Last week was a mixed bag in terms
of HF propagation. With the solar flux index just into the 90s, amateurs were
able to take advantage of the improving autumnal conditions. At times, maximum
usable frequencies over a 3,000km path were stretching up to and beyond 21MHz,
with openings to the US being reported on 15 metres. But a geomagnetic
disturbance due to a coronal hole on the sun saw the K-index soar to six on
Wednesday, with associated auroral warnings.
At noon on Wednesday the critical
frequency over the UK managed to hit 8.125MHz, as measured at RAF Fairford. But
an incoming solar wind stream above 600km/s, with a south-facing Bz magnetic
component, took its toll. By late evening Wednesday predicted MUFs over 3,000km
were below 14MHz. If the solar wind has a south-facing Bz magnetic component it
is more likely to couple with the Earth’s magnetic field and cause disruption.
An even more unsettled ionosphere saw this continue on Thursday as the K-index
hit a very stormy seven.
Next week, NOAA predicts the solar
flux index will be in the mid-90s and geomagnetic conditions may be more
settled. This could mean more fun on the HF bands.
As we move into October we can
expect HF conditions to improve on east-west paths. Make sure you are using the
latest smoothed sunspot number of 22 with VOACAP-based prediction programs for the best
results.
VHF and up:
The weekend and beginning of the
coming week looks likely to be affected by low pressure, with potentially windy
conditions in the north. The unsettled weather will also mean that GHz bands
rain scatter could be possible.
High pressure is set to move in
towards midweek and should place tropo at the top of the operating list through
to the end of the week. Models differ slightly in the exact placement of the
high, but most allow the centre to drift east across southern Britain, while
leaving a linking ridge back to another large high north of the Azores. What
this means for the VHF bands from the UK is some fairly good tropo, especially
into the near continent and across Biscay towards Spain and perhaps farther
south. Unfortunately, northern Britain remains closer to low pressure and
probably misses out on the main tropo action, although recent activity from CMEs
highlights the possibility of aurora if the sun continues to be disturbed.
There are no significant meteor
showers, this week, so continue to look before dawn for the best random meteor
scatter contacts on the lower VHF bands.
Moon declination goes
positive again on Thursday, so expect lengthening Moon windows and falling
losses this coming week as the Moon heads for perigee a week tomorrow.
