ARRL

ARRL Propagation Bulletin ARLP011 (2005)

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 18, 2005
To all radio amateurs 

SB PROP ARL ARLP011
ARLP011 Propagation de K7RA

During this reporting week, sunspot counts were higher while
geomagnetic indices were lower, a nice combination for HF operators.
Average daily sunspot counts rose nearly 25 points to 60.7, and
average daily solar flux increased nearly 22 points to 107.8.

This is a nice time to have a few more sunspots, because we are
approaching that magic time of the equinox. Despite the old urban
legend, the task of balancing an upright egg does not become easier
at the equinox, but these days are nice for HF propagation.
Sunlight is more evenly distributed across the northern and southern
hemispheres, and it should be completely equal this Sunday, March 20
at 1233z. That is the moment of the vernal equinox on the first day
of spring for the northern hemisphere, and autumnal equinox for the
southern hemisphere.

Sean Fleming, K8KHZ sent some observations about this sunspot cycle,
and suggested that the solar flux won't be going any lower.
Actually we are probably a couple of years away from the bottom.
The latest SEC prediction for smoothed 10.7 cm radio flux shows a
smoothed value of 70 around September 2006 through April 2007. In
the same March 9, 2005 prediction, they show the smoothed sunspot
cycle minimum around December 2006 and January 2007.

You can see the prediction in the back of the latest Preliminary
Report and Forecast in a PDF document at,
http://www.sec.noaa.gov/weekly/pdf/prf1541.pdf. This same chart
predicts a smoothed sunspot number of 22 for April 2005, but doesn't
show the cycle rising from the bottom to a smoothed number of 21
until December 2007. This must mean that after declining to minimum,
the solar cycle is not expected to rise back to the current level
until early 2008.

Remarks in a recent bulletin about the biggest sunspot cycle of all,
Cycle 19 back in the late 1950s, drew many email message with the
same comments from hams who were brand new in the hobby back then,
and active on either 10 or 6-meters. Many wrote, "I thought it was
always going to be like this!"

The outlook for the very near term is for sunspots and solar flux to
decline very gradually from current values until March 26-29, then
rise back to current activity around April 6-11. Geomagnetic
conditions should be slightly unsettled for March 18-19, but
otherwise quiet after that.

Jon Jones, N0JK sent an email about a major trans-equatorial opening
on March 9-10 from the United States to South America on 6-meters.
He wrote, "Here in Kansas had ZP6CW in for almost 2 hours
(0030-0230z). I worked Doug, ZP6CW for a new one! Doug reported over
50 USA QSOs on 6-meters and was spotted from W1, W3, W4, W5 to W7
(Arizona, Utah), W8, W9 and W0. CE (XQ3SIX), CX, LU and PY also
worked many in the states."

Jon continues, "6-meter Es single and double hop Es for over 12
hours. An amazing opening, both for the long duration Es in March
and the TEP links to South America this far along in cycle 23's
decline."

Marvin Bloomquist, N5AW sent in similar comments concerning the same
6-meter opening. In addition to ZP6CW (Paraguay), he noted XQ3SIX
(Talagante, Chile) working many W stations, as far north as W9 and
out west to W6/W7.

With quiet geomagnetic conditions at mid-latitudes, there were still
periods when geomagnetic activity was strong in the Arctic. The
College K index reading from Fairbanks Alaska reached 6 on March 14
and again on March 17. Look at the awesome aurora photos at
http://spaceweather.com/aurora/gallery_01mar05.htm.

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

For more information concerning radio propagation and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at,
http://www.arrl.org/tis/info/propagation.html.

Sunspot numbers for March 10 through 16 were 70, 59, 67, 77, 49, 58
and 45 with a mean of 60.7. 10.7 cm flux was 101.6, 104.9, 110.1,
113.8, 111.5, 108.2 and 104.6, with a mean of 107.8. Estimated
planetary A indices were 13, 6, 4, 6, 21, 4 and 6 with a mean of
8.6. Estimated mid-latitude A indices were 10, 3, 2, 4, 12, 3 and 4,
with a mean of 5.4.
NNNN
/EX