Can the MIPAS-Observed Pattern of Mean age of air Trends be Explained by Shifts of the Subtropical Mixing Barriers?
Abstract
Stiller et al. (2012) have derived a complex latitude-/altitude dependent pattern of linear increases and decreases (further-on called trends) of stratospheric mean age of air from MIPAS SF6 observations over the years 2002 to 2010. Similar complex trend patterns are found from MIPAS analyses for other tracers as well, like O3 (Eckert et al., 2013), NOy (Funke et al., in preparation), CFC-11, CFC-12 (Kellmann et al., 2012), and HCFC-22 (Chirkov et al., in preparation). They are also reproduced by model calculations with the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) nudged to ERA-Interim analyses. The hemispheric asymmetry in the trend patterns hints towards a shift of the global distributions of the tracers towards South, which could be realized by a shift of the subtropical mixing barriers. The positions of the subtropical mixing barriers and their dependences on altitudes, seasons, and the QBO phases have already been derived by Palazzi et al. (2011) from a set of satellite observations. In this contribution, we summarize the relevant findings and analyse the trends of the mixing barrier positions over the period of the MIPAS observations. We show that a significant shift of both the Northern and Southern hemispheric mixing barrier to the South by about 5 to 10 degrees can be derived. In our contribution, we present our analyses and provide some tentative explanations for the reasons of the shifts. Further, we analyse the impact of such a shift on observed trends of other trace species like water vapor. References: Eckert, E., et al., Drift-corrected trends and periodic variations in MIPAS IMK/IAA ozone measurements, Atmos. Chem. Phys. Discuss., 13, 17849-17900, doi:10.5194/acpd-13-17849-2013, 2013. Kellmann, S., et al., Global CFC-11 (CCl3F) and CFC-12 (CCl2F2) measurements with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS): retrieval, climatologies and trends, Atmos. Chem. Phys., 12, 11857-11875, doi:10.5194/acp-12-11857-2012, 2012. Palazzi, E. et al., Probability density functions of long-lived tracer observations from satellite in the subtropical barrier region: data intercomparison, Atmos. Chem. Phys., 11, 10579-10598, doi:10.5194/acp-11-10579-2011, 2011. Stiller, G.P. et al., Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period, Atmos. Chem. Phys., 12, 3311-3331, doi:10.5194/acp-12-3311-2012, 2012.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.A23F0338S
- Keywords:
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- 0340 ATMOSPHERIC COMPOSITION AND STRUCTURE Middle atmosphere: composition and chemistry;
- 0341 ATMOSPHERIC COMPOSITION AND STRUCTURE Middle atmosphere: constituent transport and chemistry;
- 1616 GLOBAL CHANGE Climate variability;
- 3363 ATMOSPHERIC PROCESSES Stratospheric dynamics