qsat

 QSAT: computes specific humidity at saturation. 
 q=QSAT(Ta) computes the specific humidity (kg/kg) at satuation at
 air temperature Ta (deg C). Dependence on air pressure, Pa, is small,
 but is included as an optional input.

    INPUT:   Ta - air temperature  [C]
             Pa - (optional) pressure [mb]

    OUTPUT:  q  - saturation specific humidity  [kg/kg]

0001   function q=qsat(Ta,Pa)
0002 % QSAT: computes specific humidity at saturation.
0003 % q=QSAT(Ta) computes the specific humidity (kg/kg) at satuation at
0004 % air temperature Ta (deg C). Dependence on air pressure, Pa, is small,
0005 % but is included as an optional input.
0006 %
0007 %    INPUT:   Ta - air temperature  [C]
0008 %             Pa - (optional) pressure [mb]
0009 %
0010 %    OUTPUT:  q  - saturation specific humidity  [kg/kg]
0011 
0012 % Version 1.0 used Tetens' formula for saturation vapor pressure
0013 % from Buck (1981), J. App. Meteor., 1527-1532.  This version
0014 % follows the saturation specific humidity computation in the COARE
0015 % Fortran code v2.5b.  This results in an increase of ~5% in
0016 % latent heat flux compared to the calculation with version 1.0.
0017 
0018 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0019 % 3/8/97: version 1.0
0020 % 4/7/99: version 1.2 (revised as above by AA)
0021 % 8/5/99: version 2.0
0022 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0023 
0024 if nargin==1,
0025   as_consts;
0026   Pa=P_default; % pressure in mb
0027 end;
0028 
0029 % original code
0030 % a=(1.004.*6.112*0.6220)./Pa;
0031 % q=a.*exp((17.502.*Ta)./(240.97+Ta))
0032 
0033 % as in Fortran code v2.5b for COARE
0034 ew = 6.1121*(1.0007+3.46e-6*Pa).*exp((17.502*Ta)./(240.97+Ta)); % in mb
0035 q  = 0.62197*(ew./(Pa-0.378*ew));                         % mb -> kg/kg