‰ Now 18 WPM transition file follows‰

In little more than two weeks the northern hemisphere will see the
Autumnal Equinox, marking the start of Fall north of the equator and
the beginning of Spring south of the equator.  The exact time when
both northern and southern hemispheres are bathed in equal sunlight
is 0951z, September 23, 2007.  Even with few sunspots, this is the
best time for long distance communications between hemispheres.  One
change West Coast stations may notice is the summertime openings in
the evening toward Asia on 20 and 17 meters will be shortening, but
daytime propagation should improve.  For instance, in mid August
from California to Japan, after sunset on the West Coast, around
0300z, the path on 20 meters would open, with steadily increasing
signals until sundown in Japan, around 0930z.  But at the start of
Fall, the path will close a few hours earlier, but with stronger
signals during the day.  From Texas to Brazil, with low sunspot
numbers 15 meters in mid August is not usually a reliable path. But
with one or two sunspots at the equinox, 15 meters becomes very
reliable from the middle of North America to South America.  This
year we began looking at a 3 month moving average of daily sunspot
numbers. We wanted to see if this might be a good balance between
smoothing out the daily variations to help spot trends, but three
months being a short enough period, compared to a 12 month moving
average, that it better reacts to changes.  Last months Propagation
Forecast Bulletin ARLP032 said if we saw an average sunspot number
greater then 20 for August, this would support a trend with the
sunspot minimum centered in March 2007.  Unfortunately, the average
was about half that, at 9R9.  So that makes the 3 month June July
August average 15R4 centered on July, compared to 18R7 for the end
of last month, centered on June.  Monthly averages of daily solar
flux for the same period were 88R9, 80R9, 76R5, 75R8, 79, 77R8,
74R3, 86R3, 84R4, 83R5, 77R7, 72R2, 72R4, 74R4, 73R7, 71R6 and 69R2.
For more information concerning radio propagation, see the ARRL
Technical Information Service web page.  For a detailed explanation
of the numbers used in this bulletin, see the k9la prop page off the
TIS site.  An archive of past propagation bulletins is also
available.  Monthly propagation charts between four USA regions and
twelve overseas locations are on the qst/propcharts link off the
ARRL web page.  Sunspot numbers were 15, 14, 26, 14, 15, 14 and 15
with a mean of 16R1. 10R7 cm flux was 71R6, 70R8, 70R8, 69R4, 68,
68R2, and 67R6 with a mean of 69R5. Estimated planetary A indices
were 6, 7, 11, 23, 12, 6 and 12 with a mean of 11. Estimated mid
latitude A indices were 4, 7, 9, 17, 8, 4 and 10, with a mean of
8R4‚

‰ End of 18 WPM transition file ‚