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ARRL Propagation Bulletin ARLP021 (2006)

ARLP021 Propagation de K9LA

QST de W1AW  
Propagation Forecast Bulletin 21  ARLP021
From Carl Luetzelschwab, K9LA
Fort Wayne, IN  May 26, 2006
To all radio amateurs 

ARLP021 Propagation de K9LA

Carl Luetzelschwab, K9LA, is filling in this week for regular
reporter Tad Cook, K7RA.

With respect to space weather, the past week has been relatively
quiet.  Solar activity was very low (the largest flares were several
Class B events) and geomagnetic field activity was quiet to
unsettled (the planetary A index stayed below 10).  The Sun did have
some sunspots this week -- Regions 884, 885, and 886 dotted the
solar disk, but they weren't very active.  There are also
indications that old Region 882 may be coming around again.

The forecast for the next several days, Memorial Day weekend, is for
continued low solar activity and quiet to unsettled geomagnetic
field conditions.  The probability of major flares or significantly
elevated K indices is low.  As a result, there shouldn't be any
major propagation surprises.  The 40, 30, 20, and 17 meter bands
should provide the bulk of domestic and DX contacts, but keep an eye
out for sporadic E activity.

This weekend is the CQ World-Wide WPX CW contest.  The format for
this contest is everyone works everyone, with prefixes as
multipliers.  Although the QSO point structure favors DX contacts,
the fact that prefixes are multipliers means domestic contacts can
play an important role -- which in turn means domestic propagation
can play an important role.  Being at the end of May says the
probability of sporadic E helping out on 10 meters, and maybe even
on 15, for domestic contacts is quite high.  We've already had some
good sporadic E propagation on 10 and 6 meters in the past week or
two -- hopefully it will continue.  Look for sporadic E openings
around the late morning hours and then again in the early evening
hours.  For true DX contacts, though, 40 and 20 meters will likely
be the 'bread and butter' bands for this contest at solar minimum.

Propagation Tidbit -- As we move into summer, we'll see a decrease
in daytime F2 region MUFs.  This is in large part due to a change in
the composition of the atmosphere at F2 region altitudes.  Summer
brings decreased ratios of O (atomic oxygen) to O2 (molecular
oxygen) and of O to N2 (molecular nitrogen).  Since the electron
production rate at F2 region altitudes depends on the concentration
of O, whereas the electron loss rate is controlled by O2 and N2, a
decrease in O to O2 and O to N2 ratios leads to lower daytime MUFs
in the summer.

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,  An archive of past
propagation bulletins is at

Sunspot numbers for May 18 through 24 were 0, 15, 29, 30, 32, 48 and
44 with a mean of 28.3.  10.7 cm flux was 73.3, 75.3, 76.2, 77.5,
83.1, 84.2, and 83.7, with a mean of 79.  Estimated planetary A
indices were 16, 8, 7, 7, 8, 7 and 4 with a mean of 8.1.  Estimated
mid-latitude A indices were 11, 7, 5, 4, 6, 4 and 3, with a mean of


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