New Calculation of Saturation Specific Humidity and Saturation Vapor Pressure in the COLA Atmospheric General Circulation Model

Abstract

A new method of computing the saturation specific humidity, qs, and saturation vapor pressure, es, is presented. This has been recently implemented in the Center for Ocean-Land- Atmosphere Studies (COLA) atmospheric general circulation model (AGCM). The new method offers high accuracy extending beyond the observed atmospheric temperature domain and yet is computationally competitive with most other methods used for this calculation. In addition a corresponding continuous function for the derivative of es with respect to temperature is also given. An inverse function to es is available as well. Included are small corrections to es to assure high accuracy. The design of the implementation permits the user to obtain whatever level of accuracy and detail might be desired. With this even detailed microphysical calculations with high computational efficiency can be done with small changes when the need arises.