Propagation News – 29 March 2015

Last week’s solar eclipse was a great opportunity to try out some propagation experiments. Many listeners reported the enhanced reception of distant medium wave stations at the time of maximum eclipse as the D layer of the ionosphere became less absorbing. The other data are currently being analysed for a feature in RadCom.

This week has shown how hard it can be to accurately predict solar conditions. NOAA had indicated that it expected the solar flux index to be around 100-110. In fact, at the time of writing, it was edging towards 140, thanks to a host of new sunspots. These, coupled with relatively quiet geomagnetic conditions with the K index often around two, have brought excellent HF conditions with the bands wide open to many parts of the world.

This week, predictions place the solar flux index in the range 130-140, but with continuing unsettled geomagnetic conditions. The K index could reach as high as five on Sunday 29th, due to a particle stream from a recurrent coronal hole, and four towards the end of the week. This suggests that HF conditions could be variable, with auroral-type conditions at times, which could impact signals on polar paths. Maximum usable frequencies are likely to be depressed as well.

VHF and up propagation news

This week is starting fairly windy and unsettled, with high pressure to the south of the UK, which is almost good enough, but unfortunately insufficient to develop a robust temperature inversion, and certainly not in the northern half of the UK; so expect initially marginal to flat tropo conditions.

Any hopes of slightly better conditions rest upon a weak ridge developing over southern England in the second half of the week. A recent model predicts a stronger high over Britain by Friday, with some prospect of lift conditions. So don’t give up on this week, and remember there’s always aircraft scatter to give us DX on the higher bands.

The 2015 Es season should be getting underway soon, typically in mid April from the UK on the lower VHF bands, and the 22nd to 23rd April Lyrids meteor shower is only three weeks away.

The Moon reaches apogee on Thursday meaning highest path losses and declination is decreasing giving shorter Moon windows for UK EME operators in the coming week.

Category: GB2RS Propagation News