venerdì 29 luglio 2022

Propagation News – 31 July 2022

We’ve had a week of lower solar flux indices, despite a smoothed sunspot number in the 50s. The sunspots we have had have been relatively small and pretty inconsequential.

The week started off with an SFI of 107, but then declined to 98 by Thursday. The good news is that we have had relatively settled geomagnetic conditions after a wobble at the weekend due to a high-speed solar wind stream.

Other than Sporadic-E events, the maximum usable frequency over 3,000km has struggled to get up above 18 or sometimes 21MHz during daytime. But, as we have said before, night-time MUFs have remained seasonally high, topping 14MHz over a 3,000km path most nights.

Next week, and as we enter August, we can expect more of the same. The solar flux index is predicted to rise slightly to perhaps 115 by next weekend.

But the prediction is also for more unsettled geomagnetic conditions with a maximum Kp index of four this weekend and again later in the week. This is most likely due to high-speed solar wind from coronal holes once again.

So best of luck with the IOTA contest this weekend, which will probably be dominated by operators on 20 metres with occasional Es openings on the higher bands.

VHF and up:

There have been some fleeting signs of the continuing Sporadic-E season, but events are not so commonplace in this second half of the summer. This means being alert to the typical operating windows, which traditionally are early or mid-morning and again late afternoon/early evening. At the heart of these events will usually be a weather feature, such as a jet stream, whose turbulence creates a wave motion in the atmosphere that can cause varying wind flows in the E region some 100km above the weather, and are a big contributor to the formation of Es.

In this coming week, the jet streams are very limited so it’s not looking too favourable for major Es events.

The weather pattern shows lows near the northwest of Britain driving fronts across the north, and at the same time precluding the development of Tropo, since it does not allow the development of high-pressure systems.

However, conditions in the south are a bit more supportive, so there could be occasional Tropo, especially over sea paths around the UK. There is a hint that the second half of the week will see the development of a large high more generally over the UK, so that’s the time for Tropo to shine.

The other modes such as rain scatter are not looking too strong since the frontal cloud bands tend not to be as effective as heavy thundery showers, but it’s always worth checking for aurora and meteor scatter as we move into August and within reach of the broad peak of the Perseids meteor shower.

It’s a good week for EME with positive Moon declination until Tuesday and falling path losses, but we are still more than a week from perigee. 144MHz sky noise is low but slowly increasing all week. (