Large-scale dispersion of clusters of particles in various flow patterns

Abstract

An investigation is made of the relative particle displacement tensor, eddy diffusivity, power spectra, and cospectra of the relative particle velocities for clusters of particles released in six flow patterns: cyclonic and anticyclonic centers, and trough, ridge, and inflection points to the east and west of troughs in the midtroposphere. We find that the zonal component of the eddy diffusivity is about five times the meridional component, and the eddy diffusivity for the winter is greater than that for the summer. The zonal component of the eddy diffusivity is greatest for releases at the inflection point to the west of troughs, whereas the meridional component is greatest at cyclonic centers. The smallest value of both the zonal and the meridional components of the eddy diffusivity is the value for releases at anticyclonic centers. The principal axis of diffusion is mostly oriented WSW-ENE for summer releases and WNW-ESE for winter releases. For large diffusion times, the mean square of the zonal component of the relative particle displacement is approximately proportional to the first power of time, whereas the mean square of the meridional component shows a wavy characteristic, which indicates the effect of the meridional motion of the planetary waves. The power spectra of the zonal component of the relative particle velocities are similar in all cases and show an increase in the turbulent kinetic energy with decreasing frequency, whereas the spectra of the meridional component show an energy peak near 10−2 cycles hr−1. In the high-frequency range, the spectra of both the zonal and the meridional components of the relative velocities are inversely proportional to the frequency cubed.