Sporadic-E explained
Sporadic-E is responsible for most of the long-distance contacts made on 6 meters. It arrives without warning, can be strong enough for a handheld radio, and disappears just as suddenly. This guide explains what it is, when it happens and how to make the most of it.
What sporadic-E is
The E region of the ionosphere sits roughly 90 to 130 km above the Earth. Normally its ionization is far too weak to reflect 50 MHz signals. Sporadic-E (often written Es) refers to thin, dense patches of ionization that form within this region, usually at about 100 to 110 km. A patch might be a few tens of kilometers across, and it may drift, intensify and fade over minutes to hours.
The leading explanation involves metallic ions, such as iron and magnesium, left behind by meteors. Shear in the upper atmospheric winds, driven partly by atmospheric tides, compresses these long-lived ions into thin layers. The denser the layer, the higher the frequency it can reflect. During strong events, the MUF can rise well above 50 MHz and sometimes reaches the 2 meter band.
How far signals travel
Because the layer is about 105 km high, geometry limits a single reflection to roughly 2,300 km. The shortest single-hop distance depends on the cloud's density: the higher the MUF, the shorter the skip. On 6 meters, single-hop Es typically covers 900 to 2,300 km.
When more than one cloud is active, signals can be reflected two or more times. Double-hop Es reaches about 2,300 to 4,600 km, and in peak season multi-hop chains carry signals 6,000 km or farther, for example between Europe and North America or Japan. These paths are shown in green, amber and pink on the live map.
Seasons
Sporadic-E follows a strong seasonal pattern. In each hemisphere the main season is centered on the summer solstice:
- Northern Hemisphere: the main season runs from May to August, with the peak usually from mid-June to mid-July. A smaller season appears around late December and early January.
- Southern Hemisphere: the main season runs from November to February, peaking around late December and early January, with a minor season around June and July.
Outside these periods sporadic-E still happens, but much less often. The season meter on the live page estimates the typical likelihood for today's date in each hemisphere.
Time of day
Es can appear at any hour, but there are two common peaks: one from mid-morning to midday, and another from late afternoon into early evening local time. Late-evening openings are less common but can be spectacular in peak season. Because local time matters, an opening often appears to move west through the day as the sun moves.
How to catch an opening
- Watch the live map. A cluster of cyan paths between two regions means an Es cloud has formed between them. If your area sits at one end, point your antenna along the path.
- Monitor FT8. Leaving a receiver on 50.313 MHz with FT8 software running is the most sensitive way to detect openings, because the mode decodes signals far below audible levels.
- Listen to beacons. Beacons between about 50.000 and 50.080 MHz transmit constantly. A beacon popping up from 1,500 km away is a strong hint.
- Check 10 meters. Short skip on 28 MHz from a few hundred kilometers means the Es MUF is climbing toward 50 MHz.
- Be quick. Openings can last only a few minutes. Make short, efficient contacts and keep exchanges brief so others get a chance.
Chasing multi-hop and intercontinental Es
The longest Es paths need clouds positioned at just the right spacing. They are most common in the weeks around the solstice and often appear first as single-hop openings that gradually extend. Watch for paths that end near the coast in your direction, since the next hop may be about to reach you. Many operators use 50.323 MHz for intercontinental FT8 contacts to keep them separate from busy domestic activity on 50.313 MHz; see the frequency guide.
Tip: Es signals are usually stable and strong compared with other long-distance modes. If you hear a station fading in and out with a fluttering tone on a long north-south path, it is more likely trans-equatorial propagation. The propagation guide covers how to tell them apart.