Methyl Chloride from the Aura Microwave Limb Sounder: Preliminary validation and climatology

Methyl chloride (CH3Cl), the largest natural source of stratospheric chlorine, currently accounts for about 16% of chlorine-catalyzed ozone destruction in the stratosphere. Its importance is expected to increase, however, as emission controls alter the relative contributions from natural and anthropogenic halogen sources. Thus a quantitative understanding of the CH3Cl distribution and variability will be valuable in enhancing our prognostic capability for ozone layer stability. The Microwave Limb Sounder (MLS), launched as part of NASA's Aura mission in July 2004, measures vertical profiles of temperature, cloud ice, and an extensive suite of trace gases in the middle atmosphere. With the recent release of the version 3 (v3.3) data processing algorithms, Aura MLS now provides the first daily global observations of CH3Cl. The unprecedented scope of the MLS data set makes it uniquely suited to studying the spatial, seasonal, interannual, and longer-term variations in the distribution of CH3Cl at the tropopause and in the lower stratosphere. Reprocessing of the MLS data with the v3.3 algorithms is currently underway, with the entire mission data set scheduled for completion by March 2011. We present preliminary validation results to substantiate the quality of the v3.3 MLS CH3Cl measurements and their utility for scientific studies. A preliminary global climatology of CH3Cl will also be shown.