EOS MLS observations of ozone loss in the 2004–2005 Arctic winter

Earth Observing System Microwave Limb Sounder O 3 and N 2 O are used to examine transport and chemical O 3 loss in the unusually cold 2004–2005 Arctic winter. The vortex was dynamically active, with episodic mixing events throughout the winter; descent was the dominant transport process only through late January. Before the onset of lower stratospheric chemical loss, O 3 was higher near the vortex edge than in the vortex core, causing different effects of mixing depending on the vortex region and time, either masking or mimicking chemical loss. O 3 loss ceased by 10 March because of an early final warming. Rough estimates suggest maximum vortex‐averaged O 3 loss of 1.2–1.5 ppmv between 450 and 500 K, with up to ∼2 ppmv loss in the outer vortex near 500 K. Despite record cold, chemical O 3 loss was less in 2004–2005 than in previous cold Arctic winters.