Sporadic E
| Sporadic E | |
|---|---|
| Also written | Es |
| Where | Thin patches in the E region of the ionosphere, about 100–115 km (60–70 miles) up |
| Main season | May to August in the Northern Hemisphere, peaking in June and early July |
| Second season | A smaller peak around late December and early January |
| Operating | |
| Bands | 10 m and 6 m often; 2 m occasionally |
| Single-hop range | About 500–1,400 miles |
| Multi-hop range | 2,000 miles and more |
| Duration | Minutes to several hours |
Sporadic E, often written Es, is the appearance of small, unusually dense patches of ionization in the E layer of the ionosphere. The patches return signals at frequencies far above anything the normal E layer can handle, producing sudden, strong openings on 10 meters, 6 meters and occasionally the 2-meter band over paths of roughly 500 to 1,400 miles. The name reflects its unpredictability: openings arrive with little warning and may last a few minutes or several hours.
What causes it
Sporadic E clouds form about 100 to 115 km (60 to 70 miles) up. They are thin, far denser than the surrounding E layer, and they drift, so an opening may shift from one region to another over an hour or two. The leading explanation is wind shear: winds blowing in different directions at slightly different heights sweep metal ions, left behind by burning meteors, into a thin, dense sheet. Many details are still being researched, and no one can yet forecast an individual opening.
Unlike the F layer, sporadic E has little connection to the solar cycle. It brings lively summer openings even at solar minimum, when the higher HF bands are otherwise quiet.
When it happens
In the Northern Hemisphere the main season runs from about May to August, peaking in June and early July around the summer solstice. A second, smaller season comes around late December and early January. In the Southern Hemisphere the main season falls in its own summer, around December and January. Openings can happen at any hour but are most frequent during the day and into the early evening.
Bands and distances
How far a signal travels depends on the height of the patch and the angle at which the signal meets it. A single hop covers roughly 500 to 1,400 miles, with the upper limit set by the curvature of Earth. When two patches line up, double-hop sporadic E reaches 2,000 miles or more, and in early summer, multi-hop openings on 6 meters sometimes link North America with Europe.
The higher the frequency, the denser the patch must be:
- 10 meters opens by sporadic E on many days in season. Technicians can use SSB voice from 28.300 to 28.500 MHz, which makes 10-meter Es a common first taste of long-distance contacts.
- 6 meters is the classic sporadic E band, nicknamed "the magic band" for openings that seem to appear from nowhere.
- 2 meters needs exceptionally dense ionization and opens by Es only a few times a year in a given area, often for just minutes. Because only signals meeting the patch at a shallow angle are returned, 2-meter Es contacts tend to be at the long end of the range, usually beyond 1,000 miles.
Working sporadic E
Es signals are often strong, so simple stations do well: 100 watts and a dipole or small Yagi are plenty on 6 meters. Horizontal polarization is the convention for SSB and CW. In the US the SSB calling frequencies are 50.125 MHz on 6 meters and 144.200 MHz on 2 meters, and FT8 on 50.313 MHz has made even weak 6-meter openings easy to spot.
The skip distance is a clue to how dense a patch is. As ionization builds, the skip on 10 meters shortens and then 6 meters opens. When 6-meter skip shrinks to a few hundred miles, or distant FM broadcast stations start coming in, the patch may be dense enough for 2 meters. Online spotting networks and maps of FT8 reception show openings as they happen.
Openings are short and crowded, so keep contacts brief. Call signs, a signal report and a grid square are the usual exchange.