RAINDROP CHARGE, PRECIPITATION, AND MAXWELL CURRENTS UNDER TROPICAL STORMS AND SHOWERS

Measurements of electric charges of raindrops, electric field, and Max well current were made at Abidjan (5 degrees N, 4 degrees W) from Octo ber 1988 to June 1990, The examination of the data obtained allows us to differentiate between storms and showers. The former are characteri zed by high global precipitation charge density (about 8 mu C m(-2)) a nd by raindrops, 90% of which carry a positive charge of average value 86 pC, while the average negative charge is -22 pC only. The majority of positive raindrops are generally associated with the active phase of the storm and lead to strong precipitation currents of the order of -4.3 nA m(-2), on average. These values, compared with those of the d isplacement current (J(D)), calculated from electric field records, an d with those of the experimental Maxwell current (J(M)), show that the approximation of J(M) by the displacement current alone is not valid. In those cases, the precipitation current (J(P)) must be included. Th e showers are characterized by weaker global precipitation charge dens ity (about 1.6 mu C m(-2)) and weaker charges (about 25 pC), equally d istributed between positive and negative ones. The precipitation curre nts associated with them are consequently weak, and in those cases the Maxwell current may be approximated by the displacement current alone .