Propagation News – 24 March 2019

| March 22, 2019

The Sun burst into life this week, with two new sunspots and solar flares aplenty. But before you get too excited the spots are from the outgoing solar cycle 24.

Sunspot 2736 erupted on Wednesday with a C4-class solar flare. The Earth-directed explosion sent ionisation rippling through Earth’s upper atmosphere and caused a Dellinger fade-out over parts of Europe and Africa.

A Dellinger fade-out or sudden ionospheric disturbance, SID, is an abnormally high ionisation or plasma density in the D region of the ionosphere. The SID results in a sudden increase in radio wave absorption that is most severe in the upper medium frequency and lower high frequency ranges.

The explosion also hurled a coronal mass ejection (CME) into space, which might deliver a glancing blow to Earth’s magnetic field. Although the bulk of the CME was not Earth-bound, be prepared for increased Kp indices and, or aurora on or around Saturday, the 23rd. Meanwhile tiny sunspot 2735 also appeared, helping to push the solar flux index to 77. Conditions were mixed this week, with Tuesday being lousy and Wednesday being fair.

Dean Pesnell, Project Scientist of the Solar Dynamics Observatory, said this week that solar minimum is now likely to be some time in 2020—he didn’t want to be drawn on exactly when. He added that the indications are that Solar Cycle 25 will be similar to 24, so we are not heading for a Maunder Minimum.

Next week NOAA has the solar flux index at 69, but the K-index is predicted to hit five between March 26 and 29. Conditions should then be more settled for the weekend.

VHF and up

It’s a good tropo theme again, with at least one model keeping the large area of high pressure over the country for most of the coming week. However, being centred over the country, the inversion will probably be at a low height, say around 1km or less, and there will be drier air near the surface, so look for overnight lifts, especially if there is any fog.

Another model is less enthusiastic at the end of next week, allowing low pressure to the north of Britain to bring a cold front south. This would produce rather windy weather and bring tropo to an end. This cold front could be quite active with heavy rain along it, so perhaps an opportunity for some microwave rain scatter.

The Moon is heading for apogee a week today, and its declination is negative and falling all week. The coming week will therefore see shortening Moon windows, low moon elevations and increasing losses for EMEers. The Moon up is in the early hours in Europe.

With still a month to go until the Lyrids meteor shower we’ll have to rely on random meteors around dawn for the best chance of meteor scatter DX.

Remember that if the weather fails to produce propagation there’s always aircraft reflection to fall back on for VHF DX, especially on the lower GHz bands. Just Google aircraft scatter to learn about this fascinating mode.

Category: GB2RS Propagation News