6.5 Mixing Height
For
the purposes of this guidance, mixing height is defined as the height of the
layer adjacent to the ground over which an emitted or entrained inert
non-buoyant tracer will be mixed (by turbulence) within a time scale of
about one hour or less [43]. Taken literally, the definition means
that routine monitoring of the mixing height is generally impractical. For
routine application, alternative methods are recommended for estimating
mixing heights based on readily available data.
The
Holzworth method [44] is recommended for use when representative NWS
upper-air data are available. This procedure relies on the general
theoretical principle that the lapse rate is roughly dry adiabatic (no
change in potential temperature with height) in a well-mixed daytime
convective boundary layer (CBL); the Holzworth method is described in
Section 6.5.1. Other alternatives include using estimates of mixing heights
provided in CBL model output (Weil and Brower [45]; Paine [46])
and mixing heights derived from remote sensing measurements of turbulence or
turbulence related parameters; the latter are discussed in Section 9.1.1.
6. METEOROLOGICAL DATA PROCESSING
6.1 Averaging and Sampling Strategies
6.2 Wind Direction and Wind Speed
6.2.1 Scalar Computations
6.2.2 Vector Computations
6.2.3 Treatment of Calms
6.2.4 Turbulence
6.2.5 Wind Speed Profiles
6.3 Temperature
6.3.1 Use in Plume-Rise Estimates
6.3.2 Vertical Temperature Gradient
6.4 Stability
6.4.1 Turner's method
6.4.2 Solar radiation/delta-T (SRDT) method
6.4.3
E method
6.4.4 Amethod
6.4.5 Accuracy of stability category estimates
6.5 Mixing Height
6.5.1 The Holzworth Method
6.6 Boundary Layer Parameters
6.6.1 The Profile Method
6.6.2 The Energy Budget Method
6.6.3 Surface Roughness Length
6.6.4 Guidance for Measurements in the Surface Layer
6.7 Use of Airport Data
6.8 Treatment of Missing Data
6.8.1 Substitution Procedures
6.9 Recommendations
