Abstract
Abstract. A sudden stratospheric warming (SSW) in early January 2013 caused the Arctic polar vortex to split and temperatures to rapidly rise above the threshold for chlorine activation. However, ozone in the lower stratospheric polar vortex from late December 2012 through early February 2013 reached the lowest values on record for that time of year. Analysis of Aura Microwave Limb Sounder (MLS) trace gas measurements and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) polar stratospheric cloud (PSC) data shows that exceptional chemical ozone loss early in the 2012/13 Arctic winter resulted from a unique combination of meteorological conditions associated with the early-January 2013 SSW: unusually low temperatures in December 2012, offspring vortices within which air remained well isolated for nearly 1 month after the vortex split, and greater-than-usual vortex sunlight exposure throughout December 2012 and January 2013. Conditions in the two offspring vortices differed substantially, with the one overlying Canada having lower temperatures, lower nitric acid (HNO3), lower hydrogen chloride, more sunlight exposure/higher ClO in late January, and a later onset of chlorine deactivation than the one overlying Siberia. MLS HNO3 and CALIPSO data indicate that PSC activity in December 2012 was more extensive and persistent than at that time in any other Arctic winter in the past decade. Chlorine monoxide (ClO, measured by MLS) rose earlier than previously observed and was the largest on record through mid-January 2013. Enhanced vortex ClO persisted until mid-February despite the cessation of PSC activity when the SSW started. Vortex HNO3 remained depressed after PSCs had disappeared; passive transport calculations indicate vortex-averaged denitrification of about 4 parts per billion by volume. The estimated vortex-averaged chemical ozone loss, ~ 0.7–0.8 parts per million by volume near 500 K (~21 km), was the largest December/January loss in the MLS record from 2004/05 to 2014/15.
Highlights
The Arctic winter stratosphere exhibits extreme interannual variability in dynamical conditions
We combine this information with trace gas data from the Microwave Limb Sounder (MLS) instrument on NASA’s Aura satellite and information on polar stratospheric cloud (PSC) composition from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite to show the progression of polar processing in the 2012/13 winter and to estimate chemical ozone loss
To compare the polar processing in 2012/13 with that in the other Arctic winters observed by Aura MLS, we show the evolution of N2O, HNO3, hydrogen chloride (HCl), chlorine monoxide (ClO), and O3 averaged over the total vortex area (Fig. 12)
Summary
The Arctic winter stratosphere exhibits extreme interannual variability in dynamical conditions. We examine in detail the evolution of the lower stratospheric polar vortex during the 2012/13 winter by characterizing the separated offspring vortices following the split during the January SSW We combine this information with trace gas data from the MLS instrument on NASA’s Aura satellite and information on PSC composition from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite to show the progression of polar processing in the 2012/13 winter and to estimate chemical ozone loss.
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