or view them on a web cam as they operate.

Ted Turk, WB8ADA of Euclid, Ohio calls our attention to an item in
the current June 2011 issue of Sky & Telescope, titled "Why the Sun
Had No Spots." Read it at

Jon Jones, N0JK reminds us that sporadic-E season is upon us, and
there was widespread 6 meter E-skip on April 27-28.  On 6 meters on
April 28 from Lawrence, Kansas using an FT-897 and an attic dipole
he worked VE3FZ and VE3KU around 0245z with strong SSB signals.
Sporadic-E activity on 6 and 10 meters should be increasing through
the month of May.

Larry Jones, K5ZRK of Sandersville, Mississippi is very active on 60
meters, and is wondering if his favorite band might be affected by
heavy rain and stormy weather, causing a scattering effect.  He
writes, "The night all the tornadoes hit the Southeast (he is in
south Mississippi, 90 miles from the Gulf of Mexico) which was April
27 (April 28 UTC), I ran a sked with a station on 60 meters for a
new grid square. WB0HBJ was mobile in his 18 wheeler and I was QRP
(about 3.8 watts out) and in the middle of the rain front that
extended from South Mississippi to New York and over to the
Atlantic. WB0HBJ was 800 miles away in EM09 and his signal would
peak above S9 and then drop off rapidly. He was in flat prairie land
so he was not picket fencing due to his terrain. I have noticed this
phenomenon on 60 meters before.  I was in the big band of rain and
WB0HBJ was not. I have noticed that when a station at a distance is
transmitting into the rain his signal has short strong peaks and
then drops out. I use low noise receive antennas on 60 meters that
are directional, along with a preamp. My transmit antenna was a 60
meter vertical with 120 ground radials and with the vertical I could
NOT hear him."

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 28 through May 4 were 71, 70, 76, 57, 51,
77, and 72, with a mean of 67.7. 10.7 cm flux was 110.4, 109.6,
109.5, 106.1, 109.8, 107, and 108.5, with a mean of 108.5. Estimated
planetary A indices were 3, 12, 24, 19, 20, 13, and 6, with a mean
of 13.9. Estimated mid-latitude A indices were 1, 8, 17, 13, 14, 8,
and 3, with a mean of 9.1.


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