Vertical Structure of Radiative Heating Rates of the MJO during DYNAMO

We analyze the vertical structure of radiative heating rates over the region of the tropical Indian Ocean associated with Madden Julian Oscillation (MJO) initiation during the Dynamics of the MJO/ARM MJO Investigation Experiment (DYNAMO/AMIE 2011) observational period. Using the PNNL combined radar retrieval (CombRet; Feng et al. 2014) from Gan Island, Maldives (0.69° N,73.51° E), we study the mean and variability of these heating rates during MJO convective and dry phases, as classified by the daily MJO index developed by Wheeler and Hendon (2004). Since convection happens locally on time scales less than a day, higher-resolution information contributes to understanding feedbacks of convection and clouds to the MJO. While local convection is more likely during the "convective" phase, it still occurs during “dry” phases, and clear skies are common in the “convective" phases. We develop a new technique for sorting vertically resolved heating rate data, based on the local outgoing longwave radiation (OLR). Deep convection (in particular, the vertical structure of the heating rate) looks the same regardless of the MJO phase.

We compare top-of-the-atmosphere (TOA) and surface fluxes from the CombRet product with co-located 3-hourly satellite retrievals from Clouds and the Earth’s Radiant Energy System (CERES; doi:10.5067/Terra+Aqua/CERES/SYN1degM3HOUR_L3.003A) data. The two data sets are correlated in time with correlation coefficients ranging from 0.84 to 0.94, yet the mean values differ by up to several Wm^-2. We use the OLR-sorting technique to explore discrepancies between the two data sets, including the effects of the known under-sampling of high clouds by CombRet, due to radar attenuation in heavy rainfall (Johnson et al. 2015).