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Envisat MIPAS measurements of CFC-11 and CFC-12: an add-on to ESA operational data

Lars Hoffmann(1), Reinhold Spang(1), Martin Kaufmann(1) and Martin Riese(1)

(1) Forschungszentrum Juelich, ICG-I, 52425 Juelich, Germany


Envisat MIPAS measurements cover nearly continuously the period July 2002 to March 2004. ESA offline Level 1 and Level 2 reprocessing of MIPAS measurements during this period is completed by now. Calibrated infrared radiance spectra (4-15 micron) and atmospheric data (vertical profiles of pressure, temperature, and six trace gases) are available for further analysis. A general fast forward model and an optimal estimation retrieval processor suited to derive additional trace species from MIPAS measurements as well as other mid-infrared limb-sounding experiments have been developed in Juelich. The retrieval system was applied to derive the global distributions of CFC-11 and CFC-12 abundance and aerosol extinction coefficients near 10.7 and 12.0 micron from the MIPAS radiance measurements. Error studies indicate good quality of the retrieved CFC-11 and CFC-12 data (total error 4-7%). Further studies show that the influence of a priori on the obtained results is rather minimal (below 5-10% at most heights). Comparisons against MIPAS retrievals carried out by other working groups and first successful validations with in situ measurements show that the retrieved data are suited for further scientific analysis. Climatological mean values and standard deviations compare well against results of other satellite experiments. Being long-lived trace gases, CFC-11 and CFC-12 are rather useful to study transport processes in the lower stratosphere and upper troposphere or to evaluate transport in atmospheric models. A Kalman filter approach was applied to compare the MIPAS measurements of CFC-11 and CFC-12 against simulations obtained by the Chemical Lagrangian Model of the Stratosphere (CLaMS). The diagnostics of the Kalman filter give further information on the self-consistency of the derived data and help to check the error budgets. The comparison also shows in which atmospheric regions transport modelling in CLaMS is satisfactory or might be improved.


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Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry