Convectively Coupled Kelvin Waves: From Linear Theory to Global Models

The tropical disturbances can be divided into two broad categories, one that includes fast-moving disturbances where gravity wave dynamics are clearly important and one that includes slow-moving disturbances where balanced dynamics is important. The focus here is on the first category and in particular on convectively coupled Kelvin waves (CCKW).

By looking at the physical processes such as convective inhibition, moisture and surface fluxes, we analyse and interpret the results for CCKW from a linear model (Raymond and Fuchs, 2007), a cloud-resolving model, reanalysis model output, the ECMWF full and aquaplanet model output and radiosonde data.

Large scale characteristics of wave phenomena are robust across all analysis and reanalysis datasets, i.e. phases and amplitudes of all variables show strong similarity across all datasets. They also compare well with the linear theory. The story they tell is the following: CCKW are primarily controlled by changes in deep convective inhibition, while the column moisture contribution is small. In the linear theory considered here, the instability in CCKW is primarily due to the change in buoyancy of air above the PBL. Comparing it to thermodynamic data sources (IGRA, FNL, ERAI) we see excellent agreement in the convective inhibition contribution due to changes in buoyancy of air above the PBL. We suggest that this mechanism is of primary importance for the fast moving disturbances.