Lightning

Lightning in storm clouds forms from the collisions between graupel—small hail particles—and smaller ice particles, which transfer electrons. Layers of opposing charges form as these differently sized particles rise and fall. When air can no longer insulate these layers, electricity discharges, equalizing these regions.

In cloud-to-ground lightning, a buildup of negative charge at the bottom of clouds repels electrons on Earth's surface, leaving behind positively charged particles. When descending negatively charged air—the stepped leader—meets rising positively charged particles—the upward streamer—brightening runs up the connection, producing intense flashes known as return strokes.

The rapid discharge of electricity—flowing electrons—between oppositely charged regions across a narrow filament can raise temperatures to 30,000 degrees Celsius (54,000 degrees Fahrenheit). If lightning strikes a tree, the speed of the temperature spike can almost immediately turn all its water into pressurized steam, causing it to explode.

In this series, award-winning photographer Adam Schallau accompanies each image with expert advice on how to capture the phenomenon successfully. Initially requiring the shutter to remain open for extended periods, today's technology includes a device called a lightning trigger, which senses incoming lightning and automatically manages the shutter.

Water-abundant areas that receive increased solar radiation, such as those near the equator, experience increased rates of evaporation, which produce tall clouds as moisture rises, cools, and condenses. Mountain ranges can also steer air to higher altitudes, creating collisions between atmospheric particles that generate charge imbalances—the precursors to lightning.

The most common form of lightning involves channels of electricity between oppositely charged regions within a cloud or between two clouds to reestablish electrostatic equilibrium. While cloud-to-ground lightning is understood best, research is ongoing to fully model the mechanisms behind rarer forms of lightning, such as transient luminous events.

Energized electrons from the base of clouds collide with oxygen molecules, placing them in a "singlet delta state," which makes the air conductive. Collisions continue until more than 1% of nearby oxygen is in this state—about 0.00005 seconds—matching the electrical potential of the cloud and propogating electricity in a 50-meter "step."

When the built-up layer of negative charge at the bottom of clouds is sufficiently high, a network of charge filaments will emerge. If one of the filaments meets a rising strand of positively charged particles, a highly conductive path forms, and charges across all filaments move to the path, generating lightning

Just as fire ranges from red to blue with increasing temperature, lightning's blueish-white comes from the superheating of air. Emission of light from the predominantly nitrogen and oxygen in the atmosphere provides a purple tint, with additional coloring caused by the scattering of light by humidity, hail, dust, and ash.

The rapid flow of electricity heats and pressurizes air, causing it to expand and produce a shockwave at each point along the bolt at multiple frequencies. As these shockwaves overlap, higher-frequency sounds, which produce a sudden crack, dissipate more quickly, while lower-frequency sounds—long booms and rumbles—travel farther.