The contributions of chemistry and transport to low arctic ozone in March 2011 derived from Aura MLS observations

Stratospheric and total columns of Arctic O-3 (63-90 degrees N) in late March 2011 averaged 320 and 349 DU, respectively, 50-100 DU lower than any of the previous 6 years. We use Aura Microwave Limb Sounder (MLS) O-3 observations to quantify the roles of chemistry and transport and find there are two major reasons for low O-3 in March 2011: heterogeneous chemical loss and a late final warming that delayed the resupply of O-3 until April. Daily vortex-averaged partial columns in the lowermost stratosphere (p > 133 hPa) and middle stratosphere (p < 29 hPa) are largely unaffected by local heterogeneous chemistry, according to model calculations. Very weak transport into the vortex between late January and late March contributes to the observed low ozone. The lower stratospheric (LS) column (133-29 hPa, similar to 370-550 K) is affected by both heterogeneous chemistry and transport. Because MLS N2O data show strong isolation of the vortex, we estimate the contribution of vertical transport to LS O-3 using the descent of vortex N2O profiles. Simulations with the Global Modeling Initiative (GMI) chemistry and transport model (CTM) with and without heterogeneous chemical reactions show 73 DU vortex averaged O-3 loss; the loss derived from MLS O-3 is 84 +/- 12 DU. The GMI simulation reproduces the observed O-3 and N2O with little error and demonstrates credible transport and chemistry. Without heterogeneous chemical loss, March 2011 vortex O-3 would have been at least 40 DU lower than climatology due to the late final warming that did not resupply O-3 until mid-April. Citation: Strahan, S. E., A. R. Douglass, and P. A. Newman (2013), The contributions of chemistry and transport to low arctic ozone in March 2011 derived from Aura MLS observations, J. Geophys. Res. Atmos., 118, 1563-1576, doi:10.1002/jgrd.50181.