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Propagation News – 17 July 2022

We had another rocky journey last week in terms of HF propagation. The solar flux index climbed from 137 last Saturday to 165 by Thursday, which should have brought better conditions. But the Earth was plagued again by unsettled geomagnetic conditions, with the Kp index hitting four on Monday, the 11th, and five on Tuesday, the 12th. This was due to an enhanced solar wind, which hit a velocity of 564km per second and had a strongly south-pointing Bz magnetic field. This allowed it to more efficiently couple with the Earth’s magnetic field allowing plasma to pour into the polar areas.

HF conditions were typical for this time of year, with lower maximum frequencies during the day, compared with winter, but higher MUFs at night.

Daytime F2-layer MUFs over a 3,000km path have generally been between 18 and 21MHz during the day, falling to 10 to 14MHz at night. But the early hours of the 11th were particularly good with the MUF staying above 15-16MHz.

The moral of the story is if you should wake up in the middle of the night, check out your HF radio, you might get a pleasant surprise.

Sporadic E remains the dominant mode for 10 metre propagation, bringing strong short-skip contacts around Europe and the potential for multi-hop DX.

Next week NOAA predicts that the SFI will decline to the 130s, although their predictions have not been too accurate recently. We can likely expect reasonably unsettled geomagnetic conditions with a minimum Kp index of three.

With the current sunspot activity, the solar wind is unlikely to remain calm for long and more solar flares are very likely.

VHF and up:

The current very hot and humid weather means that tropo is fairly widespread. This can be a significant feature over surrounding seas as hot dry air from the land drifts out across a cooler moist layer of air near the sea surface, giving almost continuous strong tropo.

This affects paths across the North Sea, the English Channel and the Irish Sea as well as farther afield across Biscay and south past Portugal. The Mediterranean is a hot spot of tropo during the summer, and long east-west paths are possible if you take a rig on holiday.

Closer to home, these favourable tropo conditions come to an end by midweek as low pressure moves into place over the UK and brings a chance of heavy thundery showers, with associated GHz band rain-scatter chances.

Sporadic E is still prevalent in mid-July and the jet stream pattern probably favours paths to the Baltic and Scandinavia. A high Kp index tends to suppress Es chances and this has been rather volatile lately. It’s worth checking this periodically, and the silver lining of a higher Kp index is a chance of auroral propagation.

As we move towards the end of the month, all four, relatively small, July meteor showers are still active. The largest of these is the Southern Delta-Aquariids, peaking on 30 July 2022 with a medium Zenithal Hourly Rate of 25. Remember that random meteor activity is always there and is best around dawn.

Moon declination goes positive on Monday and we passed perigee last Wednesday, so Moon visibility time and path losses will increase this week. 144MHz sky noise is low all week. (rsgb.org)

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