Moist Thermodynamics of Convectively Coupled Waves over the Western Hemisphere

Convectively coupled waves (CCWs) over the Western Hemisphere are classified based on their governing thermodynamics. It is found that only the tropical depressions (TDs; TD waves) satisfy the criteria necessary to be consid-ered a moisture mode, as in the Rossby-like wave found in an earlier study. In this wave, water vapor fluctuations play a much greater role in the thermodynamics than temperature fluctuations. Only in the eastward-propagating inertio-gravity (EIG) wave does temperature govern the thermodynamics. Temperature and moisture play comparable roles in all the other waves, including the Madden-Julian oscillation over the Western Hemisphere (MJO-W). The moist static energy (MSE) budget of CCWs is investigated by analyzing ERA5 data and data from the 2014/15 observations and modeling of the Green Ocean Amazon (GoAmazon 2014/15) field campaign. Results reveal that vertical advection of MSE acts as a primary driver of the propagation of column MSE in westward inertio-gravity (WIG) wave, Kelvin wave, and MJO-W, while horizontal advection plays a central role in the mixed Rossby gravity (MRG) and TD wave. Results also suggest that cloud radiative heating and the horizontal MSE advection govern the maintenance of most of the CCWs. Major disagree-ments are found between ERA5 and GoAmazon. In GoAmazon, convection is more tightly coupled to variations in col-umn MSE, and vertical MSE advection plays a more prominent role in the MSE tendency. These results along with substantial budget residuals found in ERA5 data suggest that CCWs over the tropical Western Hemisphere are not repre-sented adequately in the reanalysis.

Automated summary

Convectively coupled waves (CCWs) over the Western Hemisphere are classified based on their governing thermodynamics. The tropical depressions (TDs; TD waves) are the only waves considered as moisture modes, while temperature governs the thermodynamics of the eastward-propagating inertio-gravity (EIG) wave. Temperature and moisture play comparable roles in all the other waves including the Madden-Julian oscillation over the Western Hemisphere (MJO-W). The moist static energy (MSE) budget of CCWs is investigated and results reveal the primary drivers of column MSE propagation in different waves and the key factors in the maintenance of CCWs.