The Madden-Julian Oscillation (MJO) is a pattern of atmospheric circulation that drifts eastward across the tropics, circling the Earth every 30 to 60 days. The massive circulation cells of the MJO rise and fall, driving changes in short-term weather phenomena like clouds and rainfall that alter sea surface temperatures and other global climate trends as the circulation pattern traverses the Indian and Pacific Oceans.
Despite the outsized effect of the MJO on weather and climate, it’s unclear if current models effectively simulate the phenomenon. This is largely because the relationship between the bounds of convection—the upward movement of air through the atmosphere—and environmental conditions is not well understood. Identifying the relationship between convection and the environment is critical for understanding the atmospheric process itself. And models must be able to capture the nature of that relationship in order to adequately predict convection and its downstream effects on weather and climate.
With an eye on precipitation rate, the moisture content of the air, and the stability of the atmosphere, Sentić et al. sought to determine how these environmental conditions influence convection and provide means for evaluating whether current climate models are able to capture their impact.
Using observations of tropical convection and environmental conditions from the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign, the team compared observed relationships between convection and the environment with a cloud-resolving model—a high-resolution simulation capable of capturing the life cycles of single clouds and entire cloud systems.
The study revealed that the model reasonably reproduced reality, providing the scientists with a clearer picture of MJO dynamics. On the basis of their findings, the authors suggest that the stability of the atmosphere sets the stage for convection. Then the flow of wet, humid air determines how much moisture is present for precipitation, which, in the end, determines the rate of rainfall.
The study is an important step in understanding the relationship between the environment and convection within the MJO—but the origin of the stability changes that set the process in motion, the authors note, is still a mystery. (Journal of Advances in Modeling Earth Systems (JAMES), doi:10.1002/2015MS000531, 2015)
—Kate Wheeling, Freelance Writer
Citation: Wheeling, K. (2016), Illuminating the controls of convection, Eos, 97, doi:10.1029/2016EO045429. Published on 11 February 2016.