sabato 25 giugno 2022

Propagation News – 26 June 2022

As predicted, the solar flux index fell back this week, but it didn’t fall as low as experts predicted. On Thursday, it stood at 129, but with three sunspot groups about to rotate off the visible surface, it looks like it may now fall lower.

We are now well and truly into the summer season for HF propagation, which can be characterised as providing lower maximum usable frequencies during the day, but higher MUFs at night. Sporadic-E remains the most common mode of propagation on the higher bands, with F2-layer MUFs over 3,000 kilometres generally not exceeding 21MHz for most of the day. But more on Sporadic E in the VHF segment of this report.

The good news is that 20 metres stays open later, often providing paths over 3,000km up until midnight. The higher bands, that is 17 metres, 15 metres and perhaps 12 metres, may generally provide good paths to South America in the evenings, with 20-metre paths being the last to close.

But we’re afraid we may have to wait until September to see good reliable paths into North America on HF once again.

Next week, NOAA predicts that the SFI will remain around the 100 mark, so we may expect lower MUFs again, apart from Es openings. Geomagnetic conditions should generally be quiet with a maximum Kp index of two once we get over any disturbance this weekend due to a high-speed solar wind stream.

VHF and up:

The recent very warm and humid weather has produced some occasional Tropo with the British Isles being on the edge of high pressure, mainly over the near continent. This may still happen occasionally in the coming week, but the fundamental characteristic for next week is low pressure and unsettled weather over the UK. This will produce some rain, with thunderstorms a possibility, and rain scatter will crop up as a useful mode on the upper GHz bands at times.

The many online weather radar displays will allow you to keep a track of storms as they develop. When low pressure is centred over the country the showers may be longer-lasting and not decay overnight, so this period looks more promising than the usual mainly daytime shower distribution.

The Sporadic-E season is in full swing, but in a rather restrained way since openings have been fairly limited and often fleeting. The presence of jet streams on the weather charts is a good indicator of regions where Es is more likely and the coming week offers a good variety of options, so if Sporadic-E is hard to find then perhaps other parameters may not be optimal; for example, the meteor input is a crucial component in the development of Es. Check the daily conditions for jet streams on the EPI maps and Es blog.

The June meteor showers, mentioned last week, continue into early July so keep checking meteor scatter conditions between the Es.

With the Moon at maximum declination on Wednesday, Moon windows are long this week. Today, Sunday the 26th of June, the Moon is at apogee, or its furthest point from Earth, so path losses are at their highest, and for around four hours after UK Moonrise on Wednesday the Sun is close to the Moon so noise will be high at that time. (