Propagation News – 17 May 2015

It looks like we got the HF forecast for last week about right. The Kp index stormed up to six on Wednesday 6th, remaining at four for the whole day. This was due to an enhanced solar wind stream above 700 km/s and a southward-facing Bz component of the interplanetary magnetic field. This negative Bz means the solar wind coupled more easily to the earth’s magnetic field, allowing charged particles to flow towards the polar regions. The end result was visible and radio aurora and depressed maximum usable frequencies worldwide.

The estimated maximum usable frequency over a 3,000km path at noon on Monday, based on the Chilton ionosonde data, was 20.1MHz. But at noon on Wednesday it was just 18.4MHz.

The solar flux index was in the range 150-167, which would have brought lots of DX if it had not been for the geomagnetic disturbance.

With the sun currently peppered with lots of spots, next week may be a mixed bag. NOAA/USAF predicts a solar flux index of 145, declining to 115 by the end of the week. The geomagnetic prediction is for more settled conditions, which may lead to better conditions on the higher HF bands, although solar flares and incoming solar particle streams may have a sting in their tail.

VHF and up propagation

An intense area of ducting from Portugal down the west coast of Africa brought transatlantic reception of the Cape Verde 144MHz beacon in the Caribbean (PJ4) on 6 May. While still present, this will sadly be out of range for most UK stations who will have to put up with mainly poor tropo again.

Of course, if sporadic-E enables UK stations to couple into this duct, it could be a different story. Early in the week, stations in the south might take advantage of ducting in the Bay of Biscay area. To compensate, 50 and 70MHz sporadic-E is really taking off now with stations in the UK working Israel on 50MHz last Thursday lunchtime.

Be on the lookout for more frequent openings, with lunchtime and early evenings generally the best time in this early part of the season.

There are no meteor showers this week. The moon reaches maximum declination this week so for EME operators there will be longer moon windows with increasing losses as the week progresses.

Category: GB2RS Propagation News