Experimental Evaluation of Diffusion Parameters on a Local Scale by Means of No-Lift Balloons

Abstract

Lateral and vertical crosswind standard deviations of Lagrangian tracers at small scale (100?1000 m) have been evaluated during five experimental periods of 15 days at two different Italian sites-a flat country (Po Valley) and a coastal region (La Spezia Gulf)-by a moving-average method applied to single trajectories of no-lift balloons tracked by two theodolites. Values of σy and σz as a function of downwind distance in the 102?103 m range were grouped following the Pasquill stability scheme (Pasquill, 1974) and regression lines for each category (from A to E) were drawn and compared (for the two sites) with earlier estimates, i.e., Pasquill-Gifford, Singer-Smith and Moore. On the one hand, the results show a general agreement with the above estimates and, on the other, the effects of mixing-height changes during the day and the effects of different climatological conditions.