Analysis of Convectively Coupled Equatorial Kelvin Waves in a GCM with a Modified Entrainment Profile

Convectively coupled Kelvin waves are major weather producer in the tropics, however, they are not well represented in current Global Climate Models (GCM). In order to improve Kelvin wave simulations, modifications can be made in the way the convection is treated in GCM's. A key feature of convection parameterization is the process of entrainment. In this study, the consequences of enhancing the entrainment rate in the lower troposphere of a GCM are investigated with regards to how well it represents Kelvin wave observations. Kelvin waves are identified with observed outgoing long-wave radiation and simulated modeled precipitation with and without the additional entrainment scheme. Wavenumber-frequency analysis is then used to characterize the equatorial wave spectrum into wavenumber and frequency. Lagged linear regression analysis of model and reanalysis data is utilized to investigate horizontal and vertical Kelvin wave structure. The modified entrainment relationship results in slower(more realistic) Kelvin waves. A westward shift in strongest area of variance was observed west of that of observations. Regression suggests a more coherent propagation and improved vertical structure with a noticeable westward tilt as low-level entrainment is increased. Overall results reveal improved Kelvin wave signal in the model representations. However, the reasons for these improvements require further investigations.