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Research Highlights

November 2014

On the Right Track for Tropical Clouds

Scientists find the cause of moisture buildup that initiates and propels the Madden-Julian Oscillation

precipitating cloud at the start of the Madden-Julian oscillation
Clouds and the MJO. Researchers found that the large-scale vertical lifting and the decline of mid-level drying by equator-ward horizontal advection are the primary mechanisms of moistening that lead to the initiation and propagation of MJO deep convection. Photo courtesy of Adam H. Sobel, The Madden-Julian Conversation. Enlarge Image.

Results: Researchers at Pacific Northwest National Laboratory and collaborators are hot on the trail of a large and lumbering atmospheric wave. Originating in the tropics, the intra-seasonal force wields influence on weather patterns around the world. Using high-resolution regional modeling along with field data, the scientists found that the frequency of the wave's shallow-to-deep convective cloud transitions is sensitive to moisture buildup in the mid-troposphere and a large-scale lifting in the atmosphere. Simultaneous forces—the lifting and a decline in large-scale drying—result in moisture buildup leading to the initiation of the Madden-Julian Oscillation (MJO).

Why It Matters: Cracking the code of the MJO will mean better prediction of severe winter storms for the U.S. West Coast, the summer monsoon in the U.S. Southwest, Pacific hurricanes and perhaps even the El Niño weather event. The MJO is a complex, large-scale and slow-moving tropical intra-seasonal atmospheric wave with far-reaching impacts on weather patterns around the world. Understanding and modeling its initiation and propagation are two of the long-standing challenges in climate science. This research, using integrated data from field campaigns and high-resolution modeling, is providing insight into this important atmospheric enigma.  

Methods: PNNL researchers and a collaborator from the Indian Institute of Technology used observations from the 2011 ARM MJO Investigation Experiment (AMIE)/Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaigns over the Indian Ocean. For this study, they used the Weather Research and Forecasting (WRF) model, a high-resolution regional model to track the processes that lead to the rapid, shallow-to-deep convective cloud transitions associated with the initiation and propagation of the MJO. They tracked several thousand model-simulated clouds throughout the clouds' lifetime and considered various environmental factors that determine whether the clouds become deep.

The field campaign data used in their research are available at the National Center for Atmospheric Research's (NCAR's) Earth Observing Laboratory's DYNAMO Data Catalogue and at the ARM Data Archive under Gan Island, Maldives.

What's Next?  The scientists will use these findings to improve computer representations of the moistening process providing improved simulation of MJO in the relatively low-resolution global climate models.

Acknowledgments

Sponsors: The research is supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under the Atmospheric System Research Program, and the Regional and Global Climate Modeling Program.

Facilities: Computing resources for the simulations were provided by the Oak Ridge Leadership Computing Facility (OLCF) through the INCITE Climate End Station project and National Energy Research Scientific Computing Center(NERSC).

User Facility: ARM Climate Research Facility

Research Team: Samson Hagos, Zhe Feng, and Chuck Long, PNNL; Kiranmayi Landu, Indian Institute of Technology, India.

Research Area: Climate & Earth Systems Science

Reference: Hagos S, Z Feng, K Landu, and CN Long. 2014. "Advection, Moistening, and Shallow-to-Deep Convection Transitions during the Initiation and Propagation of Madden-Julian Oscillation." Journal of Advances in Modeling Earth Systems 06(3):938-949. DOI:10.1002/2014MS000335

Related Research:

The Long and Rich Life of Tropical Clouds

Mastering the Mysteries of the MJO


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Convection and Advection: Moving Moisture

Two physical concepts are important to understand how the atmosphere moves heat and moisture around the globe. The first is convection. Imagine heating a pot of water and feeling the steam and warm air rise above the pot into the cooler air as the water begins to boil. The pot water churns in a circular motion; the water on the surface cools as it hits the air and sinks to the bottom only to be heated again and rise. Advection is the horizontal movement of air, unlike the vertical movement described in convection. It usually results in warm air sliding up over cool air. Both actions influence cloud formation in the atmosphere when the air has some moisture.

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