Last week saw the solar flux index
touch 90 as large sunspot group 2671 rotated into the centre of the solar
surface. But, unfortunately, the predicted unsettled geomagnetic conditions,
caused by a high-speed coronal hole solar wind stream, pushed the K index up to
six early in the week. This hampered DX by pushing maximum useable frequencies
downward. The unsettled conditions continued until at least Wednesday the
23rd.
Sporadic-E did put in an appearance for
last weekend’s International Lighthouse and Lightship Weekend, bringing short
skip to the 40m band. This meant that many UK amateurs were able to contact
special event stations on 7MHz that would have otherwise been unworkable, other
than by ground wave. This was a good example of how Sporadic-E clouds over the
UK can often bring advantages on the lower HF bands, such as 40, 30 and 20MHz,
while we normally associate Sporadic-E with 28MHz and above.
This weekend there is a chance that a
small coronal hole may threaten us with more unsettled geomagnetic conditions.
Conditions may also be unsettled mid week due to the effects of another coronal
hole, but could improve for next weekend’s HF SSB Field Day.
Next week sunspot 2672 will be fully
facing Earth. This has already produced an M-class solar flare and a number of
lesser C-class flares, so we may be in for a bumpy ride. However, NOAA predicts
the Solar Flux Index will decline to the high 70s.
Maximum useable frequencies over a
3,000km path are still peaking around 17MHz during the day, with occasional DX
openings on the 17m band.
For this week there is still a chance
of limited Tropo options as a ridge of high pressure develops over southern
Britain. As usual for Tropo conditions it is the higher VHF, UHF and GHz bands
that fare best and, unlike with Sporadic-E, the openings can be long lasting,
especially over sea paths. Night-time is often best over the land, since there
will sometimes be a shallow surface temperature inversion to add to the one
brought by the high pressure, giving longer paths.
The second half of the week may see the
return of low pressure in the north particularly, but it will increase the
chances of some rain scatter on the GHz bands.
Sporadic-E is now nearing the end of
its main season and at the moment the jet streams look to be fairly weak,
meaning Sporadic-E will struggle to make many appearances.
As we head into the week, a new
Atlantic jet stream will appear over Scotland and Scandinavia, giving a chance
of northern Sporadic-E paths into Scandinavia and across to the States. About
this time there will also be a broad upper ridge over France and Germany, which
may also help with Sporadic-E.
There are only minor meteor showers
this week, so continue to look around dawn for the best random meteor scatter
contacts. We have negative Moon declination this week and apogee on Wednesday.
The moon doesn’t get above 20 degrees elevation after Monday and path losses
will be high. For VHF operation, the low moon elevation means high ground noise
in the beam of the antenna.