Is upper stratospheric chlorine decreasing as expected?

The monthly-mean total chlorine abundance (CL) at 55 km inferred from HALOE HCl observations increases from 1992 to 1997 and then subsequently decreas es. The pre-1997 increase is consistent with surface measurements of Cl-T t ime-lagged by around 6 years. However, a decrease after 1997 is inconsisten t with such a time lag, which would predict a peak in late 1999. Accounting for stratospheric mixing processes produces an expected stratosphere CIT w hich is in agreement with the HALOE Cl-T time series considering the uncert ainty in the HALOE data. However, the peak in Cl-T is still predicted to oc cur in later 1999 rather than 1997. We find that reasonable low frequency c hanges in transport, chlorine partitioning, anomalous buildup of organic ch lorine at 55 km, and tropospheric rainout of inorganic chlorine do not reco ncile the expected and HALOE Cl-T time series. At present, we are unable to explain hear upper stratospheric Cl-T could decrease as early as 1997.