About Sporadic E

In strawberry season, not all fruits in the garden are strawberries. This analogy illustrates the assumption that many radio hams make about Sporadic E propagation. Because it’s June, they assume that all VHF contacts are made via Sporadic E. This presentation strives to explain Sporadic E (Es) propagation and debunk such assumption.

For more on Sporadic E see https://hamradio.engineering/sporadic-e/

The E region of the ionosphere comprises a narrow layer around 100km above the surface of the Earth. It’s well above weather and other tropospheric events. It does receive quite a cooking from the sun and hence is somewhat ionised – but not as densely ionised as the higher F region above at 400km. The F region provides most HF and some sporadic VHF long distance communications.

The E region is unique in that meteors cause it to become more dense by adding ablated metal ions to the mix, thereby creating a region that behaves like an F region on steroids. This enhanced ionisation enables VHF signals to be refracted, turned back towards the Earth. Communications distances of between about 1,000 and 5,000km are possible.

There are three types of Sporadic E – northern auroral Es (distinct from radio aurora but also caused by the solar wind), equatorial Es (caused by direct sun heating), and mid-latitude Es (caused by descending metal ions). This presentation is about mid-latitude Es.

Sporadic E has many variables – the Sun’s radiation, wind shear, winds and tides, the Earth's geomagnetic field, disturbance of the geomagnetic field, meteor characteristics, time, latitude, and tropospheric effects (like mountain turbulence, jet streams and thunderstorms) creating atmospheric gravity waves that propagate upwards. As a result of the many variables, it’s impossible to predict when an Es opening will occur.

This presentation builds a model to aid understanding.

Es openings can be described statistically:
• ‘a 50MHz path will exist between the UK and Italy during 20% of days’; or
• ‘there’s a 1% chance of a 15-minute opening at 144MHz over a 2,000km path’.
And such statements can go on to state months and locations. Es is most prevalent over the summer months and less frequent in winter.

Radio hams understand that after a strong opening on one day, there may be no opening the next, but perhaps a muted opening three days later. The title is appropriate – the enhanced propagation is sporadic.

Modern communications methods like FT8 together with the PSKReporter site allow the extent of Es to be explored. But traditional methods like CW and phone (SSB) are still enjoyed.