The Diurnal Cycle and Equatorial Gravity Waves Observed during DYNAMO and their Potential Impact on the MJO

The Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign was conducted from October 2011 to March 2012 over the Indian Ocean and Maritime Continents (30°E-150°E), and it captured three episodes of the Madden-Julian Oscillations (MJO) with unprecedented amount of in-situ and remotely sensed observations from land, ships and aircrafts. In this study, precipitation estimated from the hourly Climate Prediction Center Morphing technique (CMORPH), the 3-hourly Tropical Rainfall Measuring Mission (TRMM 3B42 product), and the 3-hourly DYNAMO sounding network, are used to examine the evolution and variability of the diurnal cycles and equatorial - gravity waves during different phases of the MJO. Preliminary analyses show that precipitation has distinct diurnal variation and phase propagation during different MJO phases. Over the Maritime Continent, the diurnal cycle of rainfall is more evident during the convectively suppressed phase of MJO. Propagation of the precipitation anomalies originated over land also differs under different MJO phases: the convectively active phase features an eastward propagation due to the low-level westerly zonal wind anomaly. The predominant gravity waves propagate westward and have a distinct 2-day period, which appear to have strong connections with the diurnal cycles. A cloud-permitting regional-scale model is further employed to simulate these mesoscale structures associated with the diurnal cycle and the 2-day waves during DYNAMO. Results from the simulations are compared with observations. The ultimate goal of this study is to understand the interactions and potential impacts of the diurnal cycle and the gravity waves with/on the MJO.