Contact Info

Department of Physical and Environmental Sciences

University of Toronto Scarborough

1065 Military Trail, EV346

Toronto, Ontario, Canada

M1C 1A4 

Phone: (416) 208-2785

Email: karen.smith@utoronto.ca

Antarctic Climate Variability and Trends

 

The observed positive trends in Antarctic sea ice and the negative trends in East Antarctic surface air temperature pose a challenge to our understanding of the climate system, in that one would expect sea ice to melt and surface temperatures to increase in a warming climate, as observed in the Arctic. We use observationally-based data and global climate model integrations to investigate the relative importance of internal variability and external forcing, particularly stratospheric ozone depletion, on trends in the Antarctic climate. Our work suggests that variability in this region is large and attribution of many of the observed trends to anthropogenic climate change is challenging.


Arctic Ozone Anomalies and Surface Climate

 

In the Arctic stratosphere, total column ozone in the spring can vary, from year to year, by as much as 30%. This large interannual variability, however, is absent from many present generation climate models. We use  climate model integrations with prescribed springtime ozone anomalies to investigate the extent to which interannual variability in Arctic stratospheric ozone is able to affect the surface climate of the Northern Hemisphere extratropics. For ozone anomaly amplitudes somewhat larger than the recent observed variability, we find a significant influence on the tropospheric circulation, and the surface temperature and precipitation patterns. More interestingly, these impacts have very clear regional patterns—they are largest over the North Atlantic sector—even though the prescribed ozone anomalies are zonally symmetric. Future trends in Arctic ozone, and consequent stratosphere-troposphere coupling, may have implications for surface climate.

Stratosphere-troposphere Coupling and Linear Interference

 

Vertical fluxes of wave activity from the troposphere to the stratosphere correlate negatively with the Northern Annular Mode (NAM) in the stratosphere and subsequently in the troposphere. Recent work, including our own, has shown that stratospheric NAM variability is also negatively correlated with the amplitude of the wave pattern coherent with the climatological stationary wave field; when the climatological stationary waves are amplified or attenuated, the stratospheric jet correspondingly weakens or strengthens. The interannual variability in extratropical vertical wave activity flux into the stratosphere in both hemispheres is dominated by linear interference during the season of strongest stratosphere-troposphere coupling. What processes drive linear interference is an area of ongoing research.