The week started with a geomagnetic disturbance caused by a high-speed stream from a coronal hole, which moved past the Earth at a speed in excess of 500 kilometres per second. This was not predicted by NOAA, but it was from a long coronal hole limb that stretched towards the solar equator. It pushed the Kp index to four in the early hours of Monday, causing a depletion of the F2 layer that impacted HF for much of the morning. MUFs over a 3,000km path struggled to get up to 14MHz until 0930hrs. Meanwhile, we are seeing some more activity on the sunspot front. A new Cycle 25 region numbered 2770 rotated into view, pushing the sunspot number to 13 and the solar flux index to 73. While this isn’t too exciting, it is another step in the right direction. This sunspot region has been emitting a lot of B-class solar flares and we expect that to continue. Next week, NOAA predicts that the solar flux index will return to 69-71 with a maximum Kp index of two. At the time of writing, there were no coronal holes looking to threaten Earth.
The sporadic E season is now well past its peak, but there is always hope for openings on 10m, especially with high-efficiency modes like FT8. We expect daytime F2-layer MUFs to peak above 14MHz, with occasional openings on 18MHz. Night-time MUFS over a 3,000km path should remain above 10MHz after paths on 20m close at around 2200hrs.
VHF and up:
The VHF highlight next week is the annual Perseids meteor shower, peaking on the 12th with a huge ZHR of 100. This is the big opportunity to try meteor scatter on digimodes, with a very good chance of results. To avoid disappointment, read up on the procedures, bands and modes before you dive in.
It’s a mixed selection of propagation weather this week. The south and east had some tropo options last week and will do again into early next week, with a particularly strong indication from northern Britain across the North Sea at the end of this weekend. It also looks likely that a developing ridge from high pressure over the Atlantic will give a return of tropo potential at the end of the week, especially in the north and west. In between these two tropo periods the weather is essentially unsettled, with a tendency to produce slow-moving areas of showers. It’s quite likely that some will be heavy and thundery. This bodes well for GHz rain scatter opportunities, especially from the heavier showers.
It’s still worth a shout out for sporadic E, which is not over yet, although events are harder to find using CW or SSB. It’s not looking like a good set of jet stream charts, so as we said earlier FT8 is a good first place to look.
Moon declination is positive and rising this week so peak Moon elevations and visibility windows will follow suit. Combined with falling path losses, it’s an improving week for EME. 144MHz sky noise is low, peaking on Friday at 500K. (rsgb.org)