ARRL

ARRL Propagation Bulletin ARLP011 (2007)

SB PROP @ ARL $ARLP011
ARLP011 Propagation de K7RA

ZCZC AP11
QST de W1AW  
Propagation Forecast Bulletin 11  ARLP011
From Tad Cook, K7RA
Seattle, WA  March 9, 2007
To all radio amateurs 

SB PROP ARL ARLP011
ARLP011 Propagation de K7RA

On March 1 sunspot 944 was pointed straight at us. It was a small
sunspot, followed a few days later by another small spot, 945.
Sunspot 945 is visible in photos from March 5, just behind 944, but
both spots seemed to disappear a day or two later, before they would
have rotated off the visible solar disk. Now the Sun is blank, and
the sunspot number is zero.

The minimum non-zero sunspot number is 11, and lately sunspot
numbers move from 0 to 11 to 23 or 24, and back to 11. No solar
activity is expected for the next few days, so we will probably see
at least several days with a zero sunspot number. Geomagnetic
conditions are expected to remain quiet, at least until Monday or
Tuesday, March 12-13. The USAF predicts a Planetary A index for
March 9-15 of 5, 5, 7, 15, 20, 15 and 10. Geophysical Institute
Prague predicts quiet conditions for March 9-10, quiet to unsettled
March 11, active geomagnetic conditions for March 12, unsettled to
active March 13, unsettled March 14 and quiet to unsettled March 15.
A recurring solar wind stream is predicted for Monday, March 12, and
should produce the expected geomagnetic instability.

New predictions for the solar minimum are coming frequently of late.
The monthly smoothed sunspot number forecast for the rest of 2007
from the NOAA Space Environment Center in the weekly Preliminary
Report and Forecast has been adjusted again, the third time since
the first of the year. The revised tables are on page 9 of issue
1635, and page 10 of issues 1640 and 1644 at,
http://www.sec.noaa.gov/weekly/index.html (the table in 1640 is
mislabeled at the bottom of the page as 03 January when it is really
06 February). Currently they predict a solar minimum for right now,
with a smoothed sunspot number of 6 for March and April 2007, then
7, 8, 10, 11, 13, 16, 18 and 21 for the remaining eight months of
this year.

As mentioned in past bulletins, these are smoothed sunspot numbers,
averaged over a year. So the prediction of 6 for this month means
that if the prediction is accurate, at the end of September 2007 you
could take half the average of daily sunspot numbers for that month,
add it to half the average of daily sunspot numbers for September
2006, add the total to the monthly averages for each month in
between, divide by 12, and get 6 as the result.  Currently we're
seeing higher values, with an average daily sunspot number of 19 for
last week, 19.6 the week before, 14.6 for the week prior to that,
6.3 for the previous week, and 28.7 for the week prior to that,
which was February 1-7.

You can see an explanation of the method for determining the 12
month smoothed sunspot number at,
http://www.ngdc.noaa.gov/stp/IONO/sunspot.html.

Jim Headrick, W3CP of Stanfield, Oregon sent in a different
prediction from the Australian government. It has the solar minimum
centered on September 2007, and you can see it at,
http://tinyurl.com/2ymk92. Note that the NOAA version mentioned
previously ends in December 2007, but the one Jim sent goes through
2008 and 2009 as well. By the way, I don't know how long Jim has
been a ham, but he was born early in sunspot cycle 15, and I'm sure
he hopes to see the new cycle 24 all the way through. See a page of
all the 20th century sunspot cycles at,
http://wm7d.net/hamradio/solar/historical.shtml.

We heard from another ham enjoying low power operations at the
bottom of the cycle. Bill Raiford, NI4Y of Fredericksburg, Virginia
says he operates 10 watts on 20 meters from his car. Bill says,
"Last week I worked VK2KM and this week I worked VK2GWK from my 10
watt mobile station. No, VK isn't rare DX, but just the thought of
10 watts propagating from my vehicle in VA to VK land is quite
amazing. I am at 194 countries from my mobile."

Dave Green, VE5TLY of Ottawa, Ontario sent an interesting link from
the BBC concerning the new STEREO (Solar Terrestrial Relations
Observatory) satellites which will soon be observing coronal mass
ejections traveling through space in 3D. Read the article at,
http://news.bbc.co.uk/2/hi/science/nature/6411349.stm.

If you would like to make a comment or have a tip for our readers,
email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL
Technical Information Service at,
http://www.arrl.org/tis/info/propagation.html. For a detailed
explanation of the numbers used in this bulletin see,
http://www.arrl.org/tis/info/k9la-prop.html. An archive of past
propagation bulletins is at, http://www.arrl.org/w1aw/prop/. Monthly
propagation charts between four USA regions and twelve overseas
locations are at, http://www.arrl.org/qst/propcharts/.

Sunspot numbers for March 1 through 7 were 11, 23, 11, 24, 27, 26
and 11 with a mean of 19. 10.7 cm flux was 74.8, 75.5, 73.3, 72.5,
71.9, 71.9, and 72.9, with a mean of 73.3. Estimated planetary A
indices were 11, 5, 2, 3, 8, 18 and 14 with a mean of 8.7. Estimated
mid-latitude A indices were 7, 4, 0, 4, 6, 14 and 12, with a mean of
6.7.
NNNN
/EX