Joint Seminar: A Rossby Wave Bridge from the Tropical Atlantic to Antarctica

I will explore connections between tropical Atlantic sea surface temperatures and the climate of West Antartica.  Warming in the tropical Atlantic, associated in part with the Atlantic Multidecadal Oscillation, forces a positive response in the Southern Annular Mode, strengthening the Amundsen-Bellingshausen Sea Low in particular. Observational and reanalysis datasets and a hierarchy of atmospheric models are used to assess the seasonality and dynamical mechanism of this teleconnection. Both the reanalyses and models reveal a robust link between tropical Atlantic SSTs and the Amundsen-Bellingshausen Sea Low in all seasons except austral summer. A Rossby wave mechanism is then shown to both explain the teleconnection and its seasonality. The mechanism involves both changes in the excitation of Rossby wave activity with season, and the formation of a Rossby waveguide across the Pacific, which depends critically on the strength and extension of the subtropical jet over the West Pacific. Strong anticyclonic curvature on the poleward flank of the jet creates a reflecting surface, channeling quasi-stationary Rossby waves from the subtropical Atlantic to the Amundsen-Bellingshausen Sea region. In summer, however, the jet is weaker than in other seasons, and no longer able to keep Rossby wave activity trapped in the Southern Hemisphere. The mechanism is supported by integrations with a comprehensive atmospheric model, initial value calculations with a primitive equation model on the sphere, and Rossby wave ray tracing analysis.

The potential climate implications of these circulation anomalies will also be discussed.  Tropical Atlantic warming may explain a significant fraction of the recent warming of the Antarctic Peninsula and the dipolar change in sea ice observed around West Antarctica.

Date

11.02.2015

Time

13:30 h

Place

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

Speaker

Edwin Gerber, Columbia University

Organizers

Hauke Schmidt

Back to listing