Dynamical Impacts of Antarctic Stratospheric Ozone Depletion on the Extratropical Circulation of the Southern Hemisphere

Transcription

1 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 d Climate Change Santorini,, Greece September 25, 2007

2 Overview 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. Goal: To assess relative contributions of dynamics and radiation in determining recent tropospheric temperature trends.

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

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

5 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).

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

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

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

9 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. A natural question to ask: Are residual temperature features observed in troposphere for stratospheric- tropospheric coupling associated with sudden stratospheric warmings?

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

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

12 Conclusions 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. 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.

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

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15 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

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

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

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

19 10hPa NAM Regression Decomposition: Lag 0 T Z U Residual NAM Congruent Total Horizontal Axis: Latitude (Equator North Pole) Contour Intervals: 0.05 K, 5 m, 0.25 m/s

20 2002 Southern Hemisphere Sudden Warming Decomposition T` (65 S - 90 S) Z` (65 S - 90 S) SAM Congruent Residual Total Data Source: NCEP-NCAR Reanalysis Contour Intervals: 2 K, 75 m

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

22 Radiatively Driven Mechanism Two Components: Ozone Hole Diabatic Cooling Radiative Trigger Component Internal Tropospheric Dynamics Component Reduced Downwelling Longwave Radiation Maximum baroclinic wave generation follows shift in jet. Anomalous eddy momentum fluxes act to reinforce polewardshifted jet and prolong + SAM phase. (Lorenz and Hartmann 2001) z Surface Cooling Maximum dt/dy and jet shift poleward. y 90º S 30º S

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