Accurate Column Moist Static Energy Budget in GISS ModelE3

The column-integrated Moist Static Energy (MSE) budget is a valuable tool for studying various climate and weather phenomena, such as convectively coupled tropical waves, general synoptic-scale convective disturbances, tropical cyclones, monsoonal variability, the ITCZ, and global energy transport. However, accurately computing the MSE budget, particularly its dynamical tendency, from standard model outputs given in a daily pressure-coordinate system, poses a challenge.

In this project, we implemented model codes in a NASA-GISS GCM called ModelE3 to accurately calculate all the MSE budget terms, including work done against pressure-gradient force and frictional dissipation, which are often overlooked. Our findings indicate that, in climatological studies over the tropical belt (between 15 degrees North and 15 degrees South), these nonconventional terms are insignificant, except for the topographic regions along the Andes mountains where their magnitude becomes comparable to the other terms. In the subtropics, these terms are generally not negligible, particularly over Eurasian continental regions, where they are comparable to or exceed the other MSE budget terms.

We also utilized accurately computed budget terms to evaluate numerical errors in the dynamical tendencies (horizontal and vertical advective tendencies) computed with variables in temporally-averaged vertical-pressure-coordinate systems. Our findings indicate that the error in the vertical MSE advection, computed in the daily pressure-coordinate system, primarily arises from the vertical interpolation of variables used, rather than from the daily average. This error is significant enough to flip the sign of the vertical MSE advection in some tropical regions. Traditionally, it has been believed that top-heavy vertical-wind profiles over warm pool regions export the MSE, while bottom-heavy profiles over the eastern Pacific import the MSE. However, our accurately computed budget reveals that the vertical advection imports the MSE in the Indian Ocean, most of the western Pacific, and eastern Pacific, contradicting the conventional framework. These results highlight the importance of accurately computing the MSE budget.