Australia: The Land Where Time Began

A biography of the Australian continent 

A Rossby Wave Bridge Connecting West Antarctica to the Tropical Atlantic Ocean

Sea surface temperature changes in the Tropical Atlantic have recently been linked to circulation anomalies around Antarctica during the austral winter. A positive response in the southern annular mode that is forced by warming in the tropical Atlantic associated with the Atlantic Multidecadal Oscillation, which strengthens the Amundsen-Bellingshausen Sea Low in particular. In this study Li et al. used observational and reanalysis datasets and a hierarchy of atmospheric models to assess the seasonality and dynamic mechanisms of this teleconnection. A robust link between tropical Atlantic sea surface temperatures (SSTs) and the Amundsen-Bellingshausen Sea Low in all seasons except the austral summer was revealed by the reanalysis and the models. A Rossby wave mechanism was then shown to explain the teleconnection as well as its seasonality. The mechanism involves changes in the excitation of Rossby wave activity with season and formation of a Rossby waveguide across the Pacific, which is critically dependent on the subtropical jet strength and extension over the west Pacific. A reflecting surface is formed by the strong anticyclonic curvature on the poleward flank of the jet. And this channels quasi-stationary Rossby waves from the subtropical Atlantic to the Amundsen-Bellingshausen Sea region in Antarctica in summer, a time of year when the jet is not as strong as in other seasons and is no longer able to keep the Rossby wave activity restricted to the Southern Hemisphere. Integrations with a comprehensive atmospheric model, initial-value calculations with a primitive equation model on the sphere, and Rossby ray tracing analysis, all support this mechanism.

Sources & Further reading

1. Li, X., E. P. Gerber, D. M. Holland and C. Yoo (2015). "A Rossby Wave Bridge from the Tropical Atlantic to West Antarctica." Journal of Climate 28(6): 2256-2273.