venerdì 22 giugno 2018

Propagation News – 24 June 2018

A glancing blow from a coronal hole sent the K-index soaring to five on Tuesday, the 19th. This hadn’t been predicted by NOAA as it looked like the high-speed solar wind stream might miss us. However, by Wednesday the ionosphere had calmed down and the index returned to a more settled Kp=1. 

Much of the fun on the upper HF bands has been due to sporadic E this week, with multi-hop contacts being made across the Atlantic at times. There have also been reports of contacts into Argentina on 21MHz, which could have been be F2 layer or multi-hop sporadic E. If they were via the F2 layer, this could have been helped by two large sunspot groups currently visible, which pushed the solar flux index to 82 on Thursday, the 21st. 

There have also been reports of some excellent 40 metre propagation to various parts of the world, but this may suit night owls as it favours the early hours after midnight. 

Next week NOAA predicts the solar flux index around 70, with settled geomagnetic conditions until the 25th. We may then see the effects of an equatorial coronal hole and its associated high-speed solar wind stream push the K-index to five again with lowered maximum useable frequencies and noisy bands. So get your HF DXing in this weekend, or you may have to wait until later in the week for things to settle. 

Sporadic E will continue to bring short-skip fun on all HF bands up to 10 metres. Longer-range F2-layer propagation may peak at 14 or 18MHz as we continue in the HF summer doldrums. 

VHF and up:

There will be a large area of high pressure over, or near to, the British Isles until the end of the week, so tropo propagation will be a real prospect. It will favour paths down the Irish Sea or across Biscay to northern Spain. This direction is favoured over paths across the North Sea, where the air will be drier at lower levels and not so conducive to tropo. In the summer months night-time tropo is an option over land too, but soon fades as the Sun warms the ground and destroys the surface temperature inversion. This high pressure means that you will not see any rain scatter on the microwave bands. That leaves sporadic E, which is still in full cry and offers two primary periods to check the bands; mid-morning and late afternoon, or early evening. 

Weather features can play a part in the location of sporadic E and, based on the contribution of jet streams, it looks like paths to Scandinavia and south-east Europe could do well, as will paths to the south into Iberia. It’s also always worth looking to the Atlantic for paths to the Americas and the Caribbean with a jet stream present for much of the week. 

The June Bootids meteor shower is active from 26 June until 2 July. It peaks this Wednesday. Normally the shower is very weak, but occasional outbursts produce a hundred or more meteors per hour. 

The Moon reaches minimum declination and apogee on Thursday, so EME opportunities will be short with a low-elevation Moon and high path losses.