Constants (metpy.constants)#

A collection of meteorologically significant constant and thermophysical property values.

Earth#

Name

Symbol

Short Name

Units

Description

earth_avg_radius

\(R_e\)

Re

\(\text{m}\)

Avg. radius of the Earth 1

earth_gravity

\(g\)

g

\(\text{m s}^{-2}\)

Avg. gravity acceleration on Earth 2

gravitational_constant

\(G\)

G

\(\text{m}^{3} {kg}^{-1} {s}^{-2}\)

Gravitational constant 2

earth_avg_angular_vel

\(\Omega\)

omega

\(\text{rad s}^{-1}\)

Avg. angular velocity of Earth 1

earth_sfc_avg_dist_sun

\(d\)

d

\(\text{m}\)

Avg. distance of the Earth from the Sun 3

earth_solar_irradiance

\(S\)

S

\(\text{W m}^{-2}\)

Avg. solar irradiance of Earth 4

earth_max_declination

\(\delta\)

delta

\(\text{degrees}\)

Max. solar declination angle of Earth

earth_orbit_eccentricity

\(e\)

\(\text{None}\)

Avg. eccentricity of Earth’s orbit

earth_mass

\(m_e\)

me

\(\text{kg}\)

Total mass of the Earth (approx) 1 2

Water#

Name

Symbol

Short Name

Units

Description

water_molecular_weight

\(M_w\)

Mw

\(\text{g mol}^{-1}\)

Molecular weight of water 5

water_gas_constant

\(R_v\)

Rv

\(\text{J (K kg)}^{-1}\)

Gas constant for water vapor 2 5

density_water

\(\rho_l\)

rho_l

\(\text{kg m}^{-3}\)

Maximum recommended density of liquid water, 0-40C 5

wv_specific_heat_press

\(C_{pv}\)

Cp_v

\(\text{J (K kg)}^{-1}\)

Specific heat at constant pressure for water vapor

wv_specific_heat_vol

\(C_{vv}\)

Cv_v

\(\text{J (K kg)}^{-1}\)

Specific heat at constant volume for water vapor

water_specific_heat

\(Cp_l\)

Cp_l

\(\text{J (K kg)}^{-1}\)

Specific heat of liquid water at 0C 6

water_heat_vaporization

\(L_v\)

Lv

\(\text{J kg}^{-1}\)

Latent heat of vaporization for liquid water at 0C 7

water_heat_fusion

\(L_f\)

Lf

\(\text{J kg}^{-1}\)

Latent heat of fusion for liquid water at 0C 7

ice_specific_heat

\(C_{pi}\)

Cp_i

\(\text{J (K kg)}^{-1}\)

Specific heat of ice at 0C 7

density_ice

\(\rho_i\)

rho_i

\(\text{kg m}^{-3}\)

Density of ice at 0C

Dry Air#

Name

Symbol

Short Name

Units

Description

dry_air_molecular_weight

\(M_d\)

Md

\(\text{g / mol}\)

Nominal molecular weight of dry air at the surface of th Earth 8

dry_air_gas_constant

\(R_d\)

Rd

\(\text{J (K kg)}^{-1}\)

Gas constant for dry air at the surface of the Earth

dry_air_spec_heat_press

\(C_{pd}\)

Cp_d

\(\text{J (K kg)}^{-1}\)

Specific heat at constant pressure for dry air

dry_air_spec_heat_vol

\(C_{vd}\)

Cv_d

\(\text{J (K kg)}^{-1}\)

Specific heat at constant volume for dry air

dry_air_density_stp

\(\rho_d\)

rho_d

\(\text{kg m}^{-3}\)

Density of dry air at 0C and 1000mb

General Meteorology Constants#

Name

Symbol

Short Name

Units

Description

pot_temp_ref_press

\(P_0\)

P0

\(\text{Pa}\)

Reference pressure for potential temperature

poisson_exponent

\(\kappa\)

kappa

\(\text{None}\)

Exponent in Poisson’s equation (Rd/Cp_d)

dry_adiabatic_lapse_rate

\(\gamma_d\)

gamma_d

\(\text{K km}^{-1}\)

The dry adiabatic lapse rate

molecular_weight_ratio

\(\epsilon\)

epsilon

\(\text{None}\)

Ratio of molecular weight of water to that of dry air

1(1,2,3)

[Moritz2000]

2(1,2,3,4)

[CODATA2018]

3

[IAU2012]

4

[Kopp2011]

5(1,2,3)

[IAPWS2001]

6

[IAPWS1995]

7(1,2,3)

[WMO1966]

8

[Picard2008]