Monday, May 25, 2015

Look North (and West)

We are now well past the equinox and into summertime band conditions. Although the solstice is 4 weeks away you may notice that the sunrise and sunset times will change very little for the next 2 months, at least in these mid-northern latitudes. In the tropics and subtropics the sunrise and sunset times never change much throughout the year.

Around here summer is notable for atmospheric noise, less-spectacular propagation and lack of activity. Our summers are short enough that there is a lot of incentive to get out of the shack and enjoy the weather while it lasts. This includes antenna and tower work.

Despite this there are opportunities for some surprisingly good conditions. Also, hams far in the southern hemisphere are in their cool months and more than happy to be looking for contacts. Even in the tropics where it is always warm an air-conditioned shack can be a welcome respite from the heat. Here in the north we should pay attention to the factors that can bring some fascinating summertime openings and DX.


When you live close to the auroral zone it is common to experience attenuated or worse propagation on the polar routes. The farther north you go the worse it gets since more compass points intersect this zone, plus it takes less of a geomagnetic disturbance to shut down propagation. This makes it worthwhile to pay attention to those times when geomagnetic conditions are quiet. Right now is one of those times.

Screen shot from WM7D's web site the morning of May 25, 2015
Many of us pay attention to the geomagnetic indices (A and K) and the solar flux to get an idea of what to expect on the bands. This is not the whole story. Especially at these latitudes what can matter far more is the duration of quiet geomagnetic conditions.

Most of the literature notes this though I wonder how many pay attention. It is difficult to mentally track the indices. Seeing the data already charted is useful. I frequently refer to WM7D's web site since it shows the important information in charts right at the top of the page.

As I write this the solar flux is hovering just below 100. While not great it still promises a decent MUF. Since there have been several days of geomagnetic silence the polar paths are likely to be open when the MUF cooperates. It is typically lower looking north due to the lower solar insolation at mid-arctic (and mid-antarctic) latitudes.

Land of the Midnight Sun

With the nearness of the summer solstice the arctic region is in perpetual sunlight. From a radio perspective this means even at night in mid-latitudes the terminator (boundary between day and night) is not far away. If you can only inject your signal into the daylight you have a chance to go very far indeed.

The image above shows the location of the terminator for this date (May 25) at midnight (0400Z) at my location (FN25, Ottawa). You can see the line representing the arctic circle almost tangent to the terminator. If the solar flux is high enough and the geomagnetic indices low enough the path to Asia will open on the high bands throughout much of the evening. There is a similar long path opening southward over the antarctic during the northern winter daytime.

Putting it together

The past couple of evenings have seen some very workable openings to Asia on 20 through 15 meters. Even with the modest solar flux I worked a number of UA0's on 15 during our evening (their morning). Also heard were JA, YB, BY and more. The further south in Asia the station the poorer the signal, as a general rule. These stations are much stronger on 17 and 20, where the openings also last later into the night.

Since the path works in both directions there is a mirror opening during our morning and Asian evening. This morning was evidence of that with many Asians heard here on the high bands. I only worked a couple before the day's activities tore me from the shack.

It is not only the northern path that benefits from quiet geomagnetic conditions. This is also when the lower bands can shine. Right after sunrise the skip distance looking west (towards the darkness) is long which greatly reduces atmospheric QRN from distant weather systems. The lack of any geomagnetic disturbance also reduces absorption in the lower ionospheric layers, which keeps the low bands open longer until the sun makes the D-layer opaque.

This is a great time to look west to the Pacific. This morning I had a lengthy QSO with a VK on 30 meters about 90 minutes after my sunrise. Copy was solid even though we were both running low power and simple wire antennas. Last week I worked a ZL on 40 meters a full 60 minutes after sunrise. In both cases their signals were not strong but the band noise was very low. Unlike the evening there is no local QRN from neighbours' lighting systems and appliances. It all makes for superior conditions.

The only real problem is that I am not a morning person, therefore I don't often take advantage of these openings!

No comments:

Post a Comment

All comments are moderated, and should appear within one day of submission.