The Disturbed Arctic Lower Stratospheric Vortex and Implications for Early Winter Polar Processing and Ozone Loss in 2012/2013

An intense vortex-split sudden stratospheric warming (SSW) in early January 2013 led to a breakdown of the lower stratospheric vortex by early February. Prior to the SSW, in late November through December, the lower stratospheric vortex was cold, but highly variable in shape and position. An unusually large fraction of the disturbed, but cold, vortex was exposed to sunlight, leading to strong chlorine activation earlier than observed in any previous Arctic winter. Satellite data from NASA's Aura Microwave Limb Sounder (MLS) are analyzed along with diagnostics relevant to polar processing calculated from NASA's MERRA (Modern Era Retrospective Analysis for Research and Applications) data assimilation system fields to elucidate the dynamical processes that resulted in the chlorine activation, denitrification, and ozone loss observed in December 2012 and January 2013. In addition to temperature and temperature history diagnostics, we present detailed diagnostics of the polar vortex that define its shape, strength, position/orientation, exposure to sunlight, and spatial relationship to the area where temperatures are low enough for chlorine to be activated. These diagnostics are compared to the climatological record and to other winters during the Aura mission. In particular, the 2012/2013 early winter is compared with that of 2009/2010, during which unusual early winter ozone loss preceding an SSW has also been reported.