Propagation News – 17 September 2023

While our terrestrial weather this week was variable, it seems our space weather was equally unsettled!

We warned last week that it wouldn’t take much to cause the Kp index to rise and on Tuesday a coronal mass ejection, or CME, hit the Earth sending the Kp index to 5.67. The Bz component of the interplanetary magnetic field tipped sharply south for a long duration causing visible aurora to be seen across the north of the UK and as far south as Cornwall.

This really hit HF quite hard and good signals were scarce.

Unsettled radio conditions continued into Wednesday bringing the Maximum Usable Frequency, or MUF, over a 3,000km path down below 18MHz for most of the day. The Kp index was still around 3 or 4 on Thursday, but MUFs were recovering and were at around 28MHz over 3,000km by lunchtime.

Next week NOAA predicts that the Solar Flux Index will start the week around 165 and then decline as the week progresses, perhaps ending at around 145 to 150.

Geomagnetic conditions are forecast to be quiet, at least until the 23 September when the Kp could rise to four. But at this point in the solar cycle the risk of a solar flare, and subsequent CME, remains high every day, so watch solarham.net for up-to-date information.

And finally, a new paper by NASA’s Lisa Upton and David Hathaway indicates that sunspot maximum is now forecast to be in the Autumn of 2024. They predict a maximum sunspot number of 135, plus or minus 10, which is slightly larger than Cycle 24’s maximum of 116.4, but well below the average of 179 for Solar Cycles 1 to 23.

 VHF and up

Tropo conditions are still present over southern areas today, the 17 September. However, by early next week, low pressure will be a dominant force and the coming week looks very unsettled with rain and quite strong winds at times.

This means that any Tropo, either across the southern North Sea or down across Biscay, will not last beyond this weekend, ending today the 17 September .

The unsettled low-pressure-driven weather will mean that rain scatter is a distinct possibility on some of the more active days. The other propagation modes are the usual fall-backs of meteor scatter using random meteors and aurora, which may not be too far-fetched in view of the geomagnetic activity and visible auroras experienced recently.

The September Epsilon Perseids meteor shower has already peaked earlier in the month, but a few lingering meteors may give some truly random radio reflections.

Last week there were indications that this normally quiet period after the August Perseids and the forthcoming October Draconids can still provide some interest for persistent meteor scatter enthusiasts.

During this coming equinox week, the Moon will reach its lowest declination of the month on the 22 and 23 September . This point also coincides with the Moon being in Sagittarius, so that sky noise will be very high. This will make moon bounce operations particularly difficult towards the end of the week.

Category: GB2RS Propagation News