Advanced / Configuration Setup / Mixing Depth Computation Method

Permits the selection of the method used to compute the mixed layer depth. The mixed layer depth does not affect the trajectory computation, only the dispersion and resulting air concentrations by changing the rate of dispersion as well as providing a lid to vertical mixing of pollutants. Options include the following:

• Use meteorological model - uses the mixed layer depth value from the meteorological model. Not all model outputs provide mixed layer depths. Valid field IDs are MXHT, HPBL, and PBLH.
• From temperature profile - computes the height of the mixed layer as the height at which the potential temperature is at least two degrees greater than the minimum potential temperature. The computation is made from the top down.
• Compute from TKE profile - uses the meteorological model's TKE profile to estimate the mixing depth at the height at which the TKE either decreases by a factor of two or falls to a value of less than 0.21. Not all model outputs contain the TKE field.
• Compute using a modified Richardson number approach that includes excess temperature for convective cases.
• Set a constant value (m) - as a last resort the mixing depth can also be set to a constant value (meters). The kmixd namelist variable either contains the mixing depth value or the integers 0,1,2 indicating one of the other choices.