Measurements of NO, NOy, N2O, and O3 during SPURT: implications for transport and chemistry in the lowermost stratosphere M. I. Hegglin1,*, D. Brunner1, T. Peter1, P. Hoor2, H. Fischer2, J. Staehelin1, M. Krebsbach3, C. Schiller3, U. Parchatka2, and U. Weers1 1Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, Zurich, Switzerland 2Max Planck Institute for Chemistry, Air Chemistry, Mainz, Germany 3Institute for Chemistry and Dynamics of the Geosphere: Stratosphere, Research Centre Jülich GmbH, Jülich, Germany *now at: Department of Physics, University of Toronto, Toronto, Canada
Abstract. We present measurements of NO, NOy, O3, and
N2O within the lowermost stratosphere (LMS) over Europe
obtained during the SPURT project. The measurements cover all seasons between November 2001 and July 2003.
They span a broad band of latitudes from 30° N to 75° N and a potential temperature range from 290 to 380 K.
The measurements represent
a comprehensive data set of these tracers and reveal atmospheric
transport processes that influence tracer distributions in the
LMS. Median mixing ratios of stratospheric tracers in equivalent
latitude-potential temperature coordinates show a clear seasonal
cycle related to the Brewer-Dobson circulation, with highest values
in spring and lowest values in autumn. Vertical tracer profiles show
strong gradients at the extratropical tropopause, suggesting that
vertical (cross-isentropic) mixing is reduced above the
tropopause. Pronounced meridional gradients in the tracer mixing ratios are found on potential temperature surfaces in the LMS.
This suggests strongly reduced mixing along isentropes. Concurrent large gradients in static stability in the
vertical direction, and of PV in the meridional direction, suggest the
presence of a mixing barrier. Seasonal cycles were found in the
correlation slopes ΔO3/ΔN2O and
ΔNOy/ΔN2O well above the tropopause. Absolute slope values are smallest
in spring indicating chemically aged stratospheric air
originating from high altitudes and latitudes. Larger values were measured
in summer and autumn suggesting that a substantial fraction
of air takes a "short-cut" from the tropical tropopause region
into the extratropical LMS. The seasonal change in the composition
of the LMS has direct implications for the ozone chemistry in this region.
Comparisons of measured NO
with the critical NO value at which net ozone production
changes from negative to positive, imply ozone production
up to 20 K above the local tropopause in spring, up to 30 K in summer, and up to 40 K in
autumn. Above these heights, and in winter, net ozone production is negative.
Citation: Hegglin, M. I., Brunner, D., Peter, T., Hoor, P., Fischer, H., Staehelin, J., Krebsbach, M., Schiller, C., Parchatka, U., and Weers, U.: Measurements of NO, NOy, N2O, and O3 during SPURT: implications for transport and chemistry in the lowermost stratosphere, Atmos. Chem. Phys., 6, 1331-1350, doi:10.5194/acp-6-1331-2006, 2006.