venerdì 27 aprile 2018

Propagation News – 29 April 2018

Last weekend’s poor HF conditions, which made for a quieter than normal International Marconi Day on the 21st, were largely caused by incoming material from a large solar coronal hole. A lack of sunspots didn’t help either.

The incoming solar wind pushed the K-index up to six at one point, but conditions settled as the week went on. By Thursday the 26th the K-index was down to zero or one.

A small sunspot group pushed the solar flux index to a maximum of 77 and the sunspot number to 34. But even this had declined to 69 and 17 by Thursday.

As a result maximum usable frequencies struggled to exceed 14MHz at times and skip on the lower bands, particularly 40 metres, tended to be longer.

The Space Weather Prediction Center says we might expect another geomagnetic disturbance this weekend due to a high-speed solar wind stream.

But after that, next week’s geomagnetic conditions are predicted to be fairly settled with a maximum K-index of two. NOAA predicts the solar flux index will remain in the low to mid seventies.

One positive is that the lower solar flux means D layer absorption is also weakened. This means 40m is often open to paths around Europe during the day—do take a look at the band as it is often open to France, Germany, Switzerland and Italy, for example, when 20m is largely closed.

Putting this all together, we might expect slightly better daylight HF conditions next week with band openings on 40, 30 and up to 20, with occasional surprises on 17 metres.

We are still seeing a slight uplift in the critical frequency after sunset, and the ionosonde data show that 20 metres may remain open to DX over a 3,000km path until about 21.30 UTC.

As always, these are predictions and you need to get on the air to find out if they come true!

VHF and up:

The pressure will remain low close to the British Isles and therefore tropo is unlikely to feature much, other than transient openings around dawn. With heavy showers and thunderstorms in the forecast, it could be a good spell for rain scatter on the gigahertz bands, so radar sites such as Patrick TK5EP’s SCP map will be your friend for setting up QSOs.

Sporadic E is coming into its time now, and there have already been some openings across Europe using FT8.

Be prepared for some more traditional openings for CW and SSB signals soon. The earlier FT8 events have been linked to the positions of jet streams, but it’s very hard to be precise, since they happen most days.
For the CW and SSB signal levels it is likely that the first place to check out will be along the lines of jet streams, especially where they intersect with mountain ranges like the Alps and Pyrenees. The upper air forecast charts do show a good deal of jet stream activity over the next week, so it’s time to set up a listening watch on the beacons and clusters.

Moon declination is negative and falling all week, reaching minimum next Saturday. This coincides with apogee, so peak Moon elevations are at a minimum and losses are highest at the same time.

This is a week to check out your antenna and receiver performance using Sun-to-cold-sky noise measurements as the Sun is getting to a good maximum elevation now.