Dynamical Impacts of Antarctic Stratospheric Ozone Depletion on the Extratropical Circulation of the Southern Hemisphere Kevin M. Grise David W.J. Thompson Department of Atmospheric Science Colorado State University (Thanks also to Piers Forster) Chapman Conference on The Role of the Stratosphere in Climate and Climate Change Santorini, Greece September 25, 2007

Overview Antarctic ozone hole is forcing trends in Southern Hemisphere circulation that are consistent with positive phase of Southern Annular Mode (SAM). Antarctic ozone hole is forcing trends in Southern Hemisphere circulation that are consistent with positive phase of Southern Annular Mode (SAM). Idea: Because tropospheric trends resemble SAM, decompose these trends into component linearly congruent with SAM and residual component independent of SAM. Idea: Because tropospheric trends resemble SAM, decompose these trends into component linearly congruent with SAM and residual component independent of SAM. Goal: To assess relative contributions of dynamics and radiation in determining recent tropospheric temperature trends. Goal: To assess relative contributions of dynamics and radiation in determining recent tropospheric temperature trends.

Ozone Trends Pressure (hPa) Altitude (km) Randel and Wu (2007) Global Ozone Data Set

NCEP-NCAR Reanalysis Trends Geopotential Height (65°S - 90°S) Temperature 1979: Satellite data first available for reanalysis 2001:Last year before 2002 sudden stratospheric warming

Understanding the Trends in the Troposphere (Thompson and Solomon 2002; Gillett and Thompson 2003) The trends in the troposphere possess a spatial pattern very similar to the Southern Annular Mode (SAM).

NCEP-NCAR Reanalysis Trend Decomposition T (65°S - 90°S)Z (65°S - 90°S) Total SAM Congruent Residual Contour Intervals: 0.5 K/decade 20 m/decade

HadSM3-L64 Model Trend Decomposition Total T (65°S - 90°S)Z (65°S - 90°S) SAM Congruent Residual Model Details: Gillett et al. (2003) Contour Intervals: 0.5 K/decade 20 m/decade

Can radiation explain residual trends? Solid: Temperature Dashed: Ozone Fixed Dynamical Heating NCEP-NCAR Reanalysis HadSM3-L64 Model Temperature Trend Profiles for January (85°S) Piers Forster

Transitioning to Sudden Warmings Observed residual temperature trends in Antarctic summer troposphere are not replicated by HadSM3-L64 model and are unlikely to be caused by radiation changes from stratospheric ozone depletion. Observed residual temperature trends in Antarctic summer troposphere are not replicated by HadSM3-L64 model and are unlikely to be caused by radiation changes from stratospheric ozone depletion. A natural question to ask: Are residual temperature features observed in troposphere for stratospheric- tropospheric coupling associated with sudden stratospheric warmings? A natural question to ask: Are residual temperature features observed in troposphere for stratospheric- tropospheric coupling associated with sudden stratospheric warmings?

Northern Hemisphere Sudden Warmings Decomposition T` (60°N - 90°N)Z` (60°N - 90°N) Total NAM Congruent Residual Contour Intervals: 0.15 K, 10 m Data Source: NCEP-NCAR Reanalysis ( )(JFM)

Preliminary Radiative Arguments Fixed Dynamical Heating Calculations for January (75°N) Piers Forster Horizontal Axis: Level where 10 DU ozone is added Vertical Axis: Temperature response due to enhanced longwave forcing

Conclusions Recent stratospheric trends associated with ozone hole strongly project upon circulation of troposphere as positive phase of SAM. Recent stratospheric trends associated with ozone hole strongly project upon circulation of troposphere as positive phase of SAM. SAM predominantly explains coupling of observed Z trends into troposphere but cannot account for observed T trends coupling to surface. SAM predominantly explains coupling of observed Z trends into troposphere but cannot account for observed T trends coupling to surface. Small residual T features also exist for sudden warmings, particularly in upper troposphere. Small residual T features also exist for sudden warmings, particularly in upper troposphere. Radiation could possibly explain residual T features associated with sudden warmings but cannot explain residual T trends in Antarctic summer troposphere. Radiation could possibly explain residual T features associated with sudden warmings but cannot explain residual T trends in Antarctic summer troposphere.

Can residual temperature features associated with sudden warmings be explained by radiation? Can residual temperature features associated with sudden warmings be explained by radiation? Do residual temperature features play any role in stratospheric-tropospheric coupling? Do residual temperature features play any role in stratospheric-tropospheric coupling? Unanswered Questions

Robustness of Temperature Trends Composite of 6 Antarctic Radiosonde Stations NCEP-NCAR Reanalysis (65°S - 90°S) Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC) (Free et al. 2005) Contour Interval: 0.5 K/decade

NCEP-NCAR Reanalysis Trend Decomposition: January TZU Total SAM Congruent Residual Horizontal Axis: Latitude (South Pole  Equator)Contour Intervals: 0.25 K/decade, 20 m/decade, 0.5 (m/s)/decade

HadSM3-L64 Model Trend Decomposition: January TZU Total Residual SAM Congruent Horizontal Axis: Latitude (South Pole  Equator)Contour Intervals: 0.5 K, 20 m, 0.5 m/s

Temperature Trend Profiles Solid: Temperature Dashed: Ozone Fixed Dynamical Heating NCEP-NCAR Reanalysis HadSM3-L64 Model October (85°S) Piers Forster

10hPa NAM Regression Decomposition: Lag 0 T’Z’U’ Total Residual NAM Congruent Horizontal Axis: Latitude (Equator  North Pole)Contour Intervals: 0.05 K, 5 m, 0.25 m/s

2002 Southern Hemisphere Sudden Warming Decomposition T` (65°S - 90°S)Z` (65°S - 90°S) Total SAM Congruent Residual Contour Intervals: 2 K, 75 m Data Source: NCEP-NCAR Reanalysis

Preliminary Radiative Arguments Fixed Dynamical Heating Calculations for January (75°S) Piers Forster

Surface Cooling Radiatively Driven Mechanism 90º S30º S z y Ozone Hole Diabatic Cooling Reduced Downwelling Longwave Radiation Maximum dT/dy and jet shift poleward. Anomalous eddy momentum fluxes act to reinforce poleward- shifted jet and prolong + SAM phase. (Lorenz and Hartmann 2001) Maximum baroclinic wave generation follows shift in jet. Two Components: Radiative Trigger Component Internal Tropospheric Dynamics Component

Radiative Trigger Component NCEP-NCAR Reanalysis Trends 200 hPa Temperature (65°S - 90°S) Downward Radiation Fluxes at Surface (65°S - 90°S)