Diffusion Coefficients Calculated from Satellite Data

Abstract

Lagrangian parcel statistics are used to estimate the horizontal and vertical diffusion coefficients, K_yy and K_zz, for an inert tracer in the wintertime stratosphere. Ensembles of air parcels are placed on latitude circles and the subsequent parcel trajectories are calculated using winds derived from LIMS satellite data. The diffusion coefficients are then obtained by calculating the time rate of change of the mean squared deviation of the parcels from their center of mass. The calculational procedure for middle and high latitude ensembles is modified to remove the unrealistic ally large initial dispersion resulting from placing parcels on latitude circles. During quiet periods, when the vortex is nearly axisymmetric, K_yy ≤ 7.5 x 10⁵ m ²/s (typically 1–5 x 10⁵ m²/s) and K_zz ≈.1 m ²/s throughout the middle and high latitude stratosphere. For this same domain during a period that included a major warming, K_yy varied between 7.5 x 10⁵ and 3.75 x 106 m²/s throughout the same region, with K_zz varying between .3 and 1.4 m²/s.