Propagation News – 25 March 2018
Last week was once again dominated by unsettled geomagnetic conditions, which didn’t help HF propagation.
The K-index rose to five on Monday, the 19th, after a solar wind stream from a coronal hole, flowing faster than 550 kilometres per second, triggered a moderate G2 geomagnetic storm at higher latitudes. This can occur due to process called magnetic reconnection after charged particles that have collected in the magnetotail behind the Earth are violently accelerated back towards us after opposing magnetic fields connect. As a result, widespread visible aurora were reported across parts of Scotland. A rare phenomenon called “Steve”—a Strong Thermal Emission Velocity Enhancement—was also seen during displays of the Aurora Borealis. A Steve is a very narrow auroral arc, aligned east-west, and extending for hundreds or thousands of miles. The net effect was largely suppressed maximum usable frequencies with the Fairford ionosonde showing that even 18MHz was struggling to open during daylight on Tuesday.
By Wednesday the ionosphere still hadn’t recovered and the daytime critical frequency were still around the 5MHz mark. However, north-south paths remained reasonable, with Andy M0NKR reporting contacts into Equatorial Guinea, Congo and Cameroon via 12 metres on Monday.
Next week NOAA predicts the solar flux index will remain around 68, and HF propagation will once again be dominated by geomagnetic effects. However, the K-index is predicted to be no higher than three all week, so conditions could be better than they have been.
VHF and up
We will have another week with less than enthusiastic weather support for an enhanced tropo mode, with only the brief nearby approach of a ridge of high pressure close to southern Britain around midweek. Once again its low pressure that predominates and therefore tropo looks hard to find. There is hope that showers developing in the unsettled weather spells will give some rain scatter opportunities on the microwave bands, especially since heading into April means there is the prospect of some quite strong convection. This can create heavy rain or hail showers, perhaps even thunderstorms. Check the forecasts to make sure you don’t go off to work and leave the antennas plugged on those showery days.
There have been a handful of 10 metre sporadic E QSOs in the last week. They seem to be associated with strong jet stream activity. It will be worth making a daily check of the upper air charts on propquest.co.uk in the weather section to see if there is any potential for sporadic E related to jet stream wind-produced turbulence, and check the clusters for reports of short-skip on 10 metres.
It is a good week for EME, with moon declination at maximum this Sunday and perigee Monday, leading to lowest path losses and long moon windows.
Category: GB2RS Propagation News
