 This variability is primarily due to variability in the surface enthalpy disequilibrium ( formula_11 ) as well as in the thermodynamic structure of the troposphere, which are controlled by the large-scale dynamics of the tropical climate.These processes are modulated by factors including the sea surface temperature (and underlying ocean dynamics), background near-surface wind speed, and the vertical structure of atmospheric radiative heating.The nature of this modulation is complex, particularly on climate time-scales (decades or longer).