psvd_model: Terminal drop velocity theoretical models

In sbegueria/disdRo: Functions for working with disdrometric data

Description

This function implements the Beard model of terminal drop velocity. This is a physical approximation accounting for different factors such as viscous drag, drop oblateness, etcetera. The function implemented here is valid for drop sizes between 0.019 mm (19 µm) up to 7 mm. The function also contains the approximations of Atlas, Uplinger and Van Dijk. The Beard model is implemented by default assuming a standard atmosphere: P=101.325 kPa, T=288.15 K, and rho= 1.225 kg/m3, but other values can be provided.

Usage

psvd_model(size, model = "Beard", eta = 1.818e-05, P = 101.325,
  T = 288.15, rho = 1.225, alt = 0)

Arguments

size	Numeric. A vector of drop sizes (in mm).
model	Character. Name of the terminal velocity model to use. One 'Beard', 'Atlas', 'Uplinger' or 'VanDijk'. Defaults to 'Beard'.
eta	Numeric. A vector of air dynamic viscosity values. Deafults to 1.818e-04 kg m-1 s-1. Optional, used only in the Beard model.
P	Numeric. A vector of air pressure values. Defaults to 101.325 kPa. Optional, used only in the Beard model.
T	Numeric. A vector of air temperature values. Defaults to 288.15 K. Optional, used only in the Beard model.
rho	Numeric. A vector of air densities. Defaults to 1.225 kg m-3. Optional, used only in the Beard and Atlas models.
alt	Numeric. Elevation, which can be used if provided to estimate pressure, density and temperature of air in according to the International Standard Atmosphere. Defaults to 0 m above mean sea level. Optional, used in the Beard and Atlas models to estimate parameters 'eta', 'P', 'T' and 'rho' if no values are provided.

Value

A vector of terminal fall velocities. It will cointain NA for any drop sizes lower than 0.019 mm or larger than 7 mm (Beard model), or lower than 0.1 and larger than 7 mm for the approximations.

Examples

size <- seq(0, 6, 0.2)
psvd_model(size)
psvd_model(size, alt=2000)
psvd_model(size, model='Atlas')
psvd_model(size, model='Uplinger')
psvd_model(size, model='VanDijk')

sbegueria/disdRo documentation built on May 14, 2019, 2:39 p.m.