What principles are used for computing the mixing depth from the NCAR/NCEP reanalysis data?

---

The 2.5 degree NCAR/NCEP global reanalysis data do not have the mixed layer or planetary boundary layer depth as one of the model output fields, therefore HYSPLIT estimates the mixing depth from the potential 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.

See help file: S616.html

    * 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. Th
      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.

Roland Draxler