Mechanisms controlling the onset of simulated convectively coupled Kelvin waves

Abstract

Convectively coupled Kelvin waves (CCKW) are analysed using a cloud-resolving model to gain a better understanding of the mechanisms that initiate and drive these waves. We compare the modelled precipitation and vertical structure of a convectively coupled Kelvin wave to the mechanisms that control precipitation over warm tropical oceans: convective inhibition (CIN), saturation fraction, atmospheric stability and surface moist entropy fluxes. Our results show that the primary onset mechanism for precipitation associated with CCKW is CIN associated with a decrease in the threshold moist entropy. Saturation fraction and atmospheric instability exhibit a time lag in comparison with the rainfall evolution and are, therefore, not primary controls in the onset of these waves. The modelled CCKW evolve by starting with congestus convection, develop into deep convection and decay with the stratiform convection. The results from the presented model agree with observations and linearised models.

• convective inhibition
• saturation fraction
• moist entropy
• stable layer

6. Acknowledgments

We thank two anonymous reviewers whose comments helped improve this manuscript. This work was funded by the European Commission's 7th Framework Program, under Grant Agreement number 282672, EMBRACE project, by US National Science Foundation Grants ATM-0352639, ATM-1020149, and AGS-1056254.

Notes

Shallow CAPE integrates the buoyancy of undiluted parcels only up to the mid-troposphere (for example, refer to Kuang 2008).

Layer thickness and heights used in the definitions of DCIN and instability index represent typical observed values of characteristic regions over tropical oceans.