Long-range HF propagation showed signs of picking up this week. Whether this was
due to the slow change to better autumnal propagation, or from having a short
period of fairly settled geomagnetic conditions, is debatable.
The settled conditions didn’t last
long though as the Kp index was up to four on Thursday due to plasma from a
high-speed solar wind stream. The interplanetary magnetic field had a strong
south-facing component meaning it coupled with the earth’s magnetic field and
plasma flooded in. This brought poor HF conditions once again, with little being
heard outside of Europe on Thursday morning.
Next week the solar flux index is
predicted to be in the range 90-100, with more periods of unsettled geomagnetic
conditions at times. Optimum working frequencies on 3,000km paths during
daylight are now about 18 or 21MHz on southerly routes, such as UK to South
Africa. On easterly paths to the US, 14 or 18MHz are more likely to bring
contacts. It is similar story on the short path to Japan, where 18MHz remains
favourite, with occasional openings on 21MHz.
The Chilton Ionosonde indicated a
critical frequency of 6.425MHz at midday on Wednesday, showing that 40 metres is
not really a viable option for inter-G communications. 80 metres may be better,
but suffers badly from daytime absorption.
VHF and up propagation:
After last week’s excitement of the
Perseids meteor shower it’s back to more normal VHF conditions, with just the
tail end of the shower enhancing meteor scatter paths on the low VHF
bands.
Early in the week there will be a
weak ridge of high pressure over the UK, so some enhancement of tropo conditions
is possible, chiefly overnight. There are two main high pressure centres this
week; one over Scandinavia and the other near the Azores, and these are likely
to persist through the week. This could mean some slightly enhanced tropo
conditions up and down the North Sea as well as down towards the Azores.
The trough of low pressure between
these two highs may produce some heavy showers resulting in possible GHz bands
rain-scatter paths within the UK.
It’s still worth checking for
sporadic-E on 50 and 70MHz in both the late morning and late afternoon peak
operating windows and, with jet stream activity over the Pyrenees, the first
paths to look at should probably be those towards EA and CT.
http://rsgb.org/main/blog/news/gb2rs/propagation-news/2015/08/14/propagation-news-16-august-2015/
