Last week saw the solar flux index climb into the high 80s. Our prediction
that the weekend’s ionosphere might be unsettled was partly correct, as the
effects of a coronal hole pushed the K index to three on Sunday, but this
quickly recovered. We are now seeing a shift from predominantly summer
ionospheric conditions to autumnal. As the ionosphere starts to cool it
experiences a shift away from predominantly diatomic molecules to more monatomic
species. These are easier to ionise and, as a result, we can expect to see
better conditions and potentially higher maximum usable frequencies as we move
into September and October.
Roger, G3LDI reports that 15 metres was open
to the US on Wednesday afternoon, which bodes well for the future. And G0KYA’s
tests with 5W and WSPR on 20 metres resulted in him being picked up in Alaska
around UK sunset, which was also very positive.
Now the bad news. A very
large coronal hole on the Sun threatens to push the K index higher this weekend
as a high speed solar wind impacts the Earth. This may result in noisy bands and
suppressed MUFs, which could impact this weekend’s HF SSB Field Day
operations.
NOAA predicts the solar flux index will be in the low to mid
70s next week. Once the coronal hole effects die away we may then get some more
settled conditions. Either way, keep an eye on HF as you might be pleasantly
surprised.
And now the VHF and up propagation news:
The end of the main Sporadic-E season
is approaching rapidly now and, despite some 6m and 4m openings last Wednesday
to Eastern Europe, such events will become much rarer in September. Check the
beacons on 10m and perhaps 6m, but in general it’s back to meteor scatter for DX
on the lower VHF bands now.
The prospects of Tropo should improve as we head into the quieter
mellow days of autumn and high pressure becomes more commonplace. We should see
a ridge of high pressure lasting until mid-week when the patterns flip to become
dominated by low pressure. This means that Tropo will be worth investigating at
first and with the ridge extending over much of the country most parts of the UK
will get something out of this period. The changeover to low pressure-dominated
weather patterns from mid-week is less useful, although if there are any
significant spells of heavy rain or thundery showers, then rain scatter on the
GHz bands is a possibility.
At this time of the year, very humid
ex-tropical moisture from the States can become part of the train of low
pressure systems that cross the Atlantic and make heavy rain more
likely.
There are only minor meteor showers
this week, so continue to look around dawn for the best random meteor scatter
contacts.
Moon declination is
increasing again, going positive on Friday. Losses fall and Moon windows get
later and longer as the week progresses, with the best operating times very late
at night or early morning.
