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Propagation News – 13 September 2020

It was another week with zero sunspots, but the upside was that we had settled geomagnetic conditions. The maximum Kp index of two, but more often than not just one, was brought about by an absence of coronal holes last week. This meant that the ionosphere was pretty stable, with Maximum Useable Frequencies (MUFs) over a 3,000km path heading towards 18MHz at times.

Next week, NOAA predicts the solar flux index to be 70 and the largest Kp index to be two, so expect similar conditions. NOAA also predicts the Kp index could rise to a maximum of three on the 18th and 19th, due to a high-speed stream from a returning coronal hole.

Due to seasonal changes we do expect ionospheric conditions to improve slightly as we head towards the end of the month. We also expect to see transatlantic paths and openings to South Africa and South America improving around the time of the autumnal equinox. There will also be a gradual improvement in daytime maximum useable frequencies as we head towards autumn, but night-time MUFs will decline. Expect October to probably be the best month all round for HF propagation.

VHF and up:

It seems like the main sporadic E season is over for the summer, with even FT8 paths hard to spot on the DX clusters. So, unless something exceptional turns up, you’ll have to wait at least until the small secondary December sporadic E peak for that DX mode again.

The basic weather pattern to end the current week, and take us into early next week, has high pressure over southern areas of the UK and cloudy, unsettled weather over the north-western areas, with wind and rain. This means that there is likely to be tropo on offer over the next few days, with paths to the south across Biscay initially, and later biased more towards northern Europe.

There could be an unsettled showery period of weather in the south as the high weakens by midweek and, typically after a few hot days, there may be thundery showers, which is great news for the GHz rain scatter operators.

A temporary return of high pressure later will probably put tropo back into play again, but with a further return of unsettled weather after a day or two.

Expect a good week for EME, with the Moon at maximum declination this weekend followed by shortening Moon windows as the week progresses. Declination goes negative on Friday and this coincides with perigee, where losses are at their lowest. 144MHz sky temperatures are low apart from next Thursday morning when the Sun and Moon are very close in the sky.

No meteor showers this week, so look for the best random meteors around local dawn while the Earth is rotating towards the orbital random meteor flux. (rsgb.org)

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