thermodynamics: Thermodynamics

In metR: Tools for Easier Analysis of Meteorological Fields

Thermodynamics

Description

Functions related to common atmospheric thermodynamic relationships.

Usage

IdealGas(p, t, rho, R = 287.058)

Adiabat(p, t, theta, p0 = 1e+05, kappa = 2/7)

VirtualTemperature(p, t, e, tv, epsilon = 0.622)

MixingRatio(p, e, w, epsilon = 0.622)

ClausiusClapeyron(t, es)

DewPoint(p, ws, td, epsilon = 0.622)

Arguments

p	pressure
t	temperature
rho	density
R	gas constant for air
theta	potential temperature
p0	reference pressure
kappa	ratio of dry air constant and specific heat capacity at constant pressure
e	vapour partial pressure
tv	virtual temperature
epsilon	ratio of dry air constant and vapour constant
w	mixing ratio
es	saturation vapour partial pressure
ws	saturation mixing ratio
td	dewpoint

Details

IdealGas computes pressure, temperature or density of air according to the ideal gas law P=\rho R T.

Adiabat computes pressure, temperature or potential temperature according to the adiabatic relationship \theta = T (P0/P)^\kappa.

VirtualTemperature computes pressure, temperature, vapour partial pressure or virtual temperature according to the virtual temperature definition T(1 - e/P(1 - \epsilon))^{-1}.

MixingRatio computes pressure, vapour partial temperature, or mixing ratio according to w = \epsilon e/(P - e).

ClausiusClapeyron computes saturation pressure or temperature according to the August-Roche-Magnus formula es = a exp{bT/(T + c)} with temperature in Kelvin and saturation pressure in Pa.

DewPoint computes pressure, saturation mixing ration or dew point from the relationship ws = \epsilon es(Td)/(p - es(Td)). Note that the computation of dew point is approximated.

Is important to take note of the units in which each variable is provided. With the default values, pressure should be passed in Pascals, temperature and potential temperature in Kelvins, and density in kg/m^3. ClausiusClayperon and DewPoint require and return values in those units.

The defaults value of the R and kappa parameters are correct for dry air, for the case of moist air, use the virtual temperature instead of the actual temperature.

Value

Each function returns the value of the missing state variable.

References

http://www.atmo.arizona.edu/students/courselinks/fall11/atmo551a/ATMO_451a_551a_files/WaterVapor.pdf

See Also

Other meteorology functions: Derivate(), EOF(), GeostrophicWind(), WaveFlux(), waves

Examples

IdealGas(1013*100, 20 + 273.15)
IdealGas(1013*100, rho = 1.15) - 273.15

(theta <- Adiabat(70000, 20 + 273.15))
Adiabat(70000, theta = theta) - 273.15

# Relative humidity from T and Td
t <- 25 + 273.15
td <- 20 + 273.15
p <- 1000000
(rh <- ClausiusClapeyron(td)/ClausiusClapeyron(t))

# Mixing ratio
ws <- MixingRatio(p, ClausiusClapeyron(t))
w <- ws*rh
DewPoint(p, w) - 273.15    # Recover Td

metR documentation built on Oct. 14, 2024, 5:09 p.m.