Function to convert from specific humidity to relative humidity.

utilities/qair2rh.m

+function rh = qair2rh(qair, temp, varargin)
+% Convert specific humitidy to relative humidity.
+%
+% INPUTS:
+%   qair - Specific humidity. Dimensionless ratio of water mass /
+%       total air mass.
+%   temp - Temperature. Celsius.
+%   press - Pressure, optional. Millibar. Assume as 1013.25 if
+%       missing.
+%
+% OUTPUT:
+%   rh  - relative humidity, ratio of actual water mixing ratio to
+%       saturation mixing ratio.
+%
+% NOTES:
+%   Translated from the R code here:
+%       http://earthscience.stackexchange.com/questions/2360
+%
+% Author(s):
+%   Pierre Cazenave (Plymouth Marine Laboratory)
+
+if nargin == 2
+    press = 1013.25;
+end
+es = 6.112 * exp((17.67 * temp) / (temp + 243.5));
+e = qair * press / (0.378 * qair + 0.622);
+rh = e / es;
+rh(rh > 1) = 1;
+rh(rh < 0) = 0;