Aura Microwave Limb Sounder observations of the 2004-2005 Arctic winter: Polar processing in the lower stratosphere

A second-generation Microwave Limb Sounder (MLS) was launched as part of NASA's Earth Observing System (EOS) Aura mission in July 2004. EOS MLS is a greatly enhanced follow-on to the MLS instrument onboard the Upper Atmosphere Research Satellite (UARS). In addition to better spatial coverage and resolution, EOS MLS measures several more stratospheric species than did its predecessor. Simultaneous measurements of temperature, N2O, HNO3, H2O, HCl, ClO, and O3 provide a much more complete picture of polar processing and chemical ozone destruction in the stratosphere than has previously been possible. The 2004-2005 Arctic winter was anomalously cold in the lower stratosphere, with substantial polar stratospheric cloud formation and chlorine activation. EOS MLS measurements are used to track the evolution of these processes throughout this exceptional winter. Comparisons between the observed behavior and that predicted by the SLIMCAT chemical transport model are also shown. Ozone evolution and chemical loss are discussed in a companion paper by Manney et al.