Monin-Obukhov length estimation

Estimation of the Monin-Obukhov Length Estimate L for an agricultural area with windspeed at 10m equal to 2.5ms 1 and solar flux 500 Wm 2. 

The Monin-Obukhov length L is not a parameter that is routinely measured. Colder (1972), however, established a relation between the stability classes of Pasquill, the roughness height zo (see Section VII,B), and L. The results of his investigation are shown in Fig. 4. Alternatively, the local wind speed and cloud cover measurements are used to estimate the Pasquill stability class (Table IV). In addition, Colder developed a nonogram for relating the gradient Richardson number R-, to the more easily determined bulk Richardson number / (, ... 

The Monin-Obukhov length L can also be estimated from conventional meteorological data by first evaluating the parameter a (Fulle, 1975) ... 

The stability of the atmosphere is clearly a major influence on the dispersion of a smoke-plume. If the plume comprised a CWA rather than a harmless tracer, then the atmospheric stability would have an important effect on the extent of the downwind hazard area and on the concentrations of agent experienced within that hazard area. Atmospheric stability can be determined by direct observation - as in Figures 1-5 -or by estimation of the Monin-Obukhov length-scale, L (m), which is a height proportional to the height above a surface at which thermal effects first dominate shear (momentum) effects (Pasquill, 1962), as defined in Equation (1) ... 

Use of the equations derived in this section requires estimation of the Monin-Obukhov length L. A number of approaches are available, including the profile and gradient methods using available measurements (Arya 1999). The simplest approach based on the Pasquill stability classes will be discussed in the next section. 

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