Abstract
Abstract. Despite the record ozone loss observed in March 2011, dynamical conditions in the Arctic stratosphere were unusual but not unprecedented. Weak planetary wave driving in February preceded cold anomalies in the polar lower stratosphere in March and a relatively late breakup of the Arctic vortex in April. La Niña conditions and the westerly phase of the quasi-biennial oscillation (QBO) were observed in March 2011. Though these conditions are generally associated with a stronger vortex in mid-winter, the respective cold anomalies do not persist through March. Therefore, the La Niña and QBO-westerly conditions cannot explain the observed cold anomalies in March 2011. In contrast, positive sea surface temperature anomalies in the North Pacific may have contributed to the unusually weak tropospheric wave driving and strong Arctic vortex in late winter 2011.
Highlights
In the Arctic stratosphere, chemical ozone loss takes place each year in the late winter (WMO, 2011)
Arctic ozone loss represents the interaction between chemistry and climate: heterogeneous ozone depletion on polar stratospheric clouds (PSCs) requires the presence of halogens, sunlight and temperatures below approximately 195 K
The present analysis considers breakup dates based on the NCEP-1 (Kalnay et al, 1996), NCEP-2 (Kanamitsu et al, 2002) and NOAA Climate Prediction Center (CPC) (Gelman et al, 1986; Nagatani et al, 1988; Finger et al, 1993) meteorological reanalyses
Summary
In the Arctic stratosphere, chemical ozone loss takes place each year in the late winter (WMO, 2011). On 14 March, the Alfred Wegener Institute in Germany reported that “unusually low temperatures in the Arctic ozone layer have recently initiated massive ozone de-. Manney et al (2011) have since determined that the spring 2011 ozone loss was “unprecedented”: During the 2010–2011 winter, the Arctic vortex was the most isolated and the timeintegrated PSC volume was the largest ever observed. These conditions enabled severe ozone loss in late winter. Vortex averaged lower stratospheric ozone was unusually low beginning in late February, and by March, reached values comparable to those recently observed in the Antarctic stratosphere in September.
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