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ARRL Propagation Bulletin ARLP011 (2010)

ARLP011 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 11  ARLP011
From Tad Cook, K7RA
Seattle, WA  March 19, 2010
To all radio amateurs 

ARLP011 Propagation de K7RA

On March 6-9 we got a taste of the bad old days from 2008-2009, when
there were frequent stretches of zero sunspots.  After March 9,
activity picked up, and we hope there is no end in sight to the
much-welcome sunspots.

This week, March 11-17, average daily sunspot numbers increased from
the previous period from 12.4 to 29.4.  Thursday March 18 had a
repeat of Wednesday's sunspot number, 28.  We've looked at various
moving averages over the past few years to try to smooth out the
bumps and spot trends, and another way to look at it would be the
trailing 50-day average of daily sunspot numbers, which on March 18
was 27.34.  The fifty day period is purely arbitrary.  For the
eighteenth of each month, going back to April 18, 2009 the trailing
50 day average was 0.48, 2.44, 5.42, 7.4, 3.14, 0.48, 4.42, 7.42,
8.98, 17.44, 26.12 and 27.34.  We can see a positive trend there.

On March 11 new sunspot group 1055 emerged, which followed the
arrival of group 1054 the day prior.  1055 lasted a very brief
period, and group 1056 appeared March 17.  Today group 1054 is
fading over the western limb, and it is hard to tell from the STEREO
mission if some of the active magnetic areas just over the horizon
are new or returning sunspots, or not even fully formed sunspots at
all.  One uncertain area looks to be a day or less away, and beyond
that, the only thing visible is on the other side of the narrowing
unseen area on our Sun's far side.  At 1045z Friday morning that
blind spot covers less than 11.7% of the Sun's total area.

So far in March the average daily sunspot number is 24.2.  For all
of every month of March since the end of the last century, the
average (1999-2009) was 100.5, 203.6, 166.7, 154.3, 119.7, 81, 41,
21.3, 9.8, 15.9, and 0.77.  Sobering, isn't it?

The Vernal Equinox, marking the beginning of Spring in the Northern
Hemisphere and Fall south of the equator occurs tomorrow, March 20
at 1732z, 10:32 AM West Coast Pacific Daylight Time, or 1:32 PM EDT.
The weeks prior to and following both the Vernal and Autumnal
Equinox are favorable to HF propagation.

The latest forecast from Thursday's reading by NOAA and the U.S. Air
Force show solar flux remaining in the mid-eighties for the next
week, and planetary A index staying around five, until a brief
increase to six on March 28-29.  Geophysical Institute Prague sees
quiet conditions for all of March 19-25.

A few comments this week from readers:

"I am fortunate to have #1 DXCC but in recent years have
concentrated on 6 meters and the low bands, with lots needed on 17m
and above.  The last month has shown a great improvement in my new
ones, with one on 17m, 3 on 15m, 13 on 12m and two new ones on 10m
(5N and IS0).  Lots more to go for this OT.  73, Pat, W5OZI."
Mark Lunday, WD4ELG Greensboro, NC - FM06be, wrote, "0300 UTC on 15
Mar, 2 hours after local sunset, I worked ZK3YA and FO8RZ on 12
meters.  Makes me wonder if the activity is as much a function of
the perception of conditions (which makes amateurs go on the higher
bands) as opposed to the conditions themselves.  It's not THAT far
into the cycle yet, but everyone is itching to get on 15, 12, and 10

W3HKK in Johnstown, Ohio wrote, "Tuning around on 160 the evening of
March 14 showed exceptionally strong SSB signals into Ohio from
Virginia and the Carolinas, with very low band noise.  Didn't think
much of it until the next morning at 1045z when I again heard
booming SSB signals from the early morning 160 meter crowd. So I
tuned down to CW, and low and behold heard KL7RA (Kenai, Alaska)
calling CQ, and then a sked in 9 land, for over half an hour,
working assorted east coast stations along the way.  His signals
were a solid 569. Not many takers but he was there to be had."
A note before closing, in case anyone is confused, when we say 1030z
that is the same as 1030 UTC or 1030 Greenwich Mean Time.  It is
also the same as 3:30 AM Pacific Daylight Time or 6:30 AM Eastern
Daylight Time.
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 a detailed
explanation of the numbers used in this bulletin, see An archive of past
propagation bulletins is at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for March 11 through 17 were 31, 36, 32, 30, 28, 21,
and 28 with a mean of 29.4. 10.7 cm flux was 84.2, 89.6, 91.8, 89.4,
86.4, 85.2, and 86.7 with a mean of 87.6.  Estimated planetary A
indices were 9, 9, 4, 6, 3, 4 and 7 with a mean of 6. Estimated mid-
latitude A indices were 9, 6, 2, 2, 2, 3 and 5 with a mean of 4.1.


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