Measurements of OH(X²π) in the stratosphere by high resolution UV spectroscopy

Abstract

The hydroxyl radical, OH, is one of the key constituents which moderates the removal of stratospheric ozone. Measurements of OH have proved difficult to acquire and as a result the empirical database on OH in the stratosphere is extremely sparse. In this paper we report the first results obtained using high spectral resolution imaging ultraviolet spectroscopy to observe multiple rotational lines of OH A²Σ−X²π (0‐0) band. A 9.2 Å spectral segment from 3075.8 Å to 3085.0 Å is imaged at 0.08 Å FWHM spectral resolution allowing the simultaneous acquisition of six of the brightest OH resonance fluorescence emission lines. The high spectral resolution and low scattered light design of the instrument allows these lines to be detected above the Rayleigh scattered sunlight background. The technique permits remote sensing of stratospheric OH from a high altitude instrument. The instrument was flown to an altitude of 40 km on August 25, 1983, and again on June 12, 1986, on scientific balloons from Palestine, Texas. The OH profiles inverted from the limb scans made during these flights are reported here. These profiles represent the first measurements of the temporal variation of OH over an extended height range. The results demonstrate that the technique can be used to monitor OH from orbit.