Arctic ozone depletion observed by UARS MLS during the 1994–95 winter

During the unusually cold 1994–95 Arctic winter, the Microwave Limb Sounder observed enhanced chlorine monoxide (ClO) in late Dec and throughout Feb and early Mar. Late Dec ClO was higher than during any of the previous 3 years, consistent with the colder early winter. Between late Dec 1994 and early Feb 1995, 465 K (∼50 hPa) vortex‐averaged ozone (O 3 ) decreased by ∼15%, with local decreases of ∼30%; additional local decreases of ∼5% were seen between early Feb and early Mar. Transport calculations indicate that vortex‐averaged chemical loss between late Dec and early Feb was ∼20% at 465 K, with ∼1/4 of that masked by downward transport of O 3 . This Arctic chemical O 3 loss is not readily detectable in MLS column O 3 data.