Chemical Ozone Loss and Chlorine Activation Deduced From HALOE and OMS Measurements in Arctic Winter 1999-2000

We employ observations from HALOE and from balloon-borne instruments (on OMS-remote, OMS in-situ, and Triple) to investigate ozone loss in the stratosphere in the vortex in Arctic winter 1999-2000. Using HF and CH₄ as a long-lived tracer, we identify chemical ozone destruction and chlorine activation in the polar vortex. Reference relations, relevant for chemically undisturbed ``early vortex'' conditions are derived from the OMS-remote and in-situ balloon measurements on 19 November and 3 December 1999. Deviations from this ``early vortex'' reference are caused by chemical ozone loss and heterogeneous chlorine activation. The observations indicate severe chemical ozone loss, with a maximum loss of over 60% locally in the lower stratosphere (465-415 K) by mid-March 2000. The average loss in column ozone between 380-550 K, (deep) inside the vortex, in mid-March amounts to about 85 +/- 10 DU. The findings for winter 1999-2000 are put into perspective of Arctic ozone loss deduced from HALOE measurements in earlier cold winters (e.g., 1992-1993, 1994-1995, and 1996-1997). These winters have been reanalysed using the most recent HALOE data version. Further, additional observations were taken into account to investigate the validity of the reference relation for chemically unperturbed conditions in the early vortex.