South! 6 Meters Opens

It takes a lot of EUV to light up the ionosphere's F-layer bring 50 MHz signals down to Earth at my geomagnetic latitude. That happened this week for, as far as I know, the first time in solar cycle 25. Despite lasting only 3 minutes it made an impression on me. Here is what I found on my screen late afternoon of March 14 while I was busy elsewhere.

LU, CE and CX. It is the north-south path that is the first to open at this latitude as the MUF rises. Of course I cannot be certain that this is truly an F-layer phenomenon. There is TEP and southern hemisphere sporadic E that may be in play for part of the path. I can discount sporadic E at this end of the path since these openings have correlated well with the recent rise of the solar flux, and persistent for several days at a time of year when sporadic E is historically rare. Unfortunately for us the propagation only reached as far as the southern and central US.

It was no accident that I was monitoring the southern path. There have been ample reports of contacts between southern Europe and southern Africa, Japan and Australia and South America to the southern US. The propagation was there, tracking the solar flux and slowing creeping northward. Digital modes make it convenient to monitor the band to discover elusive openings while I go about my day. 

A friend has been using DXmaps (see screen capture at right) to plot the openings. He found them there as well. There are many tools available to help discover openings.

We are on the cusp of F-layer global communication on 6 meters. It will occur even if this solar cycle is no better than the historically weak previous cycle. What we probably won't get is extensive east-west propagation or on northerly paths from this part of the world. Time will tell.

The openings this week are most likely due to what I call the holy trinity of north-south propagation:

1. Moderately high solar flux, in the vicinity of 115 to 120
2. Equinox
3. Aftermath of a geomagnetic disturbance.

The planetary K-index was at 5 to 6 for 15 hours the previous day. During each equinox period there can be extended north-south propagation after sunrise and before sunset, assisted by gray line propagation along a great circle that intersects both geographic poles. I was not surprised to hear and work stations from southeast Asia (YB, E2) on 15 and 17 meters early to mid-morning.

On its own a solar flux of 120 is usually inadequate to raise the MUF above 50 MHz this far north. The other two factors were likely needed to open the band. A flux of 140 would significantly raise the probability of an opening without other factors coming into play. That has only occurred once this. The other two factors were in play and 6 meters didn't open here. Over the two days following the March 14 opening, as we moved past the disturbance, there was nothing heard here despite the stable solar flux.

As the solar flux rises further we'll see propagation extend to the southeast and southwest. That includes southern Africa, Central America, W6 and New Zealand. As the flux rises towards 200 we should get openings to northern Africa, most of Oceania, southern Europe and, eventually, all of Europe. 

F-layer openings to Asia are unlikely if the solar cycle continues on its current track. Of course the propagation will be better further south. At the exceptional peak of cycle 22 in 1989/1990 there were only a few days when I heard Japan, and worked none of them. In contrast, I have around 100 sporadic E contacts with Japan, via FT8. Sporadic E will remain an important propagation mode even during the cycle's peak years.

My station is ready to go so I am eager for F-layer propagation to arrive. I need it to extend my DXCC count on the magic band since sporadic E is inadequate to reach most of the world. But I am eagerly anticipating its return in May. Sporadic E will remain the dominant DX propagation mode in 2022.