Diagnosing moistening processes of the November DYNAMO MJO by Cloud Resolving Model Simulations

Cloud resolving model (CRM) simulations are used to diagnose moistening processes of the November 2011 Madden-Julian Oscillation (MJO) during the DYNAMO field campaign. Specifically, the role of wind-flux feedbacks and column radiation at altering column moisture associated with the evolution of MJO convection will be discussed. Simulations are run using Colorado State University's Regional Atmospheric Modeling System (RAMS). The domain is 825 km x 825 km with 1.5 km horizontal resolution and is centered near the middle of the DYNAMO northern sounding array. An oceanic surface is used with observed Aqua MODIS sea surface temperatures. Lateral boundary nudging via ECMWF reanalysis is applied to ensure realistic evolution of the MJO. The model is run for the entire month of November with output saved every 20-minutes.

Due to the multiscale nature of convection associated with the MJO, the relationship between rain and surface latent heat flux (LHFLX) will be shown for various time (20-minutes to daily) and space (1.5 km to 825 km) averaging scales. Results show that the relationship between rain and LHFLX across various time and space averaging scales is different during suppressed vs. active MJO days. During suppressed MJO days, the correlation coefficient between rain and LHFLX for spatial averaging scales less than ~200 km decreases as the temporal averaging scale increases. The opposite trend occurs during MJO active days – the correlation coefficient increases as the temporal averaging scale increases for spatial averaging scales less than ~200 km. This difference is perhaps explained by the shift in convection from small less organized convection during suppressed MJO days to larger well-organized convective systems during active MJO days. Weak temperature gradient diagnostics are used to show that active MJO days correspond to anomalous moistening by radiation due to decreased longwave radiation emission to space. Implications of the results will be discussed in terms of MJO theories, namely moisture-mode theory.