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Propagation News – 3 July 2022

Last week was not a good one for HF propagation in general. There were many complaints from amateurs about poor conditions that can be explained by a combination of low solar flux levels and unsettled geomagnetic conditions.

The SFI started the week last Sunday at 102 but then dropped to 98 the following day. It subsequently continued to drop, reaching 92 by Thursday. At the same time, the Kp index reached five and it continued to be unsettled into Monday.

The effects on the ionosphere were not good, with maximum usable frequencies over a 3,000km path struggling to reach 18MHz. Conditions improved as the week went on with F2-layer MUFs back into the 21MHz region by Thursday.

This is fairly typical of Summer ionospheric conditions, leaving Sporadic-E as the likely main propagation mode on 10 metres until the Autumn.

Next week NOAA predicts that the solar flux index will start to climb again, perhaps peaking at 140 by the 11 July. Geomagnetic conditions are predicted to be stable with an average Kp index of two, until the 10th when it could reach four.

As long as we don’t have any coronal mass ejections during this time this could mean slightly better F2-layer conditions next week. As always, Sporadic-E may provide loud short-skip signals on the upper bands. Watch out for multi-hop Es paths which are harder to predict.

VHF and up:

With VHF National Field Day, this weekend we would all like conditions at their best, and with the Sporadic-E season still in full swing, that’s a possibility.

The position of the jet stream is often instrumental in defining the directions that perform for Es and this weekend it looks to be a close-by jet stream over the near continent. This means paths towards central and southeast Europe plus the Baltic and Scandinavia. You might be able to get some notion of how it’s developing by Googling and looking at the ionosonde from Dourbes in Belgium for spikes in the foEs trace.

With low pressure close to Scotland over the weekend, it’s only southern UK under a weak ridge that will see any Tropo. This will typically be better overnight and around the coasts for paths into the continent across the North Sea or the English Channel.

So unless you are on the coast, your tropo options will diminish early this Sunday morning once the solar heating starts to break down the overnight temperature inversion.

The UKAC 144MHz contest on Tuesday evening looks a better prospect with high pressure nudging towards western Britain and a chance that conditions may be slightly up, even for more northern stations.

With some showery episodes likely, rain scatter is always a possibility, but decaying as the high moves in later. The clusters should tell you if aurora or random meteor scatter are viable options.

Just one meteor shower this week, the July Pegasids active from the 4 July to the 14th, but its Zenithal Hourly Rate is low at around five. Meteor showers in July are at their best around the end of the month, particularly the Southern delta-Aquariids, peaking on the 30 July. The maximum ZHR of this shower is around 25 over two days. The radiant of this shower is above the horizon in the UK during the night and early morning.

Moon declination goes negative this coming Wednesday so expect lower peak elevation and shortening Moon visibility windows for EME. Path losses are dropping as we head towards perigee a week on Wednesday. 144MHz sky noise is low all week. (rsgb.org)

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