venerdì 11 maggio 2018

Propagation News – 13 May 2018

May 11, 2018

Our forecast last week was pretty much spot-on, with poor geomagnetic conditions plaguing us from Sunday, the 6th. But before this, there was a pre-auroral HF enhancement on the Saturday that surprised many people. Steve, PJ4DX, on Bonaire in the Caribbean worked the UK on 17 metres and also made contact with Martin, M0BCT on 10 metres. He reports that Stephen, G7BXU, using a 5/8-wave vertical in Reading was also S9+ on 12 metres. Alas, things couldn’t last and we then went into a full geomagnetic storm, complete with a high K-index, noisy bands, lower maximum usable frequencies and lots of fading. At this point in the solar cycle pre-auroral enhancements are worth looking out for. They are usually triggered by the first arrival of solar coronal hole material, but are difficult to predict accurately, so keep an eye on the bands.

Now to next week’s predictions, and a lack of Earth-facing coronal holes on the Sun as of Thursday, 10 May, means this weekend may be more settled geomagnetically. Expect 20 and perhaps 17 metres to provide some good F-layer openings, and for the conditions to last until at least mid-week. NOAA then predicts the K-index could rise to perhaps six on Thursday, the 17th, probably due to a recurring coronal hole that has not yet rotated into view at the time this report was being prepared. This may be the coronal hole that caused the poor conditions 27 days earlier, around the time of International Marconi Day. So look for a possible pre-auroral enhancement from Wednesday evening or Thursday, followed by poorer F-layer HF conditions thereafter. The good news is that sporadic E is supporting strong short skip on 28MHz at times, with lots to work on FT8, CW and SSB.

VHF and up:

There have been some reasonable tropo conditions recently, but mainly limited to coastal and sea paths. A UK amateur television record-breaking 5.6GHz contact using low power video senders was made last Wednesday, between the Norfolk and Yorkshire coasts, using a shallow surface duct. This can be a relatively-common feature in the summer, but they can be very shallow; climbing the cliffs may just make you too high.

This coming week, with high pressure nearby, there will continue to be options for more tropo, but keep in mind that nocturnal cooling inversions that give some good overnight tropo soon disperse after sunrise. Looking for the high-microwave-band beacons overnight often shows them appearing after a hot day.

Tropo is not guaranteed this week since the high pressure is rather weak and often replaced by shallow areas of low pressure with an attendant risk of thundery showers, giving some possibility of rain scatter on the microwave bands.

The sporadic E season is well under way. We need to look at the location of jet streams within Europe this week, which can influence the location of sporadic E. A north-westerly jet stream over the Pyrenees could help paths to EA and CT. As usual the best advice to capture sporadic E is to remember to check 10m and 6m when you get home from work. Checking beacons, the Reverse Beacon Network and clusters should be your first tasks before having your evening meal!

The Moon reaches perigee, its closest point to Earth, on Thursday and maximum declination on Friday, so it’s a good week for EME.