Propagation News – 24 May 2015

This week has been a mixed bag in terms of solar activity. As predicted, the beginning of the week was unsettled with the Kp index hitting six on the 19th.

The solar flux index started the week at 120, but by Thursday it had declined to around 106. Next week it is expected to remain in the range 100-110, with the Kp index ranging around two to three. In other words, solar activity will be subdued, but geomagnetic conditions will remain quite settled. This means that the lower HF bands, including 14MHz and 18MHz should be quite lively, but other than sporadic-E openings we shouldn’t expect too much from 21MHz and above.

We are now heading towards summer propagation conditions, where maximum useable frequencies during the day will be lower than they are in winter. But 20 metres, in particular, may stay open longer in the evening. It is possible that by the summer solstice 14MHz may remain open all night.

This is mainly due to a change in the chemical composition of the ionosphere, with more diatomic than monatomic elements that are harder to ionise. These summer doldrums are only alleviated by the prospect of strong sporadic-E openings, although these will be mostly short skip.

VHF and up propagation

Last week we underestimated the potential for stations in the south and west for the intense area of ducting from Portugal down the west coast of Africa. There were some good tropo contacts reported from the UK and Ireland via its northerly extension.

The weather patterns for this week seem to be locked into a persistent pattern of high pressure to the south west of Britain with a ridge of high pressure extending eastwards across southern Britain and Biscay. We’ll be more optimistic about their potential for the southern UK with the possibility of tropo openings over southern Britain and down the west coast of France towards northern Spain or perhaps as far as the Canaries and Azores.

Some weather models show a more active low arriving over the UK later in the week, which may remove the chance of tropo and perhaps replace it with thundery showers and hence offer rain scatter opportunities on the higher bands.

We are well into the sporadic-E season now, and Brazil was worked on 50MHz as far East as JO02 and North to IO93 last week, so check 6m and 4m for Es in the late morning and late afternoon and around 2000 for sporadic-E enhanced trans-equatorial propagation to South America.

Category: GB2RS Propagation News