Stratospheric abundances of water and methane based on ACE‐FTS measurements

Abstract

We present solar occultation measurements of H2O and CH4 by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS). The data used here were selected from occultations spanning February to April 2004 from 0 to 79.8°N. The midlatitude volume mixing ratio (VMR) of potential water is determined as [H2O] + 2[CH4] and from [H2O] versus [CH4] correlations, then used to calculate the VMR of water vapor entering the stratosphere. We obtain 7.14 ± 0.23 ppm for potential water and 3.65 ± 0.29 ppm for water entering the stratosphere in 2004 for direct comparison with Atmospheric Trace Molecule Spectroscopy (ATMOS) data (1985–1994). We find a very small change in potential water and no change in water entering the stratosphere relative to the 1994 ATMOS data, indicating that increases observed by ATMOS and other instruments from that time period have not continued. This halt in stratospheric water vapor increases is consistent with recent water vapor measurements by other instruments.