Convectively coupled equatorial waves

Abstract

Convectively coupled equatorial waves (CCEWs) are zonally propagating planetary-synoptic scale tropical disturbances whose dynamical and convective structures evolve coherently. CCEWs play a major role in organizing tropical convection and account for a major fraction of tropical rainfall. This chapter provides a modern view of the identification, genesis, dynamics and simulation of the CCEWs. A lot of progress has been made in the recent past on the development of methods for identifying the CCEWs in observations, model output and numerical weather forecasts. It should be noted that even while several methods are devised for the identification of CCEWs, there is not a single perfect method which works seamlessly for all problems. Recent observational and modeling studies imply the role of moisture in exciting a wide spectrum of convectively coupled disturbances in the tropics. Moisture mode theory is successful in explaining the evolution, propagation and amplification of the CCEWs. Evaluation of climate model simulations reveals that the models which exhibit a higher degree of coupling between moisture and convection show higher skill in simulating the CCEWs. Recent studies have recognized the importance of realistic simulation of CCEWs in improving the subseasonal forecasts in the tropics and the extratropics. Many studies have also tried to address the regionality and seasonality of CCEWs, and such studies have pointed out the critical role of the zonal background flow and extratropical forcing in modulating the CCEWs. The chapter also highlights the open issues and challenges in CCEW research.