Causes and Consequences of Long-Term Pressure Variability and Trends over Antarctica Since 1905

Distinguishing between forced changes and low-frequency, natural variability is particularly challenging in Antarctica and the Southern Ocean, where the instrumental record is short and sparse, and the interannual variability is large.  As discussed in another presentation at this meeting, a new, seasonally resolved reconstruction of surface pressure across Antarctica nearly doubles the length of the instrumental record, providing a more appropriate context for assessing the significance of recent trends in Antarctic surface climate.  In addition, we have evaluated multiple ensembles of transient atmospheric climate model simulations extending from the late 19th Century to the near-present.  The ensembles were forced by different combinations of tropical sea surface temperatures, stratospheric ozone depletion, and external radiative forcings.  In this presentation, we will use results from these simulations to characterize the roles of stratospheric ozone depletion and tropical teleconnections in Antarctic surface pressure variability and trends, and use pressure reconstruction to assess the model’s overall skill.  Questions considered include: (1)  How well does the model reproduce the general characteristics of surface pressure, including the seasonal means, interannual variability and power spectra?  (2) How significant is the signal of stratospheric ozone depletion in the surface pressure field, and when did it emerge?  (3) What are the consequences of this ozone-related atmospheric circulation change, particularly for surface air temperature trends? (3) Have the pattern and magnitude of tropical teleconnections been consistent throughout the 20th and 21st centuries, and are recent high-latitude circulation trends (since 1979) that have been related to tropical variability unusual?