Representation of the Convectively Coupled Kelvin Waves in Modern Reanalysis Products

Abstract

Despite decades of research, fundamental questions about the convectively coupled Kelvin waves (CCKWs) remain not fully answered, including the destabilization mechanisms and the mean state modulation. To deepen our understanding and to test simple models for CCKWs, in this study we examine CCKW precipitation, vertical structure, and energetics in four modern reanalyses (RAs): the fifth version of ECMWF Reanalysis (ERA5), NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), the second version of the NCEP Climate Forecast System Reanalysis (CFSR), and the Japanese 55-year Reanalysis (JRA-55). The CCKW precipitation signal strength in the wavenumber-frequency domain and the geographical distribution of CCKW precipitation variability are reasonably represented in all RAs, although they commonly underestimate the amplitude of CCKW precipitation. Despite considerable inter-RA differences in the vertical structure of temperature and diabatic heating anomalies, the eddy available potential energy (EAPE) generation within the CCKWs is found to be associated with the second baroclinic mode whereas the first baroclinic mode damps CCKW EAPE in three out of four RAs. Geographically, the positive CCKW EAPE generation within the second baroclinic mode occurs in areas with high mean state sea surface temperature (SST). Under higher mean state SST, stronger CCKW precipitation variability is preferred through a larger second mode EAPE generation, mainly due to a stronger stratiform heating and a tighter wave-convection coupling. Our results are supportive of the simple models for CCKWs in which CCKWs are destabilized within the second baroclinic mode component.