Abstract/Summary

Atmospheric thermodynamic variables are commonly computed under approximations. Although exact formulas are available, they are rarely used. This paper addresses some potential issues arising when using approximate formulas by taking the moist static energy as an example. An important conclusion is that the temperature dependence of latent heat must be taken into account. We also demonstrate that the zero-point energies of various species do not affect the moist static energy budget. The use of an exact formula for moist static energy increases its surface value by 15 K for a typical tropical sounding. However, the change of the parcel buoyancy by using the exact formula is less dramatic, although not negligible. Calculating, for example, the CAPE for convection parameterization, the use of an exact formula is likely not be critical for the practical purposes, but quantitative discrepancies can be as large as 50–200 J/kg.