Propagation News – 21 June 2015

The sun has been relatively clear this week, apart from sunspot group 2367 that pushed the solar flux index to 136. Geomagnetic conditions have been reasonably quiet with the Kp index mostly at two to three, with two instances of it hitting four. Nevertheless, summer conditions in the northern hemisphere have taken their toll with lower maximum usable frequencies during the day, plus noisy conditions on 80m and 40m, thanks to solar absorption.

The poor HF conditions are quite normal and are believed to be due to a change in ionospheric chemistry with a shift towards more diatomic molecular components and fewer monatomic ones. These are harder to ionise due to the tighter bonding of their electrons, hence the lower overall ionisation and maximum useable frequencies during daylight hours.

This week keep a look out on 20m and 17m, with occasional F2 openings on 15m. Ten metres should continue to show sporadic-E activity at times. There is DX to be had, but you will have to work at it.

The solar flux index is predicted by the USAF to be in the 120s next week, probably thanks to sunspot group 2371, which is rotating around the sun’s limb and shows some promise.

VHF and up propagation

Tropo is often to the fore at this time of the year as warm, dry continental air drifts out across a cool sea and forms sea fog overlain by dry warm air aloft. These are ideal conditions for Tropo, since this can form lengthy surface ducts particularly across the North Sea or down to the south across Biscay to Spain and beyond. Night-time cooling and the effect of onshore sea breezes can couple inland stations to these enhanced Tropo conditions, although tends it to break down as daytime heating gets under way soon after sunrise.

The first part of the week may see elevated inversions due to an area of high pressure extending towards southern Britain from the Azores, so look for Tropo down towards the south west. After midweek, an area of low pressure will introduce more unsettled, showery weather providing some possibility for rain scatter.

Sporadic-E has been good during the past week and strong jet stream activity over Europe has probably helped greatly with this.

During next week, the jet stream activity will be weaker and probably favour more northern paths, check the propagation blog on RSGB Forums for daily updates.

Category: GB2RS Propagation News