Impact of moist thermodynamic formulations on climatological temperature fields in a global cloud-resolving model

This study investigates how climatological temperature fields in simulations are influenced by the choice of moist thermodynamic formulations. Two formulations were compared: one developed to ensure internal thermodynamic consistency, and a simpler approximation similar to those commonly used in meteorological and climate models. Sensitivity experiments using a global cloud-resolving model showed that tropical upper-tropospheric temperatures are approximately 2 K higher with the simplified formulation than with the consistent formulation. To understand these discrepancies, we compared vertical temperature structures determined by the moist adiabatic lapse rate for both formulations. The temperature difference reaches about 1.3 K at 16-km altitude for a surface temperature of 300 K, consistent with the sensitivity experiments. Analysis of the individual contributions revealed that simplifications in specific heat, latent heat, and saturation vapor pressure produce negative, positive, and positive effects, respectively, which are additive. Furthermore, the temperature difference increases exponentially with surface temperature. These results indicate that the choice of moist thermodynamic formulation has a significant impact on the reproducibility of climate fields.