In order to ascertain the degree of confidence one should place on stability classification schemes when applied to a site in non-homogeneous terrain, the differences of stability classes, calculated by various methods, for two adjacent sites (8 km apart) in a coastal urban region are examined and are found to be considerable. The cause of this difference appears to be changes in surface characteristics such as roughness, albedo, etc. and local topographically induced flow patterns (but not sea-breeze), which suggests that popular classification schemes, such as the Pasquill-Turner one, should be modified to include at least the effect of surface roughness and albedo, and thus to differentiate between various kinds of terrain.
The present study estimates the atmospheric stability for the Athens area based on Pasquill's formulation. The results are limited to examining the stability categories during the months of January (mid-winter term) and July (midsummer term). These stability classes are examined from a 44-year database consisting of hourly values of wind speed and direction, solar insolation and cloud cover. This data is regularly recorded at the National Observatory of Athens located near the city centre. The results of the work consist of diagrams with mean monthly stability class values during January and July in the period 1953-1996 and the mean daily variation of these parameters for the same months and period. Discussion of how these stability categories influence air pollution in the Athens area is made.
We characterize stability under composition, inversion, and solution of ordinary differential equations for ultradifferentiable classes, and prove that all these stability properties are equivalent.