Ertel Potential Vorticity Charging in the Tropical Atmosphere

Focusing on the zonal mean, this paper defines northward Ertel potential vorticity (EPV) flux as EPV charging and southward as EPV discharging, using electric charges in an electric circuit as an analogue to EPV substance on a globally closed isentropic surface. EPV charging can yield eastward acceleration, and EPV discharging can yield westward acceleration. NCEP Climate Forecast System Reanalysis (CFSR) monthly products are used to analyze five types of EPV flux, which are mean-advective, eddy-advective, the nontraditional Coriolis term (NCT) coupled with diabatic forcing, mean-shear-diabatic, and eddy-shear-diabatic. NCT-diabatic flux is the least uncertain term owing to the linearity and is an EPV discharger with heating. NCT-diabatic flux can yield 20 m s^-1 yr^-1 of westward acceleration near the zonal annual mean heating maximum but is ignored in most of the current global models. From the cloud base to the heating maximum, the increasing westward acceleration due to NCT can adiabatically cool the equatorward side of convection and warm the poleward side of it. The other terms are uncertain owing to nonlinearity and should be interpreted qualitatively. In the tropical heating regions, eddy-advective flux is a robust EPV discharger, and eddy-shear-diabatic flux is a robust EPV charger. In terms of spatial correlations, EPV-discharging eddy-advective flux resembles moist equatorial Rossby waves or moist mixed Rossby-gravity waves, and EPV-charging eddy-shear-diabatic flux resembles the Madden-Julian oscillation (MJO) or moist Kelvin waves. This paper discusses implications of EPV charging to phenomena including the quasi-biennial oscillation (QBO), the MJO, and the intertropical convergence zone (ITCZ).