We present an analysis of trends and variability in daily-averaged near-global Halogen Occultation Experiment (HALOE) retrievals of HF and HCl at 55 km. The goal of decomposing HALOE measurements into a series of components is to determine the temporal scales associated with variability and to estimate the trends in HF and HCl. To determine the significance of each component in the statistical model, partial correlations are calculated between the data and each model element using the rank-order correlation coefficient. We also account for the effects of serial correlation in our data (i.e., the lack of independence between consecutive points) in the determination of statistical significance. The results provide evidence of highly statistically significant slowdowns in the rates of accumulation of HF and HCl at 55 km. HF shows evidence of interannual and annual variability at 55 km that is not evident in HCl due to the short chemical lifetime of HCl. ¿ 1999 American Geophysical Union