TEMPERATURE-DEPENDENCE OF THE CLO CONCENTRATION NEAR THE STRATOPAUSE

From an analysis of Microwave Limb Sounder (MLS) ClO data near the str atopause where it is reasonable to assume that ClO is in photochemical equilibrium, it is found that there is a strong temperature dependenc e of the order of 1000 K(+/-200 K) including the effects of scaling an d the bias uncertainties in the retrieved MLS data. Results from a thr ee-dimensional model (extended UK Universities Global Atmospheric Mode lling Programme (UGAMP) general circulation model (EUGCM)) agree well with the MLS results; we obtain a temperature dependence of 950 K in t he three-dimensional model. The temperature dependencies obtained from the MLS data and the EUGCM agree quite well. with results from a pure ly photochemical box model which yields a temperature dependence of th e order of 900 K. The generally good agreement between the temperature dependence of ClO obtained from the MLS measurements, from both the p hotochemical model and the three-dimensional general circulation model does not suggest that there are major uncertainties in our understand ing of the ClO chemistry in the upper stratosphere.