Fall 2008 Issue

SSSP: Short-path
Summer Solstice Propagation

Two years ago, JE1BMJ developed a theory to explain

long-distance propagation on 6 meters. While his theory has become somewhat dated and even he is re-examining parts

of it, it is still considered a viable theory to at least partially explain the long-distance propagation. It is presented

here as a means of comparision with WB2AMU’s

article, which begins on page 6.

By Han Higasa, JE1BMJ

Figure 4. Map showing the electron density in the auroral oval at 0600 UTC on July 19, 2006.


For many years DXers on 50 MHz have been surprised by the unexpected and excellent short-path propagation from Japan to Europe and North America. In 2006, short-path QSOs from W to EU and KL7 to EU were also reported. This propagation, which occurs around the Summer Solstice of June 21st, has generally been described as “multi-hop sporadic-E” and has been reported from the 1970s onward. I would like to ask: “Who undertook the surveys or deep studies on this type of propagation?” and “Why has it been assumed to be multi-hop sporadic-E?”

SSSP, or S3P, is an acronym for Short-path Summer Solstice Propagation, a name that Chris, G3WOS, and I have called this type of propagation and that I believe not to be based on multiple hops. SSSP has been discovered in the Northern Hemisphere, but symmetrically there should also be similar propagation at the December Solstice in the Southern Hemisphere. Because the December Solstice is called the Winter Solstice in the Northern Hemisphere, one might want to call it SWSP (Short-path Winter Solstice Propagation), but in this article I will refer to both SSSP and SWSP simply as SSSP to avoid any confusion.

Here I define SSSP as the short-path propagation around the June Solstice in the Northern Hemisphere and the similar propagation around the December Solstice in the Southern Hemisphere.

In June 1999, I first found SSSP through a 50-MHz CW QSO with Toivo, OH7PI, and up to the year 2006 I continued running propagation tests called “The Six Metre Propagation Test Campaign around the Summer Solstice.” Although the amount of collected data is small and the exact mechanism is yet unknown, here I will introduce and hypothesize about the cause and nature of this type of propagation.

Why Has It Been Called “Multi-hop Sporadic-E”?

Figure 1 shows the usual model of multi-hop sporadic-E. In this model 50-MHz signals are refracted by E-layer clouds and reflected or bounced from the surface of the Earth several times between the transmitter and receiver—often described as one-hop or two-hop sporadic-E. However, I believe that assuming this mode of propagation stretches credibility when talking about summer short-path propagation between Japan and Europe.

Assuming the height of the E-cloud to be about 90 to 100 km, the maximum one-hop distance will be around 2,000 km. The distance of JA–EU propagation is between 10,000 and 12,000 km. Thus, the number of hops via classic multi-hop sporadic-E needs to be five, six, or even more. With JA–NA paths, we have a large area of sea on the path, but on the JA–EU path there is only the Eurasian continent and no water. Thus, the 50-MHz signal will be scattered and/or absorbed by the inefficient ground surface.

The short-path JA–EU QSOs seen this year are strong at the peak and the tone of CW signal is pure with little or no distortion—i.e., they do not appear to have been dispersed or scattered from, as would be expected, a signal that has been exposed to multiple reflections from the Earth’s uneven ground. Such distortion can easily be observed on EME signals. Because of this issue, I am confident that the multi-hop sporadic-E model is not adequate to explain the propagation we have experienced this summer and for which I have adopted the term SSSP.

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