Casey Dale Burleyson — Pacific Northwest National Laboratory
Samson M Hagos — Pacific Northwest National Laboratory
Zhe Feng — Pacific Northwest National Laboratory
Category
Deep convective clouds, including aerosol interactions
Description
Fig. 1. The annual distribution of the day of the year when the MJO approaches the MC for cases where the RMM amplitude decreases (blue lines) and increases (red lines) across the MC.
The processes that determine the interaction between the islands of the maritime continent (MC) and the eastward propagation of the Madden-Julian Oscillation (MJO) are poorly understood. We are undertaking a series of observational and modeling analyses aimed at understanding how clouds and precipitation over the islands of the MC lead to changes in the intensity of the MJO (inferred by the amplitude of the Real-time Multivariate MJO index [RMM]) as it crosses the MC. One component of our analysis uses the long-term measurements from the DOE Atmospheric Radiation Measurement (ARM) sites in the Tropical Western Pacific (TWP) to examine cloud radiative effects as the MJO crosses the MC. Using the ARM data and a cloud resolving model (CRM), we were able to show that the MJO modifies and is modified by the diurnal cycle of surface heating, clouds, and precipitation over the islands of the MC. Additionally, using a satellite climatology based on the TRMM 3B42 dataset we found that MJO episodes where the MJO weakens as it crosses the MC are characterized by more frequent precipitation and warmer sea surface temperatures (SSTs) south of the equator and less frequent precipitation north of the equator compared to cases where the MJO intensifies. The north-south polarity in SSTs suggests a seasonal dependence in the ability of the MJO to cross the MC. This seasonality was confirmed by looking at the annual distribution of MJO cases where the RMM index amplitude increases and decreases (Fig. 1). Consistent with the SST result, we found that MJO episodes where the MJO intensifies across the MC are more likely to occur during the northern hemisphere summer and less likely to occur during the northern hemisphere winter. In the future we will use a CRM to explore the processes responsible for this seasonality and use the satellite observations to examine the impact of interannual oscillations such as ENSO and monsoons on the ability of the MJO to cross the MC. An improved process-level understanding is a critical first step to improving the simulation of MJO intensity and propagation in climate models.
