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ARRL Propagation Bulletin ARLP023 (2000)

ARLP023 Propagation de K7VVV

QST de W1AW  
Propagation Forecast Bulletin 23  ARLP023
From Tad Cook, K7VVV
Seattle, WA  June 9, 2000
To all radio amateurs 

ARLP023 Propagation de K7VVV

A large coronal mass ejection on June 6 is raising havoc with HF
propagation. Geomagnetic conditions were rough on Wednesday, with K
indices of 3 and 4, but the big effect was measured on Thursday,
when the planetary K index was 7 at 0900 and 1200z, followed by 6 at
1500z. The planetary A index for Thursday was 53, while the College
A index (in Alaska) was 79. This indicates a severe geomagnetic
storm, which should disrupt HF communications but may provide
interesting auroral communication opportunities for VHF enthusiasts.
Regarding visible aurora effects, the chances over North America are
declining on Friday morning, although earlier in the day there was
an intense aurora visible over Asia.

To add to the excitement, there was another coronal mass ejection on
Wednesday, June 7. The latest word has solar wind providing another
disruption on Saturday, June 10.

Planetary A index should rise on Friday to 75, then drop to 40 on
Saturday, 25 on Sunday, 18 on Monday and 15 on Tuesday. Solar flux
is expected to rise over the same period, to 185 on Friday, 190 on
Saturday, 200 on Monday and 210 on Tuesday. Solar flux is expected
to peak over the short term around 245 on June 16.

Last week's bulletin mentioned monitoring WWV for the latest solar
and geophysical numbers, and both WB6RIB and W9LYN wrote to suggest
the URL of for the latest
text of the WWV bulletin that appears at 18 minutes after every

WB7QXU wrote to inquire about the significance of the various
numbers presented weekly in this bulletin. A basic explanation is
presented periodically, but has not appeared since last October. We
repeat it here now.

Amateur Radio operators who use HF generally like increased sunspots
because they correlate with better worldwide radio propagation. When
there are more sunspots, the sun puts out radiation which charges
particles in the earth's ionosphere. Radio waves bounce off of these
charged particles, and the denser these clouds of ions, the better
the HF propagation. When the ionosphere is more dense, higher
frequencies will reflect off of the ionosphere rather than passing
through to space. This is why every 11 years or so when this
activity is higher, 10 meters gets exciting. 10 meters is at a high
enough frequency, right near the top of the HF spectrum, that radio
waves propagate very efficiently when the sunspot count is high.
Because of the wavelength, smaller antennas are very efficient on
this band, so mobile stations running low power on 10 meters can
communicate world wide on a daily basis when the sunspot cycle is at
its peak.

The sunspot numbers used in this bulletin are calculated by counting
the sunspots on the visible solar surface and also measuring their
area. Solar flux is measured at an observatory in British Columbia
using an antenna pointed toward the sun tuned to 2.8 GHz, which is
at a wavelength of 10.7 cm. Energy detected seems to correlate with
sunspots and with the density of the ionosphere.

Other solar activity of concern to HF operators are solar flares and
coronal holes, which emit protons. Since the charged ions in the
ionosphere are negative, a blast of protons from the sun can
neutralize the charge and make the ionosphere less reflective.
These waves of protons can be so intense that they may trigger an
event called a geomagnetic storm.

The Planetary A index relates to geomagnetic stability.
Magnetometers around the world are used to generate a number called
the Planetary K index. You can hear the Boulder K index updated
every three hours on WWV, or by calling 303-497-3235.

A one point change in the K index is quite significant. A K index
below 3 generally means good stable conditions, and above 3 can mean
high absorption and poor reflection of radio waves. Each point
change reflects a big change in conditions.

Every 24 hours the K index is summarized in a number called the A
index. A one point change in A value is not very significant. A full
day with the K index at 3 will produce an A index of 15, K of 4
means A of 27, K of 5 means A of 48, and K of 6 means A of 80. You
can find an explanation of these numbers on the web at

The number reported here is the Planetary A index, which is a
worldwide average based on the K readings from a number of
magnetometers. The numbers reported on WWV are the Boulder K and A
index, measured in Colorado. Generally the higher the latitude of
the measuring station, the higher the K and A indices reported.
This is because the effects of geomagnetic instability tend to
concentrate toward the polar regions of the globe.

Currently we are near the peak of the solar cycle, so conditions are
generally better because of the increased ionization of the
ionosphere. But along with the increased sunspots comes more solar
flares and coronal holes, producing disturbed conditions.

Sunspot numbers for June 1 through 7 were 128, 126, 125, 139, 132,
133 and 145 with a mean of 132.6. 10.7 cm flux was 148, 187.2,
165.9, 169.7, 171, 186.4 and 180.3, with a mean of 172.6, and
estimated planetary A indices were 12, 10, 12, 12, 26, 16 and 14,
with a mean of 14.6.


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