Collision between Graupel Particles: A Field Observation and Theory

[摘要] The collision between graupel particles observed by a stroboscopic TV camera is classified by the fall velocity and the size distribution, and the total collision rate and the collision rate distribution are strictly derived.The collision was caused by the difference in fall velocity between two graupel particles, and the fall velocity and the size distribution were expressed as a power law and in an inverse exponential form, respectively. Using the fall velocity and the size distribution observed, the total collision rate of all particles and the collision rate distribution were derived strictly using a sweep-out concept. It is shown clearly that the total collision rate can be expressed a product of the sweep-out volume of the particle with mean size and the square of the total number concentration.The derived collision rate for graupel particles has a simple functional form and is valid for other precipitation particles. The applications of this collision rate expression to ice particle multiplication and to charge generation are demonstrated.

[学科分类] 大气科学