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Atmospheric Electricity

An advanced exploration of Earth's atmospheric electrical phenomena, the global electrical circuit, lightning, and related concepts.

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Historical Foundations

Early Observations and Hypotheses

The study of atmospheric electricity has roots stretching back centuries. Early experimenters like Francis Hauksbee, Isaac Newton, and Jean-Antoine Nollet observed electrical phenomena in laboratories and drew parallels to lightning. William Wall, in 1708, was among the first to note the similarity between laboratory sparks and miniature lightning.

Franklin's Groundbreaking Work

Benjamin Franklin's pivotal experiments demonstrated that atmospheric electrical phenomena were fundamentally similar to laboratory-generated electricity. By 1749, he had hypothesized that electricity could be drawn from clouds using a pointed aerial. Thomas-François Dalibard's 1752 experiment in Marly-la-Ville, France, successfully drew sparks from a cloud, validating Franklin's theory, which Franklin himself reportedly confirmed with his famous kite experiment shortly thereafter.

Expanding the Understanding

Subsequent researchers like L. G. Lemonnier, Giovanni Battista Beccaria, and Horace-Bénédict de Saussure meticulously documented diurnal and annual variations in atmospheric electrification and its relationship with altitude. Charles-Augustin de Coulomb's discovery of air's electrical conductivity in 1785 challenged prevailing notions of atmospheric gases as insulators.

Systematic Measurement and Theory

In the 19th century, figures like Francis Ronalds pioneered continuous automated recordings of atmospheric electricity at Kew Observatory, establishing the first comprehensive datasets. Lord Kelvin's innovations in electrometers further advanced measurement capabilities. Elster and Geitel proposed theories on thunderstorm electrification and discovered atmospheric radioactivity, while Pockels analyzed lightning currents through magnetic field studies. The 20th century saw continued research into high-energy particles, transient luminous events, and the role of non-thunderstorm electrical processes.

The Nature of Atmospheric Electricity

The Global Electrical Circuit

Atmospheric electricity describes the electrical charges present within a planet's atmosphere. The continuous movement of electrical charge between the Earth's surface, the atmosphere, and the ionosphere constitutes the global atmospheric electrical circuit. This phenomenon is a complex interplay of electrostatics, atmospheric physics, meteorology, and Earth science.

Atmospheric Potential Gradient

In fair weather, away from thunderstorms, the Earth's surface typically carries a negative charge, while the atmosphere above is positively charged. This creates a potential difference, resulting in an electric field directed downwards towards the ground. The average magnitude of this field near the Earth's surface is approximately 100 volts per meter (V/m), though it decreases with increasing altitude. This field drives a weak conduction current of atmospheric ions.

Ionization and Conductivity

The atmosphere is never electrically neutral due to continuous ionization from cosmic rays and natural radioactivity. These processes generate atmospheric ions, which are crucial for the atmosphere's weak electrical conductivity. This conductivity allows for the flow of small electrical currents, even in the absence of thunderstorms.

Temporal and Environmental Variations

The Carnegie Curve

Global daily cycles in the atmospheric electric field exhibit a distinct pattern, known as the Carnegie curve. This variation, with a minimum around 03 Universal Time (UT) and peaking approximately 16 hours later, has been described as the planet's fundamental electrical heartbeat. It reflects the integrated electrical activity across the globe.

Influence of Local Conditions

Atmospheric electricity is subject to significant variability. Even away from major storm systems, factors like fogs and dust storms can enhance the electric field while simultaneously diminishing the atmospheric electrical conductivity. These localized conditions play a crucial role in the dynamic behavior of atmospheric charge.

Biological Interactions

Navigation and Dispersal

The atmospheric potential gradient influences organisms. Electrostatic forces near the Earth's surface, amplified by objects like flowers and trees, are detected by insects such as bumblebees for navigation. Similarly, spiders utilize these electric fields to initiate dispersal through ballooning.

Biogenic Charge Sources

Conversely, biological activity can also contribute to atmospheric electricity. Swarming insects and birds can act as sources of biogenic charge, introducing variability into the atmospheric electrical system. This bidirectional influence highlights the intricate connection between atmospheric phenomena and the biosphere.

Subsurface Processes

The atmospheric potential gradient is also thought to influence electro-chemical processes and microbial activity beneath the Earth's surface, suggesting a deeper connection between atmospheric electrical states and terrestrial biogeochemistry.

