The Madden Julian Oscillation has a significant influence on the dynamical variability of the tropics. Its understanding will involve the assessment of the factors that cause organization of deep convection. Three mechanisms for convective organization are investigated in turn to assess their relative importance for convective organization in the ECMWF global model.

(1) Radiation

Sensitivity tests with the cloud microphysics attempt to isolate the radiative feedback with clouds. Additional tests attempt to isolate the feedback between longwave radiation and the water vapour field.

(2) Water vapour

The suggested feedback with water vapour is a result of the different adjustment timescales of convective moistening (slow advective) and drying (fast gravity waves). Thus this feedback is examined by applying the drying and moistening tendencies from the convection scheme over the different horizontal scales associated with each process, instead of locally on one gridpoint column as is currently done in current convective schemes.

(3) Gust enhanced surface fluxes

Simple convective wind gustiness parameterizations are applied both locally and non-locally to gauge their relative importance for convective organization.