Propagation News – 26 March 2023

| March 24, 2023

The solar flux index dipped a little last week, down to 148, but it didn’t last long and was back up to 159 by Thursday 23 March. We were free of major solar flares with only one M-class flare occurring on the 20 March.

Geomagnetic conditions were mainly settled as well, but that could change this weekend thanks to a large coronal hole.

The massive coronal hole on the Sun became Earth-facing on Thursday. A coronal hole is an area on the Sun’s surface with open magnetic field lines, which allows plasma to flow out. They appear dark when photographed in extreme UV light.

Although the bulk of the hole is south of the Sun’s equator, a long finger reaches out to the equator, which makes it a potential threat to Earth.

All eyes will be on the Kp index over the weekend as we expect it to increase, possibly dramatically as the solar wind impacts us. Solar wind speeds are likely to be in excess of 600km/s and continue into the weekend, resulting in isolated G1 storm levels. Keep an eye on for updates.

We are now at the spring equinox, so it is a prime time for auroral activity. The spring equinox traditionally brings greater solar activity which results in an increased frequency of auroral displays.

It is also a prime time for north-south HF paths, such as the UK to South Africa, and the UK to South America.

Next week, the US Air Force predicts that the solar flux index will decline slightly to bring it into the range of 130 to 140. Once the weekend’s solar storm declines, we may expect a few days of relatively calm geomagnetic conditions before another period of unsettled space weather is predicted for Thursday 30 and Friday the 31 March. This could see the Kp index rise to five once again.

VHF and up

The overall unsettled nature of the current weather pattern is likely to continue for much of the period through to the end of next week, except for a brief ridge of high pressure crossing the country after the weekend.

This might offer the only tropo potential for VHF operators. The rest of the time will probably be beset by bands of rain, showers and, at times, strong winds and introduce the prospect of some rain scatter on the GHz bands.

It’s a week to focus on fleeting tropo, rain scatter and aurora as modes of choice. As we said earlier, aurora is worth looking out for since the solar conditions are still very disturbed. As usual, good indicators are the Kp index values, which ideally should be five or greater to get our attention.

The meteor shower calendar is still in its quiet period, and with no major showers to look for, it would be best to try your luck with random meteors, which tend to peak just before dawn.

The Sporadic-E season has not started yet but is getting closer, say from mid-April on 10m, perhaps.

For EME operators, Moon declination reaches maximum next Tuesday meaning long Moon availability windows. Path losses increase throughout the week and 144MHz sky noise starts out moderate, falling to low next weekend.

Category: GB2RS Propagation News