Last week was characterised by reasonably settled geomagnetic conditions and a solar flux index in the low 70s. The settled conditions meant that, despite the ionosphere still suffering from the summer doldrums, there was HF DX to be had. Andy, M0NKR reports working Z81D South Sudan and TX5EG Marquesas Island on Monday as well as a string of North and South American stations on 20m in the early evening. This shows that at this point in the solar cycle quiet geomagnetic conditions can make all the difference.
Next week NOAA predicts the solar flux index will remain in the mid-70s, but we may suffer from the tail end of the geomagnetic disturbance that started on Friday the 4th. This is due to solar matter from a large Earth-facing coronal hole on the Sun. At the time this is being written we don’t know the magnetic characteristics or speed of the incoming solar wind stream so it is hard to be precise. Nevertheless, if its magnetic component is south-facing we can expect it to couple more easily with the Earth’s magnetic field and the K-index could soar as particles are channelled towards the poles.
After a potential initial positive phase we might see maximum usable frequencies to decline and the bands to be noisy, perhaps until Tuesday the 8th. The good news is that a new sunspot has just rotated into view and the rest of next week is predicted to be more settled.
VHF and up
The unsettled weather of the past week will continue through this weekend and into the first half of next week. This means that, like last week, rain scatter is one mode of choice for the GHz bands. As Sunday’s UK Microwave Group contest showed, even light patchy rain can improve 10GHz propagation so be alert, check the beacons and announce activity.
Around the middle of next week there are signs that a weak ridge of high pressure will build towards southern Britain, offering a hint of tropo across southern UK and into the continent. Paths of maximum range are probably going to be across the ridge over Biscay to Spain, Portugal and perhaps even the Canaries or the Azores.
As we approach the end of the sporadic E season, August offers decreasing chances. That said, there have been some very good days well into the second half of the month, especially when the weather is more unsettled and is driven by strong jet streams. Subjectively, these late season events can pop up at odd times, quite often biased towards the middle of the day rather than the morning and evening splits of mid-season sporadic E.
EME path losses start to fall again this week and Moon declination is rising but stays negative until Friday. UK moonrise gets later in the evening as the week progresses, so EME will be a late night or early morning activity all week.