1. Can the increase of Polar Stratospheric Clouds explain the Antarctic Winter Tropospheric warming?
Tom Lachlan-Cope
(W. M. Connolley, J. Turner, H. Roscoe, G. J. Marshall, S. R. Colwell, M. Höpfner and W. Ingram)

2. Outline Mid Tropospheric Warming Polar Stratospheric Clouds
Hadley Centre Model
PSC in the Model
Results
Conclusions

3. Mid-Tropospheric Warming
Annual and seasonal 500 hPa temperature trends (oC dec-1) over for nine radiosonde stations with longAnnual and seasonal 500 hPa temperature trends (oC dec-1) over for nine radiosonde stations with long records.

7. Polar Stratospheric Clouds
Below about 195 K, thin clouds of solid nitric acid trihydrate (NAT)
Around 5 to 10 K colder the air becomes saturated with respect to ice.
Presence of NAT facilitates the nucleation of ice onto NAT particles at ice saturation ratios of
ice clouds only just below the frost point

8. August
Volume
km3
July
June

9. Based on the model of Höpfner et al.( 2006) using ECMWF analyses.

10. Hadley Centre Model (HadAM3)
Atmosphere-only
19 levels in the vertical
2.5º x 3.75º horizontal grid
forced at the lower boundary by annually repeating SSTand sea ice concentration

11. Imposing the PSC
During June, July and August at 100 hPa with an optical depth of 0.5.
Cloud imposed by inserting given optical depth at a single level (100hPa) in the model’s radiation code
First run had the layer extending from the pole to 80ºS
Second had a layer from the pole to 70ºS

12. ERA hPa
Temperature
HadAM3 Warming

13. Pressure hPa
Red – Syowa sonde
Black- HadAM3

14. Conclusions PSC could have an effect However Need
Assumptions made on PSC thickness and extent
19 level Version of HadAM3 has not got a very good stratosphere
Need
Better observations
Better modelling

15. Solid – ISCCP
Dashed – Obs
Thick – ERA op.

16. Red – ERA op.