
Code and Numerical Aspects
Currently, the Piektuk model is coded only in Fortran 77 and can operate on PCs and/or Unixbased machines. The code is approximately 375 lines long and is available in two formats: 1) a nonsteady, column version and 2) a steadystate, fetchdependent version. The vertical coordinate system is equidistant on a logarithmic scale, allowing higher resolution near the surface. Typically, 24 vertical levels are used, with the model lid situated 1 km above the surface. The required meteorological forcing data consists of the air temperature, humidity, wind speed, and atmospheric pressure. A complete listing of variables, parameters and constants for Piektuk is given below. Comments and suggestions on how to improve the code are welcomed.
Modifications
To suit your purposes, modifications to the code may be required such as the following:
 The timestep (time) at which meteorological forcing data is available (currently set to 1800 s).
 The height (zi) of the humidity measurements (currently set to 1.24 m).
 The wind speed threshold (U10t) for blowing snow transport (currently estimated following Li and Pomeroy (1997)).
 The input variable of relative humidity with respect to ice can be modified to other humidity variables.
 Other output files can be created to observe the behaviour of additional model variables and/or parameters.
Please Note!
 The timestep (time) at which meteorological forcing data is available (currently set to 1800 s).
 The height (zi) of the humidity measurements (currently set to 1.24 m).
 The wind speed threshold (U10t) for blowing snow transport (currently estimated following Li and Pomeroy (1997)).
 The input variable of relative humidity with respect to ice can be modified to other humidity variables.
 Other output files can be created to observe the behaviour of additional model variables and/or parameters.
Model Variables
 dN  tendency for N (/m3/s)
 E  tendency for water vapour (kg/kg/s)
 N  total number concentration of particles (/m3)
 p  surface atmospheric pressure (Pa)
 Q  tendency for temperature (K/s)
 qb  blowing snow mixing ratio (kg/kg)
 Qs  sublimation rate of blowing snow (mm/d)
 Qt  transport rate of blowing snow (kg/m/s)
 QTTs  cumulative sublimation rate (mm)
 QTTt  cumulative transport rate (kg/m)
 qv  water vapour mixing ratio (kg/kg)
 RHi  relative humidity wrt ice
 s  steadystate analytical solution to qb (kg/kg)
 Sb  tendency for blowing snow mixing ratio (kg/kg/s)
 Ta  air temperature (K)
 U10  horizontal wind speed at 10 m (m/s)
 U10t  threshold wind speed for transport (m/s)
Model Constants
 alpha  shape parameter of the gamma distribution
 ar  average radius of blowing snow particles in saltation layer (m)
 cp  heat capacity of air (J/kg/K)
 D  diffusivity of water vapour in air (m2/s)
 deltar  bin size (m)
 dice  density of ice (kg/m3)
 dt  timestep (s)
 g  gravitational constant (m/s2)
 kappa  von Karman's constant
 Kt  thermal conductivity of air (W/m/K)
 lmax  limiting paramter for the eddy diffusivity (m)
 m  fifth moment of gamma distribution
 m2  second moment of gamma distribution
 Ls  latent heat of sublimation (J/kg)
 pi  Pi
 Rd  gas constant for air (J/kg/K)
 Rv  gas constant for water vapour (J/kg/K)
 rhow  density of water (kg/m3)
 t  time (s)
 time  time interval at which met. data is available (s)
 T0  freezing point (K)
 visc  viscosity (m2/s)
 zi  height of humidity measurements (m)
 zlb  lower model boundary (m)
 zub  upper model boundary (m)
 z0  momentum roughness length (without blowing snow) (m)
Model Parameters
 beta  scale parameter of gamma distribution (m)
 ei  saturation vapour pressure over ice (Pa)
 F  particle frequencies for multiple bins in saltation layer (/m3)
 Fd  diffusion parameter for phase change equation (m s/kg)
 Fk  conductivity parameter for phase change equation (m s/kg)
 Km  eddy diffusivity for momentum (m2/s)
 l  mixing length (m)
 Nu  Nusselt number
 qbsalt  saltation mixing ratio (kg/kg)
 Qext  extinction coefficient
 qis  ice saturation mixing ratio (kg/kg)
 Qsalt  saltation transport rate (kg/m2/s)
 Re  Reynolds number
 rho  air density (kg/m3)
 rhop  unit conversion parameter
 rm  mean radius of particle distribution (m)
 ueff  effective friction velocity (m/s)
 ustar  friction velocity (m/s)
 usthr  threshold friction velocity (m/s)
 usalt  saltating particle velocity (m/s)
 vis  optical visibility (m)
 vt  terminal velocity of particles (m/s)
 xi  sublimation parameter (m2/s)
 zr  reference height in saltation layer (m)
 zsalt  height of saltation layer (m)

