News & Events

Monday Noon Seminar - Causes and consequences of the westerly wind increase over the Southern Ocean

Monday, April 13, 2015, 12:00PM - 1:00PM

Speaker

David Schneider

NCAR

Location:

ARC room 620

The westerly winds over the Southern Ocean, known as the “Roaring 40s,” “Furious 50s,” and “Screaming 60s,” are among the strongest and most persistent winds on Earth. They drive the world’s largest ocean current and play key roles in the carbon cycle, the climate variability of Antarctica, the retreat of ice shelves, and Antarctic sea ice dynamics.

During the past three to four decades, the average zonal wind speed over the Southern Ocean has increased significantly, perhaps to a level unseen in the past 1000 years. This trend has important implications for climate change, and many scientists have attributed it to the Antarctic ozone hole. However, recent work suggests that changes in tropical climate have been communicated to the high southern latitudes by strong and persistent teleconnections associated with atmospheric Rossby Waves, leading to marked regional changes in atmospheric circulation and contributing to the rapid warming of the Antarctic Peninsula and West Antarctica.

In this talk, I will break down the observed wind trend into distinct seasonal and spatial patterns, and use atmospheric model simulations to test the hypothesis that these aspects of the wind trend are explained by a seasonally varying combination of tropically driven teleconnections and stratospheric ozone depletion. Specifically, during 1979-2011, ozone depletion coincided with major swings in tropical climate variability, characterized by a shift in the Pacific Decadal Oscillation (PDO) to its negative phase. This is among the first studies to directly compare and quantify the relative roles of these two phenomena in causing the wind increase over the Southern Ocean. Considering both the PDO and ozone depletion together, the model successfully simulates the major seasonal and spatial aspects of the observed trend pattern. The relative roles of stratospheric ozone depletion and tropical variability tend to vary with time period and season, and sometimes attribution is not unequivocal in the presence of large, internal variability that obscures forced signals in both the model simulations and observations. Nonetheless, these results give a strong basis for interpreting recent climate change over the Southern Ocean, and for assessing the performance of current-generation climate models.

Audience

Free and open to the public.