Variability in HDO/H₂O abundance ratios in the tropical tropopause layer

Month-to-month comparisons indicate greater seasonal variability than interannual variability between 25°S - 25°N, thus comparisons are made between February, April, August, and October averages for the years 2004 and 2005 combined.

The data indicate a pattern of seasonal variability which is clearer in the Northern Hemisphere tropics and a relationship between minimum temperature, minimum water vapor, and maximum HDO depletion, which exists beyond the estimated uncertainty in these values. The range of values observed for HDO depletion and comparisons to modeled Rayleigh distillation curves indicate an important contribution from convection in addition to gradual dehydration.