Ground‐based measurements of stratospheric ClO over Spitzbergen in the Arctic spring of 1997

We have measured stratospheric chlorine monoxide (ClO) at Ny Ålesund (79°N), on the Arctic island of Spitzbergen, during the spring of 1997 as part of a ground‐based millimeter‐wave radiometer intercomparison campaign. The presence of ClO in the stratosphere is a direct result of the catalytic destruction of ozone by chlorine and can provide a good measure of this process. Spitzbergen remained well inside the strong, cold polar spring vortex of 1997 during most of our observation period, which ran from February 7 through March 17. Measurements show a strong enhancement of lower stratospheric ClO from mid‐February through mid‐March, in substantial agreement with other measurements, and consistent with increasing daily exposure to photolytic processes liberating active chlorine. A comparison of these results with ClO observations made at McMurdo Station (78°S), Antarctica, during the austral spring of 1997 shows ClO amounts in the Arctic stratosphere that were comparable to Antarctic stratospheric values when temperatures and solar exposures were similar over a relatively short time.