Propagation News – 12 July 2015

| July 10, 2015

The sun was remarkably well-behaved during the first half of the week with few solar flares of note. The Kp index remained around one or two, apart from two excursions to three on the 7th and 9th. The solar flux index was, as predicted, around 125-135 all week.

Conditions will remain very similar next week with the solar flux index predicted to be about 115-130. Geomagnetic conditions are predicted to be quiet. However, there is an active sunspot just around the limb that was probably the cause of a coronal mass ejection observed on Monday the 6th that may cause problems later in the week.

The critical frequency as measured by the Chilton Ionosonde at midday has been around 6.3MHz, giving a predicted maximum useable frequency over a 3,000km path of about 17.9MHz.

Many people have commented on the poor HF conditions recently, but this is mainly seasonal. Good long-range HF propagation will return in the autumn. Meanwhile, keep an eye on 20m at night as the band is often open to DX at this time of year.

VHF and up propagation

There was plenty of sporadic-E and tropo about last week and these two main propagation modes are going to remain in full swing. The weather charts indicate a ridge of high pressure over southern Britain for much of the week, which will favour tropo style openings. As in the past couple of weeks, propagation can be particularly good over sea paths.

The required temperature inversions are almost a permanent feature across water in high summer as warm, dry continental air drifts out across a cool sea surface. It is worth remembering that there is nearly always a shallow nocturnal surface inversion, which forms by dawn to give some lengthy, but temporary, tropo paths inland, but these soon disappear when the sun comes up and the heating destroys the inversion.

Sporadic-E has been active on several occasions last week and with a fairly strong jet stream over northern Europe, there is every chance that the magic of sporadic-E will recur, particularly across to Eastern Europe and the Baltic. Try checking for sporadic-E mid-morning and late afternoon on 6m. The potential for paths across the Atlantic is also quite high and worth checking each evening, since the jet stream remains strong across to the States through this week.

Category: GB2RS Propagation News