estimation de Pasquill-Gifford

CONT: In order to simplify the analytical procedures involved in determining the value of [sigma], Pasquill (1961-1962) and Gifford (1961) have devised graphical schemes for determining [sigma] for the six stability categories, A to F, discussed earlier...; [sigma] values were determined from experimental observations within 1 km of ground sounds. The estimates are based on ideal meteorological conditions over flat terrain and should not be used indiscriminately for rough terrain or complex meteorological conditions. Although the Pasquill-Gifford estimates have been used on occasions for downwind distances up to 100 km under steady weather conditions, their application to buoyant plumes from tall stacks is highly speculative.