ARRL

ARRL Propagation Bulletin ARLP044 (2008)

SB PROP @ ARL $ARLP044
ARLP044 Propagation de K7RA

ZCZC AP44
QST de W1AW  
Propagation Forecast Bulletin 44  ARLP044
From Tad Cook, K7RA
Seattle, WA  October 24, 2008
To all radio amateurs 

SB PROP ARL ARLP044
ARLP044 Propagation de K7RA

Visible sunspots continued last week for eight days straight, the
longest continuous period of sunspot visibility since the twelve
days of March 23 through April 3 2008.

For this week a solar wind stream is headed our way, and may strike
October 28.  The NOAA Space Weather Prediction Center places the
predicted effect slightly later, with a predicted planetary A index
for October 27 through November 1 at 5, 8, 12, 15, 10 and 5.
Geophysical Institute Prague predicts quiet conditions for October
24, quiet to unsettled October 25, quiet October 26-27, quiet to
unsettled October 28, unsettled to active October 29, and unsettled
October 30.

Both predictions place the disturbance between this weekend's CQ
Worldwide SSB DX Contest (October 25-26) and the ARRL CW Sweepstakes
a week later.

Vince Varnas, W7FA of Portland, Oregon reports that on Sunday
October 9, at 1930-2100z, 10 meters was open to Latin America.  He
worked (I assume on phone) Brazil, Uruguay, Argentina, Honduras and
Costa Rica mostly with S9 signals.  This is a bit late in the season
for sporadic-E skip, and this was two days after the recent run of
sunspots.  Vince believes he is too far north for trans-equatorial
propagation and that it must have been via the F2 layer.

The day before, Francisco Chubaci, PU2MLC of Sao Paulo, Brazil
received a very strong 6 meter signal on October 18 from NP4A in
Ponce, Puerto Rico.  This was between 2300-0100z, and signals were a
very strong 40 dB over S9.

Mack Beal, W1PNR of Jackson, New Hampshire asked about new Cycle 24
sunspots compared to sunspots from old Cycle 23.  He heard they
change polarity, but wants more detail on how this is determined.

Yes, they do change polarity.  We can see this by looking at
magnetograms of the Sun.  Go to the web site,
http://sohowww.nascom.nasa.gov/data/realtime/realtime-mdi_mag-1024.html.
This site has an archive of recent images.  Below the top section is
a "List of Individual Images" for the current month.  The leading
characters in the filename represent year, month and day, and the
last four indicate time in UTC.  There is a link at the very bottom
called "List of all individual images" which leads to an archive for
the whole year.

You can look at images from October 10-17 to see that string of
recent sunspots.  If you click on the 10-15-2008 0941z file, you can
see a big spot in the northern hemisphere with black on the right,
white on the left.  It is tracking from left to right, and if this
were below the equator, it would be an old Cycle 23 spot.  But this
sunspot is a Cycle 24 sunspot, and note that spots above and below
the equator have opposite polarity.  So a Cycle 23 sunspot north of
the equator would have black on the left and white on the right.

Go back to the list page, and click on the "List of All Individual
Images" link on the bottom of the page so we can see spots between
March 23 and April 3 mentioned at the top of the bulletin.

Note that these spots are black on the right like the recent spots,
but it is difficult to tell which side of the equator they are on,
so the cycle status may be indeterminate.

The new cycle is said to begin when there are more new cycle spots
than old, but I have no idea over what time frame.  If we look at
only the spots from last week, since no Cycle 23 spots appear, this
must mean that Cycle 24 has started, unless we look over a longer
time period and determine that Cycle 23 spots are not in the
minority.

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 web page 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/.

Instructions for starting or ending email distribution of this
bulletin are at http://www.arrl.org/w1aw.html#email.

Sunspot numbers for October 16 through 22 were 24, 11, 0, 0, 0, 0,
and 0 with a mean of 5.  10.7 cm flux was 71.9, 70, 69.2, 69.6,
69.2, 68.8, and 67.7 with a mean of 69.5.  Estimated planetary A
indices were 4, 2, 1, 6, 2, 3 and 5 with a mean of 3.3.  Estimated
mid-latitude A indices were 5, 1, 1, 5, 2, 3 and 5 with a mean of
3.1.
NNNN
/EX