Statistical Characteristics of Three-Dimensional Particle Movement in the NCAR General Circulation Model

An analysis of the three-dimensional, large-scale movement of air particles for the winter months with the NCAR general circulation model indicates that the horizontal movement of particles in the upper troposphere is greatly affected by wave motion in mid- and high latitudes, by the field of horizontal convergence and divergence, and by mean meridional circulation in the Tropics. The mean center of mass of particles in both hemispheres generally moves toward respective poles, and the mean square of the meridional component of the particle distances generally decreases with increasing time, indicating the effect of horizontal convergence on particle movement near the subtropics. The vertical movement of the particles is affected by upward motion near the thermal equator and downward motion near the subtropical region in the Northern and Southern Hemispheres. The vertical dispersion is most intense in the Tropics and decreases toward the poles. There are two maxima of particle accumulation, one occurring near 15 degrees N, the other near 30 degrees S, and a minimum accumulation of particles appears near the thermal equator, indicating the effects of the divergence field and meridional circulation between the thermal equator and the subtropics. The mean squares of zonal, meridional, and vertical components or the distance for clusters of particles released at the Equator and 45 degrees N appear to consist of two components: a monotonically increasing component resulting essentially from turbulent diffusion, and a periodic component resulting primarily from horizontal velocity convergence and divergence of mean motion.