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.
