Fluctuations in Earth’s climate reflect the complex interactions of the atmosphere and oceans, a dynamic dance that changes with the seasons. One such interaction is the Madden-Julian Oscillation (MJO), a marriage of atmospheric circulation and tropical convection that propagates eastward above the warm regions of the Indian and Pacific Oceans.
The circulation cells are large—about 10,000 kilometers wide along the equator—and occur intraseasonally, roughly every 30 to 70 days. Because of this scale and frequency, the MJO has a big impact on global weather.
The rising and sinking motions within the MJO circulation cells produce a pattern of enhanced and suppressed convection. This convection pattern brings rainfall and induces changes in clouds and wind, which translates to variations in heat, salinity, and momentum at the ocean surface where water and atmosphere interact. The associated changes in sea surface temperature can have global consequences, but the MJO is difficult to explain theoretically or simulate in atmospheric general circulation models, and its relationship with sea surface temperature is poorly understood.
Here DeMott et al. work to fill in these knowledge gaps by reviewing published studies dealing with observations of MJO processes, theories of air-sea interactions within the MJO, and modeling studies of these feedbacks. Their review article aims to develop better insight into how air-sea interactions influence the MJO and, ultimately, how these exchanges shape weather patterns.
When the MJO inhibits convection, light winds and clear skies allow the upper few meters of the ocean to warm and separate into stable layers stratified by temperature and salinity. As MJO convection develops, windy conditions at the surface mix these layers and transfer energy stored in the upper ocean to the atmosphere.
As the MJO propagates eastward, this mixing action increases, driving currents and upsetting the stratified layers. Scientists discovered the phenomenon in the 1970s, but a comprehensive theory for the MJO and a clear understanding of the role of the ocean in the disturbance have been elusive. The researchers summarize the current understanding of these processes by analyzing results of more than 300 papers focused on the problem.
The review study found that high-resolution mixed layer ocean models can represent some of the complicated air-sea interactions and recommended that scientists use coupled simulations and evaluate them in terms of the observed relationship between convection and sea surface temperature and associated variables.
A full assessment of air-sea interactions within the MJO requires a combination of methods, including modeling studies, process-oriented diagnostics, and careful measures of the environmental moisture profile and heat budget of the MJO. A comprehensive approach is central to improving our knowledge of ocean-atmospheric coupled feedbacks. (Reviews of Geophysics, doi:10.1002/2014RG000478, 2015)
—Lily Strelich, Freelance Writer
Citation: Strelich, L. (2015), Convection cycles, atmosphere, and ocean work symbiotically, Eos, 96, doi:10.1029/2015EO040415. Published on 30 November 2015.