‰ Now 18 WPM transition file follows ‰

Over the past week, sunspot activity has again declined, with the
average daily sunspot number down over 7 points to 18.  Geomagnetic
activity was much more stable this week, with the planetary and mid
latitude A indexes less than half what they were the week before.
The mid latitude A index was actually down to 0 on both weekend
days, May 5 and 6.  The next period of higher geomagnetic activity
is expected around May 25 to 27.  Geophysical Institute Prague
projects quiet conditions for May 11 and 12, quiet to unsettled May
13, unsettled May 14 and 15, and quiet again on May 16 and 17.  The
US Air Force over those same days, May 11 to 17, expects a planetary
A index of 5, 5, 8, 8, 10, 10 and 5, a slightly different scenario.
May 6 was the halfway point between the Vernal, or Spring, equinox
and the Summer solstice.  This weekend, compared to the first day of
Spring, when observing propagation between the center of the United
States and Europe, we expect much shorter openings on the low
portion of the HF spectrum.  This is because the hours of darkness
are best for 80, 60 and 40 meters, and the first day of Spring has a
longer night than what we currently see.  For much of the 24 hour
day the MUF over this path would be higher than in March, except the
six hours between 1430 to 2030z, a period over most of which there
is daylight on both ends of the path.  April 30 through May 3 saw
sunspot numbers ranging from 32 to 38, more than 20 points higher
than the usual daily readings of late.  Several readers reported
better propagation on these dates.  Randy Crews, W7TJ of Spokane,
Washington said that 20 meters was still good for the Pacific and
for stateside stations until 0600z.  Vic Alfonsi, WA6MCL of Corona,
California noted similar propagation until around 0400z.  Probably
the reason for 20 appearing to close earlier in Southern California
than in Washington State was because during Spring and Summer, the
higher latitudes have more daylight.  On May 4, my sunset in Seattle
at 47R7 degrees north latitude was around 0318z, approximately the
same as Spokane, but Southern California at 34 degrees north was 45
minutes earlier at 0233z.  But Seattles longitude is about 4 degrees
to the west of Los Angeles, which is another factor for a later
sunset.  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
link off the TIS web page.  An archive of past propagation bulletins
is also available.  Monthly propagation charts between four USA
regions and twelve overseas locations on the qst/propcharts link off
the ARRL web page.  Sunspot numbers were 33, 19, 18, 14, 12, 12 and
18 with a mean of 18. 10R7 cm flux was 83R1, 82R5, 81, 78R1, 75R7,
73R4, and 72R1, with a mean of 78. Estimated planetary A indices
were 4, 2, 3, 2, 18, 14 and 5 with a mean of 6R9. Estimated mid
latitude A indices were 2, 1, 0, 0, 11, 11 and 3, with a mean of 4‚

‰ End of 18 WPM transition file ‰