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HF News
Active region 4079 turned out to be not quite so bad as we predicted. The sunspot spanned an area the size of roughly 10 planet Earths, so we expected more.
It was regions 4081 and 4082 that produced most of the flare activity last week.
Two filament eruptions also occurred within two hours of each other. The first event began at 16:20 UTC on May 6 in the southern hemisphere and was responsible for a plasma wave across the surface of the Sun.
The second filament eruption began in the northern hemisphere around 17:50 UTC to the northeast of AR 4079. A large amount of plasma was flung to the north. The filament eruptions on Tuesday the 6th did produce coronal mass ejections, however an Earth-directed component was not apparent, so we dodged a bullet!
The solar wind speed remained high for most of last week which didn’t help propagation. This helped push the Kp index to five across the weekend of the 3rd and 4th. Things were more settled later in the week, and on Thursday the 8th, the solar wind speed was down to around 500 Km/s and the Kp index sat at three, but MUFs over a 3,000km path were still down to about 20MHz.
An Earth-facing coronal hole may add to the solar wind over the weekend of the 10th/11th. So it looks like summer HF propagation is kicking in, with lower daytime MUFs, but higher nighttime ones.
Next week, NOAA predicts that the SFI will be in the range 155-165. Settled geomagnetic conditions are forecast for the beginning of the week commencing the 12th. Unsettled geomagnetic conditions are forecast for the 16th-19th when we could see the Kp index rise to five again, coupled with poorer propagation and reduced MUFs.
VHF and up
Tropo has been a key propagation mode during the previous couple of weeks, but there have been variations in the location and timings of these conditions.
Sometimes this will be due to increased moisture below the temperature inversion, so although the cloudier areas have been cool, they have probably done better for Tropo.
This is due to the improved quality of the inversion, which performs better when there is a big moisture contrast across it, such as you find with these layers of cloud.
Otherwise, we find the better conditions are driven by night-time cooling forming a low inversion near the ground which tends to disperse during the morning as the Sun warms it away. This should still be positive for the 70cm UKAC on Tuesday 13th over eastern areas, perhaps less so farther west.
Good conditions will last into next week, but not everywhere. The main change will see an area of showery rain, possibly thundery, moving north into western Britain over this weekend and perhaps some central areas early next week. This raises the prospect of some GHz band rain scatter in the west.
Meteor scatter saw the peak of the Eta Aquariids last week, and in the decaying tail of activity, together with other lesser showers this should keep an enhanced meteor input for the coming week.
The Sporadic-E season typically runs from May to mid-September and the daily jet stream blogs have started on www.propquest.co.uk.
As usual, the main season offers two periods of activity, one in the morning and the second late afternoon/evening. Remember Es is not guaranteed since it depends upon many factors, but jet streams help, and these are shown on the web site maps. Use the map clusters to find out where, if any, activity is starting on 10m and then follow it up in frequency through the lower VHF bands. The 4m CW contest on Sunday 11th could benefit from some early-season Es, but it’s probably a big ask in early May.
EME path losses are at their maximum but falling after apogee on Friday the 9th. Moon declination is negative, reaching minimum this coming Thursday so we’ll have very short Moon windows and low peak elevation. 144MHz sky noise is moderate, increasing to high by next Friday.