Simulations of Convectively Coupled Kelvin Waves (CCKWs) With Three Different Cumulus Parameterization Schemes

Abstract

Convectively coupled Kelvin waves (CCKWs) significantly influence tropical rainfall variability; however, accurately simulating these waves remains a challenge in atmospheric modeling. Cumulus parameterization is a critical element in model-generated CCKW activity among the various factors. This study investigated the impact of cumulus parameterization on CCKW simulation by analyzing the coupling mechanism between tropical convection and Kelvin waves, expanding on the stratiform instability theory. This theory suggests that CCKWs are enhanced through a positive feedback loop between stratiform heating and temperature. We aimed to minimize contamination from large-scale environmental influences by employing the Weather Research and Forecasting (WRF) model configured for tropical channel simulations with spectral nudging. We assessed three distinct cumulus parameterization schemes: Grell-Freitas (GF), Multi-scale Kain-Fritsch (MSKF), and New Tiedtke (NTDK). Our analysis revealed that the NTDK scheme simulates the strongest CCKW signal, whereas the GF and MSKF schemes exhibit weaker signals. The vertical-mode decomposition of diabatic heating and temperature identified two prominent modes corresponding to deep convection and stratiform precipitation. The results demonstrated that NTDK shows the most favorable conditions for CCKW enhancement, characterized by substantial contributions from the second mode of heating and temperature anomalies. These aspects underline the critical role of cumulus parameterization for the enhancement of CCKWs, highlighting the importance of accurately representing stratiform instability to reduce deficiencies in CCKW modeling.