Experimental evaluation of diffusion parameters at local scale by means of no-lift balloons

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 sigma_y and sigma_x as a function of downwind distance in the 100-1000 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.