Global distribution of mean age of stratospheric air from MIPAS SF6 measurements G. P. Stiller1, T. von Clarmann1, M. Höpfner1, N. Glatthor1, U. Grabowski1, S. Kellmann1, A. Kleinert1, A. Linden1, M. Milz1,*, T. Reddmann1, T. Steck1, H. Fischer1, B. Funke2, M. López-Puertas2, and A. Engel3 1Forschungszentrum Karlsruhe and University of Karlsruhe, Inst. für Meteorologie und Klimaforschung, Karlsruhe, Germany 2Instituto de Astrofísica de Andalucía CSIC, Granada, Spain 3Institut für Atmosphäre und Umwelt, J.W. Goethe Universität Frankfurt am Main, Frankfurt, Germany *now at: Institutionen för Rymdvetenskap, Luleå Tekniska Universitet, Kiruna, Sweden
Abstract. Global distributions of profiles of sulphur hexafluoride (SF6) have been retrieved
from limb emission spectra recorded by the Michelson Interferometer
for Passive Atmospheric Sounding (MIPAS) on Envisat covering the period September 2002
to March 2004. Individual SF6 profiles have a precision of 0.5 pptv below 25 km altitude and a vertical
resolution of 4–6 km up to 35 km altitude. These data have been validated versus
in situ observations obtained during balloon flights of a cryogenic whole-air sampler.
For the tropical troposphere a trend of 0.230±0.008 pptv/yr has been
derived from the MIPAS data, which is in excellent agreement with the trend from ground-based flask and in situ
measurements from the National Oceanic and Atmospheric Administration Earth System Research Laboratory, Global Monitoring Division.
For the data set currently available, based on at least three days of data per
month, monthly 5° latitude mean values have a 1σ standard error of 1%. From the global
SF6 distributions, global daily and monthly distributions of the apparent mean age of air
are inferred by application of the tropical tropospheric trend derived from MIPAS data. The inferred
mean ages are provided for the full globe up to 90° N/S, and have a 1σ standard error of 0.25 yr.
They range between 0 (near the tropical tropopause) and 7 years (except for situations
of mesospheric intrusions) and agree well with earlier observations. The seasonal
variation of the mean age of stratospheric air indicates episodes of severe intrusion
of mesospheric air during each Northern and Southern polar winter observed,
long-lasting remnants of old, subsided polar winter air over the spring and
summer poles, and a rather short period of mixing with midlatitude air and/or
upward transport during fall in October/November (NH) and April/May (SH),
respectively, with small latitudinal gradients, immediately before the new polar
vortex starts to form. The mean age distributions further confirm that SF6
is destroyed in the mesosphere to a considerable degree. Model calculations
with the Karlsruhe simulation model of the middle atmosphere (KASIMA) chemical transport
model agree well with observed global distributions of the mean
age only if the SF6 sink reactions in the mesosphere are included in the model.
Citation: Stiller, G. P., von Clarmann, T., Höpfner, M., Glatthor, N., Grabowski, U., Kellmann, S., Kleinert, A., Linden, A., Milz, M., Reddmann, T., Steck, T., Fischer, H., Funke, B., López-Puertas, M., and Engel, A.: Global distribution of mean age of stratospheric air from MIPAS SF6 measurements, Atmos. Chem. Phys., 8, 677-695, doi:10.5194/acp-8-677-2008, 2008.