Types of lightning and what each one means

01

What is the difference between cloud-to-ground and intracloud lightning?[1][2]

Cloud-to-ground lightning connects the cloud base to the surface and is the type that causes casualties and fires. Intracloud lightning stays within a single cloud, and is the most common form overall. Both produce thunder and both are detected by radio-based networks.

The ratio is genuinely uncertain, and quoted figures depend on where and how it was measured. Satellite work combining optical total-flash counts with ground networks found a mean near 2.6 to 2.9 in-cloud flashes per ground flash over the United States, with local values from about 1 over the Rockies and Appalachians to 8 or 10 in the upper Midwest. NOAA's National Severe Storms Laboratory quotes 5 to 10 as a global rule of thumb. Treat any single number as an average hiding a wide spread.

The regional pattern behind that spread is consistent. Deep tropical storms keep more of their discharges internal, while shallow winter storms send a larger share of theirs to ground.

Some intracloud flashes cover enormous horizontal distances. Discharges that crawl along the underside of a storm's anvil, nicknamed anvil crawlers, can run for tens of kilometers in a single flash, which is why lightning sometimes appears to ripple across the whole sky at once.

Cloud-to-ground (CG)

the minority of discharges, and the dangerous type

Intracloud (IC)

the most common. Seen as diffuse flickering inside the cloud

Cloud-to-cloud

bridges separate clouds, sometimes over long horizontal distances

Cloud-to-air

discharges into clear air without completing a path to ground

02

What is the difference between positive and negative lightning?[1][2]

About 90% of cloud-to-ground strikes are negative, delivering electrons from the cloud base with a typical peak current near 30,000 amperes. Positive strikes originate from the storm's upper positive charge region, are roughly ten times rarer, and can reach peak currents around 400,000 amperes.

Positive strikes also tend to hold their current for longer, a property called continuing current. That extra duration pushes more energy into whatever was hit, which is why positive lightning starts a disproportionate share of wildfires and does outsized damage to structures.

Because the positive charge sits near the storm top, these strikes often travel far horizontally before turning toward the ground. A positive strike can land more than 10 km from the rain, under apparently clear sky, which is where the phrase bolt from the blue comes from. Winter storms and dissipating storms both produce a higher proportion of positive strikes than a summer storm in its prime.

03

What is sheet lightning and heat lightning?

Neither is a distinct type of lightning. Sheet lightning is an ordinary flash whose channel is hidden by cloud, so you see only diffuse illumination. Heat lightning is a normal strike so far away that its thunder never reaches you, typically beyond 16 km.

Heat lightning is a persistent misnomer. Heat does not create a special silent form of lightning; distance simply removes the sound. A live lightning map makes this obvious, because the silent flashes on your horizon appear on the map as ordinary strikes with ordinary positions.

04

What are sprites, elves and blue jets?

They are discharges above thunderstorms rather than below them, known collectively as transient luminous events. Sprites are red flashes between roughly 50 and 90 km altitude, elves are expanding rings of light near 100 km, and blue jets are cones that climb from cloud tops toward 50 km.

Sprites were first photographed in 1989, by accident, when a low-light camera being tested for a rocket flight happened to record one over a distant storm. Pilots had been reporting strange flashes above storms for decades and were mostly not believed until then.

A sprite lasts only a few milliseconds and is usually triggered by a strong positive cloud-to-ground strike, so they are a rare by-product of the most powerful ordinary lightning. None of these upper-atmosphere discharges pose any hazard at ground level, and radio detection networks do not map them.

05

Is ball lightning real?[3]

Ball lightning is widely reported but poorly understood. Thousands of eyewitness accounts describe glowing spheres lasting several seconds, and one 2012 Chinese observation captured a spectrum by chance, but no laboratory has reliably reproduced it and no single theory is accepted.

The 2012 measurement, made accidentally by researchers studying ordinary lightning, showed silicon, iron and calcium in the glow, consistent with vaporised soil. That supports one leading hypothesis, but a single spectrum is not a settled explanation.