Atmos. Chem. Phys. Discuss., 9, 16331-16360, 2009
© Author(s) 2009. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). A final paper in ACP is not foreseen.
Information-based mid-upper tropospheric methane derived from Atmospheric Infrared Sounder (AIRS) and its validation
X. Xiong1,2, C. Barnet1, J. Wei1,2, and E. Maddy1,2
1NOAA/NESDIS/Center for Satellite Applications and Research, Camp Springs, Maryland, USA
2Perot Systems Government Services, Fairfax, Virginia, USA

Abstract. Atmospheric Infrared Sounder (AIRS) measurements of methane (CH4) generally contain about 1.0 degree of freedom and are therefore dependent on a priori assumptions about the vertical methane distribution as well as the temperature lapse rate and the amount of moisture. Thus it requires that interpretation and/or analysis of the CH4 spatial and temporal variation based on the AIRS retrievals need to use the averaging kernels (AK). To simplify the use of satellite retrieved products for scientific analysis, a method based on the information content of the retrievals is developed, in which the AIRS retrieved CH4 in the layer from 50 to 250 hPa below the tropopause is used to characterize the mid-upper tropospheric CH4 in the mid-high latitude regions. The basis of this method is that in the mid-high latitude regions the maximum sensitive layers of AIRS to CH4 have a good correlation with the tropopause heights, and these layers are usually between 50 and 250 hPa below the tropopause. Validation using the aircraft measurements from NOAA/ESRL/GMD and the campaigns INTEX-A and -B indicated that the correlation of AIRS mid-upper tropospheric CH4 with aircraft measurements is ~0.6–0.7, and its the bias and rms difference are less than ±1% and 1.2%, respectively. Further comparison of the CH4 seasonal cycle indicated that the cycle from AIRS mid-upper tropospheric CH4 is in a reasonable agreement with NOAA aircraft measurements. This method provides a simple way to use the thermal infrared sounders data to approximately analyze the spatial and temporal variation CH4 in the upper free tropospere without referring the AK. This method is applicable to derive tropospheric CH4 as well as other trace gases for any thermal infrared sensors.

Citation: Xiong, X., Barnet, C., Wei, J., and Maddy, E.: Information-based mid-upper tropospheric methane derived from Atmospheric Infrared Sounder (AIRS) and its validation, Atmos. Chem. Phys. Discuss., 9, 16331-16360, doi:10.5194/acpd-9-16331-2009, 2009.
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