Propagation News – 14 May 2023

| May 12, 2023

Our topsy-turvy world of HF propagation continued last week with geomagnetic storms, solar flares, coronal mass ejections, proton events and more.

The good news is that the solar flux index was at 170 by Thursday, but the bad news was that we had two episodes where the Kp index hit five and there were at least five M-class flares.

At least one of these flares was responsible for a coronal mass ejection, or CME, which swept past the Earth on the 10 May with a solar wind speed close to 700km/s. Although it was fierce, it was relatively short-lived and the Kp index was back to three on Thursday 11 May.

The CME caused the maximum usable frequency over 3,000km to decline to around 21MHz at times on Wednesday, but by Thursday morning it was back up to nearly 28MHz.

The high proton flux also caused problems on the 10 May. The protons, mainly from CMEs, move down the Earth’s magnetic field lines into the polar regions, and cause massive ionisation of the polar D region leading to increased, or total, absorption of HF waves.

This effect may last for as long as ten days and is called a Polar Cap Absorption event, or PCA. This affects signals going over the poles, such as the UK to the west coast of Canada and the USA, or to Japan and the far east.

Meanwhile, we are now under way with the Sporadic-E season, so make the most of the short skip and potential multi-hop Sporadic-E DX on 14 to 28MHz.

Next week, the Space Weather Prediction Centre has the Solar Flux Index declining slightly into the 150s. This is still more than enough to maintain DX on 21MHz and higher at times. It also predicts that the Kp index will be no higher than a stable 2 all week.

However, that is hard to believe, with the level of solar activity at the moment, and we could reasonably expect the Earth to be hit with a CME or two at some stage. This could see the Kp index rising with the potential of reduced MUFs at times.

 VHF and up

After a very unsettled end to the week, with lots of rain scatter reported, it will soon quieten down as a ridge of high pressure builds across the country to give some limited Tropo opportunities for the start of the weekend.

This will not last long and by this evening, it will be heading back to unsettled with low pressure, heavy rain and rain scatter. This unsettled theme will last through the first half of the new week together with strong north-easterly winds. Thereafter, high pressure will build again for the second half of the week, providing further Tropo options.

Keep a watch for aurora, especially in view of the current unsettled solar state. CMEs will mean a very unsteady Kp index and anything higher than five should get your attention for auroral propagation. No significant meteor showers are expected this week, but QSOs using random meteors are always a possibility in the dawn hours.

Likely to be of interest in the summer months ahead, there have already been Sporadic-E openings on 6m CW and FT8 into Europe. Early evening trans-equatorial 6m FT8 QSOs to South America, the Indian Ocean and the South Atlantic were reported from the UK last week.

Check for daily blogs and make use of the DX cluster and map plots to see where the actual centres of activity are located.

Timings can be a bit random early in the season, but there tends to be two ‘openings’ per day – one in the morning and a second during the late afternoon or early evening.

Moon declination is rising, going positive again next Tuesday. But last Thursday’s perigee means path losses are on the increase. 144MHz sky noise is low until Friday when the Sun and Moon are close in the sky for the whole Moon window. Things return to normal early on Saturday and sky noise is moderate.

Category: GB2RS Propagation News