Collisional charging in ice and charge separation in thunderstorms

LABORATORY AND FIELD STUDIES INDICATE THAT THUNDERSTORM ELECTRIFICATION CAN BE ATTRIBUTED TO REBOUNDING COLLISIONS BETWEEN SMALL ICE PARTICLES AND HAIL. THE FUNDAMENTAL MECHANISM OF CHARGE SEPARATION HAS DEFIED EXPLANATION FOR MANY YEARS, BUT RECENT EXPERIMENTS OFFER NEW CLUES, LEADING TO A QUANTITATIVE THEORY OF THE MICROPHYSICAL PROCESS. THE THEORY EXPLAINS THE SYSTEMATIC DEPENDENCE OF CHARGE AND MASS TRANSFER ON TEMPERATURE, COLLISION SPEEDS AND GROWTH RATES THAT HAVE BEEN OBSERVED IN LABORATORY STUDIES. APPLIED TO STORM DYNAMICS, THE THEORY DESCRIBES HOW THE UPPER PORTIONS OF THUNDERCLOUDS BECOME POSITIVELY CHARGED, WHILE THE NEGATIVE CHARGE RESIDES ON HAIL IN THE LOWER REGIONS.