Propagation News – 16 April 2017

| April 13, 2017

Last week was a mixed bag again in terms of HF propagation. While the solar flux index was stuck in the mid 70s, geomagnetic disturbances due to coronal hole effects made their mark. The K index hit four on Tuesday and brought a pre-auroral enhancement. With the critical frequency over the UK almost reaching 7MHz, this meant the maximum useable frequency over 3,000km just exceeded 21MHz for a brief spell. But by Wednesday conditions were much worse and even 14MHz was struggling to open.

Due to the Easter holiday, this report is being prepared a day early, but we’ll try to give you a feel for how propagation may pan out next week.

Firstly, NOAA predicts the solar flux index will rise over the next week into the 80s and even low 90s. But as usual HF conditions will be mainly governed by geomagnetic effects.

The first half of the week may be unsettled due to a high speed solar wind stream. This may see the K index rise to five with associated auroral conditions. We may then have a little respite for the rest of the week.

Looking forward to International Marconi Day on Saturday the 22nd of April, HF conditions may be settled. But they then get much worse with NOAA predicting a K index of up to six from Sunday the 23rd onwards due to another recurrent coronal hole.

On the face of it, the next week looks very promising with high pressure dominating the charts in several models for the next week or so. This is quite a common feature at this time of the year and the only problem, so far as Tropo goes, is that these Spring highs can often have cold dry air near the surface under the inversions, which is generally seen as a poor contributor to an ideal Tropo event.

Mid April is when we can often expect super refraction propagation across the North Sea to start making itself felt by an increasing number of continental beacons becoming audible on the VHF, UHF and microwave bands. Warmer air blowing out across the cold sea can lead to the formation of some very strong ducts.

With EME, the early part of the week sees an early morning, waning, moon with high moon-path degradation. As the week progresses the moon will also climb higher in the sky to be visible until around lunchtime. As the moon declination improves (in the northern hemisphere) the degradation will also reduce.

Meteor shower activity will start to build towards the end of April and the Lyrid meteor shower will peak on the morning of the 22nd of April. This coincides with a weak crescent moon so it may also result in a good visual display. The Lyrids can sometimes show in higher than normal reflections, so it may be worth trying for that elusive locator.

Category: GB2RS Propagation News