Just after we filed the propagation report last Friday we heard that a new large
sunspot had just appeared. This pushed the solar flux index to 72, but more
interesting was the fact that it appeared to have a reverse magnetic polarity to
the rest of the spots in solar cycle 24. This means it may be the second spot
seen of the new solar cycle 25. Time will tell, although this doesn’t
necessarily mean that the new cycle is about to burst into life. We may still be
at sunspot minimum for another 12 months or so.
Also last Sunday saw the Kp
index rocket to seven due to the effects of an incoming high-speed solar wind
stream. This was unexpected and caught space weather watchers unawares. It has
now been linked to a coronal mass ejection that occurred earlier in the week
that scientists didn’t think would impact the Earth. This just goes to show how
hard it is to predict what the Sun is going to do one week in advance! The CME
knocked the bands for six last weekend with a virtual total lack of signals
across HF most of Sunday. With this information we are cautious about predicting
what will happen over the next seven days!
What we can say is that the
Sun is likely to remain fairly spotless, so the risk of solar flares is minimal.
Sunspot number 2720, which did spark a number of flares on Friday, the 24th, has
now rotated out of view, leaving a fairly blank canvas. Maximum usable
frequencies are therefore due to return to seasonal averages, with 20 and
perhaps occasionally 17 metres providing the most HF DX.
We are now
moving towards the autumnal equinox so north-south paths may also start to
improve, but we may have to wait another month or so for an improvement in
east-west paths, such as UK to North America.
VHF propagation
news:
Last Sunday’s 10GHz contest saw some excellent rain scatter propagation
over the UK, with QSOs well up to the 400km mark. But the next spell of weather
is looking much more settled with high pressure on the charts for much of next
week. This could bring tropo back on the agenda for most areas of the country at
times. That makes it a good week to get down to the multimode ends of the bands
on VHF and UHF. Remember, tropo is a relatively long-lasting mode, so there is
plenty of time to make the QSOs, unlike sporadic E, which can be very transient
indeed. Also unlike sporadic E, tropo tends to get better on higher frequency
bands, so 23cm is better than 70cm, which is better than 2m. The sporadic E
season is just about over for this year and, although there can be openings into
early September, they are hard to find and usually short-lasting.
Our
most predictable propagation source, the Moon, is at positive declination all
week and reaches perigee early on Saturday morning so it’s a good week for EME
tests, with long availability and low losses. The Moon follows a 28-day cycle,
where the plane of its orbit moves from south of the equator or negative
declination, to north and back. Its distance from the Earth changes from closest
or perigee to furthest, apogee.
Currently maximum declination and
perigee almost coincide, favouring stations in the northern hemisphere, but this
difference drifts slowly. By 2022 this situation will have reversed and southern
hemisphere stations will get this coincidence.
