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

Abstract

Stratospheric and total columns of Arctic O3 (63–90oN) 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) O3 observations to quantify the roles of chemistry and transport and find there are two major reasons for low O3 in March 2011: heterogeneous chemical loss and a late final warming that delayed the resupply of O3 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, ~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 O3 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 O3 loss; the loss derived from MLS O3 is 84 ± 12 DU. The GMI simulation reproduces the observed O3 and N2O with little error and demonstrates credible transport and chemistry. Without heterogeneous chemical loss, March 2011 vortex O3 would have been at least 40 DU lower than climatology due to the late final warming that did not resupply O3 until mid‐April.

The version 3 OMI NO<sub>2</sub> standard product

“…The SPv3 AMF calculation uses the GMI threedimensional CTM simulation in the troposphere and stratosphere (Duncan et al, 2007;Strahan et al, 2013). The GMI CTM uses a stratosphere-troposphere chemical mechanism, natural and anthropogenic emissions, and aerosol fields from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model (Chin et al, 2014).…”

Fundamental differences between Arctic and Antarctic ozone depletion

“…4 and 5). The unusual meteorology of this year has been explored by several studies (6)(7)(8), and a rich suite of observations of stratospheric chemical composition has been presented from both ground-based and satellite methods (e.g., refs. 4, 7, and 9-11).…”

“…Recent studies by several groups suggest that unusual meteorological conditions (and associated transport of ozone) accounted for some of the apparent 2011 decreases in Arctic ozone at this level and in the total ozone column compared with typical Arctic years. One study suggested that chemical loss accounted for perhaps half of the apparent reduction in the Arctic total ozone column observed in 2011 (8), whereas another deduced only a 23% contribution from chemistry (14). The differences between these studies show that there are large uncertainties in the meteorological parameters needed to quantify chemical losses distinct from dynamical effects in the Arctic.…”

Comparison of ECHAM5/MESSy Atmospheric Chemistry (EMAC) simulations of the Arctic winter 2009/2010 and 2010/2011 with Envisat/MIPAS and Aura/MLS observations

“…Manney et al, 2011;Sinnhuber et al, 2011;Arnone et al, 2012;Kuttippurath et al, 2012;Hommel et al, 2014). The dynamical perspective, and thus the exceptional dynamical conditions of this winter, was discussed in detail by Hurwitz et al (2011), Isaksen et al (2012, Strahan et al (2013), and Shaw and Perlwitz (2014). Although the Arctic winter 2009/2010 was one of the warmest winters on record (Dörn-brack et al, 2012), it was distinguished by an exceptionally cold stratosphere (colder than the climatological mean) from mid-December 2009 to mid-January 2010, leading to prolonged PSC formation and significant denitrification (e.g.…”