Propagation News – 22 May 2016

| May 20, 2016

This week the solar flux index managed to remain mostly above 100, thanks in part to large sunspot number 2546. The region appears to be quite stable and not a likely threat for any significant solar flares. Geomagnetic conditions remained unsettled with the K-index hitting four at times and often hovering between two and three. This was due to ongoing coronal hole activity and the associated high speed solar wind streams. This is likely to continue as a coronal hole positioned near the solar equator was threatening to send the K-index higher on Friday, the 20th.

As we head towards midsummer, heating in the northern hemisphere, coupled with a change in the ionospheric chemistry, will see daytime critical frequencies reduce from their spring highs. We can see this by looking at the noontime critical frequencies as measured by the Chilton ionosonde near Harwell. In mid-April the critical frequency was exceeding 7MHz on good days. This month it is struggling to get past 6MHz. However, night time critical frequencies are remaining higher, which is a signature of summer HF propagation. By June we may see 20 metres remaining open all night.

Contacts via sporadic-E on 10m should be abundant, but keep an eye on 20m at night as it might throw up a few surprises after dark.

VHF and up propagation news

There are conflicting views of the weather story for the next week. However, one common theme in the model outputs is that for brief period we will find a weak ridge of high pressure nearby during the first part of the week. This may produce limited tropo, especially overnight and in the early mornings. From about mid-week, the high weakens and a slack pressure pattern remains. This will mean a more showery weather type with options for rain scatter on the GHz bands from any heavy thundery showers.

Sporadic-E is always a viable option any day during the summer months from May to August, so it’s worth checking first on 10m for short skip conditions within Europe and then moving up to higher bands as any opening develops. Quite often, the greater ranges are found as each band opens. This is because over time, the sporadic-E patch will usually slowly descend within the E region, shortening the path length.

For EME operators, the Moon’s declination is at its lowest on Tuesday so there will be short windows, but losses are decreasing all week as the Moon’s orbit brings it closer to the earth.

Remember that as well as our natural satellite there is always VHF DX potential using the many operational man-made satellites. Look on the AMSAT-UK website for details.

Category: GB2RS Propagation News