Propagation News – 26 April 2020

Last week showed how difficult it can be to prepare HF propagation predictions. We said that we expected the Sun to remain settled throughout the week. But on Wednesday, the 15th, there was a stealthy, slow-moving coronal mass ejection off the Sun that barely appeared in the SOHO spacecraft imagery. However, this CME was Earth-directed and around midday on Monday, the 20th, it hit. The net result was the Kp index rose to five and MUFs were adversely affected, after an initial positive phase that saw MUFs over a 3,000km path rise above 18MHz. HF conditions were still down on Tuesday, with bands above 20 metres pretty much closed. But luckily, by Wednesday things were pretty much back to normal.

The highlight of the week has been a gradual increase in sporadic E on 10 metres. There have been numerous openings, mainly into Spain and the Canary Islands, with other fleeting openings into Sweden and Germany. While signal strengths haven’t been too strong so far, it bodes well for the sporadic E season, which is likely to ramp up over the next week or so. The message is keep an eye on 10 metres.

Next week NOAA predicts a continued quiet Sun with a solar flux index around 69. With zero sunspots predicted again it does begin to look like we are close to sunspot minimum.

Geomagnetic conditions are predicted to be settled, with a Kp index of around two to three, other than on Monday, the 27th, when it could rise to four.

VHF and up

We have a hybrid of weather types during the coming week, with the last of any tropo fading as this bulletin goes out. Thereafter, it looks more unsettled with a chance of showery rain, initially in the south-west, but more generally as we run into next week. This is because an Atlantic low should develop south of Iceland and a cold front become slow-moving over western Britain at the end of next week. In this latter part of the week, high pressure builds from Biscay across northern France.

So, expect some tropo at first, but ending this weekend and perhaps in south-eastern areas late next week. Rain scatter looks more favourable again with several areas of showery rain or fronts involved from this weekend onwards.

In view of the approaching start of the sporadic E season we would expect to find some openings, but as we said earlier any have been brief so far. It would seem that nobody has told the jet streams to get into line! I cannot say that this looks like a strong lead this week.

The peak of the ongoing Lyrids meteor shower is over, so expect declining meteor scatter activity this week.

Moon declination is positive all week and reaches its maximum on Tuesday. We are past apogee, so EME path losses will continue to fall—144MHz sky noise is low all week.

Category: GB2RS Propagation News