This week saw a perfect example of how the sun affects HF propagation. As we predicted last week, a high-speed solar wind stream hit the earth on Tuesday. This pushed the K-index to five as the incoming plasma had a south-facing Bz field that enabled it to more easily couple to the Earth’s magnetic field.
The result was that on the afternoon of Tuesday the 3rd, 10 metres was alive with signals during the initial positive phase of the subsequent geomagnetic storm. Stations from Columbia and the Falklands were very strong as the maximum usable frequency headed past 40MHz on southerly paths. Even stations in Belgium could be heard via backscatter on 28MHz.
By Wednesday the incoming solar wind was still fierce at up to 750 kilometres per second. The noon critical frequency as measured by the Chilton ionosonde was 10.15MHz, giving a predicted maximum usable frequency over a 3,000km path of 36MHz and pushing the K-index to five. Usually the secondary phase of a geomagnetic storm sees critical frequencies plummet, but that didn’t seem to happen with this event.
Next week, NOAA predicts that the solar flux index will be in the range 110-125 with a continued risk of geomagnetic disturbances, especially on the 13th and 14th. This season stills remains a good time to be on HF.
VHF and up propagation news
With some very good tropospheric conditions still fresh in our memory from last weekend, it’s probably going to be the complete opposite for a while. Deep lows will pass by the far north-west and produce generally windy conditions across much of the country during the coming week. There is, however, a possibility of high pressure over the continent that may just lift conditions over the south of England at times in the second half of the week. This may connect the southernmost counties into what will probably be some very good tropo within Europe.
For meteor scatter enthusiasts, the Taurids meteor shower, which has a broad peak from 5 to 12 November, may provide some large fireballs and long, strong trails.
For EME operators, declination is now negative, reaching its lowest next Saturday, meaning short windows with increasing losses as the Moon reaches apogee, its furthest point away from Earth, on Sunday.Hits : 808