venerdì 22 gennaio 2021

Propagation News – 24 January 2021

Last week was defined by a lack of sunspots, but otherwise reasonably settled geomagnetic conditions. However, towards the end of the week, the Sun woke up with regions 2797 and 2798 becoming active. The sunspot number rose to 25 on Thursday, although the solar flux index remained in the 70s, reaching 77 on Thursday. This is good news as the Sun had remained spotless for some time.

By this weekend the spots will have rotated to be more Earth-centric and we shall have to see what happens to the solar flux index. They may continue to grow or could diminish. Meanwhile, a large solar coronal hole near the Sun’s equator will also become geoeffective on Friday, which may result in an elevated Kp index at the beginning of next week. NOAA predicts the solar flux index will remain in the mid to high 70s next week and the Kp index will be in the range of two to three. This will rather depend on the interplanetary magnetic field of the solar wind, emanating from the coronal hole. If its Bz swings south we can expect it to couple more easily with the Earth’s magnetic field and the Kp index could rise further.

So, HF propagation may remain subdued with little of note. However, this is a good time of year for low-band operations, with top band and 80m coming into their own after sunset and around sunrise. Signals from stations to the west, such as from North America, can peak just before our sunrise and there is often SSB activity around 3.795MHz. Why not take a look?

Higher up the bands, daytime maximum usable frequencies over a 3,000km path are reaching and often exceeding 21MHz. Daytime critical frequencies are in the range 5-6MHz, which means 40m remains a band for longer-range contacts. 60 metres, or five Megahertz, would be a better HF choice for near-vertical incidence skywave, or NVIS, contacts around the UK.

VHF and up:

The current spell of unsettled weather seems likely to continue through the coming week. This means that other issues like rain, snow and strong winds are the themes we will have to adapt to. In amateur radio terms it will be thin pickings, primarily rain scatter on the microwave bands as active fronts and showers pass by. That said, winter rain scatter is nothing like as intense as it is in the summer, so don’t expect too much. Keep an eye on your beacons and rainfall radar maps, and make a noise on reflectors and social media if you catch rain scatter propagation.

It’s hard to find any other benefits in the weather charts, and certainly no sign of high pressure and Tropo. We are also past the window of typical midwinter Sporadic-E, but that’s not to say the odd path won’t appear for digital modes like FT8, since unsettled weather brings a good supply of jet streams.

Moon declination reaches maximum on Tuesday so we’ll have long Moon windows and high peak Moon elevations all week. As we are past apogee, path losses will be falling. 144MHz sky noise starts moderate, but dips below 180 kelvin on Thursday.

There are no significant meteor showers again this week, so continue to check pre-dawn for the best random meteor contacts.

And that’s all from the propagation team this week. (