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キーワード:
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要旨:
Inverse modeling is a useful tool to retrieve CH4 fluxes; however, evaluation of the applied chemical
transport model is an important step before using the inverted emissions. For inversions using column
data one concern is how well the model represents stratospheric and tropospheric CH4 respectively when
assimilating total column measurements. In this study atmospheric CH4 from three inverse models is
compared to FTS (Fourier Transform Spectrometry), satellite and in situ measurements. Using the FTS
measurements the model biases are separated into stratospheric and tropospheric contributions. When
averaged over all FTS sites the model bias amplitudes (absolute model to FTS differences) are 7.4±5.1
ppb, 6.7±4.8 ppb, and 8.1±5.5 ppb in the troposphere for the models TM3, TM5-4DVAR, LMDz-PYVAR, respectively, and 4.3±9.9 ppb, 4.7±9.9 ppb, and 6.2±11.2 ppb in the stratosphere. The
tropospheric model biases show a latitudinal gradient for all models, however there are no clear
latitudinal dependencies for stratospheric model biases visible except with the LMDz-PYVAR model.
The latitudinal gradient is not present in a comparison with in situ measurements, which is attributed to
the different longitudinal coverage of FTS and in situ measurements. Similarly, a latitudinal pattern
exists in model biases in vertical CH4 gradients in the troposphere, which indicates vertical transports of
tropospheric CH4 is not represented correctly in the models.
