Diurnal Cycle of Cloudiness and Precipitation During DYNAMO

This study examines the diurnal cycle of precipitation and cloud type using S-Polka radar reflectivity during the DYNAMO field campaign. The diurnal cycle of cloud population exhibits different characteristics during the passage of the convectively enhanced and suppressed phases of the Madden-Julian oscillation (MJO). An afternoon peak in isolated convection following the diurnal warming of SST is only apparent during the suppressed phase of the MJO. During the enhanced phase of the MJO, the diurnal cycle of total rainfall is dominated by organized convective and stratiform rainfall peaking at early morning hours. The observed atmospheric states during the field campaign are examined to understand the driving mechanisms of these changes in the diurnal cycle of cloud population and rainfall associated with the MJO, since previous studies have suggested that the nonlinear feedback of the diurnal cycle is important to the MJO. However, budget analyses of momentum, temperature, and moisture suggest that the diurnal cycle has no significant nonlinear feedback onto the daily or longer timescale over the Indian basin during the DYNAMO period. This suggests that changes in the diurnal cycle of cloud population and precipitation perhaps result from the large-scale modulation of the environment by the MJO, but that they do not drive the MJO.