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)

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

Mid-Tropospheric Warming Annual and seasonal 500 hPa temperature trends (oC dec-1) over 1971-2003 for nine radiosonde stations with longAnnual and seasonal 500 hPa temperature trends (oC dec-1) over 1971-2003 for nine radiosonde stations with long records.

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 1.05-1.1 ice clouds only just below the frost point

August Volume km3 July June

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

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

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

ERA 40 500 hPa Temperature 2001-1979 HadAM3 Warming

Pressure hPa Red – Syowa sonde Black- HadAM3

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

Solid – ISCCP Dashed – Obs Thick – ERA op.

Red – ERA op.