Propagation News – 12 March 2023

It was business as usual last week with the solar flux index in the 180s, numerous C-class flares and, at the time of writing, 13 M-class flares over the past seven days.

The Kp index has been mostly settled for this part of the cycle, averaging two to three all week. But this doesn’t mean there has been little activity on the Sun, just that any eruptions have been directed away from Earth.

For example, a large prominence eruption off the Sun on 7 March resulted in a coronal mass ejection that stretched hundreds of thousands of kilometres into space.

It is this type of activity that makes space weather predictions difficult. If it had been Earth-facing, we could have ended up with a highly-raised Kp index and extensive aurora. As it was, the event had little or no effect on Earth.

Maximum usable frequencies continue to be high, but we are starting to see the effects of the Summer ionospheric changes that will see daytime MUFs decline.

The MUF over a 3,000km path often doesn’t exceed 28MHz now until later in the morning.

This is due to a seasonal change in the ionospheric chemistry and a shift from monatomic species to diatomic ones, which are harder to ionise.

So, make the most of 10m as by mid-summer we may lose long-range propagation on 28MHz, other than through Sporadic-E events.

We mentioned last week that this is a good time for North-South paths as we head towards the Spring equinox. That is, good paths to South Africa and South America are more likely now than they were a few months back. There have been a lot of stations on 10m in the late afternoon from South America so make the most of the propagation.

Next week, NOAA predicts similar solar flux index figures, with the SFI being in the range of 170 to 185. The Kp index is predicted to be at two or three, with perhaps more unsettled geomagnetic conditions on Wednesday 15 March.

As always, see the website for more up-to-date information.

VHF and up

The unsettled winter weather has yet to give way to spring, so it’s primarily low-pressure systems and periods of rain or snow that we will be dealing with in the next week or so.

Whether it’s rain or snow, this unsettled pattern limits any Tropo options, and leaves only GHz band rain-scatter as a propagation mode to explore. Generally speaking, the rain, or perhaps the point where the snow is melting as it falls, should provide better reflections, whereas in very cold areas, where it is all snow, reflections may be weaker. This probably means that it will be southern areas that perform better with rain scatter.

For the next few weeks, there are no significant meteor showers and therefore the pre-dawn random meteors will be the best options. Aurora, on the other hand, tends to favour the spring and autumn months, so in view of the current state of solar activity, as mentioned in the previous section, you should continue to monitor the Kp index for signs of activity and check the bands if it gets to the point that Kp equals five.

For EME operators, after minimum declination this Thursday, Moon availability windows will start to lengthen. Path losses will continue to fall but we are still a week from the Moon’s perigee – its closest point to Earth. 144MHz sky noise is high, reaching over 2,800 Kelvin on Thursday.

Category: GB2RS Propagation News