Propagation News – 1 October 2017

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.

Category: GB2RS Propagation News