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This is the list of fallspeed models used by snowProperties to compute the terminal fallspeed

By default the Boehm1992 model is used

The keyword arguments of the models such as the thermodynamic properties of the air are set by default, but can be overloaded by passing a dictionary of arguments

3.2.2. Fallspeed models

snowScatt.fallSpeed._fallSpeedModels.Boehm1989(diam, mass, area, rho_air=1.2038631624242195, nu_air=1.4268199689249358e-05)

Böhm, J. (1989).A general equation for the terminal fall speed of solid hydrometeors (Vol. 46) (No. 15). doi: 10.1175/1520-0469(1989)046〈2419:AGEFTT〉2.0.CO;2915B

Parameters:

• diam (array(Nparticles) double) – spectrum of diameters of the particles [meters]
• rho_air (scalar double) – air density [kilograms/meter**3]
• nu_air (scalar double) – air kinematic viscosity [meters**2/seconds]
• mass (array(Nparticles) double) – mass of the particles [kilograms]
• area (array(Nparticles) double) – cross section area [meters**2]

Returns:

vterm_bohm – terminal fallspeed computed according to the model [meters/second]

Return type:

array(Nparticles) double

snowScatt.fallSpeed._fallSpeedModels.Boehm1992(diam, mass, area, rho_air=1.2038631624242195, nu_air=1.4268199689249358e-05, as_ratio=1.0)

Bohm, J.(1992).A general hydrodynamic theory for mixed-phase microphysics. Part I: Drag and fall speed of hydrometeors.Atmospheric research,27(4), 253–274

Parameters:

• diam (array(Nparticles) double) – spectrum of diameters of the particles [meters]
• rho_air (scalar double) – air density [kilograms/meter**3]
• nu_air (scalar double) – air kinematic viscosity [meters**2/seconds]
• mass (array(Nparticles) double) – mass of the particles [kilograms]
• area (array(Nparticles) double) – cross section area [meters**2]
• as_ratio (scalar double) – Correction factor for the calculation of area ration in non-spherical symmetric particles. See Karrer et al. 2020

Returns:

vterm_bohm – terminal fallspeed computed according to the model [meters/second]

Return type:

array(Nparticles) double

snowScatt.fallSpeed._fallSpeedModels.HeymsfieldWestbrook2010(diaSpec, mass, area, rho_air=1.2038631624242195, nu_air=1.4268199689249358e-05, k=0.5)

Heymsfield, A. J. & Westbrook, C. D. Advances in the Estimation of Ice Particle Fall Speeds Using Laboratory and Field Measurements. Journal of the Atmospheric Sciences 67, 2469-2482 (2010). equations 9-11

Parameters:

• diaSpec (array(Nparticles) double) – spectrum of diameters of the particles [meters]
• rho_air (scalar double) – air density [kilograms/meter**3]
• nu_air (scalar double) – air kinematic viscosity [meters**2/seconds]
• mass (array(Nparticles) double) – mass of the particles [kilograms]
• area (array(Nparticles) double) – cross section area [meters**2]
• k (scalar double) – tuning coefficient for turbulent flow defaults to 0.5

Returns:

velSpec – terminal fallspeed computed according to the model [meters/second]

Return type:

array(Nparticles) double

snowScatt.fallSpeed._fallSpeedModels.KhvorostyanovCurry2005(diam, mass, area, rho_air=1.2038631624242195, nu_air=1.4268199689249358e-05, smooth=False)

Khvorostyanov, V. I., & Curry, J. A. (2005). Fall velocities of hydrometeors in the atmosphere: Refinements to a continuous analytical power law.Journal of the Atmospheric Sciences,62(12), 4343-4357. doi: 10.1175/JAS3622.1

Parameters:

• diam (array(Nparticles) double) – spectrum of diameters of the particles [meters]
• rho_air (scalar double) – air density [kilograms/meter**3]
• nu_air (scalar double) – air kinematic viscosity [meters**2/seconds]
• mass (array(Nparticles) double) – mass of the particles [kilograms]
• area (array(Nparticles) double) – cross section area [meters**2]
• smooth (scalar bool) – Decide wheather or not use the smooth approximation for the estimation of the drag coefficient from the Best number X

Returns:

velSpec – terminal fallspeed computed according to the model [meters/second]

Return type:

array(Nparticles) double

snowScatt.fallSpeed._fallSpeedModels.correctionFooteduToit(vel, rho_air, temperature, rho0=1.2038631624242195, T0=293.15)

Correction of the terminal fallspeed due to non standard air density. Use Foote, G. B. & Du Toit, P. S. Terminal Velocity of Raindrops Aloft. Journal of Applied Meteorology 8, 249–253 (1969). Here it is assumed that the standard conditions are p=101325 Pa, T=20°C and thus air_density = 1.2038631624242195 kg/m**3

Parameters:

• vel (array(Nvel) - double) – vector of terminal fallSpeed assumed at mean sea level conditions
• rho_air (scalar double) – actual air density kg/m**3
• temperature (scalar double) – actual air temperature
• rho0 (scalar double) – standard air density
• T0 (scalar double) – standard temperature

Returns:

corrected_velocity – Corrected by air viscosity scaling due to non standard air density and temperature

Return type:

array(Nvel) - double