Diurnal Convection and Mesoscale Organization during DYNAMO

The Madden Julian oscillation (MJO) is a topic that has received fervent attention in recent decades, 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 initially takes place 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, suite of radars, and surface observing systems.

There is mounting evidence that tropospheric moistening is prerequisite to the production of heavy rainfall in the deep convective phase of the MJO, though the source of moisture has yet to be quantitatively established from observations. Motivated by this outstanding issue, the basis of the present study is formulated by the following three observations during DYNAMO undisturbed periods, which precede the MJO deep-convective envelope: 1) assessment of the moisture budget reveals a large contribution from shallow vertical fluxes (i.e., shallow/congestus convection); 2) there was a pronounced diurnal cycle in convection; and 3) convection was often manifest in Rayleigh–Benard cellular organization. Preliminary results of an ongoing investigation of the diurnal cycle in convection in DYNAMO, with focus on mesoscale organization and its relationship with the moisture field, will be discussed.