Contact time in ice-ice collision

CARANTI, GIORGIO; AGUIRRE VARELA, GUILLERMO GABRIEL; PEREYRA, RODOLFO GUILLERMO

Alabama

Conferencia; 11th International Conference on Atmospheric Electricity (ICAE); 1999

International Commission on Atmospheric Electricity

There is strong indication that the interactions among ice particles in clouds are the main cause for their electrification. Therefore characterization of the collisions themselves is of great importance. In this work, we present measurements of contact time in metal-metal, ice-metal, and ice-ice collisions by a simple electrical method. The method assumes that the ice is conductive enough to allow a measurable CUITentto flow during contact. The experiments were carried out in a cold room under controlled ambient conditions. Temperatures between -3 to -25°C and impact velocities 0.5 to 2.5 mis were used for particles formed from tri-distilled water. Preliminary measurements suggest times much longer than theory predicts for ice and for elastic collisions. Onecm spheres at the above velocities give times between 200 and 600¡..¡.swhen they collide with a plane ice surface. These times are more compatible with plastic deformation than with elastic interactions. Variability is also very 1arge, successive collisions of the same sphere can give very different contact times. It was possible to observe that on some occasions fracture developed after the first impact which affected the following one resulting in larger contact times, sometimes, by a factor greater than 2. The yield for the beginning of cracking or plastic flow whichever comes first could be estimated as about 7 bars assuming constant stress during the deformation at -10°C. Implications for the mechanisms of charge separation in ice-ice collision are discussed.