E_EQ_WATER Equilibrium water vapor pressure over liquid water Calculate the equilibrium water vapor pressure over a plane surface of liquid water according to Sonntag, 1994. The coefficients for units of K for temperature and Pa for the partial pressure are quoted in Helten et al., 1999. I have verified that these coefficients are consistent with the ones given in Leiterer et al., 1997, with the only difference that the ones in the Leiterer et al. paper are for partial pressure in units of hPa. The temperature of 0C corresponds to 273.15K. (Not 273.16K, as stated in the Leiterer paper.) The formula (T in K, Ew in Pa): Ew(T) = exp[ a/T + b + cT + dT^2 + e ln(T) ] References: Sonntag, D., Advancements in the field of hygrometry, Meteorologische Zeitschrift, 3, 51-66, 1994. Helten, M. et al, In-flight comparison of MOZAIC and POLINAT water vapor measurements, JGR, 104, 26.087-26.096, 1999. Leiterer U. et al, Improvements in Radiosonde Humidity Profiles Using RS80/RS90 Radiosondes of Vaisala, Beitr. Phys. Atmosph., 70(4), 319-336, 1997. FORMAT ew = e_eq_water(T) OUT ew = Equilibrium water vapor pressure in [Pa]. IN T = Temperature in [K].
0001 % E_EQ_WATER Equilibrium water vapor pressure over liquid water 0002 % 0003 % Calculate the equilibrium water vapor pressure over a plane surface 0004 % of liquid water according to Sonntag, 1994. 0005 % 0006 % The coefficients for units of K for temperature and Pa for the partial 0007 % pressure are quoted in Helten et al., 1999. I have verified that 0008 % these coefficients are consistent with the ones given in Leiterer et 0009 % al., 1997, with the only difference that the ones in the Leiterer et 0010 % al. paper are for partial pressure in units of hPa. 0011 % 0012 % The temperature of 0C corresponds to 273.15K. (Not 273.16K, as stated 0013 % in the Leiterer paper.) 0014 % 0015 % The formula (T in K, Ew in Pa): 0016 % 0017 % Ew(T) = exp[ a/T + b + cT + dT^2 + e ln(T) ] 0018 % 0019 % References: 0020 % 0021 % Sonntag, D., Advancements in the field of hygrometry, Meteorologische 0022 % Zeitschrift, 3, 51-66, 1994. 0023 % 0024 % Helten, M. et al, In-flight comparison of MOZAIC and POLINAT water 0025 % vapor measurements, JGR, 104, 26.087-26.096, 1999. 0026 % 0027 % Leiterer U. et al, Improvements in Radiosonde Humidity Profiles Using 0028 % RS80/RS90 Radiosondes of Vaisala, Beitr. Phys. Atmosph., 70(4), 0029 % 319-336, 1997. 0030 % 0031 % FORMAT ew = e_eq_water(T) 0032 % 0033 % OUT ew = Equilibrium water vapor pressure in [Pa]. 0034 % IN T = Temperature in [K]. 0035 0036 % 2003-03-28 Created by Stefan Buehler 0037 0038 function ew = e_eq_water(T) 0039 0040 % Coefficients for Ew: 0041 a = -6096.9385; 0042 b = 21.2409642; 0043 c = -2.711193e-2; 0044 d = 1.673952e-5; 0045 e = 2.433502; 0046 0047 ew = exp( a./T + b + c*T + d*T.^2 + e*log(T) );