ARRL

ARRL Propagation Bulletin ARLP021 (2003)

SB PROP @ ARL $ARLP021
ARLP021 Propagation de K9LA

ZCZC AP21
QST de W1AW  
Propagation Forecast Bulletin 21  ARLP021
From Carl Luetzelschwab, K9LA
Ft Wayne, IN  May 23, 2003
To all radio amateurs 

SB PROP ARL ARLP021
ARLP021 Propagation de K9LA

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

During the reporting period (Friday May 16 through Thursday May 22),
solar activity was low. Geomagnetic field activity was generally
quiet to unsettled during the first half of the period, and then
increased to active to minor storm at the end of the period due to
increased solar wind (from coronal hole activity) that reached Earth
on Wednesday.

Solar activity is forecast to be low for the next three days.
Geomagnetic field activity for the next three days is forecast to
have roughly a 40 percent probability of being active, with slightly
quieter conditions as we move into the weekend.

Last week's Propagation Forecast bulletin ARLP020 included the
comment that "disturbed conditions occur more often when the solar
cycle has passed the peak and is headed down." Historical data
indeed shows that geomagnetic storms (the G in the WWV report) occur
more frequently during the decline of a solar cycle, whereas big
solar flares can cause polar cap absorption events (the S in the WWV
report).

Radio blackouts (the R in the WWV report) occur more frequently at
the peak of a solar cycle. So the good news is that big solar flares
probably won't be causing too many problems in the foreseeable
future.

That leaves the bad news. The plot covering the peak of Cycle 21 to
the present (shown on the ARRLWeb version of this bulletin at
http://www.arrl.org) shows the smoothed sunspot number versus the
number of days in the month when the planetary A index (Ap) was less
than or equal to 7 (signifying quiet conditions). The thin green
line following the spiky Ap data is a trend line to more clearly
indicate what's happening.

The web plot confirms that the declining phase of a solar cycle is
the period with the most geomagnetic field activity (where the trend
line is lowest). So for the next year or two we'll have to put up
with a much higher probability of disturbed conditions. At least
there's some seasonal relief to this, with the summer and winter
months quieter than the months around the equinoxes.

The web plot also shows that the quietest period (when the trend
line is highest) is a year or two after solar minimum. Your author
looks back fondly on the consistently excellent 160-meter
propagation conditions during the winters of '96 and '97 when much
DX was worked with his modest station - those conditions will be
back.

For contest enthusiasts, this weekend is CQ World Wide WPX CW. For a
general picture of propagation for the contest, let's look at SSNe
(the effective sunspot number - the sunspot number that forces the
model of the F region to a best fit to real-time worldwide F region
ionosonde data).

Eyeballing the SSNe plot at http://www.nwra-az.com/spawx/ssne24.html
shows SSNe to be in the neighborhood of 60 and heading down (as of
Thursday evening). Plugging this value into your favorite
propagation prediction software will show that 20 and 40-meters (and
75-meters to an extent) will be the workhorse bands for the contest.

15-meters will be right on the borderline between good and not good,
and which way it goes will depend on the day-to-day variation of the
ionosphere and the geomagnetic field activity.

10-meters is going to be tough going for the contest, with low
probabilities of any consistent F region openings to the major
overseas ham population areas (Europe and Japan). This is not
surprising, as Cycle 23 is definitely in its decline.

A good piece of advice for 10-meters (and even for 15 and 20-meters)
is to monitor the NCDXF beacons. If this isn't feasible, keep an eye
on the trend of SSNe during the contest (it is updated hourly).
Since it's tied to real-time F region ionosonde data, it will
reflect to a certain degree the impact of geomagnetic field activity
on the F region (for example, note the nice short duration increase
in SSNe early on Thursday due to the effect of the solar wind speed
increase the day before).

If SSNe gets up to 80 or so, that may mean 15-meters will be
productive, and it may even signal the possibility of a 10-meter
opening. And don't give up completely on 10-meters, as we still
could have domestic QSOs via sporadic E (CQ WPX format is anybody
work anybody) and even trans-equatorial propagation into South
America.

Regardless of the propagation conditions for CQ WPX CW, jump in and
have some fun. Contests are an excellent way to pick up new states,
countries, and zones for your WAS, DXCC, and WAZ awards.

Sunspot numbers for May 15 through 21 were 97, 97, 81, 79, 75, 77,
and 79, with a mean of 83.6. 10.7 cm flux was 99.2, 102.6, 102.4,
109, 114.7, 117.1, and 119.3, with a mean of 109.2. Estimated
planetary A indices were 23, 9, 9, 10, 12, 12, and 20, with a mean
of 13.6.
NNNN
/EX