The Amplification of Madden–Julian Oscillation Boosted by Temperature Feedback

Abstract

Due to a small Coriolis force in tropics, the theoretical study of Madden–Julian oscillation (MJO) often assumes weak temperature gradient balance, which neglects the temperature feedback (manifested in the temperature tendency term). In this study, the effect of the temperature feedback on the MJO is investigated by using the MJO trio-interaction model, which can capture the essential large-scale features of the MJO. The scale analysis indicates that the rotation effect is strong for the MJO scales, so that the temperature feedback is as important as the moisture feedback (manifested in the moisture tendency term); the latter is often considered to be critical for MJO. The experiments with the theoretical model show that the temperature feedback has significant impact on the MJO’s maintenance. When the temperature feedback is turned off, the simulated MJO cannot be maintained over the warm pool. This is because the temperature feedback could boost the energy generation. Without the temperature feedback, only the latent heat can be generated. With the temperature feedback, not only the latent heat but also the enthalpy (and therefore the available potential energy) can be generated. Therefore, the total energy generation is more efficient with the temperature feedback, favoring the self-maintenance of the MJO. Further investigation shows that this effect of the temperature feedback on MJO amplification can be inferred from observations. The findings here indicate that the temperature feedback could have nonnegligible impacts on the MJO and have implications in the simulation of MJO.