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Authors: Muscari, G.* 
de Zafra, R. L.* 
Title: Reply to comment by Rolf Müller and Simone Tilmes on ‘‘Middle atmospheric O3, CO, N2O, HNO3, and temperature profiles during the warm Arctic winter 2001–2002’’
Issue Date: 20-Sep-2008
Series/Report no.: / 113 (2008)
DOI: 10.1029/2008JD010292
Keywords: remote sensing
polar stratosphere
Subject Classification01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous 
Abstract: [1] Muscari et al. [2007] (hereafter referred to as M07) analyzed Arctic winter stratospheric conditions for 2001–2002 by means of ground-based measurements of stratospheric trace gases and temperature from Thule Air Base, Greenland (76.5°N, 68.7°W). The paper characterized stratospheric air masses observed over Thule from 20 January to 5 March 2002. Topics that were discussed included: the passage of both the polar vortex and the Aleutian high over Thule, with significant changes in ozone mixing ratio and temperature values; variations of measured O3 total column; vertical descent of air masses observed by means of CO measurements; observations of "ozone pockets" [Manney et al., 1995]; the correlation between illumination fraction and ozone mixing ratio at 900 K, indicating the relative significance of dynamics and photochemistry on ozone concentration at this altitude; the complete absence of polar stratospheric clouds, as concurrently monitored with a lidar system at Thule; and a qualitative (not quantitative) estimation of local ozone deficiency by means of N2O/O3 correlations. Müller and Tilmes [2008] (hereafter referred to as MT08) question the significant ozone deficiencies reported by M07 inside the vortex, which, as also pointed out by M07, are difficult to explain by heterogeneous chemistry during the warm winter 2001–2002. Nonetheless, M07 did speculate that heterogeneous activation of halogen compounds during mid-December and early January could have been the origin of the substantial ozone deficiency observed at the end of January/beginning of February in the small portion of the vortex core sampled by the Ground-Based Millimeter-Wave Spectrometer (GBMS). MT08 question this claim, as it "cannot be reconciled with the current understanding of halogen driven chemical ozone destruction in the Arctic." They suggest flaws in the N2O selection criteria used by M07 in order to identify intravortex N2O/O3 correlations, arising from their contention that GBMS measurements of N2O do not have the necessary spatial resolution needed for the task. MT08 favor instead the use of Potential Vorticity (PV) fields from European Centre Medium-Range Weather Forecasts (ECMWF) analyses. [2] As a result of the criticism of MT08, we have looked at N2O/O3 correlations from independent measurements carried out by the Odin Sub-Millimeter Radiometer (Odin/SMR) [Murtagh et al., 2002] and have also reprocessed the GBMS O3 measurements using a different deconvolution technique. The GBMS O3 reanalysis furnishes a significantly smaller qualitative estimate of local ozone loss (here and in the following we use "ozone loss" specifically to indicate an ozone deficiency due to heterogeneous activation of halogen compounds) and is consistent with the Odin/SMR data (section 2). This has resulted in a corrected and enriched version of Figure 9a of M07 (see Figure 2 in section 2). Although we value the comments of MT08 which prompted us to reanalyze GBMS ozone data, correcting and improving Figure 9 of M07 and the related discussion, we do reject some of the comments of MT08 concerning the N2O selection criteria used by M07, and reiterate the choice of GBMS N2O measurements rather than ECMWF PV values to separate air masses located inside, outside, or at the edge of the polar vortex (section 3). Furthermore, we stress that the use of N2O/O3 correlation curves to determine ozone loss inside the vortex, in particular near its edge (a region often called "the outer vortex"), can indeed cause an overestimation of local ozone loss near the vortex edge region and possibly also an overestimation of the vortex averaged loss (section 4).
Description: Reply to comment by Rolf Müller and Simone Tilmes on "Middle atmospheric O3, CO, N2O, HNO3, and temperature profiles during the warm Arctic winter 2001–2002"
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