A climatology of turbulent dispersion in the troposphere

The authors present properties of turbulent, meridional mixing along isentr opic surfaces within the troposphere. Twice-daily wind fields analyses from the European Centre for Medium-Range Weather Forecasts numerical weather p rediction model for 1992 are used to calculate Lagrangian trajectories of l arge ensembles of particles. The ensemble-averaged rms growth of the meridi onal relative dispersion over the first 10 days after particle release is u sed to quantify mixing properties. These properties are considered as a fun ction of height in the atmosphere, season, and geographic region. Results a re characterized by release latitude and flow regime and compared with simp le theories. All three dispersive regimes-exponential, ballistic, and Richardson-Obukhov -that have been documented in previous studies are found to be important. T he extratropics are found to display superdiffusive growth of the relative rms dispersion, consistent with the nonlocal character of midlatitude mixin g. The Tropics are characterized by exponential growth of the rms dispersio n, consistent with locally constant eddy timescales. Some evidence for zona l inhomogeneity in dispersion growth rates is found.