Chemical ozone destruction occurs over both polar regions in local winter-spring. In the Antarctic, essentially complete removal of lower-stratospheric ozone currently results in an ozone hole every year, whereas in the Arctic, ozone loss is highly variable and has until now been much more limited. Here we demonstrate that chemical ozone destruction over the Arctic in early 2011 was--for the first time in the observational record--comparable to that in the Antarctic ozone hole. Unusually long-lasting cold conditions in the Arctic lower stratosphere led to persistent enhancement in ozone-destroying forms of chlorine and to unprecedented ozone loss, which exceeded 80 per cent over 18-20 kilometres altitude. Our results show that Arctic ozone holes are possible even with temperatures much milder than those in the Antarctic. We cannot at present predict when such severe Arctic ozone depletion may be matched or exceeded.

[1] Ground-based measurements of total aerosol optical depth (AOD), e.g., tropospheric and stratospheric aerosol, have been established at the Koldewey station in Ny-Å lesund, Spitzbergen (Norway, 78.95°N, 11.93°E), since 1991. The basic instrumentation is a multichannel photometer using sunlight. New instruments have been developed to extend the measurement period to polar night. The new instruments are a Sun and Moon photometer (1995) and a star photometer (1996). The instruments and applied methods for aerosol optical depth retrieval for Sun, Moon, and star measurements are briefly discussed. The year-round measurements made it possible to study in detail the interannual and seasonal variations of total AOD in the Arctic. The seasonal variation and the long-term trend of tropospheric aerosol optical depth are discussed, taking into account the stratospheric AOD measured by the Stratospheric Aerosol and Gas Experiment (SAGE II). The lowest tropospheric aerosol optical depth values occur in late summer and fall. Each year, strong Arctic haze events were recorded not only during spring but also in late winter as the first star photometer measurements clearly show. Five-day backward trajectories were used to analyze possible sources for high tropospheric AOD. Elevated tropospheric aerosol optical depth appears for northeasterly, easterly, or westerly winds. Finally, the long-term changes of tropospheric AOD have been assessed. A small positive trend of the tropospheric aerosol optical depth is found for the vicinity of Spitzbergen during the measurement period.

The HALogen Occultation Experiment (HALOE) instrument on UARS observes vertical profiles of ozone and other gases of interest for atmospheric chemistry using the solar occultation technique. A broadband radiometer in the 9.6-ttm band is used for ozone measurements. Version 17 ozone retrieved by HALOE is intercompared successfully with about 400 profiles of other sounders, including ozonesondes, lidars, balloons, rocketsondes, and other satellites. Usually, the HALOE data are within the error range of the correlative measurements between about 100 and 0.03 mbar atmospheric pressure. Between about 30 and 1 mbar, HALOE agrees typically within 5%, with a tendency to be low. In the first year of data, larger errors sometimes occur in the lower stratosphere due to the necessary correction for Pinatubo aerosol effects, but these differences do not exceed 20%. The data show internal consistency for sunrise and sunset events at the same locations. Some examples of observed ozone distributions, including polar regions, are given.

Abstract. The winter 1996/97 was quite unusual with late vortex formation and polar stratospheric cloud (PSC) development and subsequent record low temperatures in March. Ozone depletion in the Arctic vortex is determined using ozonesondes. The diabatic cooling is calculated with PV-theta mapped ozone mixing ratios and the large ozone depletions, especially at the center of the vortex where most PSC existence was predicted, enhances the diabatic cooling by up to 80%. The average vortex chemical ozone depletion from January 6 to April 6 is 33, 46, 46, 43, 35. 33. 32 and 21% in air masses ending at 375,400, 425, 450, 475. 500, 525, and 550 K (about 14 -22 km). This depletion is corrected for transport of ozone across the vortex edge calculated with reverse domain-filling trajectories. 375 K is in fact below the vortex, but the calculation method is applicable at this level with small changes. The column integrated chemical ozone depletion amounts to about 92 DU (21%), which is comparable to the depletions observed during the previous four winters.

No abstract