The ball antenna for the vertical electric field

The vertical electric component of the SR is recorded with a ball antenna — a conductive sphere placed on an insulated mast, which acts as a capacitive sensor of the vertical electric field of the atmosphere. This component complements the two horizontal magnetic components and together they form the standard triad of measured SR quantities Tatsis 2024.

The vertical electric field of the SR reaches on the order of hundreds of nV/m, or a spectral density in units of nV/m/√Hz Tatsis 2024. The electric component is particularly sensitive to frequency shifts of the resonances and is used to study global storm dynamics, since it responds to changes in the distribution of lightning sources in the cavity.

A disadvantage of electric measurement is its greater sensitivity to local atmospheric influences (wind, precipitation, charge accumulation on the antenna) and to anthropogenic interference from the power grid. For this reason electric and magnetic measurements are usually combined, in order to exploit the strengths of both and to cross-check the consistency of the data.