[HCDX] Propagation report

["Mike Terry" <miketerry73@xxxxxxxxxxxxxx>]

Solar data for the period from 15 to 21 November , compiled by Neil Clarke,
G0CAS.

Solar activity was very low on the 17th and the 21st and low on the
remaining days. Only five C-class solar flares took place during the period,
the largest being a C5/SF on the 19th. No effect on propagation occurred
from these flares. The solar flux averaged 104 and varied little day to day.
The 90-day solar flux average on the 21st was 106, that's one unit down on
last week. X-ray flux levels averaged B1.9 units. Geomagnetic activity was
quiet until the 20th, when, due to a small coronal hole on the sun's
northern hemisphere, activity increased to unsettled levels with an Ap index
of 18 and 16 on the 20th and 21st. On the 15th and 18th the Ap was only 3
units. The average was Ap 8. The ACE spacecraft saw solar wind speeds
increase from 320 kilometres per second to 650 by the 21st. Particle
densities were low except on the 20th, when they increased to 15 particles
per cubic centimetre. Bz varied between minus 8 and plus 8 nanoTeslas except
for the 20th, when it varied between minus and plus 13 nanoTeslas.

It took the ionosphere some time to recover from the storms of the previous
week, but the low geomagnetic figures brought an expected, though rather
patchy, improvement in HF propagation. This was particularly marked over
east-west or trans-polar paths, with some strong trans-Atlantic openings
reported. All continents were again workable up to 28MHz. However, the
shorter days in the northern hemisphere are now leading the higher bands to
close earlier. This will now continue until after the winter solstice. The
low geomagnetic levels meant that almost no VHF aurora was reported. The
Leonids meteor shower, which peaked on the 19th, proved disappointing, with
unexpectedly low meteor rates reported.

The solar forecast. This week solar activity is expected to be low to
moderate. The solar flux should be in the 120s, but a decline should start
to take place towards the weekend of 4 and 5 December. Geomagnetic activity
is expected to be mostly quiet, although unsettled conditions could take
place after midweek. MUFs during daylight hours at equal latitudes should be
about 27MHz for the south and 24MHz for the north. The darkness hour lows
are expected to be about 8MHz. Paths this week to South Africa should have a
maximum usable frequency, with a 50 per cent success rate, of around 31MHz.
The optimum working frequency, with a 90 per cent success rate, should be
about 24MHz. The best time to try this path should be between 0800 and
1600UTC.

The RSGB propagation news is also available in a Saturday update
http://www.keele.ac.uk/depts/por/update.htm , posted every Saturday evening
and for more on propagation generally, see
http://www.rsgb.org/society/psc.htm.

(RSGB)



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