Where does dipole collide?

In electromagnetism a dipole is a pair of equal and opposite charges separated by a small distance, summarised by a dipole moment whose size is charge times separation and whose direction points from negative to positive; it is the leading term in the multipole expansion of any neutral charge distribution and sets the field of polar molecules and the radiation of oscillating charges. Jackson's Classical electrodynamics and Griffiths's Introduction to electrodynamics derive the dipole field and potential. The referent is a charge configuration and its moment, the parent concept from which the antenna and climate uses borrow only the image of two opposite poles.[1][2]

Unit

The dipole moment, charge multiplied by separation, in coulomb-metres

Recovery means

Not applicable

Measured by

Determined from the far-field potential's inverse-square-cubed falloff or from a molecule's measured polarity

In antenna engineering a dipole is a straight radiator fed at its centre and split into two collinear arms, the half-wave dipole being the canonical case whose length is near half the operating wavelength; driven by an oscillating current it radiates a doughnut-shaped pattern broadside to the wire. Balanis's Antenna theory gives its current distribution, radiation resistance, and pattern. The referent is a physical radiating structure, named for the two-pole charge picture that drives it but distinct as a construct from the electrostatic dipole moment and entirely unrelated to an ocean-temperature seesaw.[3]

Unit

The radiator's length in wavelengths, with its radiation resistance and pattern

Recovery means

Not applicable

Measured by

Characterised by the measured radiation pattern, input impedance, and gain versus arm length

In climate science the Indian Ocean Dipole is a coupled ocean-atmosphere mode in which sea-surface temperatures in the western and eastern tropical Indian Ocean swing out of phase, warm in the west while cool in the east or the reverse, reshaping rainfall around the basin. Saji and colleagues' A dipole mode in the tropical Indian Ocean identified the pattern and a dipole mode index for it. The referent is a basin-scale climate oscillation, which borrows the word only for its two-opposite-poles geometry and is a wholly different construct from a charge pair or a radiating wire.[4]

Unit

The dipole mode index, the west-minus-east sea-surface-temperature anomaly difference

Recovery means

Not applicable

Measured by

Tracked by the dipole mode index computed from gridded sea-surface-temperature anomalies in the two poles