Cloud-radiation interaction in the Madden-Julian Oscillation

Abstract

Several recent modelling studies propose that the cloud-radiation interaction may affect the amplitude and phase speed of the Madden-Julian Oscillation (MJO). This study examines the effect of cloud-radiation interaction on the MJO using long-term observations from ISCCP and ERBE, supplemented by short-term measurements from several field experiments including TOGA COARE, ARM and CAVE. The vertical profiles of radiative heating are calculated using the CCM3 Column Radiation Model. All datasets are filtered using a 30-70 day bandpass filter. The long-term MJO composites are constructed using linear correlation and linear regression with respect to surface precipitation.

Variation of clouds in the MJO is dominated by variation of the upper troposphere stratiform clouds, with cloud top around 250 mb and cloud base above 700 mb. The column-integrated radiative heating is nearly in phase with the column-integrated convective heating, and its amplitude is about 10-20% of that of the convective heating. The vertical profile of the radiative heating is dominated by cloud top cooling around 250 mb and cloud base warming below 250 mb.

It is shown that the radiative heating does not generate positive eddy available potential energy for the MJO. Therefore, the radiative heating does not amplify the MJO.