A large coronal hole on the Sun didn’t affect the HF bands earlier in the last
week as its associated high-speed solar wind stream hadn’t had time to reach
Earth. However, this was probably the quiet before the geomagnetic storm as the
solar material was predicted to reach us at around 450-500km per second sometime
around Friday, 1 June.
As the coronal hole is large, and on the Sun’s
equator, it is perfectly positioned to deposit a mass of charged particles into
the Earth’s magnetic field if its Bz magnetic component is south facing, so
enabling coupling. The upshot is that this weekend is probably going to see very
unsettled geomagnetic and possibly even auroral conditions. And in view of the
hole’s elongated shape we may not see much respite until around Tuesday, 5 June,
or even Wednesday, the 6th. So expect lowered maximum usable frequencies, noisy
bands and poor conditions as the ionosphere is depleted—not really a good
forecast for National Field Day weekend! After Wednesday, 6 June we can probably
expect the bands to recover slowly.
The good news is that summer
propagation conditions are just about with us, so expect the 20m HF band to
remain open longer, perhaps even after sunset, although a lack of decent
sunspots is not really helping. The high-speed solar wind may also adversely
impact sporadic E formation, so for research purposes keep an eye on 10m over
the weekend, but do hear what we have to say in the VHF section about sporadic E
too.
VHF and up:
Weather-wise it looks like more of the same with
high pressure holding on over much of the country, with just the occasional
spell when there are likely to be a few heavy thundery showers in the south,
chiefly up to this weekend. So this week it’s time to dust off the tropo bands
at VHF and UHF and try for those unusually long distance paths, say across the
North Sea or south-east into Europe. Remember that paths across the sea can be
very reliable from coast to coast, but once a portion of the path crosses the
land, the daytime heating can destroy the needed temperature inversions, so they
will only work during the night time.
Apart from the odd bit of rain
scatter from those early thunderstorms, the other mode of choice will be
sporadic E. The season is coming to one of its fabled peaks in early June. Some
say it’s to do with extra meteor showers, others not so convinced. Whatever
provides the fuel, the weather triggers in the lower atmosphere are what
probably controls the location.