Atmospheric electricity is always present, and during fine weather away from thunderstorms, the air above the surface of Earth is positively charged, while the Earth's surface charge is negative. This can be understood in terms of a
difference of potential between a point of the Earth's surface, and a point somewhere in the air above it. Because the atmospheric electric field is negatively directed (meaning toward the ground) in fair weather, the convention is to refer to the potential gradient, which has the opposite sign (meaning the electrical potential increases with distance from the ground) and is about 100 V/m at the surface, at a distance from thunderstorms. variation has been described as "the fundamental electrical heartbeat of the planet". Even away from thunderstorms, atmospheric electricity can be highly variable, but, generally, the electric field is enhanced in fogs and dust whereas the atmospheric electrical conductivity is diminished.
Links with biology The atmospheric potential gradient leads to an ion flow from the positively charged atmosphere to the negatively charged earth surface. Over a flat field on a day with clear skies, the atmospheric potential gradient is approximately 120 V/m. Objects protruding these fields, e.g. flowers and trees, can increase the electric field strength to several kilovolts per meter. These near-surface electrostatic forces are detected by organisms such as the bumblebee to navigate to flowers The atmospheric potential gradient is also thought to affect sub-surface electro-chemistry and microbial processes. On the other hand, swarming insects and birds can be a source of biogenic charge in the atmosphere, likely contributing to a source of electrical variability in the atmosphere.
Near space The electrosphere layer (from tens of kilometers above the surface of the Earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential. The
ionosphere is the inner edge of the
magnetosphere and is the part of the atmosphere that is ionized by solar radiation. (
Photoionization is a physical process in which a photon is incident on an atom, ion or molecule, resulting in the ejection of one or more electrons.)
Cosmic radiation The Earth, and almost all living things on it, are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from
protons to
iron and larger
nuclei derived sources outside the
Solar System. This radiation interacts with atoms in the atmosphere to create an
air shower of secondary ionising radiation, including
X-rays,
muons,
protons,
alpha particles,
pions, and
electrons. Ionization from this secondary radiation ensures that the atmosphere is weakly conductive, and the slight current flow from these ions over the Earth's surface balances the current flow from thunderstorms. ''
St. Elmo's Fire'' is an electrical phenomenon in which luminous
plasma is created by a
coronal discharge originating from a
grounded object.
Ball lightning is often erroneously identified as St. Elmo's Fire, whereas they are separate and distinct phenomena. Although referred to as "fire", St. Elmo's Fire is, in fact,
plasma, and is observed, usually during a
thunderstorm, at the tops of trees, spires or other tall objects, or on the heads of animals, as a brush or star of light. Corona is caused by the electric field around the object in question
ionizing the air molecules, producing a
faint glow easily visible in low-light conditions. Approximately 1,000 – 30,000
volts per centimeter is required to induce St. Elmo's Fire; however, this is dependent on the
geometry of the object in question. Sharp points tend to require lower voltage levels to produce the same result because electric fields are more concentrated in areas of high curvature, thus discharges are more intense at the end of pointed objects. St. Elmo's Fire and normal sparks both can appear when high electrical voltage affects a gas. St. Elmo's fire is seen during thunderstorms when the ground below the storm is electrically charged, and there is high voltage in the air between the cloud and the ground. The voltage tears apart the air molecules and the gas begins to glow. The nitrogen and oxygen in the Earth's atmosphere causes St. Elmo's Fire to fluoresce with blue or violet light; this is similar to the mechanism that causes neon signs to glow.
Earth-Ionosphere cavity The
Schumann resonances are a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earth's electromagnetic field spectrum. Schumann resonance is due to the space between the surface of the Earth and the conductive ionosphere acting as a
waveguide. The limited dimensions of the earth cause this waveguide to act as a resonant cavity for electromagnetic waves. The cavity is naturally excited by energy from lightning strikes.
Electrical system grounding Atmospheric charges can cause undesirable, dangerous, and potentially lethal charge potential buildup in suspended electric wire power distribution systems. Bare wires suspended in the air spanning many kilometers and isolated from the ground can collect very large stored charges at high voltage, even when there is no thunderstorm or lightning occurring. This charge will seek to discharge itself through the path of least insulation, which can occur when a person reaches out to activate a power switch or to use an electric device. To dissipate atmospheric charge buildup, one side of the electrical distribution system is connected to the earth at many points throughout the distribution system, as often as on every support
pole. The one earth-connected wire is commonly referred to as the "protective earth", and provides path for the charge potential to dissipate without causing damage, and provides redundancy in case any one of the ground paths is poor due to corrosion or poor ground conductivity. The additional electric grounding wire that carries no power serves a secondary role, providing a high-current short-circuit path to rapidly blow fuses and render a damaged device safe, rather than have an ungrounded device with damaged insulation become "electrically live" via the grid power supply, and hazardous to touch. Each
transformer in an alternating current distribution grid segments the grounding system into a new separate circuit loop. These separate grids must also be grounded on one side to prevent charge buildup within them relative to the rest of the system, and which could cause damage from charge potentials discharging across the transformer coils to the other grounded side of the distribution network. == See also ==