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ARRL Propagation Bulletin ARLP012 (2010)

ARLP012 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 12  ARLP012
From Tad Cook, K7RA
Seattle, WA  March 26, 2010
To all radio amateurs 

ARLP012 Propagation de K7RA

Average daily sunspot numbers were down nearly five points this week
to 24.6.  New sunspot group 1057 appeared on March 23, and by March
24 was thirty-eight times its original size.  It covered ten
one-millionths of the solar hemisphere on Tuesday, and on Wednesday
it grew to 380 one millionths.

On Thursday new sunspot group 1058 appeared, and the total area for
both groups expanded to 401 millionths of the solar hemisphere.
Total sunspot area has not been this large since February 8, when
the total was 460 one-millionths.  (The numbers given for Wednesday
are a revision of the numbers for the same day given in yesterday's
ARRL Letter.)

The largest area covered during all of 2009 was 380 on October 29,
followed by 310 on December 18.  March 23 through April 3 2008 was a
period of very strong sunspot activity, and on March 26-28 the area
covered by three sunspots was 520, 510 and 410 one-millionths of the
solar surface.

The Spring Equinox was last Saturday, March 20, and HF radio
conditions are good, with quiet geomagnetic conditions.  NOAA and
the U.S. Air Force predict solar flux of 88 for today, March 26, and
89 for March 27-31.  This is higher than the average solar flux for
this week, 84.2, and last week, 87.6, and the week before, 78.6.

Our reporting week for data at the end of this bulletin is always
Thursday through Wednesday, and we haven't reported a weekly average
solar flux above 89 since Propagation Forecast Bulletin ARLP007,
which had 90.6 on February 11-17.

NOAA predicts a bit more geomagnetic activity (but not much!)
rising from a planetary A index of 5 on March 26 to 7 on March 27
and 8 for March 28-31.

Geophysical Institute Prague expects quiet to unsettled conditions
March 26, quiet March 27-29, quiet to unsettled March 30-31, and a
return to quiet for April 1, the day that NOAA predicts a planetary
A index of five.  Last week for the first time we presented the
trailing 50-day average of daily sunspot numbers, 27.34.  This week
it is 28.18.

This weekend is the CQ World Wide WPX SSB Contest.  HF conditions
should be good.

Harry Gross, KC2FYJ of Mineola, New York wrote in with questions
about the numbering of sunspot groups, which is different than the
sunspot number.

Harry asked, "First, what's the scheme (e.g. why is a particular
group referred to as 1055, for example)?  Is it the 55th group seen
in 2010 perhaps?  Or is it something more esoteric?"

"Second, how do you decide that a particular group is 'returning?' I
presume it's because it's circled the Sun and is returning on the
other side again.  However, how can you be certain it's the same
group, since there is a wide (but now narrowing, thanks to STEREO)
area were we can't observe on the far side of the Sun?  Couldn't the
group have disappeared, and a new one formed in its place?"

The sunspot groups are numbered consecutively, starting with 0, and
when group 9999 emerges, the next new group will be 0 again.  I have
also seen them expressed as five digits, so the current sunspot 1057
this week would be 11057.

If you go to and look at the Archives
section in the upper right, change the date to June 15, 2002 and
click View.

Note the numbers on the solar image on the left side are up in the
9990+ range.  Now click "Forward" on the upper right to advance the
date to June 16.   Note the piece about "Sunspot Zero."  I don't
know why the image doesn't show sunspot 2.  Perhaps it emerged, was
numbered, then faded in less than a day.  Perhaps that is also why
paging backward does not produce sunspot 9999.

It looks like we went from group 321 to 1057 over the past seven
years.  If sunspot groups were to continue emerging at the same
rate, which has been slow recently, it could take us until April 14,
2095 to reach group 0 again, a pretty rough guess.  That will be
less than a month and a half short of my birthday at age 143,
perhaps around Solar Cycle 32.  I get my information second hand
regarding which groups are returning, and do no direct observation

I think they can be recognized possibly from magnetic signatures,
and also the timing.  It takes about 27.5 days for a complete solar
rotation, but it varies with latitude, because the Sun is a big ball
of (very hot) gas.  At the equator the period is less than 26 days,
and toward the poles it is about 36 days.  A few references on this
can be found on the web at,, and

John Buttolph, N1JB of Lake Elmore, Vermont wrote in with
information on a Navy map (see showing
letter designations for each time zone.  Z or Zulu time as we all
know is for the prime meridian, or Greenwich Mean Time.  But when it
is 1200Z, it is 0400U on the West Coast, and 0700R in Newington,

Click on the map for greater detail.  John wrote, "The world is
divided into 24 time zones, and each is assigned a letter.  The U.S.
Navy, as well as civil aviation, uses the letter 'Z' (phonetically
'Zulu') to refer to the time at the prime meridian.  Proceeding
eastward from Greenwich, the zones are designated with the Latin
alphabet letters beginning with 'A' or 'Alpha' time. [I do not know
why the prime meridian time zone was given the last letter of the
alphabet rather than the first!] Not all letters of the alphabet are
used. For various reasons having to do with population centers and
other cultural reasons, the time zones do not strictly follow the
meridian lines, and some time zones vary by the half-hour."

Matt Pastorcich, KJ4NBM of Mobile, Alabama was surprised to work
VK2JB, John Baylis in Hobart, Tasmania last Saturday, March 20 at
1246z using PSK31 on 20 meters.  That isn't a promising time for
that 9,300 mile short path route, and Matt was even more surprised
to learn that John was running 2 watts into a loop antenna made for
80 meters.  Matt uses a vertical.  A better time would be
0500z-1000z, or even better would be 30 meters around 0730z-1300z or
40 meters 0800-1200z.

Wolf Urban, DK8MZ in Fuerstenfeldbruck Germany wrote to comment on
15 meters.  Nearly two weeks ago, on Saturday, March 13 he worked
Rob Struppeck, V73RS on the southernmost island of Kwajalein Atoll.
Wolf uses a TH3 Yagi at 12 meters high, and said that Rod had a very
robust S9 signal on 15 meter SSB.

Wolf thinks this is a hopeful sign, and said, "I can't remember when
I last heard such a strong signal from that part of the world, (the
most difficult one for the Europeans on the high bands) even during
periods of much higher solar activity!"

Don't miss K9LA, Carl Luetzelschwab's excellent monthly propagation
column in WorldRadio, available free online at,  Just right-click on the image
of the front cover to download the PDF, and find Carl's column on
ionosphere modeling on page 36.
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 18 through 24 were 28, 24, 25, 25, 17, 26,
and 27 with a mean of 24.6. 10.7 cm flux was 85.8, 84.4, 83.5, 84.8,
82.5, 83.9, and 84.4 with a mean of 84.2.  Estimated planetary A
indices were 5, 4, 7, 2, 2, 2 and 3 with a mean of 3.6. Estimated
mid- latitude A indices were 4, 2, 5, 0, 0, 0 and 2 with a mean of


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