Atmospheric Electricity and Near Space

The Electrosphere

The region extending from tens of kilometers above the Earth's surface up to the ionosphere is known as the electrosphere. This layer possesses high electrical conductivity and maintains a relatively constant electric potential. It forms the inner boundary of the magnetosphere.

Ionization by Solar Radiation

The ionosphere, a key component of the upper atmosphere, is significantly ionized by solar radiation. This process, known as photoionization, involves photons interacting with atmospheric atoms and molecules, leading to the ejection of electrons. This ionization is fundamental to the electrical properties of the upper atmosphere.

Cosmic Radiation's Influence

Secondary Ionizing Radiation

The Earth and its atmosphere are continuously bombarded by cosmic rays originating from beyond the Solar System. These high-energy particles, primarily protons and atomic nuclei, interact with atmospheric atoms to produce extensive air showers of secondary ionizing radiation, including X-rays, muons, and electrons. This secondary radiation ensures the atmosphere remains weakly conductive.

Balancing Atmospheric Currents

The ionization generated by cosmic rays leads to a slight current flow over the Earth's surface. This current plays a vital role in balancing the electrical current generated by thunderstorms, contributing to the overall stability of the global atmospheric electrical circuit. The characteristic parameters of these ions, such as mobility and lifetime, vary significantly with altitude.

Thunderstorms and Lightning

The Atmosphere's Battery

Thunderstorms function as massive atmospheric batteries, generating substantial potential differences—up to 400,000 volts—between the upper atmosphere (electrosphere) and the Earth's surface. This charge separation within cumulonimbus clouds, driven by collisions between ice particles and graupel, is the precursor to lightning.

Lightning Phenomena

Lightning discharges are rapid releases of atmospheric charge. A typical cloud-to-ground lightning bolt can carry tens of thousands of amperes and millions of volts, emitting light, radio waves, X-rays, and gamma rays. The plasma temperature within lightning channels can reach extreme levels, approaching 28,000 Kelvin. The energy released by an average thunderstorm is immense, comparable to a 20-kiloton nuclear warhead.

Corona Discharges (St. Elmo's Fire)

St. Elmo's Fire is a visible electrical discharge, a form of plasma, occurring from grounded objects like spires or animal heads during thunderstorms. It arises from a coronal discharge caused by strong electric fields ionizing surrounding air molecules. While often mistaken for ball lightning, it is a distinct phenomenon, typically glowing blue or violet due to nitrogen and oxygen excitation.

Earth-Ionosphere Cavity

Resonant Electromagnetic Waves

The space between the Earth's surface and the conductive ionosphere acts as a natural waveguide. This cavity resonates with electromagnetic waves, particularly in the extremely low frequency (ELF) range, creating Schumann resonances. These resonances are primarily excited by the global network of lightning discharges.

Electrical System Grounding

Dissipating Atmospheric Charge

Atmospheric charges can accumulate on overhead power distribution systems, posing a risk of dangerous discharge. To mitigate this, electrical systems are connected to the Earth at multiple points, commonly at each support pole. This grounding provides a path for atmospheric charge to dissipate safely.

Protective Earth and Redundancy

The "protective earth" wire serves to dissipate accumulated charge and provides a high-current path for short circuits, enabling fuses to blow and preventing damage to equipment or hazards to users. Each transformer in an AC grid segments the grounding system, requiring grounding on one side to prevent charge buildup relative to other parts of the network.

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References

References

  1.  See Flashes in the Sky: Earth's Gamma-Ray Bursts Triggered by Lightning
  2.  Vladimir A. Rakov, Martin A. Uman (2003) Lightning: Physics and Effects. Cambridge University Press
  3.  Encyclopedia of Geomagnetism and Paleomagnetism - Page 359
A full list of references for this article are available at the Atmospheric electricity Wikipedia page

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Important Notice

This page has been meticulously generated by an Artificial Intelligence, drawing upon a comprehensive analysis of publicly available data. It is intended solely for advanced informational and educational purposes, targeting higher education students and researchers.

This content is not a substitute for professional scientific consultation. The information provided herein is based on a snapshot of data and may not be entirely exhaustive, up-to-date, or applicable to all specific contexts. Always consult peer-reviewed literature, official scientific documentation, and qualified experts for critical research, practical applications, or safety-related decisions.

The creators of this page assume no liability for any errors, omissions, or consequences arising from the use of this information.