*KBLT* is a flag used to set the vertical turbulence computational method,
that is how the turbulent velocity variances are computed from either the heat
and momentum fluxes or the model profiles of wind and temperature. Three different
computational approaches (Beljaars/Holtslag, Kanthar/Clayson, Hanna - see the technical
documentation for details) are defined. Another option is the use the TKE
(Turbulent Kinetic Energy) output from the meteorological model provided in the
input meteorological data file. Not all model data contain the TKE field. Another
option is a special case where the input meteorological data are assumed to contain
the 3-dimensional component velocity variance fields, usually a measured component.

- 1 - Beljaars/Holtslag and Betchov/Yaglom
- 2 - Kanthar/Clayson (
**DEFAULT**) - 3 - TKE field from the input meteorology data file
- 4 - Measured velocity variances from the input meteorology
- 5 - Hanna

*KDEF* defines the way the horizontal turbulence is computed. The default
approach is to compute the horizontal mixing in proportion to the vertical mixing
using one of the methods defined above (see the technical documentation for details).
The original computation was to compute the mixing from the deformation of the
horizontal wind field. The limitation of this method is that for shorter-range
dispersion simulations (<100 km) the deformation parameterization used in
conjunction with larger scale meteorological fields will not reflect the diurnal
variations in horizontal turbulence. Using diurnal sensitive methods will not
effect longer-range calculations because the particles are distributed over many
meteorological grid cells where variations in the transport vector dominate the
horizontal dispersion process.

- 0 - In proportion to the vertical turbulence (
**DEFAULT**) - 1 - Computed from the velocity deformation

*KBLS* defines how the stability is computed. Normally when turbulent fluxes
(heat and momentum) are available from the meteorological data file, they are used to
compute stability. Sometimes it may be desirable to force the stability to be computed
from the wind and temperature profiles, especially if the fluxes represent long-time
period averages rather than instantaneous values. If fluxes are not present, the
profiles are used for the stability computation.

- 1 - Heat and momentum fluxes (
**DEFAULT**) - 2 - Wind and temperature profiles

**Vertical and Horizontal Lagrangian Timescales**

*?SCALE?* defines the time in seconds that the turbulence is no longer
autocorrelated. These values are used to convert various mixing coefficients
into turbulent velocities. Different values are defined for vertical and horizontal
components. The horizontal Lagrangian time scale default value is about equal to 1/f,
the Coriolis parameter. Also the vertical time scale is further divided into stable and
unstable conditions. The Lagrangian time scale also controls the transition of the
dispersion rate from linear to square root growth as a function of time. Setting the
stable vertical Lagrangian time scale (VSCALES) to -1 will result in the Hanna vertical
Lagrangian Time Scale to be used, which varies in space and time and is calculated based
on the vertical velocity variance estimated in the vertical turbulence scheme. Setting
VSCALES=0 will result in the Hanna Lagrangian Time Scale to be used (VSCALES=-1) if
HYSPLIT is run in STILT mode (ichem=8), otherwise VSCALES will be set to 5.0.
When the Hannal Lagrangian time scale is set, the unstable vertical Lagrangian
time scale (VSCALEU) is not used.

- 200.0 =
*VSCALEU*vertical Lagrangian time scale (sec) for unstable PBL - 5.0 =
*VSCALES*vertical Lagrangian time scale (sec) for stable PBL - 10800.0 =
*HSCALE*horizontal Lagrangian time scale (sec)

*KZMIX* determines if any additional processing is to be performed on the
vertical mixing profile. The current default is for no adjustments. In previous versions
the boundary layer mixing profile was replaced with its average value. This compensated
for some meteorological data sets with poor vertical data resolution that might result
in particles being trapped near the surface due to insufficient mixing. The last two
options are scale factors that can be applied to the mixing coefficients and currently
are not available for modification through the GUI.

- 0 - NONE vertical diffusivity in PBL varies with height (
**DEFAULT**) - 1 - Vertical diffusivity in PBL single average value
- 2 - scale boundary-layer values multiplied by
*TVMIX* - 3 - scale free-troposphere values multiplied by
*TVMIX*

*KMIXD* is used to control how the boundary layer depth is computed. In addition
to acting as a vertical lid to particle dispersion (advection is not affected), the
mixed layer depth is also used to scale the boundary layer mixing coefficients and
computing turbulent fluxes from wind and temperature profiles. The default is to use
the value provided by the meteorological model through the input data set (KMIXD=0). If those are not available,
the computation will use the temperature profiles (KMIXD=1).
If HYSPLIT is run in STILT mode (ICHEM=8), then the default is to
use a modified Richardson # approach (KMIXD=3) that includes excess temperature for convective
cases for estimating the mixed layer depth. See the technical document for details
on these schemes. Setting KMIXD in the SETUP.CFG will over-ride the defaults.
Another option to
use for testing is to replace the index value (0,1,2,3) with a value greater than 10.
In this situation, that value will be used as the mixed layer depth and will be constant
for the duration of the
simulation.

- 0 = Use meteorological model MIXD if available (
**DEFAULT**) - 1 = Compute from the temperature profile
- 2 = Compute from the TKE profile. (Requires that TKE be available.)
- 3 = Compute from modified Richardson number (
**STILT MODE DEFAULT**) (new in hysplit.v5.0.0) - > = 10 use this value as a constant

*KMIX0* is a related parameter that sets the minimum mixing depth. The default
value is 150 meters and is related to the typical vertical resolution of the meteorological
data. A resolution near the surface of 15 hPa is typical of pressure-level data files. This
suggests that it is difficult to infer a mixed layer depth of less than 150 m
(10 m per hPa) for most meteorological input data.

- 150 = The minimum mixing depth (
**DEFAULT**)

**Puff Growth Computation Method**

*KPUFF* is the flag to use either the linear with time or the empirical fit
with time dispersion equations for the horizontal growth rate of puffs. This parameter
does not affect particle dispersion. The linear with time approach suggests that not
all turbulent scales have been sampled and puffs grow in proportion to increasing time.
The empirical fit equation is similar but the rate of puff growth decreases with time.
Slower puff growth rate in the linear approach is represented by the separation of puffs
after splitting due to variations in the flow. The empirical approach should only be used
in those situations where puff splitting is constrained because of memory or computing
time limitations.

- 0 = Linear with time puff growth (
**DEFAULT**) - 1 = Empirical fit to the puff growth

*TKERD and TKERN * are the ratios of the vertical to the horizontal turbulence
for daytime and nighttime, respectively. *TKER{D|N}* is defined as W'2/(U'2+V'2).
A zero value forces the model to compute a TKE ratio consistent with its turbulence
parameterization. A non-zero value forces the vertical and horizontal values derived
from the TKE to match the specified ratio. This option is only valid with *KBLT=3*.
The *Urban* button increases the internal TKE by 40% and slightly raises the
nighttime ratio to account for enhanced turbulence in an urban setting. The landuse
file supplied with the model is not of sufficient resolution to define urban areas and
hence the urban setting applies to all points in the computational domain.

- 0.18 =
*TKERD*day (unstable) turbulent kinetic energy ratio - 0.18 =
*TKERN*night (stable) turbulent kinetic energy ratio

**Other Turbulence Parameters Not Defined in GUI**

- 1.0 =
*TVMIX*vertical mixing scale factor (in conjunction with*KZMIX* - 1 =
*KRAND*method to calculate random number (1=precompute 2=dynamic 3=none 4=random initial seed number and dynamic)