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ARRL Propagation Bulletin ARLP031 (1998)

ARLP031 Propagation de K7VVV

Propagation Forecast Bulletin 31  ARLP031
From Tad Cook, K7VVV
Seattle, WA  July 31, 1998
To all radio amateurs

ARLP031 Propagation de K7VVV

Solar activity was a bit higher this week, with average solar flux
up nearly 14 points and sunspot numbers higher by about six points.
Last Thursday, July 23 had a planetary A index of 37, exactly like
the previous Thursday.  A few days later geomagnetic indices had
settled down, and after Saturday conditions were quite stable.
Solar activity is still lower than most forecasters predicted for
this point in the solar cycle, but perhaps we can take some cheer by
comparing current conditions with a year ago.  Average solar flux
this week is about 45 points higher than the average solar flux for
the same week last year.  You can peruse last year's propagation
bulletins if you look on the ARRL web site at

Over this weekend, Friday through Sunday, predicted solar flux
should decline to 112, 110 and 108, and planetary A index should be
around 10 each day.  Solar flux is expected to bottom out just above
100 around August 9-13, then rise above 110 after mid-month and back
around 120 after August 20.  Look for disturbed conditions around
August 17-21, with the highest A and K indices around August 19 and
20.  This is due to a recurring coronal hole rotating back into a
position which should affect earth.

A good way to visualize the rotation of the sun with sunspots and
coronal holes drifting across the visible solar disk is to look at
the Marshall Space Weather bureau 10 day solar animation site on the
web at

Radio telescopes have finally located the SOHO spacecraft rotating
slowly near its original position.  It is not far off course, and it
still may be possible to establish contact and get it working again.
If not, it might be feasible to put similar instruments in another
proposed orbital craft called Triana, the proposed craft that is
supposed to beam a live picture of the earth back to a web page on
the internet.

The loss of SOHO has been a big disappointment for solar observers.
Things went awry when ground control turned off a gyroscope, hoping
to extend the life of the instrument.  When a previously unknown
software error caused the craft to spin out of control, craft
computers looked to the gyroscope for emergency guidance and due to
the lack of signal misjudged the position in relation to the sun.
When this happened, solar panels turned away from the sun and SOHO
lost power.

In August, particularly later in the month, we may start to see some
Fall conditions on HF with higher usable frequencies during
daylight. 20 meters should be the most reliable band for long range
communications, but look for occasional openings on 15 meters and
trans-equatorial conditions on 10 and 12 meters.

Interesting events continued on VHF this week, with six and two
meter openings from Hawaii to the West Coast.  There was a report of
six meter propagation from South America to Israel from PY5CC, and
N5JHV worked Japan after 0030Z on six.

Sunspot Numbers for July 23 through 29 were 129, 110, 85, 80, 109,
116 and 115 with a mean of 106.3.  10.7 cm flux was 115.4, 125.2,
121.7, 119.1, 119.5, 121.3 and 119.5, with a mean of 120.2, and
estimated planetary A indices were 37, 22, 16, 6, 6, 6, and 6, with
a mean of 14.1.


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