Sensitivity of Antarctic climate to the distribution of ozone depletion Nathan Gillett, University of East Anglia Sarah Keeley, University of East Anglia Thanks to: Julia Crook, Susan Solomon, Dave Thompson, Piers Forster.

Introduction Observations and modelling strongly suggest that stratospheric ozone depletion has induced a trend towards the positive phase of the tropospheric Southern Annular Mode 1—2 months after the maximum depletion in the mid-stratosphere. Observations and modelling strongly suggest that stratospheric ozone depletion has induced a trend towards the positive phase of the tropospheric Southern Annular Mode 1—2 months after the maximum depletion in the mid-stratosphere. Is Antarctic climate most sensitive to ozone depletion in the lowermost stratosphere, or ozone depletion in the mid- and upper-stratosphere? Is Antarctic climate most sensitive to ozone depletion in the lowermost stratosphere, or ozone depletion in the mid- and upper-stratosphere? Are zonaly asymmetries in the distribution of ozone important for the climate response? Are zonaly asymmetries in the distribution of ozone important for the climate response?

How important is lower stratospheric depletion? Max depletion occurs 1-2 months later in the lowermost stratosphere compared to the mid-stratosphere. Max depletion occurs 1-2 months later in the lowermost stratosphere compared to the mid-stratosphere. Surface temperature is more sensitive to ozone depletion near the tropopause. Surface temperature is more sensitive to ozone depletion near the tropopause. Some authors have suggested that the troposphere may be responding mainly to depletion near the tropopause. Some authors have suggested that the troposphere may be responding mainly to depletion near the tropopause. Source: Hansen et al. (1997) Source: Solomon et al. (2006)

Model experiments A control and three perturbed simulations of the 64-level version of Hadley Centre slab mode (HadSM3- L64) were carried out with: A control and three perturbed simulations of the 64-level version of Hadley Centre slab mode (HadSM3- L64) were carried out with: (a) Ozone depletion throughout the stratosphere (Randel and Wu, 1999). (a) Ozone depletion throughout the stratosphere (Randel and Wu, 1999). (b) Ozone depletion in the lowermost stratosphere only (below 164 hPa). (b) Ozone depletion in the lowermost stratosphere only (below 164 hPa). (c) Ozone depletion in the mid- and upper-stratosphere only (above 164 hpa). (c) Ozone depletion in the mid- and upper-stratosphere only (above 164 hpa).

Temperature Geopotential height Simulated response to O 3 depletion in the whole stratosphere Lowermost stratosphere Mid- and upper- stratosphere

Mechanisms of response We diagnosed changes in zonal mean SW, LW and dynamical heating in response to depletion in the whole stratosphere. We diagnosed changes in zonal mean SW, LW and dynamical heating in response to depletion in the whole stratosphere. SW heating LW heating Dynamical heating

Zonal asymmetry of ozone Almost all climate models contain specified zonal mean ozone, except for CCMs. Almost all climate models contain specified zonal mean ozone, except for CCMs. But in October the ozone hole is usually not centred over the pole. But in October the ozone hole is usually not centred over the pole. Gabriel et al. (2007) find significant local effects of zonal asymmetries in ozone in the Northern Hemisphere. Gabriel et al. (2007) find significant local effects of zonal asymmetries in ozone in the Northern Hemisphere. Could the larger zonal asymmetries in the Southern Hemisphere have a significant influence on the stratosphere/troposphere? Could the larger zonal asymmetries in the Southern Hemisphere have a significant influence on the stratosphere/troposphere? TOMS ozone

Zonal asymmetry experiements Two simulations of HadSM3-L64, one with: Two simulations of HadSM3-L64, one with: 3D ozone variations taken from ERA-40, July 2000-June D ozone variations taken from ERA-40, July 2000-June The zonal mean of the same ozone field. The zonal mean of the same ozone field.

October 50 hPa ozone anomaly from zonal mean (mg kg -1, from ERA-40) Simulated October 50 hPa temperature response to zonal asymmetry in ozone

Zonal mean response to zonal asymmetry in ozone in October Temperature (°C) Geopotential Height (m) Large zonal mean stratospheric temperature response indicative of a weakened Brewer-Dobson circulation. No significant zonal mean temperature response in troposphere, but significant local surface cooling below stratospheric cooling over Ross Sea.

Conclusions Antarctic tropospheric climate is mainly sensitive to ozone depletion in the mid- and upper- stratosphere (above 164 hPa). Antarctic tropospheric climate is mainly sensitive to ozone depletion in the mid- and upper- stratosphere (above 164 hPa). Zonal asymmetries in ozone in the Southern Hemisphere, which have likely grown in magnitude with ozone depletion, can induce a zonal mean temperature response comparable to that due to ozone depletion itself. Zonal asymmetries in ozone in the Southern Hemisphere, which have likely grown in magnitude with ozone depletion, can induce a zonal mean temperature response comparable to that due to ozone depletion itself.