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Propagation News – 15 December 2019

This week NOAA and NASA produced their latest forecast for the upcoming solar cycle. It predicts that we will be at solar minimum in April 2020, plus or minus six months. We should therefore begin to see a slow rise in new cycle sunspots towards the end of 2020. It says the next cycle is likely to be similar to the last one and will peak in July 2025, plus or minus eight months, with a smoothed sunspot number of 115. This is not exactly exciting, but is roughly line with how solar cycle 24 performed. Cycle 24 peaked in April 2014 with an average sunspot number of 82. More importantly it says there is no indication of an approaching Maunder-type minimum.
This last week was characterised by quiet geomagnetic conditions with a maximum Kp index of three. There were no sunspots and the solar flux index hovered between 70 and 72. Next week NOAA predicts unsettled geomagnetic conditions between the 18th and the 21st due to coronal hole activity. Needless to say the solar flux index will remain around 70, reflecting a lack of sunspots.

Daytime critical frequencies as measured by the Chilton Digisonde are currently in the range of 4.8-6.1MHz, which makes 40m difficult for short skip. Maximum usable frequencies over a 3,000km path are reaching 18MHz at times, with occasional openings up to 21MHz. But you may find the 14MHz band more reliable.

Eighty metres should remain open to both short-skip and DX during the night, after a short dip just after sunset. By 1830 UTC the F layer should stabilise and the band may become more usable, especially for paths over 100km.

VHF and up:
The coming week shows that we once again have predominantly low pressure systems over the UK, mostly centred over the north of Britain or even further to the north. This will mean several occasions when there could be some rain scatter on the microwave bands to chase down.

For completeness we need to consider tropo, but with a total absence of high pressure areas, it is unlikely to feature much during the next week.

Something of a wild card next. Winter sporadic E is not unknown, and with a strong set of jet streams over the country during the first part of the week, it is just possible that a check on the clusters may reveal some unseasonal sporadic E on bands like 10m and 6m, particularly on the digital modes like FT8. It may also lead to some good days on the HF bands for short-skip paths on, say 20m, and perhaps give some boosted local net propagation on LF bands like 80m, long after the foF2 has dipped below 3.5MHz.

We will be just past the peak of the Geminids meteor shower on Saturday night, but there may still be some activity for the meteor scatter folk into the coming week as the shower tails off. That is until the Ursids shower starts to become dominant from around the middle of the week, peaking on the Sunday through Monday. Although not a large shower, there have been occasional meteor numbers beyond that normally expected, so it might be worth waiting up for.

Now to EME. The Moon will be waning throughout this week. As the Moon also moves closer to perigee by midweek, its closest point to the Earth, this will mean low path loss. Sky noise also reaches its lowest at midweek, so with low libration, the overall prospects for EME operation look very good. (rsgb.org)

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