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| Titel |
Possible causes for the observation of exceptionally high N2O mixing ratios in the tropical lower stratosphere |
| VerfasserIn |
Farahnaz Khosrawi, Rolf Mueller, Michael H. Proffitt, Joachim Urban, Donal Murtagh |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035105
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| Zusammenfassung |
| A modified form of tracer-tracer correlations of N2O and O3 has been used as a tool for
evaluation atmospheric photochemical models, like CTMs and CCMs. 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 where we applied satellite observations from the Odin-Sub Millimeter
Radiometer (Odin/SMR) we found large differences between model simulation
and Odin/SMR observations in the tropics. The N2O averages we derived from
Odin/SMR observations at potential temperature levels between 500 and 650Â K
were much higher than the N2O values we derived from the model simulations.
Further, these values are much higher than what up to now has been measured.
Validation studies comparing Odin/SMR N2O data with other data shows that the
Odin/SMR N2O data is of good quality. Further, checking the method we applied did
also not reveal any errors. Since our data is averaged over bins of fixed N2O we
found that these bins contain a relatively low number of data points compared to the
other bins. Furthermore, these values occur with a seasonal dependence showing a
maximum in winter and a minimum in summer. Thus, since we cannot find an
error in our analyses or in the Odin/SMR data, a scientific explanation could be
that these high values are caused by local dynamical processes in the tropics, e.g.
overshooting convection, that are not well represented in the model simulations. To test
this hypothesis we will apply our method to other satellite data sets with a high
coverage in the tropics as e.g., MLS, MIPAS-ENVSIAT or CRISTA. If these high
values are also found in other satellite observations we additionally perform model
simulations to track the process by which these high values are caused in the lower
stratosphere. |
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