Propagation News – 10 September 2023

The propagation team was caught out last week by two coronal mass ejections, or CMEs, that came off the edge of the Sun. The arrival of those CMEs on the 3 September eventually pushed the Kp index to 5.67.

In its report, Spaceweather.com said that it was possible that a CME arrived on the 2 September, but its weak impact was masked by a chaotic stream of solar wind already blowing around Earth at the time.

At this time of year, even weak CMEs can do a good job of sparking auroras as a result of the Russell-McPherron effect, which boosts geomagnetic activity around the equinoxes.

So much for saying that we could expect quiet geomagnetic conditions last week!

The Solar Flux Index declined to 131 but has since recovered to reach 147 on Thursday the 7 September, with eight active regions visible. We had a number of M-class solar flares last week, but nothing too damaging.

With the Kp index back to one on the 7 September, we saw daytime MUFs rising again, heading above 24.9MHz over a 3,000km path. There were lots of Chinese and Japanese stations on 21MHz FT8 around 1100UTC on Thursday. And up on 12m FT8, even more of the same. DX stations included Thomas, KH0/KC0W on the Mariana Islands in the Pacific.

While the 10m band was just about open as well, it offered slim pickings compared with the 12m band.

Next week NOAA predicts that the Solar Flux Index will increase over the week to hit perhaps 155 by next weekend. Geomagnetic conditions remain variable with a Kp index of three or four forecast for the 12 to the 16 September.

This weekend the geomagnetic forecast is that it will be quiet although, with so many sunspots visible at the moment, it wouldn’t take much for a CME to disrupt things. As always, keep an eye on solarham.net for near real-time updates.

 VHF and up

The RSGB 144MHz Trophy produced good DX on 2m into Poland and Sweden, so we guess that Tropo performed for us this week.

This spell of hot sunny weather, due to high pressure, does mean Tropo was the mode of choice for the end of this current week, ending today the 10 September, especially across the North Sea.

However, unsettled weather is gradually encroaching from the west, introducing some thundery rain into western areas, and this will spread east.

Although the Tropo will cease, Gigahertz bands rain scatter is a likely replacement although very isolated rather than the widespread nature of a good Tropo event. It should be noted that next week is not fully determined by all models with quite a spread of outcomes. Either way, it’s Tropo or rain scatter for most areas next week.

It’s always possible that meteor scatter and aurora could show during this period. The early morning, around dawn, is usually the best time to look for random meteor scatter activity in the absence of any major meteor showers. For aurora, it’s best to follow the solar data from spaceweather.com to pick up early alerts and an increasing Kp index.

For EME stations, Moon declination is at its highest this weekend but with apogee, the Moon’s furthest point from Earth, next Tuesday, path losses are high. 144MHz sky noise is low for most of the week except for Thursday and Friday when the Moon and Sun are very close, meaning high solar noise in the beamwidth of antennas.

Category: GB2RS Propagation News