Interannual variations in the dehydration of the Southern Polar stratosphere: microphysical modeling and POAM III observations

The Integrated Microphysics and Chemistry on Trajectories (IMPACT) model is used to model dehydration and aerosol extinction in the Southern Polar vortex during the 1998-2003 winters. The model is applied to approximately 2000 individual air parcels which are advected through the vortex using an isentropic trajectory calculation on UKMO wind and temperature fields. The temperature and pressure histories supplied by the trajectory code are used by IMPACT to calculate ice cloud formation and sedimentation, leading to the seasonal dehydration of the stratosphere. Simulation results are validated by the Polar Ozone and Aerosol Measurement (POAM) III satellite instrument.

Comparisons of POAM data to the model results help to constrain the microphysical parameters influencing dehydration. An overview of several parameters will be presented, along with ranges of acceptable values. Preliminary results suggest a high ice accommodation coefficient coupled with heterogeneous nuclei in 1-5 percent of aerosols provides good agreement with the POAM data. The percentages of heterogeneous nuclei and possible UKMO temperature biases will be discussed for all available years.