Lightning Strikes Up: The Return Stroke Revelation

Everything you think you know about lightning is backwards. That brilliant white-hot bolt splitting the sky? It's racing upward, not downward. The visible lightning strike is actually the grand finale of an invisible electromagnetic dance between earth and sky.

The Invisible Prelude

Before you see anything, a faint electrical channel called a stepped leader creeps down from the thundercloud at about 150 kilometers per second. It's dim, branching, and completely invisible to your eyes. As this leader descends, it's essentially asking the ground: "Anyone down there want to complete this circuit?"

When the leader gets within 15-50 meters of the surface, the ground shouts back. Positive charges begin streaming upward in what scientists call upward streamers. Tall trees, buildings, telephone poles—anything that sticks up—starts launching these streamers skyward. It's an electromagnetic auction, and the winner gets struck by lightning.

The Flash You Actually See

The moment a streamer connects with the stepped leader, the sky short-circuits to the ground. In that instant, a massive current explodes upward along the channel. This is the return stroke—and it's what your eyes perceive as lightning.

The return stroke is ridiculously fast and hot:

• Speed: 100,000 kilometers per second (one-third the speed of light)
• Peak current: typically 30,000 amperes, sometimes exceeding 200,000 amperes
• Temperature: 30,000°C—five times hotter than the surface of the Sun
• Duration: reaches the cloud base in about 100 microseconds

That superheated channel explosively expands the surrounding air, creating the thunderclap you hear seconds later.

Why the Confusion?

For centuries, humans assumed lightning traveled from cloud to ground because that's the direction it seems to move. The downward stepped leader is so dim that we don't see it. The upward return stroke is so bright and fast that our brains process it as a singular downward flash.

High-speed cameras finally revealed the truth in the 20th century. When you slow lightning down to thousands of frames per second, you can see the faint leader descending, then the brilliant return stroke racing upward.

Recent research from 2025 found that stepped leaders actually speed up as they approach the ground—increasing velocity by an average of 69% near the surface. The faster the leader, the more powerful the return stroke. It's as if the lightning knows it's about to hit and accelerates for maximum impact.

True Upward Lightning

There's also a rare phenomenon where lightning genuinely starts at the ground and travels only upward. This happens from extremely tall structures like skyscrapers or mountain peaks, usually triggered right after a nearby downward strike. These upward propagating discharges skip the stepped leader phase entirely and launch directly skyward.

So the next time you see a lightning bolt, remember: you're watching electricity explode upward at 100,000 kilometers per second, heating the air to temperatures that would vaporize steel in microseconds. The sky doesn't strike the earth—the earth strikes back.