Propagation News – 28 June 2015

| June 26, 2015

What a week it has been in terms of solar activity and its effects on HF propagation. We’ve had everything thrown at us. On Sunday we started with a series of strong M-class X-ray flares. One of these resulted in a full halo coronal mass ejection. The halo effect observed means the CME was coming straight towards earth.

On Monday we had a proton radiation storm, which impacted HF radio propagation through the polar regions, a so-called Polar Cap Absorption Event. And on Tuesday we had the big one with the arrival of the CME from Sunday’s flare. This pushed the Kp index to eight, with dire effects on the F2 layer and ionospheric propagation, with aurora and depressed critical frequencies.

The Chilton Ionosonde struggled to get any returns from the F2 layer on Tuesday morning and all that could be heard were a few weak European signals on 20m. By early afternoon the critical frequency was 4.350MHz, giving a maximum usable frequency of about 16.8MHz on 3,000km paths. By Thursday the K index hit six again thanks to another CME.

So, this week has been characterised by dismal HF conditions with sporadic-E being disrupted as well. Next week is predicted to be more settled with a solar flux index in the 120s and quieter geomagnetic conditions, so HF propagation may improve.

VHF and up propagation

We are still in the peak period for sporadic-E and the weather triggers, chiefly jet streams in the upper atmosphere, are still likely to be present for the coming week. There was more good sporadic-E across Europe last week with some six metre openings to the Caribbean and the Americas, plus Auroral Es to Scandinavia and two metre paths to southern Italy. Expect more of the same.

Longer-term weather models are showing good potential for enhanced tropo conditions in the coming week. A ridge of high pressure should develop across southern England today, and soon build to form a large high over southern UK which moves into the North Sea and Scandinavia by mid-week. By this time, a trough may bring some heavy thundery showers into southwestern Britain from France to give a chance of rain scatter on the gigahertz bands.

Remember that tropo paths across the sea can remain active throughout 24 hours, but inland stations may benefit during night-time and early morning, before the sun breaks down any temperature inversion. Often tropo tends to be better on the higher bands, like 70cm and 23cm, and is often long-lasting compared with the fleeting lower band QSOs via sporadic-E.

Category: GB2RS Propagation News