Lightning is one of nature's most spectacular phenomena, characterized by a massive electrical discharge that occurs between clouds or from a cloud to the ground.
This powerful event not only illuminates the sky but also poses significant risks, making its detection and monitoring crucial for public safety and various industries. In this blog entry, we take a look at what lightning is and how we monitor it.
What is lightning?
Lightning forms within storm clouds where updraughts propel tiny water droplets to the top of the cloud, turning them into ice. Some ice particles grow into hail, while others remain small. As hail falls through the cloud, it collides with smaller ice particles, transferring electrons and creating a negative charge in the hail and a positive charge in the ice particles. The updraughts continue to carry the positively charged ice particles upwards, while the negatively charged hail falls, creating a charge separation within the cloud.
The charge separation causes negative charge to build at the base of the cloud. This causes electrons near the ground's surface to be repelled. This leaves the ground and the objects on it with a positive charge. As the charge continues to build, attraction between the cloud and the ground grows stronger. This causes the electrical insulation of the air begin to break down. This allows electrons to shoot down from the cloud cutting through the air at around 270,000 miles per hour. A flow of electrons is an electrical current. The electrical current transferred is of the order 10 -100 kA, which causes the optical flash we see that is lightning. Furthermore the intense currents rapidly heat the air causing a shockwave which is heard as thunder.
Types of lightning
Lightning can manifest in various forms, each with unique characteristics:
- Ball lightning - an incredibly rare form of lightning in which a persistent and moving luminous white or coloured sphere is seen. There is various hypothesis but the leading one is that the luminous sphere could be a bubble of glowing soil particles which was formed when the lightning strike hit the ground.
- Rocket lightning - a very rare and unexplained form of lightning in which the speed of propagation of the lightning strike is slow enough to be perceptible to the eye. These are normally seen at the top of the thunderclouds.
- Pearl-necklace lightning - a rare form of lightning, also termed 'chain lightning' or 'beaded lightning', in which variations of brightness along the discharge path give rise to a momentary appearance similar to pearls on a string.
- Ribbon lightning - ordinary cloud-to-ground lightning that appears to be spread horizontally into a ribbon of parallel luminous streaks when a very strong wind is blowing at right angles to the observer's line of sight.
- Forked lightning - lightning in which many luminous branches from the main discharge channel are visible.
- Sheet lightning - the popular name applied to a 'cloud discharge' form of lightning in which the emitted light appears diffuse and there is an apparent absence of a main channel because of the obscuring effect of the cloud.
- Streak lightning - a lightning discharge which has a distinct main channel, often tortuous and branching, the discharge may be from cloud to ground or from cloud to air.
READ MORE: What causes thunder and lightning?
Monitoring lightning: The Met Office LEELA system
The Met Office employs the LEELA (Lightning Electromagnetic Emission Location by Arrival time difference) system to monitor lightning. LEELA is an automatic lightning location network consisting of ten sensors positioned across Europe. This system detects pulses of radio waves, known as 'sferics,' emitted during lightning strikes at a very low frequency (VLF). These sferics travel great distances, reflected between the Earth's surface and the ionosphere, similar to light in a fiber optic cable.
To pinpoint the exact location of thunderstorms, LEELA uses a network of sensors that detect sferics at slightly different times. Through a technique called multi-lateration, the system calculates the arrival time difference (ATD) of sferics at each sensor, determining the precise location of the lightning stroke.
READ MORE: Learn about lightning
Applications and limitations of LEELA
LEELA data is invaluable for identifying hazardous weather associated with thunderstorms, such as intense precipitation, severe icing, wind shear, turbulence, and strong wind gusts. This information is crucial for public safety, aviation, and other industries. LEELA provides continuous lightning data in Met Office bulletins, 24 hours a day, 365 days a year.
However, LEELA has some limitations:
- It does not yet discriminate between different types of lightning (e.g., in-cloud or cloud-to-ground).
- Its accuracy and sensitivity diminish at longer ranges.
- It does not cover the entire globe, with areas like Far East Asia, Russia, South East Asia, Australia, mainland USA, and the Pacific typically out of range.
- LEELA only reports the time and location of lightning strokes, not their intensity, polarity, or other attributes.
Despite these limitations, LEELA is a significant advancement in lightning detection, offering twice the detection capability of its predecessor, ATDnet, with comparable accuracy.
READ MORE: Check out our live lightning strike map
Lightning is a fascinating natural phenomenon. Understanding its formation and characteristics is essential for appreciating its impact. The Met Office's LEELA system plays a crucial role in monitoring lightning, providing vital data to mitigate the risks associated with thunderstorms.
As technology advances, systems like LEELA will continue to enhance our ability to predict and respond to hazardous weather, ensuring greater safety and preparedness.
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