Characterization of the composition, structure, and seasonal variation of the mixing layer above the extratropical tropopause as revealed by MOZAIC measurements

Abstract

[1] The chemical composition of the mixing layer above the tropopause, which is mainly influenced by stratosphere troposphere exchange, impacts the chemistry and radiative balance of the troposphere. A better understanding of its seasonal and spatial variation is needed to reduce uncertainties of global chemistry-transport models. In this paper, we use the Measurements of Ozone, Water Vapour, Nitrogen Oxides and Carbon Monoxide by Airbus In-Service Aircraft (MOZAIC) ozone and carbon monoxide data from 2003. The five MOZAIC aircraft fly daily between Europe and North America and between Europe and Asia, at 9-12 km crossing the tropopause when transecting upper level troughs. We present a new coordinate system consisting of potential vorticity on the y axis and the angle between the local PV surface and the horizontal on the x axis to study the mixing that occurs in the tropopause region. This coordinate system allows us to view the typical distribution of ozone and CO within upper level troughs. Using in situ measurements and a Lagrangian analysis, we have identified a mixing layer associated with stirring and mixing in the tropopause region between 2 and 6 pvu. Regional variations of the ozone and CO distributions and chemical anomalies between the center and the borders of the upper level troughs are found within the mixing layer.Citation: Brioude, J., J.-P. Cammas, O. R. Cooper, and P. Nedelec (2008), Characterization of the composition, structure, and seasonal variation of the mixing layer above the extratropical tropopause as revealed by MOZAIC measurements, J. Geophys. Res., 113, D00B01,

In situ temperature measurements in the upper troposphere and lowermost stratosphere from 2 decades of IAGOS long-term routine observation

“…The median ozone mixing ratio in the UT is 60 ppb, median CO mixing ratio is 90 ppb, and median PV is 0.5 PVU. Within the LMS, the median values for O 3 (310 ppb), for CO (40 ppb), and for PV (7 PVU) are consistent with previous studies (Pan et al, 2004;Kunz et al, 2008;Brioude et al, 2009;Schmidt et al, 2010). …”

“…The differences cannot be explained by the chosen definition to determine the different layers within the UTLS region. For example, ozone observations show seasonal variations with values between 350 and 640 ppb, which are robust values for stratospheric air masses with a typical seasonality (Brioude et al, 2009). Additionally we use CO observations (from 2002CO observations (from to 2008 and PV with similar results.…”

How stratospheric are deep stratospheric intrusions?

“…A mixing zone in the tropopause region has been postulated, and the resulting chemical composition has been investigated in numerous studies (e.g. Danielsen, 1968;Shapiro, 1976Shapiro, , 1978Shapiro, , 1980Lelieveld et al, 1997;Hintsa et al, 1998;Zahn et al, 1999;Fischer et al, 2000;Hoor et al, 2002Hoor et al, , 2004Pan et al, 2004Pan et al, , 2007Brioude et al, 2006Brioude et al, , 2008Sprung and Zahn, 2010;Hegglin et al, 2009;Vogel et al, 2011). The development of aerosol layers -of volcanic origin, from biomass burning or from deserts -around the tropopause is discussed by Trickl et al (2013).…”

Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF<sub>6</sub> and CO<sub>2</sub>

“…which are intermediate between the extratropical troposphere and the stratosphere (Fischer et al, 2000;Hoor et al, 2002Hoor et al, , 2004Pan et al, 2004;Krebsbach et al, 2006;Brioude et al, 2008). This layer has been referred to as the extratropical tropopause layer (ExTL) Pan et al, 2004).…”