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| Titel |
Possible impact of QBO and upwelling on satellite measurements of N2O in the tropical lower stratosphere |
| VerfasserIn |
F. Khosrawi, R. Mueller, M. H. Proffitt, J. Urban, G. Stiller, M. Kiefer, L. Froidevaux, A. Lambert, D. Kinnison, M. Riese, D. Murtagh |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065214
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| Zusammenfassung |
| A modified form of tracer-tracer correlations of N2O and O3 has been used as a tool for the
evaluation of atmospheric photochemical models. Thereby, the data is organized
monthly for both hemispheres by partitioning the data into altitude (or potential
temperature) bins and then averaged over a fixed interval of N2O. In our recent model
evaluation study we applied satellite observations from the Odin-Sub Millimeter
Radiometer (Odin/SMR) and found large differences between model simulations and
Odin/SMR observations in the tropics. At 500Â K these differences are probably
partly caused by the large vertical O3 gradients occuring in the tropics which cannot
entirely be resolved by the rather coarse vertical resolution of Odin/SMR of 3Â km
and partly by inaccuracies in the model simulations of transport in the tropical
stratosphere. The N2O averages we derived from Odin/SMR observations at potential
temperature levels at 650Â K were much higher than the N2O values we derived
from the model simulations. Further, these values are much higher than the highly
accurate ground-based observations of N2O derived in the troposphere which is
the only source region of this trace gas. Furthermore, these values occur with a
seasonal dependence showing a maximum in winter and a minimum in summer. By
comparing several years of Odin/SMR measurements we found that these values
also occur with an interannual variability. We applied our method to other satellite
data sets as Aura/MLS, MIPAS/ENVISAT and CRISTA and model simulations of
WACCM. We found that the exceptionally high values of N2O found in the monthly
averages by Odin/SMR are also found in the monthly averages derived from CRISTA
and MIPAS which as Odin/SMR provide N2O measurements with a high vertical
resolution. Thus, the exceptionally high absolute values of N2O found in the data of
instruments with high vertical resolution might be related to some (partly well-known)
bias problems or instrument noise which needs further assessment. However, the
seasonal and interannual variability of these values is most probably caused by local
dynamical processes in the tropics as e.g. the seasonal cycle of tropical upwelling and
the QBO, the latter of which is usually not well represented in model simulations. |
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