Surf electrification

Abstract

Two distinct mechanisms are known to produce positive space charge over the sea. They are the jet-drop process produced by the bursting of bubbles at the air-sea interface and the electrode effect, which is the result of the interaction between the geoelectric field and atmospheric ions. There has been uncertainty as to the relative importance of these mechanisms in the electrification measured in beach areas. An experiment was performed on the east coast of Barbados in which atmospheric space-charge density and potential gradient were measured both inside and outside the surf zone. An abrupt change in both space-charge density and potential gradient was always observed upon traversing the surf zone, indicating that an amount of positive space-charge density, at least comparable in magnitude to that associated with the electrode effect outside the zone, was produced inside the zone by the surf. Measurements of Aitken nuclei, conductivity, and small ion density on the shore do not indicate that additional ionization took place in the surf and there were not enough natural small ions available to account for the space charge. These findings led to the conclusion that the bulk of the space charge probably resided on particles that originally left the surf zone by means of the jet-drop process.