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ARRL Propagation Bulletin ARLP006 (1998)

ARLP006 Propagation de K7VVV

Propagation Forecast Bulletin 6  ARLP006
From Tad Cook, K7VVV
Seattle, WA  February 6, 1998
To all radio amateurs

ARLP006 Propagation de K7VVV

This solar cycle seems to be in the doldrums. Average sunspot
number last week was less than half what it was the week before,
and average solar flux was down about nine points. The ninety day
average for solar flux drifted down from 97 to 96, and flux values
were below that level on every day, indicating a general downward
trend over the short term.

Even more disturbing though is the regression in solar activity
over the past few months. Average solar flux for November, 1997
was 99.5, for December it was 98.7, and for January it was 93.4.
This new cycle was already showing progress slower and later than
expected, and now it seems to be gradually retreating rather than
progressing. The NOAA prediction for those three months was that
the smoothed solar flux would be 102, 109 and 116, and this month
would be 122.

Last week geomagnetic activity was running a bit higher. The worst
day was Friday, January 30, when Planetary A index was 19 and the
K index went as high as five.

For the short term the solar flux is expected to gradually
increase to around the mid-nineties by February 10, then drift
back around 90 after mid-month, then possibly mid-nineties or
above by February 22, then back to 90 by month's end. No
geomagnetic disturbances are predicted, although unsettled
conditions could return around February 26-28. The predicted solar
flux for February 6-8 is 86 for each day.

W6PYK wrote to ask if we take into account the sun's rotational
period in forecasting conditions. The paragraph above is based
upon projections by NOAA which use the solar rotation to try to
predict when active regions may come into view again.

N0EG wrote to point out an interesting website at, operated by the DX Listener's Club of Norway.
This site has some nice graphs of sunspot numbers, solar flux and
planetary A indices, as well as daily solar data, all selectable
in either English or Norwegian. N0EG wanted to know what the
references such as "K indices: 3322 3211" meant. Each digit is a
single K index value for each three hour period in a 24-hour day.
The grouping in four digits has no significance, except that each
group represents 12 hours out of a day.

Sunspot Numbers for January 29 through February 4 were 71, 41, 37,
25, 23, 39 and 26 with a mean of 37.4. 10.7 cm flux was 93.6, 91,
89.4, 90.7, 89.1, 88.8 and 89.1, with a mean of 90.2, and
estimated planetary A indices were 8, 19, 9, 7, 3, 3, and 8, with
a mean of 8.1.


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