how does lightning work

To begin, let’s examine how lightning forms. The building blocks of lightning are Thunderstorms. The storm itself is essentially a large-scale Heat engine. Heat is converted into kinetic energy via convection, as warm moist air ascends, expands, and cools. At higher altitudes where the temperature drops below freezing, ice crystals and hailstones form.

In addition to the physical processes occurring in the storm, there is also an electric component. Turbulence within the storm leads to the separation of charge. Lighter positively-charged ice crystals are carried upward by updrafts. Heavier negatively-charged hailstones and supercooled water droplets are pulled downward by gravity. Think of this as a cosmic version of a static electricity generator. Friction causes electrons to be transferred from the rising ice crystals to the falling hailstones. This process is referred to as non-inductive charge separation and is the primary mechanism.

Charge separation results in distinctly different regions within the cloud. The upper part of the cloud will accumulate a net positive charge while the middle and lower portions of the cloud will develop a net negative charge. Additionally, a smaller localized positive charge may develop near the base of the cloud, close to the Ground, as a result of interaction with the earth’s surface. This electrical imbalance provides the conditions necessary for lightning to develop.

Breaking down air’s electrical insulation

For lightning to form, an electrical insulating barrier must be broken. Typically, this occurs when the large amount of negative charge accumulated in the lower portion of the cloud develops a significant enough electrical field such that it causes free movement of electrons in the surrounding air molecules. Free electrons and ions then combine to create a conductive pathway (a stepped leader) that descends from the cloud toward the Ground in discrete segments (typically 50 to 100 meters long) at approximately 200,000 m/s. The stepped leader continues until it reaches a location where it can establish contact with the Ground.

Establishing contact between cloud and Ground

Once the stepped leader establishes contact with either the Ground or a positively-charged area of another cloud, a complete conductive channel is created. This channel is formed when a negatively-charged stepped leader contacts a positively-charged object located on or near the Ground. Objects that commonly act as positive sources include trees, buildings, transmission towers, and even bare open Ground. A positive source (positive streamer or “Ground streamer”) develops on or near the Ground as a result of being influenced by the enormous negative charge present at the tip of the descending stepped leader. When one of these positive streamers meets a descending stepped leader, a complete conductive channel is developed between the cloud and the Ground.

Formation of the bright flash: return stroke

Once a complete conductive channel is formed between the cloud and the Ground, the intense return stroke occurs. The return stroke is the brilliant flash of light we observe as lightning. During this brief period, an extremely large quantity of electrons flow down through the conductive pathway from the negatively charged cloud toward the positively charged Ground. This large influx of electrons creates extreme Heat within the conductive pathway. Temperatures produced in some cases are estimated to be greater than 30,000 Kelvin (more than 54,000° f), making them hotter than the surface of the sun. The rapid increase in temperature produces a tremendous expansion of gas in the conductive pathway. This rapid expansion generates an explosive force that creates an acoustic wave that is heard as thunder. Since light travels significantly faster than sound, we always see the flash before hearing the boom. The return stroke travels back up through the conductive pathway from the Ground toward the cloud at speeds exceeding 1/3 c.

Different Types of lightning

Not all lightning strikes land on or near the earth’s surface. Depending on where in the environment the discharge takes place, there are several types of lightning:

cloud-to-Ground (cg): although this type represents only about 20-25% of total lightning discharges, it is perhaps the most destructive form. It is characterized by discharge from a cloud to a location on or near the earth’s surface.
Intra-Cloud (ic): also referred to as sheet lightning, Intra-Cloud discharges occur entirely within a single cloud, between areas of opposing charges. Sheet lightning can illuminate nearly an entire cloud.
cloud-to-cloud (cc): discharge occurs between two separate clouds.
Ground-to-cloud (gc): much less common than cg-type lightning, gc discharges originate from a positive charge located on or near the earth’s surface (for example, on top of a tall structure such as a transmission tower). They travel upward to negatively charged regions in clouds. Some studies indicate that gc-type discharges may sometimes be initiated by an existing cg-type flash that occurred nearby.

Heat lightning refers to visible light from distant Thunderstorms’ lightning flashes where audible thunder has dissipated prior to arriving at the observer.

Current research and recent findings

Research into lightning remains an ongoing area of study. One recent advancement includes data collected using instruments installed on orbiting platforms, including nasa’s GLM aboard NOAA’s GOES-r series satellites. Such information is proving invaluable for collecting detailed knowledge regarding global distribution patterns and intensities of lightning activity. Another area of ongoing research involves other effects that appear in association with powerful lightning discharges and take place in regions far above Thunderstorms in the upper atmosphere — so-called tles (transient luminous events), which can be seen extending to the edge of outer space. These events likely arise from strong electromagnetic impulses generated by these powerful discharges, specifically those originating from positively charged regions of clouds (the upper portion). Powerful positive lightning strokes are believed to cause tles.

Why understanding lightning is important

Knowledge gained from studying lightning is vital for predicting severe weather, developing ways to protect life-saving equipment, vehicles and other sensitive electronic systems and potentially applying insights related to atmospheric chemistry.

How hot does a lightning strike get?

A lightning bolt heats the air immediately adjacent to it to approximately 30,000 Kelvin (about 54,000°f), five times hotter than the surface of our sun.

What causes thunder?

The shockwave responsible for producing thunder occurs when heated air expands rapidly along a lightning bolt’s conductive pathway. Rapidly-heated air expands violently and quickly produces pressure waves that arrive at your ears as sound.

Will lightning hit the same place twice?

Yes, lightning often hits the same spot multiple times; particularly structures that provide an easy path for electrical discharges to reach Ground level — such as skyscrapers — receive multiple hits each year.

Does ‘Heat lightning’ really exist?

No — Heat lightning is simply light emitted from distant Thunderstorms’ lightning flashes where no sound arrives after it disappears due to attenuation over great distances