6:15 PM - 7:30 PM
[AAS21-P22] Comparisons between NICAM-TM and GOSAT/TANSO-FTS TIR CO2 data
Keywords:CO2, satellite remote sensing, GOSAT
Comparisons of the differences of CO2 concentrations on 500 hPa and 200 hPa (500 hPa minus 200 hPa) between TIR CO2 data and NICAM-TM CO2 data showed that the differences of the TIR CO2 data were larger than those of the NICAM-TM CO2 data because of the negative bias of the mid-tropospheric TIR data. The CO2 differences between the two pressure levels of the TIR data were particularly large (~8 ppmv) in low latitudes; this characteristic was not seen both in the NICAM-TM CO2 data and the a priori CO2 data (NIES-TM05). Next, we applied the latitude-dependent correction factors to the TIR CO2 data on 500 hPa, and then compared the CO2 differences on 500 hPa and 200 hPa. In low latitudes (25⁰S-25⁰N), the CO2 differences between the two pressure levels of the TIR data became closer to the CO2 differences of the NICAM-TM CO2 data and the a priori CO2 data when we applied the correction factor estimated over Bangkok. On the other hand, in northern high latitudes (northern latitudes of ~40⁰N), most of the CO2 differences between the two pressure levels of the TIR data were positive unlike the NICAM-TM CO2 and the a priori CO2 data when we applied the correction factor estimated over Amsterdam. In boreal summer, surface CO2 concentrations are lower than middle and upper tropospheric CO2 concentrations; in that sense, the correction factor applied here was not appropriate in northern high latitudes in summer. These results suggest that the magnitude of the negative bias seen in TIR CO2 data would vary depending on seasons as well as regions, and therefore, we should estimate a latitude-dependent correction factor for each season.
Furthermore, we compared time series of TIR CO2 data with those of NICAM-TM CO2 data and the a priori CO2 data for several different regions that were categorized in terms of climatic divisions and latitude bands [Niwa et al., 2011]. Our preliminary results showed that the seasonal variations of the TIR CO2 data in some regions were closer to those of the NICAM CO2 data than of the a priori CO2 data. For future work, we should review how to compare the three CO2 data sets, and then closely analyze the differences in seasonal variations among the three data sets globally.
We thank the staff and engineers of Japan Airlines, the JAL Foundation, and JAMCO Tokyo for supporting the CONTRAIL project.