Atmospheric stability characterization using the Pasquill method: A critical evaluation

Publication date: August 2018
Source:Atmospheric Environment, Volume 187
Author(s): Jonathan D.W. Kahl, Hillary L. Chapman
The Pasquill system was designed to describe dispersion conditions and was never intended to be a "stand-alone" measure of stability, but it has nevertheless been used to characterize stability in a wide range of applications unrelated to atmospheric dispersion. In this study we evaluate whether the method's underlying assumptions are sufficiently robust for characterizing stability, and whether the method provides acceptable characterizations when used as a stability classification tool outside the context of atmospheric dispersion.Observed temperature lapse rates at six locations across Eurasia largely fail to support the Pasquill method's "exclusivity" assumptions prohibiting the identification of stable classes during daytime, unstable classes at night, and all non-neutral classes during day/night transition and overcast periods. While observed nighttime stability is mostly stable or neutral and thus largely consistent with the Pasquill method, daytime lapse rates frequently indicate stable conditions. Moreover, the majority of lapse rates during day/night transition periods are non-neutral. Substantial seasonal variability is observed in diurnal stability variations and is unaccounted for in the Pasquill system. When compared with observed stability based on lapse rates, the Pasquill classification scheme exhibits a strong neutral bias at most sites. The method performs particularly poorly during daytime, correctly identifying instability in only 1%–29% of cases at the sites analyzed. Nighttime stability is correctly identified more frequently, but the strength of nocturnal stability is overestimated at all sites analyzed.

Graphical abstract

https://ift.tt/2LtL1uh