Accession Number : ADA107262
Title : A Computational Study of the Modification of Raindrop Size Distributions in Subcloud Downdrafts.
Descriptive Note : Doctoral thesis,
Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
Personal Author(s) : Borchers,Robert George
Report Date : Aug 1981
Pagination or Media Count : 161
Abstract : A computational study is made of the variation of steady-state raindrop-size distributions (0.004 cm less than or equal to radius less than or equal to 0.40 cm) in adiabatic subcloud downdrafts of constant magnitude. The cloud base drop-size distribution is assumed to be Marshall-Palmer. The microphysical processes progressively introduced are evaporation, collision-coalescence, aerodynamic and collisional breakup of drops. Collision-coalescence and breakup area treated through a stochastic model. Thermodynamic and hydrometeoric variables of temperature, relative humidity, total liquid water, rainfall rate and radar reflectivity are computed as functions of height below cloud base along with the drop-size distributions. It is found that evaporation tends to deplete, as expected, the smaller members of the droplet population. Computed raindrop-size distributions agree quite well with measured maritime raindrop spectra reported in the literature, the agreement being better for the higher precipitation rates measured. Other results of the study, as anticipated, are (1) that the downdraft remains unsaturated in the presence of precipitation, the degree of subsaturation increasing with the strength of the downdraft, and (2) that the temperature in the downdraft lies between the moist-adiabatic and the dry-adiabatic lapse rates of temperature.
Descriptors : *RAINDROPS , STEADY STATE , SIZES(DIMENSIONS) , DISTRIBUTION , MODIFICATION , WIND , MOTION , THESES , COALESCENCE , STATISTICAL ANALYSIS , EVAPORATION , COLLISIONS , AERODYNAMICS
Subject Categories : Meteorology
Distribution Statement : APPROVED FOR PUBLIC RELEASE