Glossary unit conversions

Glossary

Thermodynamic terms

• Enthalpy. Total internal energy of thermodynamic system, plus the product of pressure and volume. Changes in enthalpy are equivalent to heat flux in closed systems at constant pressure.
• Potential temperature. Temperature that any parcel would attain if it were adiabatically compressed or expanded to 10⁵ Pa.
• Triple point. Temperature and pressure conditions in which a substance can coexist as solid, liquid, and gas (vapour) and satisfy thermodynamic equilibrium. In the case of water, this occurs at 273.16 K and 6.12 Pa.

Constants

Variable	Value
Molar mass of carbon	0.01201 kg mol-1
Molar mass of water	0.01801505 kg mol-1
Molar mass of dry air	0.02897 kg mol-1
Ein	2.17×10−5 J mol-1
Gravity acceleration	9.80665 m s-2
Density of liquid water	1000 kg m-3
Density of fresh snow	100 kg m-3
Triple point of water	273.16 K
Thermal conductivity of liquid water	0.57\ W m-1 K-1
Specific heat of ice	2093 J kg-1 K-1
Specific heat of water	4186 J kg-1 K-1
Specific heat of dry air (constant pressure)	1005 J kg-1 K-1
Specific heat of water vapour (constant pressure)	1859 J kg-1 K-1
Latent heat of melting	33400 J kg-1
Latent heat of vaporization (triple point)	2.5×106 J kg-1
Latent heat of sublimation (triple point)	2.834×106 J kg-1
Typical oxygen mixing ratio	0.209 mol O2 mol-1
Ideal gas constant	8.31451 J mol-1 K-1
Boltzmann constant	1.38065×10-23 m2 kg s-2 K-1
Avogrado's number	6.0221409×1023
Stefan-Boltzmann constant	5.6696e×10-8 W m-2 K-4
von Kármán constant	0.40

Useful Constants and Conversions

Temperature:

• 0°C = 273.15 K

Pressure:

• 1 Pa ≡ 1 N m^-2
• 1 Pa = 10⁻⁵ bar
• 1 Pa = 9.8692×10⁻⁶ atm
• 1 Pa = 7.5006×10⁻³ mmHG
• 1 Pa = 145.04×10⁻⁶ psi

Moisture:

• 1 mm = 1 L m^-2
• 1 mm = 1 kg m²

Latent heat:

• 2272 J g^-1 -> 1 mm day^-1 = 2272000 W kg^-1 / 86400 s day^-1 = 26.2963 W m^-2
• 1 kg m^-2 s^-1 = 2272000 W m^-2

Carbon Flux:

• 1 μmol m^-2 s^-1 = 0.010368 tC ha^-1 day^-1
• 1 μmol m^-2 s^-1 = 3.786912 tC ha^-1 yr^-1
• 1 μmol m^-2 s^-1 = 1.2×10^-8 kg m^-2 s^-1

Time:

• 1 day = 86400 s
• 1 day = 1440 min
• 1 hour = 3600 s
• 1 year = 365.2425 day
• 1 year = 31556952 s

Biomass:

• 1 kg m^-2 = 10 tC ha^-1