The Diurnal Cycle of Moistening by Shallow Convection during DYNAMO

The Madden Julian oscillation (MJO) is a topic receiving fervent attention at present, owing to our inability to adequately describe its underlying dynamics. Through international efforts, the Dynamics of the MJO (DYNAMO) field campaign was conducted over October 2011-March 2012 in order to sample the coupling between convection and deep circulation that usually initiates in the tropical Indian Ocean. During a special observing period from 1 October-30 November, two MJOs were sampled by the DYNAMO observational network, which included a fully operational sounding network and suite of radars. DYNAMO sounding observations demonstrate a strong diurnal cycle in moistening during periods of suppressed and deepening convective activity, which corresponds with a diurnal cycle in sea surface temperature and surface evaporation. Convection during these suppressed and preconditioning periods was predominately shallow and non-raining, and exhibited open-cellular organization (consistent with an unstable boundary layer). A vertically pointing, W-band radar was situated at the equator on R/V Revelle during DYNAMO, which provides dense information on lightly- and non-raining shallow cumulus activity. Observations from this radar will be discussed with focus on the diurnal cycle of convection, and comparisons will be made with observations from the sounding network. Example of the diurnal cycle of clouds during the MJO suppressed period (12 October 2011), showing afternoon growth and hexagonal open-cell organization.